Numerical study of the light output intensity of the bilayer organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Lu, Feiping

2017-02-01

The structure of organic light-emitting diodes (OLEDs) is one of most important issues that influence the light output intensity (LOI) of OLEDs. In this paper, based on a simple but accurate optical model, the influences of hole and electron transport layer thickness on the LOI of bilayer OLEDs, which with N,N0- bis(naphthalen-1-yl)-N,N0- bis(phenyl)- benzidine (NPB) or N,N'- diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4-diamine (TPD) as hole transport layer, with tris(8-hydroxyquinoline) aluminum (Alq3) as electron transport and light emitting layers, were investigated. The laws of LOI for OLEDs under different organic layer thickness values were obtained. The results show that the LOI of devices varies in accordance with damped cosine or sine function as the increasing of organic layer thickness, and the results show that the bilayer OLEDs with the structure of Glass/ITO/NPB (55 nm)/Alq3 (75 nm)/Al and Glass/ITO/TPB (60 nm)/Alq3 (75 nm)/Al have most largest LOI. When the thickness of Alq3 is less than 105 nm, the OLEDs with TPD as hole transport layer have larger LOI than that with NPB as hole transport layer. The results obtained in this paper can present an in-depth understanding of the working mechanism of OLEDs and help ones fabricate high efficiency OLEDs.

Polyethers with pendent phenylvinyl substituted carbazole rings as polymers for hole transporting layers of OLEDs

NASA Astrophysics Data System (ADS)

Griniene, R.; Liu, L.; Tavgeniene, D.; Sipaviciute, D.; Volyniuk, D.; Grazulevicius, J. V.; Xie, Z.; Zhang, B.; Leduskrasts, K.; Grigalevicius, S.

2016-01-01

Polyethers containing pendent 3-(2-phenylvinyl)carbazole moieties have been synthesized by the multi-step synthetic routes. Full characterization of their structures is presented. The polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 370 °C. The glass transition temperatures of the amorphous materials were in the range of 56-658 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of about 5.6 eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting layer. The device containing hole-transporting layers of poly{9-[6-(3-methyloxetan-3-ylmethoxy)hexyl]-3-(2-phenylvinyl)carbazole} exhibited the best overall performance with a maximum photometric efficiency of about 4.0 cd/A and maximum brightness exceeding 6430 cd/m2.

Doped hole transport layer for efficiency enhancement in planar heterojunction organolead trihalide perovskite solar cells

DOE PAGES

Wang, Qi; Bi, Cheng; Huang, Jinsong

2015-05-06

We demonstrated the efficiency of a solution-processed planar heterojunction organometallic trihalide perovskite solar cell can be increased to 17.5% through doping the hole transporting layer for reducing the resistivity. Doped Poly(triaryl amine) (PTAA) by 2,3,5,6-Tetrafluoro-7,7,8,8-Tetracyanoquinodimethane (F4-TCNQ) reduced device series resistance by three-folds, increasing the device fill factor to 74%, open circuit voltage to 1.09 V without sacrificing the short circuit current. As a result, this study reveals that the high resistivity of currently broadly applied polymer hole transport layer limits the device efficiency, and points a new direction to improve the device efficiency.

Facile thiol-ene thermal crosslinking reaction facilitated hole-transporting layer for highly efficient and stable perovskite solar cells

DOE PAGES

Li, Zhong'an; Zhu, Zonglong; Chueh, Chu -Chen; ...

2016-08-08

A crosslinked organic hole-transporting layer (HTL) is developed to realize highly efficient and stable perovskite solar cells via a facile thiol-ene thermal reaction. This crosslinked HTL not only facilitates hole extraction from perovskites, but also functions as an effective protective barrier. Lastly, a high-performance (power conversion efficiency: 18.3%) device is demonstrated to show respectable photo and thermal stability without encapsulation.

Dependence of the Carrier Transport Characteristics on the Buried Layer Thickness in Ambipolar Double-Layer Organic Field-Effect Transistors Investigated by Electrical and Optical Measurements

NASA Astrophysics Data System (ADS)

Zhang, Le; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

2013-05-01

By using current-voltage (I-V) measurements and optical modulation spectroscopy, we investigated the dependence of the carrier behaviour on the film thickness of the buried pentacene layer in C60/pentacene ambipolar double-layer organic field-effect transistors (OFETs). It was found that the buried pentacene layer not only acted as a hole transport layer, but also accounted for the properties of the C60/pentacene interface. The hole and electron behaviour exhibited different thickness dependence on the buried pentacene layer, implying the presence of the spatially separated conduction paths. It was suggested that the injected holes transported along the pentacene/gate dielectric interface, which were little affected by the buried pentacene layer thickness or the upper C60 layer; while, the injected electrons accumulated at the C60/pentacene interface, which were sensitive to the interfacial conditions or the buried pentacene layer. Furthermore, it was suggested that the enhanced surface roughness of the buried pentacene layer was responsible for the observed electron behaviour, especially when dpent>10 nm.

Improved efficiency of NiOx-based p-i-n perovskite solar cells by using PTEG-1 as electron transport layer

NASA Astrophysics Data System (ADS)

Groeneveld, Bart G. H. M.; Najafi, Mehrdad; Steensma, Bauke; Adjokatse, Sampson; Fang, Hong-Hua; Jahani, Fatemeh; Qiu, Li; ten Brink, Gert H.; Hummelen, Jan C.; Loi, Maria Antonietta

2017-07-01

We present efficient p-i-n type perovskite solar cells using NiOx as the hole transport layer and a fulleropyrrolidine with a triethylene glycol monoethyl ether side chain (PTEG-1) as electron transport layer. This electron transport layer leads to higher power conversion efficiencies compared to perovskite solar cells with PCBM (phenyl-C61-butyric acid methyl ester). The improved performance of PTEG-1 devices is attributed to the reduced trap-assisted recombination and improved charge extraction in these solar cells, as determined by light intensity dependence and photoluminescence measurements. Through optimization of the hole and electron transport layers, the power conversion efficiency of the NiOx/perovskite/PTEG-1 solar cells was increased up to 16.1%.

Variable Gap Conjugated Polymers

DTIC Science & Technology

2005-12-01

conducting gold interfacial layer interjected between the ITO glass electrode and the PEDOT/PSS hole transport layer . A family of low band gap, and near IR...which can be used as both electrochromics and as the hole transport layers in light emitting diodes. Hybrid electrochromic and electroluminescent (EC...MEH-PPV, P3HT, etc.) in order to blanket the solar spectrum. Initial device results on these multi-component blends are promising. In addition, we

Hole-transport material variation in fully vacuum deposited perovskite solar cells

NASA Astrophysics Data System (ADS)

Polander, Lauren E.; Pahner, Paul; Schwarze, Martin; Saalfrank, Matthias; Koerner, Christian; Leo, Karl

2014-08-01

This work addresses the effect of energy level alignment between the hole-transporting material and the active layer in vacuum deposited, planar-heterojunction CH3NH3PbIx-3Clx perovskite solar cells. Through a series of hole-transport materials, with conductivity values set using controlled p-doping of the layer, we correlate their ionization potentials with the open-circuit voltage of the device. With ionization potentials beyond 5.3 eV, a substantial decrease in both current density and voltage is observed, which highlights the delicate energetic balance between driving force for hole-extraction and maximizing the photovoltage. In contrast, when an optimal ionization potential match is found, the open-circuit voltage can be maximized, leading to power conversion efficiencies of up to 10.9%. These values are obtained with hole-transport materials that differ from the commonly used Spiro-MeO-TAD and correspond to a 40% performance increase versus this reference.

Transient electroluminescence on pristine and degraded phosphorescent blue OLEDs

NASA Astrophysics Data System (ADS)

Niu, Quan; Blom, Paul W. M.; May, Falk; Heimel, Paul; Zhang, Minlu; Eickhoff, Christian; Heinemeyer, Ute; Lennartz, Christian; Crǎciun, N. Irina

2017-11-01

In state-of-the-art blue phosphorescent organic light-emitting diode (PHOLED) device architectures, electrons and holes are injected into the emissive layer, where they are carried by the emitting and hole transporting units, respectively. Using transient electroluminescence measurements, we disentangle the contribution of the electrons and holes on the transport and efficiency of both pristine and degraded PHOLEDs. By varying the concentration of hole transporting units, we show that for pristine PHOLEDs, the transport is electron dominated. Furthermore, degradation of the PHOLEDs upon electrical aging is not related to the hole transport but is governed by a decrease in the electron transport due to the formation of electron traps.

Improving hole injection efficiency by manipulating the hole transport mechanism through p-type electron blocking layer engineering.

PubMed

Zhang, Zi-Hui; Ju, Zhengang; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

2014-04-15

The p-type AlGaN electron blocking layer (EBL) is widely used in InGaN/GaN light-emitting diodes (LEDs) for electron overflow suppression. However, a typical EBL also reduces the hole injection efficiency, because holes have to climb over the energy barrier generated at the p-AlGaN/p-GaN interface before entering the quantum wells. In this work, to address this problem, we report the enhancement of hole injection efficiency by manipulating the hole transport mechanism through insertion of a thin GaN layer of 1 nm into the p-AlGaN EBL and propose an AlGaN/GaN/AlGaN-type EBL outperforming conventional AlGaN EBLs. Here, the position of the inserted thin GaN layer relative to the p-GaN region is found to be the key to enhancing the hole injection efficiency. InGaN/GaN LEDs with the proposed p-type AlGaN/GaN/AlGaN EBL have demonstrated substantially higher optical output power and external quantum efficiency.

Inverted bulk-heterojunction organic solar cells with the transfer-printed anodes and low-temperature-processed ultrathin buffer layers

NASA Astrophysics Data System (ADS)

Itoh, Eiji; Sakai, Shota; Fukuda, Katsutoshi

2018-03-01

We studied the effects of a hole buffer layer [molybdenum oxide (MoO3) and natural copper oxide layer] and a low-temperature-processed electron buffer layer on the performance of inverted bulk-heterojunction organic solar cells in a device consisting of indium-tin oxide (ITO)/poly(ethylene imine) (PEI)/titanium oxide nanosheet (TiO-NS)/poly(3-hexylthiopnehe) (P3HT):phenyl-C61-butyric acid methylester (PCBM)/oxide/anode (Ag or Cu). The insertion of ultrathin TiO-NS (˜1 nm) and oxide hole buffer layers improved the open circuit voltage V OC, fill factor, and rectification properties owing to the effective hole blocking and electron transport properties of ultrathin TiO-NS, and to the enhanced work function difference between TiO-NS and the oxide hole buffer layer. The insertion of the TiO-NS contributed to the reduction in the potential barrier at the ITO/PEI/TiO-NS/active layer interface for electrons, and the insertion of the oxide hole buffer layer contributed to the reduction in the potential barrier for holes. The marked increase in the capacitance under positive biasing in the capacitance-voltage characteristics revealed that the combination of TiO-NS and MoO3 buffer layers contributes to the selective transport of electrons and holes, and blocks counter carriers at the active layer/oxide interface. The natural oxide layer of the copper electrode also acts as a hole buffer layer owing to the increase in the work function of the Cu surface in the inverted cells. The performance of the cell with evaporated MoO3 and Cu layers that were transfer-printed to the active layer was almost comparable to that of the cell with MoO3 and Ag layers directly evaporated onto the active layer. We also demonstrated comparable device performance in the cell with all-printed MoO3 and low-temperature-processed silver nanoparticles as an anode.

Charge-transport anisotropy in black phosphorus: critical dependence on the number of layers.

PubMed

Banerjee, Swastika; Pati, Swapan K

2016-06-28

Phosphorene is a promising candidate for modern electronics because of the anisotropy associated with high electron-hole mobility. Additionally, superior mechanical flexibility allows the strain-engineering of various properties including the transport of charge carriers in phosphorene. In this work, we have shown the criticality of the number of layers to dictate the transport properties of black phosphorus. Trilayer black phosphorus (TBP) has been proposed as an excellent anisotropic material, based on the transport parameters using Boltzmann transport formalisms coupled with density functional theory. The mobilities of both the electron and the hole are found to be higher along the zigzag direction (∼10(4) cm(2) V(-1) s(-1) at 300 K) compared to the armchair direction (∼10(2) cm(2) V(-1) s(-1)), resulting in the intrinsic directional anisotropy. Application of strain leads to additional electron-hole anisotropy with 10(3) fold higher mobility for the electron compared to the hole. Critical strain for maximum anisotropic response has also been determined. Whether the transport anisotropy is due to the spatial or charge-carrier has been determined through analyses of the scattering process of electrons and holes, and their recombination as well as relaxation dynamics. In this context, we have derived two descriptors (S and F(k)), which are general enough for any 2D or quasi-2D systems. Information on the scattering involving purely the carrier states also helps to understand the layer-dependent photoluminescence and electron (hole) relaxation in black phosphorus. Finally, we justify trilayer black phosphorus (TBP) as the material of interest with excellent transport properties.

Atomic Layer Deposition of TiO2 for a High-Efficiency Hole-Blocking Layer in Hole-Conductor-Free Perovskite Solar Cells Processed in Ambient Air.

PubMed

Hu, Hang; Dong, Binghai; Hu, Huating; Chen, Fengxiang; Kong, Mengqin; Zhang, Qiuping; Luo, Tianyue; Zhao, Li; Guo, Zhiguang; Li, Jing; Xu, Zuxun; Wang, Shimin; Eder, Dominik; Wan, Li

2016-07-20

In this study we design and construct high-efficiency, low-cost, highly stable, hole-conductor-free, solid-state perovskite solar cells, with TiO2 as the electron transport layer (ETL) and carbon as the hole collection layer, in ambient air. First, uniform, pinhole-free TiO2 films of various thicknesses were deposited on fluorine-doped tin oxide (FTO) electrodes by atomic layer deposition (ALD) technology. Based on these TiO2 films, a series of hole-conductor-free perovskite solar cells (PSCs) with carbon as the counter electrode were fabricated in ambient air, and the effect of thickness of TiO2 compact film on the device performance was investigated in detail. It was found that the performance of PSCs depends on the thickness of the compact layer due to the difference in surface roughness, transmittance, charge transport resistance, electron-hole recombination rate, and the charge lifetime. The best-performance devices based on optimized TiO2 compact film (by 2000 cycles ALD) can achieve power conversion efficiencies (PCEs) of as high as 7.82%. Furthermore, they can maintain over 96% of their initial PCE after 651 h (about 1 month) storage in ambient air, thus exhibiting excellent long-term stability.

Cuprous Oxide as a Potential Low-Cost Hole-Transport Material for Stable Perovskite Solar Cells.

PubMed

Nejand, Bahram Abdollahi; Ahmadi, Vahid; Gharibzadeh, Saba; Shahverdi, Hamid Reza

2016-02-08

Inorganic hole-transport materials are commercially desired to decrease the fabrication cost of perovskite solar cells. Here, Cu2O is introduced as a potential hole-transport material for stable, low-cost devices. Considering that Cu2O formation is highly sensitive to the underlying mixture of perovskite precursors and their solvents, we proposed and engineered a technique for reactive magnetron sputtering. The rotational angular deposition of Cu2O yields high surface coverage of the perovskite layer for high rate of charge extraction. Deposition of this Cu2O layer on the pinhole-free perovskite layer produces devices with power conversion efficiency values of up to 8.93%. The engineered Cu2O layers showed uniform, compact, and crack-free surfaces on the perovskite layer without affecting the perovskite structure, which is desired for deposition of the top metal contact and for surface shielding against moisture and mechanical damages. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum Dot Light-Emitting Devices: Beyond Alignment of Energy Levels

DOE PAGES

Zaiats, Gary; Ikeda, Shingo; Kinge, Sachin; ...

2017-08-25

Multinary semiconductor nanoparticles such as CuInS 2, AgInS 2, and the corresponding alloys with ZnS hold promise for designing future quantum dot light-emitting devices (QLED). The QLED architectures require matching of energy levels between the different electron and hole transport layers. In addition to energy level alignment, conductivity and charge transfer interactions within these layers determine the overall efficiency of QLED. By employing CuInS 2-ZnS QDs we succeeded in fabricating red-emitting QLED using two different hole-transporting materials, polyvinylcarbazole and poly(4- butylphenyldiphenylamine). Despite the similarity of the HOMO-LUMO energy levels of these two hole transport materials, the QLED devices exhibit distinctlymore » different voltage dependence. The difference in onset voltage and excited state interactions shows the complexity involved in selecting the hole transport materials for display devices.« less

Quantum Dot Light-Emitting Devices: Beyond Alignment of Energy Levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaiats, Gary; Ikeda, Shingo; Kinge, Sachin

Multinary semiconductor nanoparticles such as CuInS 2, AgInS 2, and the corresponding alloys with ZnS hold promise for designing future quantum dot light-emitting devices (QLED). The QLED architectures require matching of energy levels between the different electron and hole transport layers. In addition to energy level alignment, conductivity and charge transfer interactions within these layers determine the overall efficiency of QLED. By employing CuInS 2-ZnS QDs we succeeded in fabricating red-emitting QLED using two different hole-transporting materials, polyvinylcarbazole and poly(4- butylphenyldiphenylamine). Despite the similarity of the HOMO-LUMO energy levels of these two hole transport materials, the QLED devices exhibit distinctlymore » different voltage dependence. The difference in onset voltage and excited state interactions shows the complexity involved in selecting the hole transport materials for display devices.« less

High work-function hole transport layers by self-assembly using a fluorinated additive

DOE PAGES

Mauger, Scott A.; Li, Jun; Özmen, Özge Tüzün; ...

2013-10-30

The hole transport polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) derives many of its favorable properties from a PSS-rich interfacial layer that forms spontaneously during coating. Since PEDOT:PSS is only usable as a blend it is not possible to study PEDOT:PSS without this interfacial layer. Through the use of the self-doped polymer sulfonated poly(thiophene-3-[2-(2-methoxyethoxy) ethoxy]-2,5-diyl) (S-P3MEET) and a polyfluorinated ionomer (PFI) it is possible to compare transparent conducting organic films with and without interfacial layers and to understand their function. Using neutron reflectometry, we show that PFI preferentially segregates at the top surface of the film during coating and forms a thermally stable surfacemore » layer. Because of this distribution we find that even small amounts of PFI increase the electron work function of the HTL. We also find that annealing at 150°C and above reduces the work function compared to samples heated at lower temperatures. Using near edge x-ray absorption fine structure spectroscopy and gas chromatography we show that this reduction in work function is due to S-P3MEET being doped by PFI. Organic photovoltaic devices with S-P3MEET/PFI hole transport layers yield higher power conversion efficiency than devices with pure S-P3MEET or PEDOT:PSS hole transport layers. Additionally, devices with a doped interface layer of S-P3MEET/PFI show superior performance to those with un-doped S-P3MEET.« less

TFB:TPDSi2 interfacial layer usable in organic photovoltaic cells

DOEpatents

Marks, Iobin J [Evanston, IL; Hains, Alexander W [Evanston, IL

2011-02-15

The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode; an active organic layer comprising an electron-donating organic material and an electron-accepting organic material; and an interfacial layer formed between the anode and active organic layer, where the interfacial layer comprises a hole-transporting polymer characterized with a hole-mobility higher than that of the electron-donating organic material in the active organic layer, and a small molecule that has a high hole-mobility and is capable of crosslinking on contact with air.

Vapochromic LED

DOEpatents

Kunugi, Yoshihito; Mann, Kent R.; Miller, Larry L.; Exstrom, Christopher L.

2003-06-17

A sandwich device was prepared by electrodeposition of an insoluble layer of oligomerized tris(4-(2-thienyl)phenyl)amine onto conducting indium-tin oxide coated glass, spin coating the stacked platinum compound, tetrakis(p-decylphenylisocyano)platinum tetranitroplatinate, from toluene onto the oligomer layer, and then coating the platinum complex with aluminum by vapor deposition. This device showed rectification of current and gave electroluminescence. The electroluminescence spectrum (.lambda..sub.max =545 nm) corresponded to the photoluminescence spectrum of the platinum complex. Exposure of the device to acetone vapor caused the electroemission to shift to 575 nm. Exposure to toluene vapor caused a return to the original spectrum. These results demonstrate a new type of sensor that reports the arrival of organic vapors with an electroluminescent signal. The sensor comprises (a) a first electrode; (b) a hole transport layer formed on the first electrode; (c) a sensing/emitting layer formed on the hole transport layer, the sensing/emitting layer comprising a material that changes color upon exposure to the analyte vapors; (d) an electron conductor layer formed on the sensing layer; and (e) a second electrode formed on the electron conductor layer. The hole transport layer emits light at a shorter wavelength than the sensing/emitting layer and at least the first electrode comprises an optically transparent material.

Vapochromic LED

DOEpatents

Kunugi, Yoshihito; Mann, Kent R.; Miller, Larry L.; Exstrom, Christopher L.

2002-01-15

A sandwich device was prepared by electrodeposition of an insoluble layer of oligomerized tris(4-(2-thienyl)phenyl)amine onto conducting indium-tin oxide coated glass, spin coating the stacked platinum compound, tetrakis(p-decylphenylisocyano)platinum tetranitroplatinate, from toluene onto the oligomer layer, and then coating the platinum complex with aluminum by vapor deposition. This device showed rectification of current and gave electroluminescence. The electroluminescence spectrum (.mu..sub.max =545 nm) corresponded to the photoluminescence spectrum of the platinum complex. Exposure of the device to acetone vapor caused the electroemission to shift to 575 nm. Exposure to toluene vapor caused a return to the original spectrum. These results demonstrate a new type of sensor that reports the arrival of organic vapors with an electroluminescent signal. The sensor comprises (a) a first electrode; (b) a hole transport layer formed on the first electrode; (c) a sensing/emitting layer formed on the hole transport layer, the sensing/emitting layer comprising a material that changes color upon exposure to the analyte vapors; (d) an electron conductor layer formed on the sensing layer; and (e) a second electrode formed on the electron conductor layer. The hole transport layer emits light at a shorter wavelength than the sensing/emitting layer and at least the first electrode comprises an optically transparent material.

Recombination zone in white organic light emitting diodes with blue and orange emitting layers

NASA Astrophysics Data System (ADS)

Tsuboi, Taiju; Kishimoto, Tadashi; Wako, Kazuhiro; Matsuda, Kuniharu; Iguchi, Hirofumi

2012-10-01

White fluorescent OLED devices with a 10 nm thick blue-emitting layer and a 31 nm thick orange-emitting layer have been fabricated, where the blue-emitting layer is stacked on a hole transport layer. An interlayer was inserted between the two emitting layers. The thickness of the interlayer was changed among 0.3, 0.4, and 1.0 nm. White emission with CIE coordinates close to (0.33, 0.33) was observed from all the OLEDs. OLED with 0.3 nm thick interlayer gives the highest maximum luminous efficiency (11 cd/A), power efficiency (9 lm/W), and external quantum efficiency (5.02%). The external quantum efficiency becomes low with increasing the interlayer thickness from 0 nm to 1.0 nm. When the location of the blue- and orange-emitting layers is reversed, white emission was not obtained because of too weak blue emission. It is suggested that the electron-hole recombination zone decreases nearly exponentially with a distance from the hole transport layer.

Carbazole/triarylamine based polymers as a hole injection/transport layer in organic light emitting devices.

PubMed

Wang, Hui; Ryu, Jeong-Tak; Kwon, Younghwan

2012-05-01

This study examined the influence of the charge injection barriers on the performance of organic light emitting diodes (OLEDs) using polymers with a stepwise tuned ionization potential (I(p) approximately -5.01 - -5.29 eV) between the indium tin oxide (ITO) (phi approximately -4.8 eV) anode and tris(8-hydroxyquinolinato) aluminium (Alq3) (I(p) approximately -5.7 eV) layer. The energy levels of the polymers were tuned by structural modification. Double layer devices were fabricated with a configuration of ITO/polymer/Alq3/LiF/Al, where the polymers, Alq3, and LiF/Al were used as the hole injection/transport layer, emissive electron transport layer, and electron injection/cathode, respectively. Using the current density-voltage (J-V), luminescence-voltage (L-V) and efficiencies in these double layer devices, the device performance was evaluated in terms of the energy level alignments at the interfaces, such as the hole injection barriers (phi(h)(iTO/polymer) and phi(h)(polymer/Alq3)) from ITO through the polymers into the Alq3 layer, and the electron injection barrier (phi(e)(polymer/Alq3) or electron/exciton blocking barrier) at the polymer/Alq3 interface.

High-Performance Semitransparent Perovskite Solar Cells with 10% Power Conversion Efficiency and 25% Average Visible Transmittance Based on Transparent CuSCN as the Hole-Transporting Material

DOE PAGES

Jung, Jae Woong; Chueh, Chu-Chen; Jen, Alex K. -Y.

2015-07-06

High-performance planar heterojunction perovskite (CH3NH3PbI3) solar cell (PVSC) is demonstrated by utilizing CuSCN as a hole-transporting layer. Efficient hole-transport and hole-extraction at the CuSCN/CH3NH3PbI3 interface facilitate the PVSCs to reach 16% power conversion efficiency (PCE). In addition, excellent transparency of CuSCN enables high-performance semitransparent PVSC (10% PCE and 25% average visible transmittance) to be realized.

Flexible ITO-free organic solar cells applying aqueous solution-processed V2O5 hole transport layer: An outdoor stability study

NASA Astrophysics Data System (ADS)

Lima, F. Anderson S.; Beliatis, Michail J.; Roth, Bérenger; Andersen, Thomas R.; Bortoti, Andressa; Reyna, Yegraf; Castro, Eryza; Vasconcelos, Igor F.; Gevorgyan, Suren A.; Krebs, Frederik C.; Lira-Cantu, Mónica

2016-02-01

Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V2O5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC60BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V2O5.

Passivated p-type silicon: Hole injection tunable anode material for organic light emission

NASA Astrophysics Data System (ADS)

Zhao, W. Q.; Ran, G. Z.; Xu, W. J.; Qin, G. G.

2008-02-01

We find that hole injection can be enhanced simply by selecting a lower-resistivity p-Si anode to match an electron injection enhancement for organic light emitting diodes with ultrathin-SiO2-layer-passivated p-Si anode (Si-OLED). For a Si-OLED with ordinary AlQ electron transport layer, the optimized resistivity of the p-Si anode is 40Ωcm; for that with n-doped Bphen electron transport layer, it decreases to 5Ωcm. Correspondingly, the maximum power efficiency increases from 0.3to1.9lm /W, even higher than that of an indium tin oxide control device (1.4lm/W). This passivated p-type silicon is a hole injection tunable anode material for OLED.

Solid state photosensitive devices which employ isolated photosynthetic complexes

DOEpatents

Peumans, Peter; Forrest, Stephen R.

2009-09-22

Solid state photosensitive devices including photovoltaic devices are provided which comprise a first electrode and a second electrode in superposed relation; and at least one isolated Light Harvesting Complex (LHC) between the electrodes. Preferred photosensitive devices comprise an electron transport layer formed of a first photoconductive organic semiconductor material, adjacent to the LHC, disposed between the first electrode and the LHC; and a hole transport layer formed of a second photoconductive organic semiconductor material, adjacent to the LHC, disposed between the second electrode and the LHC. Solid state photosensitive devices of the present invention may comprise at least one additional layer of photoconductive organic semiconductor material disposed between the first electrode and the electron transport layer; and at least one additional layer of photoconductive organic semiconductor material, disposed between the second electrode and the hole transport layer. Methods of generating photocurrent are provided which comprise exposing a photovoltaic device of the present invention to light. Electronic devices are provided which comprise a solid state photosensitive device of the present invention.

Improvement of the photovoltaic parameters of perovskite solar cells using a reduced-graphene-oxide-modified titania layer and soluble copper phthalocyanine as a hole transporter.

PubMed

Nouri, Esmaiel; Mohammadi, Mohammad Reza; Xu, Zong-Xiang; Dracopoulos, Vassilios; Lianos, Panagiotis

2018-01-24

Functional perovskite solar cells can be made by using a simple, inexpensive and stable soluble tetra-n-butyl-substituted copper phthalocyanine (CuBuPc) as a hole transporter. In the present study, TiO 2 /reduced graphene oxide (T/RGO) hybrids were synthesized via an in situ solvothermal process and used as electron acceptor/transport mediators in mesoscopic perovskite solar cells based on soluble CuBuPc as a hole transporter and on graphene oxide (GO) as a buffer layer. The impact of the RGO content on the optoelectronic properties of T/RGO hybrids and on the solar cell performance was studied, suggesting improved electron transport characteristics and photovoltaic parameters. An enhanced electron lifetime and recombination resistance led to an increase in the short circuit current density, open circuit voltage and fill factor. The device based on a T/RGO mesoporous layer with an optimal RGO content of 0.2 wt% showed 22% higher photoconversion efficiency and higher stability compared with pristine TiO 2 -based devices.

Tunable Transport Gap in Phosphorene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Saptarshi; Zhang, Wei; Demarteau, Marcel

2014-08-11

In this paper, we experimentally demonstrate that the transport gap of phosphorene can be tuned monotonically from ~0.3 to ~1.0 eV when the flake thickness is scaled down from bulk to a single layer. As a consequence, the ON current, the OFF current, and the current ON/OFF ratios of phosphorene field effect transistors (FETs) were found to be significantly impacted by the layer thickness. The transport gap was determined from the transfer characteristics of phosphorene FETs using a robust technique that has not been reported before. The detailed mathematical model is also provided. By scaling the thickness of the gatemore » oxide, we were also able to demonstrate enhanced ambipolar conduction in monolayer and few layer phosphorene FETs. The asymmetry of the electron and the hole current was found to be dependent on the layer thickness that can be explained by dynamic changes of the metal Fermi level with the energy band of phosphorene depending on the layer number. We also extracted the Schottky barrier heights for both the electron and the hole injection as a function of the layer thickness. In conclusion, we discuss the dependence of field effect hole mobility of phosphorene on temperature and carrier concentration.« less

Transport limited interfacial carrier relaxation in a double-layer device investigated by time-resolved second harmonic generation and impedance spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Le; Taguchi, Dai; Li, Jun; Manaka, Takaaki; Iwamoto, Mitsumasa

2011-02-01

The interfacial carrier relaxation in an indium tin oxide/polyimide/pentacene/Au double-layer device was studied in both time and frequency domains by using time-resolved second harmonic generation (TR-SHG) and impedance spectroscopy (IS), respectively. Although both hole and electron injection into the pentacene layer and their accumulation at the pentacene/polyimide interface were revealed in TR-SHG, it was only observed in IS under the hole injection condition. The "contradiction" between the two methods for the same carrier relaxation process was explained on the basis of a model, transport limited interfacial carrier relaxation, in which the quasistatic state governs the one-directional carrier transport.

Simulation of hole-mobility in doped relaxed and strained Ge layers

NASA Astrophysics Data System (ADS)

Watling, Jeremy R.; Riddet, Craig; Chan, Morgan Kah H.; Asenov, Asen

2010-11-01

As silicon based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching the limits of their performance with scaling, alternative channel materials are being considered to maintain performance in future complementary metal-oxide semiconductor technology generations. Thus there is renewed interest in employing Ge as a channel material in p-MOSFETs, due to the significant improvement in hole mobility as compared to Si. Here we employ full-band Monte Carlo to study hole transport properties in Ge. We present mobility and velocity-field characteristics for different transport directions in p-doped relaxed and strained Ge layers. The simulations are based on a method for over-coming the potentially large dynamic range of scattering rates, which results from the long-range nature of the unscreened Coulombic interaction. Our model for ionized impurity scattering includes the affects of dynamic Lindhard screening, coupled with phase-shift, and multi-ion corrections along with plasmon scattering. We show that all these effects play a role in determining the hole carrier transport in doped Ge layers and cannot be neglected.

Hole transport in c-plane InGaN-based green laser diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Yang; Liu, Jianping, E-mail: jpliu2010@sinano.ac.cn; Tian, Aiqin

2016-08-29

Hole transport in c-plane InGaN-based green laser diodes (LDs) has been investigated by both simulations and experiments. It is found that holes can overflow from the green double quantum wells (DQWs) at high current density, which reduces carrier injection efficiency of c-plane InGaN-based green LDs. A heavily silicon-doped layer right below the green DQWs can effectively suppress hole overflow from the green DQWs.

Low-temperature solution-processed hydrogen molybdenum and vanadium bronzes for an efficient hole-transport layer in organic electronics.

PubMed

Xie, Fengxian; Choy, Wallace C H; Wang, Chuandao; Li, Xinchen; Zhang, Shaoqing; Hou, Jianhui

2013-04-11

A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL). The oxygen vacancy plays an essential role for TMOs when they are employed as HTLs: TMO films with excess oxygen are highly undesirable for their application in organic electronics. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hole-transport limited S-shaped I-V curves in planar heterojunction organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Zhang, Minlu; Wang, Hui; Tang, C. W.

2011-11-01

Current-voltage (I-V) characteristics of planar heterojunction organic photovoltaic cells based on N',N'-Di-[(1-naphthyl)-N',N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB) and C60 are investigated. Through variation of the layer thickness and composition, specifically chemical doping NPB with MoOx, we show that the hole-transport limitation in the NPB layer is the determining factor in shaping the I-V characteristics of NPB/C60 cells.

Enhancing Photovoltaic Performance of Inverted Planar Perovskite Solar Cells by Cobalt-Doped Nickel Oxide Hole Transport Layer.

PubMed

Xie, Yulin; Lu, Kai; Duan, Jiashun; Jiang, Youyu; Hu, Lin; Liu, Tiefeng; Zhou, Yinhua; Hu, Bin

2018-04-25

Electron and hole transport layers have critical impacts on the overall performance of perovskite solar cells (PSCs). Herein, for the first time, a solution-processed cobalt (Co)-doped NiO X film was fabricated as the hole transport layer in inverted planar PSCs, and the solar cells exhibit 18.6% power conversion efficiency. It has been found that an appropriate Co-doping can significantly adjust the work function and enhance electrical conductivity of the NiO X film. Capacitance-voltage ( C- V) spectra and time-resolved photoluminescence spectra indicate clearly that the charge accumulation becomes more pronounced in the Co-doped NiO X -based photovoltaic devices; it, as a consequence, prevents the nonradiative recombination at the interface between the Co-doped NiO X and the photoactive perovskite layers. Moreover, field-dependent photoluminescence measurements indicate that Co-doped NiO X -based devices can also effectively inhibit the radiative recombination process in the perovskite layer and finally facilitate the generation of photocurrent. Our work indicates that Co-doped NiO X film is an excellent candidate for high-performance inverted planar PSCs.

Low resistivity ZnO-GO electron transport layer based CH{sub 3}NH{sub 3}PbI{sub 3} solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Muhammad Imran, E-mail: imranrahbar@scme.nust.edu.pk, E-mail: amirhabib@scme.nust.edu.pk; Hussain, Zakir; Mujahid, Mohammad

Perovskite based solar cells have demonstrated impressive performances. Controlled environment synthesis and expensive hole transport material impede their potential commercialization. We report ambient air synthesis of hole transport layer free devices using ZnO-GO as electron selective contacts. Solar cells fabricated with hole transport layer free architecture under ambient air conditions with ZnO as electron selective contact achieved an efficiency of 3.02%. We have demonstrated that by incorporating GO in ZnO matrix, low resistivity electron selective contacts, critical to improve the performance, can be achieved. We could achieve max efficiency of 4.52% with our completed devices for ZnO: GO composite. Impedancemore » spectroscopy confirmed the decrease in series resistance and an increase in recombination resistance with inclusion of GO in ZnO matrix. Effect of temperature on completed devices was investigated by recording impedance spectra at 40 and 60 {sup o}C, providing indirect evidence of the performance of solar cells at elevated temperatures.« less

Efficient organic solar cells using copper(I) iodide (CuI) hole transport layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Ying; Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London SW7 2AZ; Yaacobi-Gross, Nir

We report the fabrication of high power conversion efficiency (PCE) polymer/fullerene bulk heterojunction (BHJ) photovoltaic cells using solution-processed Copper (I) Iodide (CuI) as hole transport layer (HTL). Our devices exhibit a PCE value of ∼5.5% which is equivalent to that obtained for control devices based on the commonly used conductive polymer poly(3,4-ethylenedioxythiophene): polystyrenesulfonate as HTL. Inverted cells with PCE >3% were also demonstrated using solution-processed metal oxide electron transport layers, with a CuI HTL evaporated on top of the BHJ. The high optical transparency and suitable energetics of CuI make it attractive for application in a range of inexpensive large-area optoelectronicmore » devices.« less

Polyethers containing 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole chromophores as solution processed materials for hole transporting layers of OLEDs

NASA Astrophysics Data System (ADS)

Krucaite, G.; Tavgeniene, D.; Xie, Z.; Lin, X.; Zhang, B.; Grigalevicius, S.

2018-02-01

Two polyethers containing electroactive pendent 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole moieties have been synthesized by the multi-step synthetic route. Full characterization of their structures is presented. The polymers represent derivatives of very high thermal stability with initial thermal degradation temperatures of 425 °C and 431 °C. Glass transition temperatures of the amorphous materials were also very high and reached values of 154 °C and 163 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of 5.84 eV and 5.93 eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting material. An electroluminescent device containing hole-transporting layer (HTL) of the polymer with electroactive 4-carbazolyl-7-phenylbenzo[c]-1,2,5-thiadiazole moieties exhibited turn on voltage of 6.2 V, maximum photometric efficiency of 2.5 cd/A and maximum brightness exceeding 300 cd/m2. The device containing HTL of the polymer with 4-carbazolyl-7-(1-naphtyl)benzo[c]-1,2,5-thiadiazole moieties demonstrated turn on voltage of 5.2 V, maximum photometric efficiency of 1.6 cd/A and maximum brightness exceeding 1500 cd/m2. The efficiencies were about 30-90% higher than that of the device containing widely used hole transporting layers of poly(9-vinylcarbazole).

Multilayer organic based structures with enhanced hole transport

NASA Astrophysics Data System (ADS)

Mladenova, D.; Sinigersky, V.; Budurova, D.; Dobreva, T.; Karashanova, D.; Dimov, D.; Zhivkov, I.

2010-11-01

Multilayer Organic Based Devices (OBDs) were constructed by subsequent casting of organic films (from polymers, soluble in the same organic solvent). The problem with dissolution of the underlying layer was avoided by using electrophoretic deposition technique. Optimized conditions for electrophoretic deposition (EPD) of thin films with homogeneous and smooth surfaces, as confirmed by SEM, were found. The EPD, carried out at constant current, requires continuous increase of the voltage between the electrodes. In this way the decreased deposition rate caused by the decreased concentration of the material in the suspension and the increased thickness of the film deposited is compensated. The SEM images and the current voltage characteristics recorded, show that the hole transport polyvinylcarbazole (PVK) underlayer survive the treatment with the suspension used for the electrophoretic deposition of the active poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene vinylene] electroluminescent layer. The PVK hole transport layer increases the device current, as confirmed by the current-voltage measurements. The results obtained demonstrate the possibility of OBDs preparation for electroluminescent and photovoltaic applications.

Room-temperature processed tin oxide thin film as effective hole blocking layer for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Tao, Hong; Ma, Zhibin; Yang, Guang; Wang, Haoning; Long, Hao; Zhao, Hongyang; Qin, Pingli; Fang, Guojia

2018-03-01

Tin oxide (SnO2) film with high mobility and good transmittance has been reported as a promising semiconductor material for high performance perovskite solar cells (PSCs). In this study, ultrathin SnO2 film synthesized by radio frequency magnetron sputtering (RFMS) method at room temperature was employed as hole blocking layer for planar PSCs. The room-temperature sputtered SnO2 film not only shows favourable energy band structure but also improves the surface topography of fluorine doped SnO2 (FTO) substrate and perovskite (CH3NH3PbI3) layer. Thus, this SnO2 hole blocking layer can efficiently promote electron transport and suppress carrier recombination. Furthermore, the best efficiency of 13.68% was obtained for planar PSC with SnO2 hole blocking layer prepared at room temperature. This research highlights the room-temperature preparation process of hole blocking layer in PSC and has a certain reference significance for the usage of flexible and low-cost substrates.

[Influence of MnO3 on Photoelectric Performance in Organic Light Emitting Diodes].

PubMed

Guan, Yun-xia; Chen, Li-jia; Chen, Ping; Fu, Xiao-qiang; Niu, Lian-bin

2016-03-01

Organic Light Emitting Diodes (OLEDs) has been a promising new research point that has received much attention recently. Emission in a conventional OLED originates from the recombination of carriers (electrons and holes) that are injected from external electrodes. In the device, Electrons, on the other hand, are injected from the Al cathode to an electron-transporting layer and travel to the same emissive zone. Holes are injected from the transparent ITO anode to a hole-transporting layer and holes reach an emitting zone through the holetransporting layer. Electrons and holes recombine at the emissive film to formsinglet excited states, followed by emissive light. It is because OLED is basically an optical device and its structure consists of organic or inorganic layers of sub-wavelength thickness with different refractive indices. When the electron and holes are injected through the electrodes, they combine in the emission zone emitting the photons. These photons will have the reflection and transmission at each interface and the interference will determine the intensity profile. The emissive light reflected at the interfaces or the metallic electrode returns to the emissive layer and affects the radiation current efficiency. Microcavity OLED can produce saturated colors and narrow the emission spetrum as a new kind of technique. In the paper, we fabricate microcavity OLED using glass substrate. Ag film acts as the anode reflector mirror; NPB serves as the hole-transporting material; Alq3 is electron-transporting material and organic emissive material; Ag film acts as cathode reflector mirror. The microcavity OLED structures named as A, B, C and D are glass/Ag(15 nm)/MoO3 (x nm)/NPB(50 nm)/Alq3 (60 nm)/A1(100 nm). Here, A, x = 4 nm; B, x = 7 nm; C, x = 10 nm; D, x = 13 nm. The characteristic voltage, brightness and current of these devices are investigated in the electric field. The luminance from the Devices A, B, C and D reaches the luminance of 928, 1 369, 2 550 and 2 035 cd x m(-2), respectively at 13 V. At 60 mA x cm(-2), the current efficiency of the microcavity OLEDs using MnO3 are about 2.2, 2.6, 3.1 and 2.6 cd x A(-2) respectively. It is found that electrons are majority carriers and holes are minority carriers in this microcavity OLEDs. MnO3 film can improve hole injection ability from 4 to 10 nm. In addition, hole injection ability is increased with the increasing thickness of the MnO3 film.

Switching Hole and Electron Transports of Molecules on Metal Oxides by Energy Level Alignment Tuning.

PubMed

Bao, Zhong-Min; Xu, Rui-Peng; Li, Chi; Xie, Zhong-Zhi; Zhao, Xin-Dong; Zhang, Yi-Bo; Li, Yan-Qing; Tang, Jian-Xin

2016-08-31

Charge transport at organic/inorganic hybrid contacts significantly affects the performance of organic optoelectronic devices because the unfavorable energy level offsets at these interfaces can hinder charge injection or extraction due to large barrier heights. Herein, we report a technologically relevant method to functionalize a traditional hole-transport layer of solution-processed nickel oxide (NiOx) with various interlayers. The photoemission spectroscopy measurements reveal the continuous tuning of the NiOx substrate work function ranging from 2.5 to 6.6 eV, enabling the alignment transition of energy levels between the Schottky-Mott limit and Fermi level pinning at the organic/composite NiOx interface. As a result, switching hole and electron transport for the active organic material on the composite NiOx layer is achieved due to the controlled carrier injection/extraction barriers. The experimental findings indicate that tuning the work function of metal oxides with optimum energy level offsets can facilitate the charge transport at organic/electrode contacts.

Rational Design of Molecular Hole-Transporting Materials for Perovskite Solar Cells: Direct versus Inverted Device Configurations.

PubMed

Grisorio, Roberto; Iacobellis, Rosabianca; Listorti, Andrea; De Marco, Luisa; Cipolla, Maria Pia; Manca, Michele; Rizzo, Aurora; Abate, Antonio; Gigli, Giuseppe; Suranna, Gian Paolo

2017-07-26

Due to a still limited understanding of the reasons making 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) the state-of-the-art hole-transporting material (HTM) for emerging photovoltaic applications, the molecular tailoring of organic components for perovskite solar cells (PSCs) lacks in solid design criteria. Charge delocalization in radical cationic states can undoubtedly be considered as one of the essential prerequisites for an HTM, but this aspect has been investigated to a relatively minor extent. In marked contrast with the 3-D structure of Spiro-OMeTAD, truxene-based HTMs Trux1 and Trux2 have been employed for the first time in PSCs fabricated with a direct (n-i-p) or inverted (p-i-n) architecture, exhibiting a peculiar behavior with respect to the referential HTM. Notwithstanding the efficient hole extraction from the perovskite layer exhibited by Trux1 and Trux2 in direct configuration devices, their photovoltaic performances were detrimentally affected by their poor hole transport. Conversely, an outstanding improvement of the photovoltaic performances in dopant-free inverted configuration devices compared to Spiro-OMeTAD was recorded, ascribable to the use of thinner HTM layers. The rationalization of the photovoltaic performances exhibited by different configuration devices discussed in this paper can provide new and unexpected prospects for engineering the interface between the active layer of perovskite-based solar cells and the hole transporters.

Spectral observations of hole injection with transition metal oxides for an efficient organic light-emitting diode

NASA Astrophysics Data System (ADS)

Chiu, Tien-Lung; Chuang, Ya-Ting

2015-02-01

Transition metal oxides, such as molybdenum trioxide (MoO3), tungsten trioxide (WO3) and vanadium pent-oxide (V2O5), are well-known hole injection materials used for organic electronic devices. These materials promote work functions of anodes, reduce energy barriers, and facilitate hole transport at the interface between the inorganic anode and organic hole-transporting layer (HTL). In this study, we characterized the transmittance spectra and work function of these materials. Furthermore, we employed a hole-injection layer (HIL) in a blue phosphorescent organic light-emitting diode (OLED) to evaluate their hole-injection capacity by detecting the variation in the emission spectra. Thus, we utilized an OLED structure that has fast electron transporting dynamics to establish the recombination zone located at emitting layer and a partial HTL close to the anode. We used these three transition metal oxides individually as HILs sandwiched between the ITO anode and HTL and concluded that the strength of emissive light from the HTL was determined by their hole-injection capacity, depending on work function. The small amount of HTL emission light of the V2O5 OLED was explained by the high work function of 5.8 eV for the V2O5 film. However, the V2O5 OLED demonstrated the least favorable optoelectrical performance because of its low transmittance and high resistance of the V2O5 film. Ultimately, the 5 nm-MoO3 OLED exhibited the highest device performance because of its high material conductivity and transparency in the visible band.

Light emission in forward and reverse bias operation in OLED with amorphous silicon carbon nitride thin films

NASA Astrophysics Data System (ADS)

Reyes, R.; Cremona, M.; Achete, C. A.

2011-01-01

Amorphous silicon carbon nitride (a-SiC:N) thin films deposited by magnetron sputtering were used in the structure of an organic light emitting diode (OLED), obtaining an OLED operating in forward and reverse bias mode. The device consist of the heterojunction structure ITO/a-SiC:N/Hole Transport Layer (HTL)/ Electron Transport Layer (ETL)/a-SiC:N/Al. As hole transporting layer was used a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline - 6 - carboxyaldehyde - 1,1'- diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq3) is used as electron transport and emitting layer. A significant increase in the voltage operation compared to the conventional ITO/MTCD/Alq3/Al structure was observed, so the onset of electroluminescence occurs at about 22 V in the forward and reverse bias mode of operation. The electroluminescence spectra is similar in both cases, only slightly shifted 0.14 eV to lower energies in relation to the conventional device.

Investigation of mixed-host organic light emitting diodes

NASA Astrophysics Data System (ADS)

Yeh Yee, Kee

One of the limiting factors to the OLED stability or lifetime is the charge buildup at the bilayer heterojunction (HJ) between the hole transport layer (HTL) and electron transport layer (ETL). In recent years, this abrupt interface has been moderated by mixing HTL and ETL to form a single mixed-host, light emitting layer. For uniformly mixed-host (UM) OLED, the device lifetime and also the efficiency were improved due to the spatial broadening of the recombination zone. Similar device architectures, such as the step-wise graded mixed-host (SGM-OLED) and the continuously graded mixed-host (CGM-OLED) have also been implemented by a number of researchers. In this work, a premix of hole transport material (HTM) and electron transport material (ETM), namely TPD and Alq, is prepared for one-step thermal evaporation of the mixed-host light emitting layer (EML). Depending on the evaporation rate, the CGM-OLEDs with different concentration profiles of HTM and ETM in the EML are obtained, which are inversely proportional to each other.

Interlayer electron-hole pair multiplication by hot carriers in atomic layer semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Barati, Fatemeh; Grossnickle, Max; Su, Shanshan; Lake, Roger; Aji, Vivek; Gabor, Nathaniel

Two-dimensional heterostructures composed of atomically thin transition metal dichalcogenides provide the opportunity to design novel devices for the study of electron-hole pair multiplication. We report on highly efficient multiplication of interlayer electron-hole pairs at the interface of a tungsten diselenide / molybdenum diselenide heterostructure. Electronic transport measurements of the interlayer current-voltage characteristics indicate that layer-indirect electron-hole pairs are generated by hot electron impact excitation. Our findings, which demonstrate an efficient energy relaxation pathway that competes with electron thermalization losses, make 2D semiconductor heterostructures viable for a new class of hot-carrier energy harvesting devices that exploit layer-indirect electron-hole excitations. SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Air Force Office of Scientific Research.

Amorphous Hole-Transporting Material based on 2,2'-Bis-substituted 1,1'-Biphenyl Scaffold for Application in Perovskite Solar Cells.

PubMed

Magomedov, Artiom; Sakai, Nobuya; Kamarauskas, Egidijus; Jokubauskaitė, Gabrielė; Franckevičius, Marius; Jankauskas, Vygintas; Snaith, Henry J; Getautis, Vytautas

2017-05-04

Perovskite solar cells are considered a promising technology for solar-energy conversion, with power conversion efficiencies currently exceeding 20 %. In most of the reported devices, Spiro-OMeTAD is used for positive-charge extraction and transport layer. Although a number of alternative hole-transporting materials with different aromatic or heteroaromatic fragments have already been synthesized, a cheap and well-performing hole-transporting material is still in high demand. In this work, a two-step synthesis of a carbazole-based hole-transporting material is presented. Synthesized compounds exhibited amorphous nature, good solubility and thermal stability. The perovskite solar cells employing the newly synthesized material generated a power conversion efficiency of 16.5 % which is slightly lower than that obtained with Spiro-OMeTAD (17.5 %). The low-cost synthesis and high performance makes our hole-transport material promising for applications in perovskite-based optoelectronic devices. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improved performance of organic solar cells with solution processed hole transport layer

NASA Astrophysics Data System (ADS)

Bhargav, Ranoo; Gairola, S. P.; Patra, Asit; Naqvi, Samya; Dhawan, S. K.

2018-06-01

This work is based on Cobalt Oxide as solution processed, inexpensive and effective hole transport layer (HTL) for efficient organic photovoltaic applications (OPVs). In Organic solar cell (OSC) devices ITO coated glass substrate used as a transparent anode electrode for light incident, HTL material Co3O4 dissolve in DMF solvent deposited on anode electrode, after that active layer material (donor/acceptor) deposited on to HTL and finally Al were deposited by thermal evaporation used as cathode electrode. These devices were fabricated with PCDTBT well known low band gap donor material in OSCs and blended with PC71BM as an acceptor material using simplest device structure ITO/Co3O4/active layer/Al at ambient conditions. The power conversion efficiencies (PCEs) based on Co3O4 and PEDOT:PSS have been achieved to up to 3.21% and 1.47% with PCDTBT respectively. In this study we reported that the devices fabricated with Co3O4 showed better performance as compare to the devices fabricated with well known and most studied solution processed HTL material PEDOT:PSS under identical environmental conditions. The surface morphology of the HTL film was characterized by (AFM). Lastly, we have provided Co3O4 as an efficient hole transport material HTL for solution processed organic photovoltaic applications.

Role of Near Substrate and Bulk Polymer Morphology on Out-of-Plane Space-Charge Limited Hole Mobility.

PubMed

Turner, Johnathan; Gadisa, Abay

2016-12-07

Charge transport is a central issue in all types of organic electronic devices. In organic films, charge transport is crucially limited by film microstructure and the nature of the substrate/organic interface interactions. In this report, we discuss the influence of active layer thickness on space-charge limited hole transport in pristine polymer and polymer/fullerene bulk heterojunction thin films (∼15-300 nm) in a diode structure. According to the results, the out-of-plane hole mobility in pristine polymers is sensitive to the degree of polymer chain aggregation. Blending the polymers with a fullerene molecule does not change the trend of hole mobility if the polymer tends to make an amorphous structure. However, employing an aggregating polymer in a bulk heterojunction blend gives rise to a marked difference in charge carrier transport behavior compared to the pristine polymer and this difference is sensitive to active layer thickness. In aggregating polymer films, the thickness-dependent interchain interaction was found to have direct impact on hole mobility. The thickness-dependent mobility trend was found to correspond well with the trend of fill factors of corresponding bulk heterojunction solar cells. This investigation has a vital implication for material design and the development of efficient organic electronic devices, including solar cells and light-emitting diodes.

Measurement of Small Molecular Dopant F4TCNQ and C 60F 36 Diffusion in Organic Bilayer Architectures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jun; Rochester, Chris W.; Jacobs, Ian E.

2015-12-03

The diffusion of molecules through and between organic layers is a serious stability concern in organic electronic devices. In this paper, the temperature-dependent diffusion of molecular dopants through small molecule hole transport layers is observed. Specifically we investigate bilayer stacks of small molecules used for hole transport (MeO-TPD) and p-type dopants (F4TCNQ and C 60F 36) used in hole injection layers for organic light emitting diodes and hole collection electrodes for organic photovoltaics. With the use of absorbance spectroscopy, photoluminescence spectroscopy, neutron reflectometry, and near-edge X-ray absorption fine structure spectroscopy, we are able to obtain a comprehensive picture of themore » diffusion of fluorinated small molecules through MeO-TPD layers. F4TCNQ spontaneously diffuses into the MeO-TPD material even at room temperature, while C 60F 36, a much bulkier molecule, is shown to have a substantially higher morphological stability. Finally, this study highlights that the differences in size/geometry and thermal properties of small molecular dopants can have a significant impact on their diffusion in organic device architectures.« less

Electroactive polymers containing 3-arylcarbazolyl units as hole transporting materials for OLEDs

NASA Astrophysics Data System (ADS)

Krucaite, G.; Liu, L.; Tavgeniene, D.; Peciulyte, L.; Grazulevicius, J. V.; Xie, Z.; Zhang, B.; Grigalevicius, S.

2015-04-01

Monomers and their polymers containing 3-arylcarbazolyl electrophores have been synthesized by the multi-step synthetic route. The materials were characterized by thermo-gravimetric analysis, differential scanning calorimetry and electron photoemission technique. The polymers represent materials of high thermal stability having initial thermal degradation temperatures in the range of 331-411 °C. The glass transition temperatures of the amorphous polymeric materials were in the rage of 148-175 °C. The electron photoemission spectra of thin layers of monomers showed ionization potentials in the range of 5.6-5.65 eV. Hole-transporting properties of the polymers were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole-transporting layers of polyether with 3-naphthylcarbazolyl groups exhibited the best overall performance with a maximum current efficiency of 3.3 cd/A and maximum brightness of about 1000 cd/m2.

Conjugated polyelectrolyte hole transport layer for inverted-type perovskite solar cells

PubMed Central

Choi, Hyosung; Mai, Cheng-Kang; Kim, Hak-Beom; Jeong, Jaeki; Song, Seyeong; Bazan, Guillermo C.; Kim, Jin Young; Heeger, Alan J.

2015-01-01

Organic–inorganic hybrid perovskite materials offer the potential for realization of low-cost and flexible next-generation solar cells fabricated by low-temperature solution processing. Although efficiencies of perovskite solar cells have dramatically improved up to 19% within the past 5 years, there is still considerable room for further improvement in device efficiency and stability through development of novel materials and device architectures. Here we demonstrate that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer (instead of acidic PEDOT:PSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative to PEDOT:PSS, this work is the first report on the use of an organic hole transport material that enables the formation of uniform perovskite films with complete surface coverage and the demonstration of efficient, stable perovskite/fullerene planar heterojunction solar cells. PMID:26081865

Novel Solvent-free Perovskite Deposition in Fabrication of Normal and Inverted Architectures of Perovskite Solar Cells

PubMed Central

Nejand, Bahram Abdollahi; Gharibzadeh, Saba; Ahmadi, Vahid; Shahverdi, H. Reza

2016-01-01

We introduced a new approach to deposit perovskite layer with no need for dissolving perovskite precursors. Deposition of Solution-free perovskite (SFP) layer is a key method for deposition of perovskite layer on the hole or electron transport layers that are strongly sensitive to perovskite precursors. Using deposition of SFP layer in the perovskite solar cells would extend possibility of using many electron and hole transport materials in both normal and invert architectures of perovskite solar cells. In the present work, we synthesized crystalline perovskite powder followed by successful deposition on TiO2 and cuprous iodide as the non-sensitve and sensitive charge transport layers to PbI2 and CH3NH3I solution in DMF. The post compressing step enhanced the efficiency of the devices by increasing the interface area between perovskite and charge transport layers. The 9.07% and 7.71% cell efficiencies of the device prepared by SFP layer was achieved in respective normal (using TiO2 as a deposition substrate) and inverted structure (using CuI as deposition substrate) of perovskite solar cell. This method can be efficient in large-scale and low cost fabrication of new generation perovskite solar cells. PMID:27640991

Observation of hole hopping via dopant in MoOx-doped organic semiconductors: Mechanism analysis and application for high performance organic light-emitting devices

NASA Astrophysics Data System (ADS)

Qiao, Xianfeng; Chen, Jiangshan; Li, Xinglin; Ma, Dongge

2010-05-01

Conduction mechanism in molybdenum trioxide (MoOx)-doped hole- and electron-type organic semiconductors is investigated. The used hole-transporting materials are N ,N'-diphenyl-N ,N'-bis(1-naphthylphenyl)-1, 1'-biphen4, 4'-diamine, 4',4″-tri(N-carbazolyl)triphenylamine, 4, 4'-N,N-dicarbazole-biphenyl, and pentacene and the used electron-transporting material is (8-quinolinolato) aluminum (Alq3). It can be seen that the hole conductivity is significantly enhanced upon MoOx doping, and more importantly, dominant hole current could be realized in a typical electron-transport material Alq3 by doping MoOx. Hence, high efficiency organic light-emitting devices can also be achieved even using MoOx-doped Alq3 film as hole transporting layer. The mechanism investigation indicates that the MoOx plays an important role in the hole transport. It is showed that the MoOx serves as the hole hopping sites, whereas the used organic materials serve as the transport medium and determine the magnitude of transport current. Furthermore, it is found that doping MoOx into the organic materials also reduces the energy and position disorders of the doped organic films, which are well demonstrated by the study on transport characteristics of the doped films at various temperatures.

Effect of inserting a hole injection layer in organic light-emitting diodes: A numerical approach

NASA Astrophysics Data System (ADS)

Lee, Hyeongi; Hwang, Youngwook; Won, Taeyoung

2015-01-01

For investigating the effect of inserting a hole injection layer (HIL), we carried out a computational study concerning organic light-emitting diodes (OLEDs) that had a thin CuPc layer as the hole injection layer. We used S-TAD (2, 2', 7, 7'-tetrakis-(N, Ndiphenylamino)-9, 9-spirobifluoren) for the hole transfer layer, S-DPVBi (4, 4'-bis (2, 2'-diphenylvinyl)-1, 1'-spirobiphenyl) for the emission layer and Alq3 (Tris (8-hyroxyquinolinato) aluminium) for the electron transfer layer. This tri-layer device was compared with four-layer devices. To this tri-layer device, we added a thin CuPc layer, which had a 5.3 eV highest occupied molecular orbital (HOMO) level and a 3.8 eV lowest unoccupied molecular orbital (LUMO) level, as a hole injection layer, and we chose this device for Device A. Also, we varied the LUMO level or the HOMO level of the thin CuPc layer. These two devices were identified as Device C and Device D, respectively. In this paper, we simulated the carrier injection, transport and recombination in these four devices. Thereby, we showed the effect of the HIL, and we demonstrated that the characteristics of these devices were improved by adding a thin layer of CuPc between the anode and the HTL.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

NASA Astrophysics Data System (ADS)

Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

2007-06-01

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

Towards lightweight and flexible high performance nanocrystalline silicon solar cells through light trapping and transport layers

NASA Astrophysics Data System (ADS)

Gray, Zachary R.

This thesis investigates ways to enhance the efficiency of thin film solar cells through the application of both novel nano-element array light trapping architectures and nickel oxide hole transport/electron blocking layers. Experimental results independently demonstrate a 22% enhancement in short circuit current density (JSC) resulting from a nano-element array light trapping architecture and a ˜23% enhancement in fill factor (FF) and ˜16% enhancement in open circuit voltage (VOC) resulting from a nickel oxide transport layer. In each case, the overall efficiency of the device employing the light trapping or transport layer was superior to that of the corresponding control device. Since the efficiency of a solar cell scales with the product of JSC, FF, and VOC, it follows that the results of this thesis suggest high performance thin film solar cells can be realized in the event light trapping architectures and transport layers can be simultaneously optimized. The realizations of these performance enhancements stem from extensive process optimization for numerous light trapping and transport layer fabrication approaches. These approaches were guided by numerical modeling techniques which will also be discussed. Key developments in this thesis include (1) the fabrication of nano-element topographies conducive to light trapping using various fabrication approaches, (2) the deposition of defect free nc-Si:H onto structured topographies by switching from SiH4 to SiF 4 PECVD gas chemistry, and (3) the development of the atomic layer deposition (ALD) growth conditions for NiO. Keywords: light trapping, nano-element array, hole transport layer, electron blocking layer, nickel oxide, nanocrystalline silicon, aluminum doped zinc oxide, atomic layer deposition, plasma enhanced chemical vapor deposition, electron beam lithography, ANSYS HFSS.

High-performance and environmentally stable planar heterojunction perovskite solar cells based on a solution-processed copper-doped nickel oxide hole-transporting layer.

PubMed

Kim, Jong H; Liang, Po-Wei; Williams, Spencer T; Cho, Namchul; Chueh, Chu-Chen; Glaz, Micah S; Ginger, David S; Jen, Alex K-Y

2015-01-27

An effective approach to significantly increase the electrical conductivity of a NiOx hole-transporting layer (HTL) to achieve high-efficiency planar heterojunction perovskite solar cells is demonstrated. Perovskite solar cells based on using Cu-doped NiOx HTL show a remarkably improved power conversion efficiency up to 15.40% due to the improved electrical conductivity and enhanced perovskite film quality. General applicability of Cu-doped NiOx to larger bandgap perovskites is also demonstrated in this study. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modulating Hole Transport in Multilayered Photocathodes with Derivatized p-Type Nickel Oxide and Molecular Assemblies for Solar-Driven Water Splitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shan, Bing; Sherman, Benjamin D.; Klug, Christina M.

2017-08-31

We report here a new photocathode composed of a bi-layered doped NiO film topped by a macro-mesoporous ITO (ioITO) layer with molecular assemblies attached to the ioITO surface. The NiO film containing a 2% K+ doped NiO inner layer and a 2% Cu2+ doped NiO outer layer provides sufficient driving force for hole transport after injection to NiO by the molecular assembly. The tri-layered oxide, NiK0.02O | NiCu0.02O | ioITO, sensitized by a ruthenium polypyridyl dye and functionalized with a nickel-based hydrogen evolution catalyst, outperforms its counterpart, NiO | NiO | ioITO, in photocatalytic hydrogen evolution from water over amore » period of several hours with a Faradaic yield of ~90%.« less

Potential application of CuSbS2 as the hole transport material in perovskite solar cell: A simulation study

NASA Astrophysics Data System (ADS)

Teimouri, R.; Mohammadpour, R.

2018-06-01

CH3 NH3 PbI3 (MAPbI3) thin film solar cells, which are reported at laboratory efficiency scale of nearly 22%, are the subject of much attention by energy researchers due to their low cost buildup, acceptable efficiency, high absorption coefficient and diffusion length. The main purpose of this research is to simulate the structure of thin film perovskite solar cells through numerical simulation of SCAPS based on the empirical data for different hole transport layers. After simulating the initial structure of FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD solar cell, the hole transport layer Spiro-OMeTAD thickness was optimized on a small scale using modeling. The researchers also sought to reduce the amount of this material and the cost of construction. Ultimately, an optimum thickness of 140 nm was obtained for this cell with efficiency of 22.88%. The effect of employing alternative inorganic hole transport layer was investigated as a substitute for Spiro-OMeTAD; Copper antimony sulphide (CuSbS2) was selected due to abundant and available material and high open circuit voltage of about 988 mV. Thickness variations were also performed on a MAPbI3/CuSbS2 solar cell. Finally, It has obtained that perovskite solar cell with 120 nm-thick of CuSbS2 has 23.14% conversion efficiency with acceptable VOC and JSC values.

Formation of BaSi2 heterojunction solar cells using transparent MoOx hole transport layers

NASA Astrophysics Data System (ADS)

Du, W.; Takabe, R.; Baba, M.; Takeuchi, H.; Hara, K. O.; Toko, K.; Usami, N.; Suemasu, T.

2015-03-01

Heterojunction solar cells that consist of 15 nm thick molybdenum trioxide (MoOx, x < 3) as a hole transport layer and 600 nm thick unpassivated or passivated n-BaSi2 layers were demonstrated. Rectifying current-voltage characteristics were observed when the surface of BaSi2 was exposed to air. When the exposure time was decreased to 1 min, an open circuit voltage of 200 mV and a short circuit current density of 0.5 mA/cm2 were obtained under AM1.5 illumination. The photocurrent density under a reverse bias voltage of -1 V reached 25 mA/cm2, which demonstrates the significant potential of BaSi2 for solar cell applications.

Highly efficient organic electroluminescent diodes realized by efficient charge balance with optimized electron and hole transport layers

NASA Astrophysics Data System (ADS)

Khan, M. A.; Xu, Wei; Wei, Fuxiang; Bai, Yu; Jiang, X. Y.; Zhang, Z. L.; Zhu, W. Q.

2007-11-01

Highly efficient organic electroluminescent devices (OLEDs) were developed based on 4,7-diphenyl-1, 10-phenanthroline (BPhen) as the electron transport layer (ETL), tris-(8-hydroxyquinoline) aluminum (Alq 3) as the emission layer (EML) and N,Ń-bis-[1-naphthy(-N,Ńdiphenyl-1,1'-biphenyl-4,4'-diamine)] (NPB) as the hole transport layer (HTL). The typical device structure was glass substrate/ ITO/ NPB/ Alq 3/ BPhen/ LiF/ Al. Since BPhen possesses a considerable high electron mobility of 5×10 -4 cm 2 V -1 s -1, devices with BPhen as ETL can realize an extremely high luminous efficiency. By optimizing the thickness of both HTL and ETL, we obtained a highly efficient OLED with a current efficiency of 6.80 cd/A and luminance of 1361 cd/m 2 at a current density of 20 mA/cm 2. This dramatic improvement in the current efficiency has been explained on the principle of charge balance.

Toward Revealing the Critical Role of Perovskite Coverage in Highly Efficient Electron-Transport Layer-Free Perovskite Solar Cells: An Energy Band and Equivalent Circuit Model Perspective.

PubMed

Huang, Like; Xu, Jie; Sun, Xiaoxiang; Du, Yangyang; Cai, Hongkun; Ni, Jian; Li, Juan; Hu, Ziyang; Zhang, Jianjun

2016-04-20

Currently, most efficient perovskite solar cells (PVKSCs) with a p-i-n structure require simultaneously electron transport layers (ETLs) and hole transport layers (HTLs) to help collecting photogenerated electrons and holes for obtaining high performance. ETL free planar PVKSC is a relatively new and simple structured solar cell that gets rid of the complex and high temperature required ETL (such as compact and mesoporous TiO2). Here, we demonstrate the critical role of high coverage of perovskite in efficient ETL free PVKSCs from an energy band and equivalent circuit model perspective. From an electrical point of view, we confirmed that the low coverage of perovskite does cause localized short circuit of the device. With coverage optimization, a planar p-i-n(++) device with a power conversion efficiency of over 11% was achieved, implying that the ETL layer may not be necessary for an efficient device as long as the perovskite coverage is approaching 100%.

Enhanced efficiency and air-stability of NiOX-based perovskite solar cells via PCBM electron transport layer modification with Triton X-100.

PubMed

Lee, Kisu; Ryu, Jaehoon; Yu, Haejun; Yun, Juyoung; Lee, Jungsup; Jang, Jyongsik

2017-11-02

We modified phenyl-C61-butyric acid methyl ester (PCBM) for use as a stable, efficient electron transport layer (ETL) in inverted perovskite solar cells (PSCs). PCBM containing a surfactant Triton X-100 acts as the ETL and NiO X nanocrystals act as a hole transport layer (HTL). Atomic force microscopy and scanning electron microscopy images showed that surfactant-modified PCBM (s-PCBM) forms a high-quality, uniform, and dense ETL on the rough perovskite layer. This layer effectively blocks holes and reduces interfacial recombination. Steady-state photoluminescence and electrochemical impedance spectroscopy analyses confirmed that Triton X-100 improved the electron extraction performance of PCBM. When the s-PCBM ETL was used, the average power conversion efficiency increased from 10.76% to 15.68%. This improvement was primarily caused by the increases in the open-circuit voltage and fill factor. s-PCBM-based PSCs also showed good air-stability, retaining 83.8% of their initial performance after 800 h under ambient conditions.

Flexible diode of polyaniline/ITO heterojunction on PET substrate

NASA Astrophysics Data System (ADS)

Bera, A.; Deb, K.; Kathirvel, V.; Bera, T.; Thapa, R.; Saha, B.

2017-10-01

Hybrid organic-inorganic heterojunction between polyaniline and ITO film coated on flexible polyethylene terephthalate (PET) substrate has been prepared through vapor phase polymerization process. Polaron and bipolaron like defect states induced hole transport and exceptional mobility makes polyaniline a noble hole transport layer. Thus a p-n junction has been obtained between the hole transport layer of polyaniline and highly conductive n-type layer of ITO film. The synthesis process was carried out using FeCl3 as polymerizing agent in the oxidative chemical polymerization process. The prepared polyaniline has been found to be crystalline on characterization through X-ray diffraction measurement. X-ray photoelectron spectroscopic measurements were done for compositional analysis of the prepared film. The UV-vis-NIR absorbance spectra obtained for polyaniline shows the characteristics absorbance as observed for highly conductive polyaniline and confirms the occurrence of partially oxidized emeraldine form of polyaniline. The energy band gap of the polyaniline has been obtained as 2.52 eV, by analyzing the optical transmittance spectra. A rectifying behavior has been observed in the electrical J-V plot, which is of great significance in designing polymer based flexible electronic devices.

Efficient hybrid white organic light-emitting diodes for application of triplet harvesting with simple structure

NASA Astrophysics Data System (ADS)

Hwang, Kyo Min; Lee, Song Eun; Lee, Sungkyu; Yoo, Han Kyu; Baek, Hyun Jung; Kim, Young Kwan; Kim, Jwajin; Yoon, Seung Soo

2016-08-01

In this study, we fabricated hybrid white organic light-emitting diodes (WOLEDs) based on triplet harvesting with a simple structure. All the hole transporting material and host in the emitting layer (EML) of devices utilized the same material N,N'-di-1-naphthalenyl-N,N'-diphenyl [1,1':4',1″:4″,1‴-quaterphenyl]-4,4‴-diamine (4P-NPD), which is known to be blue fluorescent material. Simple hybrid WOLEDs were fabricated with blue fluorescent, green and red phosphorescent materials. We investigated the effect of triplet harvesting (TH) by an exciton generation zone on simple hybrid WOLEDs. The simple hybrid WOLEDs characteristically had a dominant hole mobility, so an exciton generation zone was expected in the EML. Additionally, the optimal the thickness of the hole transporting layer and electron transporting layer was fabricated a simple hybrid WOLEDs. The simple hybrid WOLED exhibits a maximum luminous efficiency of 29.3 cd/A and a maximum external quantum efficiency of 11.2%. The Commission Internationale de l'Éclairage (International Commission on Illumination) coordinates were (0.45, 0.43) at about 10,000 cd/m2.

Highly efficient and stable inverted perovskite solar cell employing PEDOT:GO composite layer as a hole transport layer.

PubMed

Yu, Jae Choul; Hong, Ji A; Jung, Eui Dae; Kim, Da Bin; Baek, Soo-Min; Lee, Sukbin; Cho, Shinuk; Park, Sung Soo; Choi, Kyoung Jin; Song, Myoung Hoon

2018-01-18

The beneficial use of a hole transport layer (HTL) as a substitution for poly(3,4-ethlyenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is regarded as one of the most important approaches for improving the stability and efficiency of inverted perovskite solar cells. Here, we demonstrate highly efficient and stable inverted perovskite solar cells by applying a GO-doped PEDOT:PSS (PEDOT:GO) film as an HTL. The high performance of this solar cell stems from the excellent optical and electrical properties of the PEDOT:GO film, including a higher electrical conductivity, a higher work function related to the reduced contact barrier between the perovskite layer and the PEDOT:GO layer, enhanced crystallinity of the perovskite crystal, and suppressed leakage current. Moreover, the device with the PEDOT:GO layer showed excellent long-term stability in ambient air conditions. Thus, the enhancement in the efficiency and the excellent stability of inverted perovskite solar cells are promising for the eventual commercialization of perovskite optoelectronic devices.

Hydrophobic Organic Hole Transporters for Improved Moisture Resistance in Metal Halide Perovskite Solar Cells.

PubMed

Leijtens, Tomas; Giovenzana, Tommaso; Habisreutinger, Severin N; Tinkham, Jonathan S; Noel, Nakita K; Kamino, Brett A; Sadoughi, Golnaz; Sellinger, Alan; Snaith, Henry J

2016-03-09

Solar cells based on organic-inorganic perovskite semiconductor materials have recently made rapid improvements in performance, with the best cells performing at over 20% efficiency. With such rapid progress, questions such as cost and solar cell stability are becoming increasingly important to address if this new technology is to reach commercial deployment. The moisture sensitivity of commonly used organic-inorganic metal halide perovskites has especially raised concerns. Here, we demonstrate that the hygroscopic lithium salt commonly used as a dopant for the hole transport material in perovskite solar cells makes the top layer of the devices hydrophilic and causes the solar cells to rapidly degrade in the presence of moisture. By using novel, low cost, and hydrophobic hole transporters in conjunction with a doping method incorporating a preoxidized salt of the respective hole transporters, we are able to prepare efficient perovskite solar cells with greatly enhanced water resistance.

Towards All-Inorganic Transport Layers for Wide-Band-Gap Formamidinium Lead Bromide-Based Planar Photovoltaics

DOE PAGES

Subbiah, Anand S.; Mahuli, Neha; Agarwal, Sumanshu; ...

2017-07-21

Hybrid perovskite photovoltaic devices heavily rely on the use of organic (rather than inorganic) charge-transport layers on top of a perovskite absorber layer because of difficulties in depositing inorganic materials on top of these fragile absorber layers. However, in comparison to the unstable and expensive organic transport materials, inorganic charge-transport layers provide improved charge transport and stability to the device architecture. Here, we report photovoltaic devices using all-inorganic transport layers in a planar p-i-n junction device configuration using formamidinium lead tribromide (FAPbBr 3) as an absorber. Efficient planar devices are obtained through atomic layer deposition of nickel oxide and sputteredmore » zinc oxide as hole- and electron-transport materials, respectively. Using only inorganic charge-transport layers resulted in planar FAPbBr 3 devices with a power conversion efficiency of 6.75% at an open-circuit voltage of 1.23 V. In conclusion, the transition of planar FAPbBr 3 devices making from all-organic towards all-inorganic charge-transport layers is studied in detail.« less

Towards All-Inorganic Transport Layers for Wide-Band-Gap Formamidinium Lead Bromide-Based Planar Photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subbiah, Anand S.; Mahuli, Neha; Agarwal, Sumanshu

Hybrid perovskite photovoltaic devices heavily rely on the use of organic (rather than inorganic) charge-transport layers on top of a perovskite absorber layer because of difficulties in depositing inorganic materials on top of these fragile absorber layers. However, in comparison to the unstable and expensive organic transport materials, inorganic charge-transport layers provide improved charge transport and stability to the device architecture. Here, we report photovoltaic devices using all-inorganic transport layers in a planar p-i-n junction device configuration using formamidinium lead tribromide (FAPbBr 3) as an absorber. Efficient planar devices are obtained through atomic layer deposition of nickel oxide and sputteredmore » zinc oxide as hole- and electron-transport materials, respectively. Using only inorganic charge-transport layers resulted in planar FAPbBr 3 devices with a power conversion efficiency of 6.75% at an open-circuit voltage of 1.23 V. In conclusion, the transition of planar FAPbBr 3 devices making from all-organic towards all-inorganic charge-transport layers is studied in detail.« less

Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin

2015-06-28

We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){submore » 3} as phosphorescent red dopant in electron transport layer.« less

Addressing the efficiency roll-off in a fluorescent OLED by facile electron transport layer doping and carrier confinement

NASA Astrophysics Data System (ADS)

Soman, Anjaly; M, Manuraj; Unni, K. N. Narayanan

2018-05-01

Organic light emitting diodes (OLEDs) often face the issue of decreasing power efficiency with increasing brightness. Loss of charge carrier balance is one of the factors contributing to the efficiency roll-off. We demonstrate that by using a combination of doped electron transport layer (ETL) and a specially chosen electron blocking layer (EBL) having high hole mobility, this efficiency roll-off can be effectively suppressed. A tris-(8-hydroxyquinoline) aluminium (Alq3) based OLED has been fabricated with 2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H,11H-10-(2-benzothiazolyl) quinolizino-[9,9a, 1n gh]coumarin (C545T) as the emissive dopant. Bulk doping of the ETL with lithium fluoride (LiF) was optimized to increase the luminous intensity as well as the current efficiency. An EBL with high hole mobility introduced between the EML and the hole transport layer (HTL) improved the performance drastically, and the device brightness at 9 V got improved by a factor of 2.5 compared to that of the control device. While increasing the brightness from 100 cd/m2 to 1000 cd/m2, the power efficiency drop was 47% for the control device whereas only a drop of 15% was observed for the modified device. The possible mechanisms for the enhanced performance are discussed.

Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boccard, Mathieu; Holman, Zachary C.

Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide beingmore » shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.« less

Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boccard, Mathieu; Holman, Zachary C.

With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphousmore » silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.« less

Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

DOE PAGES

Boccard, Mathieu; Holman, Zachary C.

2015-08-14

With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphousmore » silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.« less

Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch Polymer-Metal Oxide Hybrid Solar Cells.

PubMed

Park, Jong Hwan; Jung, Youngsuk; Yang, Yooseong; Shin, Hyun Suk; Kwon, Soonchul

2016-10-05

For efficient solar cells based on organic semiconductors, a good mixture of photoactive materials in the bulk heterojunction on the length scale of several tens of nanometers is an important requirement to prevent exciton recombination. Herein, we demonstrate that nanoporous titanium dioxide inverse opal structures fabricated using a self-assembled monolayer method and with enhanced infiltration of electron-donating polymers is an efficient electron-extracting layer, which enhances the photovoltaic performance. A calcination process generates an inverse opal structure of titanium dioxide (<70 nm of pore diameters) providing three-dimensional (3D) electron transport pathways. Hole-transporting polymers was successfully infiltrated into the pores of the surface-modified titanium dioxide under vacuum conditions at 200 °C. The resulting geometry expands the interfacial area between hole- and electron-transport materials, increasing the thickness of the active layer. The controlled polymer-coating process over titanium dioxide materials enhanced photocurrent of the solar cell device. Density functional theory calculations show improved interfacial adhesion between the self-assembled monolayer-modified surface and polymer molecules, supporting the experimental result of enhanced polymer infiltration into the voids. These results suggest that the 3D inverse opal structure of the surface-modified titanium dioxide can serve as a favorable electron-extracting layer in further enhancing optoelectronic performance based on organic or organic-inorganic hybrid solar cell.

Causes and effects of a hole. [in Antarctic ozone layer

NASA Technical Reports Server (NTRS)

Margitan, J. J.

1987-01-01

Preliminary results from the U.S. National Ozone Expedition (NOZE) to Antarctica are reviewed. The NOZE ozonesonde measurements showed significant vertical structure in the hole, with 80 percent depletion in some of the 1 km layers but only 20 percent in adjacent layers. The depletion was confined to the 12-20 km region, beginning first at higher altitude and progressing downward. This is strong evidence against the theory that the ozone hole is due to solar activity producing odd nitrogen at high altitudes which is transported downwards, leading to enhanced odd-nitrogen catalytic cycles that destroy ozone. Nitrous oxide data show unusually low concentrations within the polar vortex, which is evidence against the theory that the hole is caused by a purely dynamical mechanism in which rising air motions within the polar vortex lead to reduced column densities of ozone. It is tentatively concluded that a chemical mechanism involving man-made chlorofluorocarbons is the likely cause of ozone depletion in the hole.

Operational stability of electrophosphorescent devices containing p and n doped transport layers

NASA Astrophysics Data System (ADS)

D'Andrade, Brian W.; Forrest, Stephen R.; Chwang, Anna B.

2003-11-01

The operational stability of low-operating voltage p-i-n electrophosphorescent devices containing fac-tris(2-phenylpyridine) iridium as the emissive dopant is investigated. In these devices, Li-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) served as an n-type electron transport layer, or as an undoped hole blocking layer (HBL), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane doped 4,4',4″-tris(3-methylphenylphenylamino) triphenylamine served as a p-type hole transport layer. The glass transition temperature of BPhen can be increased by the addition of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq), resulting in improved morphological stability, thereby reducing device degradation. When thermally stable BAlq was used as a HBL in both p-i-n and undoped devices, the extrapolated operational lifetime (normalized to an initial luminance of 100 cd/m2) of the p-i-n and undoped devices are 18 000 and 60 000 h, respectively, indicating that the presence of p and n dopants can accelerate device degradation.

Ligand-Asymmetric Janus Quantum Dots for Efficient Blue-Quantum Dot Light-Emitting Diodes.

PubMed

Cho, Ikjun; Jung, Heeyoung; Jeong, Byeong Guk; Hahm, Donghyo; Chang, Jun Hyuk; Lee, Taesoo; Char, Kookheon; Lee, Doh C; Lim, Jaehoon; Lee, Changhee; Cho, Jinhan; Bae, Wan Ki

2018-06-19

We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.

Narrow Band Gap Lead Sulfide Hole Transport Layers for Quantum Dot Photovoltaics.

PubMed

Zhang, Nanlin; Neo, Darren C J; Tazawa, Yujiro; Li, Xiuting; Assender, Hazel E; Compton, Richard G; Watt, Andrew A R

2016-08-24

The band structure of colloidal quantum dot (CQD) bilayer heterojunction solar cells is optimized using a combination of ligand modification and QD band gap control. Solar cells with power conversion efficiencies of up to 9.33 ± 0.50% are demonstrated by aligning the absorber and hole transport layers (HTL). Key to achieving high efficiencies is optimizing the relative position of both the valence band and Fermi energy at the CQD bilayer interface. By comparing different band gap CQDs with different ligands, we find that a smaller band gap CQD HTL in combination with a more p-type-inducing CQD ligand is found to enhance hole extraction and hence device performance. We postulate that the efficiency improvements observed are largely due to the synergistic effects of narrower band gap QDs, causing an upshift of valence band position due to 1,2-ethanedithiol (EDT) ligands and a lowering of the Fermi level due to oxidation.

PEDOT: PSS: rGO nanocomposite as a hole transport layer (HTLs) for P3HT:PCBM based organic solar cells

NASA Astrophysics Data System (ADS)

Tiwari, D. C.; Dwivedi, Shailendra Kumar; Dipak, Pukhrambam; Chandel, Tarun

2018-05-01

This paper reports the fabrication process of organic solar cell (OSCs) having structure ITO/PEDOT:PSS:rGO/P3HT:PCBM/Al. In this cell, poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) is ultrasonically mixed with thermally reduced graphene oxide (rGO), which was used as a hole transport layer (HTLs). In order to investigate structural, morphological and optical properties of nanocomposite, XRD, FE-SEM and UV-vis spectroscopy were carried out. We have observed, Jsc = 6.5mA/cm2, Voc = 212 mV, FF=0.31 and PCE of 0.43% from fabricated organic solar cell.

Understanding the Photovoltaic Performance of Perovskite-Spirobifluorene Solar Cells.

PubMed

Song, Zhen; Liu, Jiang; Wang, Gang; Zuo, Wentao; Liao, Cheng; Mei, Jun

2017-11-03

Lead halide perovskite solar cells with remarkable power conversion efficiency have attracted much attention in recent years. However, there still exist many problems with their use that are not completely understood, and further studies are needed. Herein, the hole-transport layer dependence of the photovoltaic performance of perovskite solar cells is investigated in detail. It is found that devices freshly prepared using pristine 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and Li-doped spiro-OMeTAD as hole-transport layers exhibit S-shaped current density-voltage curves with poor fill factors. The devices show progressively improved fill factors and efficiencies upon exposure to air, which is attributed to air-induced conductivity improvement in the spiro-OMeTAD layer. After introducing a cobalt salt dopant (FK209) into the spiro-OMeTAD layer, the corresponding devices show remarkable performance without the need of air exposure. These results confirm that the dopant not only increases the conductivity of spiro-OMeTAD layer, but also tunes the surface potential, which helps to improve charge transport and reduce the recombination loss. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

25th anniversary article: charge transport and recombination in polymer light-emitting diodes.

PubMed

Kuik, Martijn; Wetzelaer, Gert-Jan A H; Nicolai, Herman T; Craciun, N Irina; De Leeuw, Dago M; Blom, Paul W M

2014-01-01

This article reviews the basic physical processes of charge transport and recombination in organic semiconductors. As a workhorse, LEDs based on a single layer of poly(p-phenylene vinylene) (PPV) derivatives are used. The hole transport in these PPV derivatives is governed by trap-free space-charge-limited conduction, with the mobility depending on the electric field and charge-carrier density. These dependencies are generally described in the framework of hopping transport in a Gaussian density of states distribution. The electron transport on the other hand is orders of magnitude lower than the hole transport. The reason is that electron transport is hindered by the presence of a universal electron trap, located at 3.6 eV below vacuum with a typical density of ca. 3 × 10¹⁷ cm⁻³. The trapped electrons recombine with free holes via a non-radiative trap-assisted recombination process, which is a competing loss process with respect to the emissive bimolecular Langevin recombination. The trap-assisted recombination in disordered organic semiconductors is governed by the diffusion of the free carrier (hole) towards the trapped carrier (electron), similar to the Langevin recombination of free carriers where both carriers are mobile. As a result, with the charge-carrier mobilities and amount of trapping centers known from charge-transport measurements, the radiative recombination as well as loss processes in disordered organic semiconductors can be fully predicted. Evidently, future work should focus on the identification and removing of electron traps. This will not only eliminate the non-radiative trap-assisted recombination, but, in addition, will shift the recombination zone towards the center of the device, leading to an efficiency improvement of more than a factor of two in single-layer polymer LEDs. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carrier Injection and Transport in Blue Phosphorescent Organic Light-Emitting Device with Oxadiazole Host

PubMed Central

Chiu, Tien-Lung; Lee, Pei-Yu

2012-01-01

In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD. PMID:22837713

V2O5 thin film deposition for application in organic solar cells

NASA Astrophysics Data System (ADS)

Arbab, Elhadi A. A.; Mola, Genene Tessema

2016-04-01

Vanadium pentoxide V2O5 films were fabricated by way of electrochemical deposition technique for application as hole transport buffer layer in organic solar cell. A thin and uniform V2O5 films were successfully deposited on indium tin oxide-coated glass substrate. The characterization of surface morphology and optical properties of the deposition suggest that the films are suitable for photovoltaic application. Organic solar cell fabricated using V2O5 as hole transport buffer layer showed better devices performance and environmental stability than those devices fabricated with PEDOT:PSS. In an ambient device preparation condition, the power conversion efficiency increases by nearly 80 % compared with PEDOT:PSS-based devices. The devices lifetime using V2O5 buffer layer has improved by a factor of 10 over those devices with PEDOT:PSS.

[White organic light emitting device with dyestuff DCJTB blended in polymer].

PubMed

Zhang, Yan-Fei; Xu, Zheng; Zhang, Fu-Jun; Wang, Yong; Zhao, Su-Ling

2008-04-01

The Alq3 and DCJTB were blended with poly (N-vinylcarbazole) (PVK) in different weight ratios and spin coated into films. Multilayer devices with the light emitting layer PVK : Alq3 : DCJTB were fabricated, and their structure was ITO/ PVK : Alq3 : DCJTB/ BCP/Alq3/LiF/Al in which BCP and Alq3 were employed as the hole-blocking and electron-transporting layers respectively, PVK is the blue light-emitting as well as hole-transporting layer. The mass proportion of PVK relative to Alq3 was tuned while the quality ratio of PVK to DCJTB remained (100 : 1). Finally, fairly pure and stabile white emission was achieved when PVK : Alq3 : DCJTB was 100 : 5 : 1. The CIE coordinate was (0.33, 0.36) at 14 V, which is very stable at various biases (10-14 V).

Fused Methoxynaphthyl Phenanthrimidazole Semiconductors as Functional Layer in High Efficient OLEDs.

PubMed

Jayabharathi, Jayaraman; Ramanathan, Periyasamy; Karunakaran, Chockalingam; Thanikachalam, Venugopal

2016-01-01

Efficient hole transport materials based on novel fused methoxynaphthyl phenanthrimidazole core structure were synthesised and characterized. Their device performances in phosphorescent organic light emitting diodes were investigated. The high thermal stability in combination with the reversible oxidation process made promising candidates as hole-transporting materials for organic light-emitting devices. Highly efficient Alq3-based organic light emitting devices have been developed using phenanthrimidazoles as functional layers between NPB [4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl] and Alq3 [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq3/LiF/Al, a maximum luminous efficiency of 5.99 cd A(-1) was obtained with a maximum brightness of 40,623 cd m(-2) and a power efficiency of 5.25 lm W(-1).

Effect of trapped electrons on the transient current density and luminance of organic light-emitting diode

NASA Astrophysics Data System (ADS)

Lee, Jiun-Haw; Chen, Chia-Hsun; Lin, Bo-Yen; Shih, Yen-Chen; Lin, King-Fu; Wang, Leeyih; Chiu, Tien-Lung; Lin, Chi-Feng

2018-04-01

Transient current density and luminance from an organic light-emitting diode (OLED) driven by voltage pulses were investigated. Waveforms with different repetition rate, duty cycle, off-period, and on-period were used to study the injection and transport characteristics of electron and holes in an OLED under pulse operation. It was found that trapped electrons inside the emitting layer (EML) and the electron transporting layer (ETL) material, tris(8-hydroxyquinolate)aluminum (Alq3) helped for attracting the holes into the EML/ETL and reducing the driving voltage, which was further confirmed from the analysis of capacitance-voltage and displacement current measurement. The relaxation time and trapped filling time of the trapped electrons in Alq3 layer were ~200 µs and ~600 µs with 6 V pulse operation, respectively.

MoS2: a two-dimensional hole-transporting material for high-efficiency, low-cost perovskite solar cells

NASA Astrophysics Data System (ADS)

Kohnehpoushi, Saman; Nazari, Pariya; Abdollahi Nejand, Bahram; Eskandari, Mehdi

2018-05-01

In this work MoS2 thin film was studied as a potential two-dimensional (2D) hole-transporting material for fabrication of low-cost, durable and efficient perovskite solar cells. The thickness of MoS2 was studied as a potential factor in reaching high power conversion efficiency in perovskite solar cells. The thickness of the perovskite layer and the different metal back contacts gave distinct photovoltaic properties to the designed cells. The results show that a single sheet of MoS2 could considerably improve the power conversion efficacy of the device from 10.41% for a hole transport material (HTM)-free device to 20.43% for a device prepared with a 0.67 nm thick MoS2 layer as a HTM. On the back, Ag and Al collected the carriers more efficiently than Au due to the value of their metal contact work function with the TiO2 conduction band. The present work proposes a new architecture for the fabrication of low-cost, durable and efficient perovskite solar cells made from a low-cost and robust inorganic HTM and electron transport material.

MoS2: a two-dimensional hole-transporting material for high-efficiency, low-cost perovskite solar cells.

PubMed

Kohnehpoushi, Saman; Nazari, Pariya; Nejand, Bahram Abdollahi; Eskandari, Mehdi

2018-05-18

In this work MoS 2 thin film was studied as a potential two-dimensional (2D) hole-transporting material for fabrication of low-cost, durable and efficient perovskite solar cells. The thickness of MoS 2 was studied as a potential factor in reaching high power conversion efficiency in perovskite solar cells. The thickness of the perovskite layer and the different metal back contacts gave distinct photovoltaic properties to the designed cells. The results show that a single sheet of MoS 2 could considerably improve the power conversion efficacy of the device from 10.41% for a hole transport material (HTM)-free device to 20.43% for a device prepared with a 0.67 nm thick MoS 2 layer as a HTM. On the back, Ag and Al collected the carriers more efficiently than Au due to the value of their metal contact work function with the TiO 2 conduction band. The present work proposes a new architecture for the fabrication of low-cost, durable and efficient perovskite solar cells made from a low-cost and robust inorganic HTM and electron transport material.

A Molecular Beam Deposition of DNA Nanometer Films

DTIC Science & Technology

2007-01-01

device structure consists of ITO/PEDOT:PSS (50 nm)/NPB (30 nm)/ Alq3 (40 nm)/BCP (20 nm)/ Alq3 (10 nm)/Li:Al, while the Bi- OLED has an additional DNA...layer; DNA- CTMA is an electron blocking layer (EBL); NPB is used as hole transport layer; Alq3 is used for both the electron transport layer and the...N,N’-bis(naphthalen-1-yl)-N,N’- bis(phenyl)benzidine)], Alq3 [tris-(8-hydroxyquinoline) aluminum] and BCP [2,9- Dimethyl-4,7-diphenyl-1,10

Oxasmaragdyrins as New and Efficient Hole-Transporting Materials for High-Performance Perovskite Solar Cells.

PubMed

Mane, Sandeep B; Sutanto, Albertus Adrian; Cheng, Chih-Fu; Xie, Meng-Yu; Chen, Chieh-I; Leonardus, Mario; Yeh, Shih-Chieh; Beyene, Belete Bedemo; Diau, Eric Wei-Guang; Chen, Chin-Ti; Hung, Chen-Hsiung

2017-09-20

The high performance of the perovskite solar cells (PSCs) cannot be achieved without a layer of efficient hole-transporting materials (HTMs) to retard the charge recombination and transport the photogenerated hole to the counterelectrode. Herein, we report the use of boryl oxasmaragdyrins (SM01, SM09, and SM13), a family of aromatic core-modified expanded porphyrins, as efficient hole-transporting materials (HTMs) for perovskite solar cells (PSCs). These oxasmaragdyrins demonstrated complementary absorption spectra in the low-energy region, good redox reversibility, good thermal stability, suitable energy levels with CH 3 NH 3 PbI 3 perovskite, and high hole mobility. A remarkable power conversion efficiency of 16.5% (V oc = 1.09 V, J sc = 20.9 mA cm -2 , fill factor (FF) = 72%) is achieved using SM09 on the optimized PSCs device employing a planar structure, which is close to that of the state-of-the-art hole-transporting materials (HTMs), spiro-OMeTAD of 18.2% (V oc = 1.07 V, J sc = 22.9 mA cm -2 , FF = 74%). In contrast, a poor photovoltaic performance of PSCs using SM01 is observed due to the interactions of terminal carboxylic acid functional group with CH 3 NH 3 PbI 3 .

High-performance inverted planar heterojunction perovskite solar cells based on a solution-processed CuOx hole transport layer.

PubMed

Sun, Weihai; Li, Yunlong; Ye, Senyun; Rao, Haixia; Yan, Weibo; Peng, Haitao; Li, Yu; Liu, Zhiwei; Wang, Shufeng; Chen, Zhijian; Xiao, Lixin; Bian, Zuqiang; Huang, Chunhui

2016-05-19

During the past several years, methylammonium lead halide perovskites have been widely investigated as light absorbers for thin-film photovoltaic cells. Among the various device architectures, the inverted planar heterojunction perovskite solar cells have attracted special attention for their relatively simple fabrication and high efficiencies. Although promising efficiencies have been obtained in the inverted planar geometry based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) sulfonic acid ( PSS) as the hole transport material (HTM), the hydrophilicity of the PSS is a critical factor for long-term stability. In this paper, a CuOx hole transport layer from a facile solution-processed method was introduced into the inverted planar heterojunction perovskite solar cells. After the optimization of the devices, a champion PCE of 17.1% was obtained with an open circuit voltage (Voc) of 0.99 V, a short-circuit current (Jsc) of 23.2 mA cm(-2) and a fill factor (FF) of 74.4%. Furthermore, the unencapsulated device cooperating with the CuOx film exhibited superior performance in the stability test, compared to the device involving the PSS layer, indicating that CuOx could be a promising HTM for replacing PSS in inverted planar heterojunction perovskite solar cells.

Time-of-flight Measurement Of Hole-tunneling Properties And Emission Color Control In Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Kurata, K.; Kashiwabara, K.; Nakajima, K.; Mizoguchi, Y.; Ohtani, N.

2011-12-01

Hole transport properties of organic light-emitting diodes (OLEDs) with a thin hole-blocking layer (HBL) were evaluated by time-of-flight measurement. Electroluminescence (EL) spectra of OLEDs with various HBL thicknesses were also evaluated. The results clearly show that the time-resolved photocurrent response and the emission color strongly depend on HBL thickness. This can be attributed to hole-tunneling through the thin HBL. We successfully fabricated a white OLED by controlling the thickness of HBL.

Exciton Transport and Perfect Coulomb Drag

NASA Astrophysics Data System (ADS)

Nandi, Debaleena

2013-03-01

Exciton condensation is realized in closely-spaced bilayer quantum Hall systems at νT = 1 when the total density in the two 2D electron layers matches the Landau level degeneracy. In this state, electrons in one layer become tightly bound to holes in the other layer, forming a condensate similar to the Cooper pairs in a superconductor. Being charge neutral, these excitons ought to be free to move throughout the bulk of the quantum Hall fluid. One therefore expects that electron current driven in one layer would spontaneously generate a ``hole'' current in the other layer, even in the otherwise insulating bulk of the 2D system. We demonstrate precisely this effect, using a Corbino geometry to defeat edge state transport. Our sample contains two essentially identical two-dimensional electron systems (2DES) in GaAs quantum wells separated by a thin AlGaAs barrier. It is patterned into an annulus with arms protruding from each rim that provide contact to each 2DES separately. A current drag geometry is realized by applying a drive voltage between the outer and inner rim on one 2DES layer while the two rims on the opposite layer are connected together in a closed loop. There is no direct electrical connection between the two layers. At νT = 1 the bulk of the Corbino annulus becomes insulating owing to the quantum Hall gap and net charge transport across the bulk is suppressed. Nevertheless, we find that in the drag geometry appreciable currents do flow in each layer. These currents are almost exactly equal magnitude but, crucially, flow in opposite directions. This phenomenon reflects exciton transport within the νT = 1 condensate, rather than its quasiparticle excitations. We find that quasiparticle transport competes with exciton transport at elevated temperatures, drive levels, and layer separations. This work represents a collaboration with A.D.K. Finck, J.P. Eisenstein, L.N. Pfeiffer and K.W. West. This work is supported by the NSF under grant DMR-1003080.

A novel perovskite solar cell design using aligned TiO2 nano-bundles grown on a sputtered Ti layer and a benzothiadiazole-based, dopant-free hole-transporting material.

PubMed

Ameen, Sadia; Nazim, M; Akhtar, M Shaheer; Nazeeruddin, Mohammad Khaja; Shin, Hyung-Shik

2017-11-16

This work highlights the utilization of a novel hole-transporting material (HTM) derived from benzothiadiazole: 4-(3,5-bis(trifluoromethyl)phenyl)-7-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole (CF-BTz-ThR) and aligned TiO 2 nano-bundles (TiO 2 NBs) as the electron transporting layer (ETL) for perovskite solar cells (PSCs). The aligned TiO 2 NBs were grown on titanium (Ti)-coated FTO substrates using a facile hydrothermal method. The newly designed CF-BTz-ThR molecule with suitable highest occupied molecular orbital (HOMO) favored the effective hole injection from perovskite deposited aligned TiO 2 NBs thin film. The PSCs demonstrated a power conversion efficiency (PCE) of ∼15.4% with a short circuit current density (J sc ) of ∼22.42 mA cm -2 and an open circuit voltage (V oc ) of ∼1.02 V. The efficiency data show the importance of proper molecular engineering whilst highlighting the advantages of dopant-free HTMs in PSCs.

The x-ray time of flight method for investigation of ghosting in amorphous selenium-based flat panel medical x-ray imagers.

PubMed

Rau, A W; Bakueva, L; Rowlands, J A

2005-10-01

Amorphous selenium (a-Se) based real-time flat-panel imagers (FPIs) are finding their way into the digital radiology department because they offer the practical advantages of digital x-ray imaging combined with an image quality that equals or outperforms that of conventional systems. The temporal imaging characteristics of FPIs can be affected by ghosting (i.e., radiation-induced changes of sensitivity) when the dose to the detector is high (e.g., portal imaging and mammography) or the images are acquired at a high frame rate (e.g., fluoroscopy). In this paper, the x-ray time-of-flight (TOF) method is introduced as a tool for the investigation of ghosting in a-Se photoconductor layers. The method consists of irradiating layers of a-Se with short x-ray pulses. From the current generated in the a-Se layer, ghosting is quantified and the ghosting parameters (charge carrier generation rate and carrier lifetimes and mobilities) are assessed. The x-ray TOF method is novel in that (1) x-ray sensitivity (S) and ghosting parameters can be measured simultaneously, (2) the transport of both holes and electrons can be isolated, and (3) the method is applicable to the practical a-Se layer structure with blocking contacts used in FPIs. The x-ray TOF method was applied to an analysis of ghosting in a-Se photoconductor layers under portal imaging conditions, i.e., 1 mm thick a-Se layers, biased at 5 V/ microm, were irradiated using a 6 MV LINAC x-ray beam to a total dose (ghosting dose) of 30 Gy. The initial sensitivity (S0) of the a-Se layers was 63 +/- 2 nC cm(-2) cGy(-1). It was found that S decreases to 30% of S0 after a ghosting dose of 5 Gy and to 21% after 30 Gy at which point no further change in S occurs. At an x-ray intensity of 22 Gy/s (instantaneous dose rate during a LINAC x-ray pulse), the charge carrier generation rate was 1.25 +/- 0.1 x 10(22) ehp m(-3) s(-1) and, to a first approximation, independent of the ghosting dose. However, both hole and electron transport showed a strong dependence on the ghosting dose: hole transport decreased by 61%, electron transport by up to approximately 80%. Therefore, degradation of both hole and electron transport due to the recombination of mobile charge carriers with trapped carriers (of opposite polarity) were identified as the main cause of ghosting in this study.

Low‐Temperature Combustion Synthesis of a Spinel NiCo2O4 Hole Transport Layer for Perovskite Photovoltaics

PubMed Central

Papadas, Ioannis T.; Ioakeimidis, Apostolos; Armatas, Gerasimos S.

2018-01-01

Abstract The synthesis and characterization of low‐temperature solution‐processable monodispersed nickel cobaltite (NiCo2O4) nanoparticles (NPs) via a combustion synthesis is reported using tartaric acid as fuel and the performance as a hole transport layer (HTL) for perovskite solar cells (PVSCs) is demonstrated. NiCo2O4 is a p‐type semiconductor consisting of environmentally friendly, abundant elements and higher conductivity compared to NiO. It is shown that the combustion synthesis of spinel NiCo2O4 using tartaric acid as fuel can be used to control the NPs size and provide smooth, compact, and homogeneous functional HTLs processed by blade coating. Study of PVSCs with different NiCo2O4 thickness as HTL reveals a difference on hole extraction efficiency, and for 15 nm, optimized thickness enhanced hole carrier collection is achieved. As a result, p‐i‐n structure of PVSCs with 15 nm NiCo2O4 HTLs shows reliable performance and power conversion efficiency values in the range of 15.5% with negligible hysteresis. PMID:29876223

Tuning charge balance in PHOLEDs with ambipolar host materials to achieve high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Padmaperuma, Asanga B.; Koech, Phillip K.; Cosimbescu, Lelia

2009-08-27

The efficiency and stability of blue organic light emitting devices (OLEDs) continue to be a primary roadblock to developing organic solid state white lighting. For OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage in a white light emitting device.1 It is generally accepted that such high quantum efficiency, can only be achieved with the use of organometallic phosphor doped OLEDs. Blue OLEDs are particularly important for solid state lighting. The simplest (and therefore likely the lowest cost) method of generating white light is to downmore » convert part of the emission from a blue light source with a system of external phosphors.2 A second method of generating white light requires the superposition of the light from red, green and blue OLEDs in the correct ratio. Either of these two methods (and indeed any method of generating white light with a high color rendering index) critically depends on a high efficiency blue light component.3 A simple OLED generally consists of a hole-injecting anode, a preferentially hole transporting organic layer (HTL), an emissive layer that contains the recombination zone and ideally transports both holes and electrons, a preferentially electron-transporting layer (ETL) and an electron-injecting cathode. Color in state-of-the-art OLEDs is generated by an organometallic phosphor incorporated by co-sublimation into the emissive layer (EML).4 New materials functioning as hosts, emitters, charge transporting, and charge blocking layers have been developed along with device architectures leading to electrophosphorescent based OLEDs with high quantum efficiencies near the theoretical limit. However, the layers added to the device architecture to enable high quantum efficiencies lead to higher operating voltages and correspondingly lower power efficiencies. Achievement of target luminance power efficiencies will require new strategies for lowering operating voltages, particularly if this is to be achieved in a device that can be manufactured at low cost. To avoid the efficiency losses associated with phosphorescence quenching by back-energy transfer from the dopant onto the host, the triplet excited states of the host material must be higher in energy than the triplet excited state of the dopant.5 This must be accomplished without sacrificing the charge transporting properties of the composite.6 Similar problems limit the efficiency of OLED-based displays, where blue light emitters are the least efficient and least stable. We previously demonstrated the utility of organic phosphine oxide (PO) materials as electron transporting HMs for FIrpic in blue OLEDs.7 However, the high reluctance of PO materials to oxidation and thus, hole injection limits the ability to balance charge injection and transport in the EML without relying on charge transport by the phosphorescent dopant. PO host materials were engineered to transport both electrons and holes in the EML and still maintain high triplet exciton energy to ensure efficient energy transfer to the dopant (Figure 1). There are examples of combining hole transporting moieties (mainly aromatic amines) with electron transport moieties (e.g., oxadiazoles, triazines, boranes)8 to develop new emitter and host materials for small molecule and polymer9 OLEDs. The challenge is to combine the two moieties without lowering the triplet energy of the target molecule. For example, coupling of a dimesitylphenylboryl moiety with a tertiary aromatic amine (FIAMBOT) results in intramolecular electron transfer from the amine to the boron atom through the bridging phenyl. The mesomeric effect of the dimesitylphenylboryl unit acts to extend conjugation and lowers triplet exciton energies (< 2.8 eV) rendering such systems inadequate as ambipolar hosts for blue phosphors.« less

Carbon materials for enhancing charge transport in the advancements of perovskite solar cells

NASA Astrophysics Data System (ADS)

Hu, Ruiyuan; Chu, Liang; Zhang, Jian; Li, Xing'ao; Huang, Wei

2017-09-01

Organic-inorganic halide perovskite solar cells (PSCs) have become a new favorite in the photovoltaic field, due to the boosted efficiency up to 22.1%. Despite a flow of achievements, there are certain challenges to simultaneously meet high efficiency, large scale, low cost and high stability. Due to the low cost, extensive sources, high electrical conductivity and chemical stability, carbon materials have made undeniable contributions to play positive roles in developing PSCs. Carbon materials not only have the favorable conductivity but also bipolar advantage, which can transfer both electrons and holes. In this review, we will discuss how the carbon materials transfer charge or accelerate charge transport by incorporation in PSCs. Carbon materials can replace transparent conductive oxide layers, and enhance electron transport in electron transport layers. Moreover, carbon materials with continuous structure, especially carbon nanotubes and graphene, can provide direct charge transport channel that make them suitable additives or even substitutes in hole transport layers. Especially, the successful application of carbon materials as counter electrodes makes the devices full-printable, low temperature and high stability. Finally, a brief outlook is provided on the future development of carbon materials for PSCs, which are expected to devote more contributions in the future photovoltaic market.

Molecularly "engineered" anode adsorbates for probing OLED interfacial structure-charge injection/luminance relationships: large, structure-dependent effects.

PubMed

Huang, Qinglan; Evmenenko, Guennadi; Dutta, Pulak; Marks, Tobin J

2003-12-03

Molecule-scale structure effects at organic light-emitting diodes (OLED) anode-organic transport layer interfaces are probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine molecules differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure, charge injection and electroluminescence properties. Dramatic variations in hole injection magnitude and OLED performance can be correlated with the molecular structures and electrochemically derived heterogeneous electron-transfer rates of such triarylamine fragments, placed precisely at the anode-hole transport layer interface. Very bright and efficient ( approximately 70 000 cd/m2 and approximately 2.5% forward external quantum efficiency) OLEDs have thereby been fabricated.

Aerosol-assisted chemical vapor deposition of ultra-thin CuOx films as hole transport material for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Zhang, Zhixin; Chen, Shuqun; Li, Pingping; Li, Hongyi; Wu, Junshu; Hu, Peng; Wang, Jinshu

This paper reports on the fabrication of CuOx films to be used as hole transporting layer (HTL) in CH3NH3PbI3 perovskite solar cells (PSCs). Ultra-thin CuOx coatings were grown onto FTO substrates for the first time via aerosol-assisted chemical vapor deposition (AACVD) of copper acetylacetonate in methanol. After incorporating into the PSCs prepared at ambient air, a highest power conversion efficiency (PCE) of 8.26% with HTL and of 3.34% without HTL were achieved. Our work represents an important step in the development of low-cost CVD technique for fabricating ultra-thin metal oxide functional layers in thin film photovoltaics.

Tunable photoelectric response in NiO-based heterostructures by various orientations

NASA Astrophysics Data System (ADS)

Luo, Yidong; Qiao, Lina; Zhang, Qinghua; Xu, Haomin; Shen, Yang; Lin, Yuanhua; Nan, Cewen

2018-02-01

We engineered various orientations of NiO layers for NiO-based heterostructures (NiO/Au/STO) to investigate their effects on the generation of hot electrons and holes. Our calculation and experimental results suggested that bandgap engineering and the orientation of the hole transport layer (NiO) were crucial elements for the optimization of photoelectric responses. The (100)-orientated NiO/Au/STO achieved the highest photo-current density (˜30 μA/cm2) compared with (111) and (110)-orientated NiO films, which was attributed to the (100) films's lowest effective mass of photogenerated holes (˜1.82 m0) and the highest efficiency of separating and transferring electron-holes of the (100)-orientated sample. Our results opened a direction to design a high efficiency photoelectric solar cell.

An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic-inorganic hybrid perovskite solar cells.

PubMed

Seo, Seongrok; Park, Ik Jae; Kim, Myungjun; Lee, Seonhee; Bae, Changdeuck; Jung, Hyun Suk; Park, Nam-Gyu; Kim, Jin Young; Shin, Hyunjung

2016-06-02

NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis.

Simulation of mixed-host emitting layer based organic light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riku, C.; Kee, Y. Y.; Ong, T. S.

2015-04-24

‘SimOLED’ simulator is used in this work to investigate the efficiency of the mixed-host organic light emitting devices (MH-OLEDs). Tris-(8-hydroxyquinoline) aluminum(3) (Alq{sub 3}) and N,N-diphenyl-N,N-Bis(3-methylphenyl)-1,1-diphenyl-4,4-diamine (TPD) are used as the electron transport layer (ETL) material and hole transport layer (HTL) material respectively, and the indium-doped tin oxide (ITO) and aluminum (Al) as anode and cathode. Three MH-OLEDs, A, B and C with the same structure of ITO / HTM (15 nm) / Mixed host (70 nm) / ETM (10 nm) /Al, are stimulated with ratios TPD:Alq{sub 3} of 3:5, 5:5, and 5:3 respectively. The Poole-Frenkel model for electron and hole mobilities is employedmore » to compute the current density-applied voltage-luminance characteristics, distribution of the electric field, carrier concentrations and recombination rate.« less

Two-Step Physical Deposition of a Compact CuI Hole-Transport Layer and the Formation of an Interfacial Species in Perovskite Solar Cells.

PubMed

Gharibzadeh, Saba; Nejand, Bahram Abdollahi; Moshaii, Ahmad; Mohammadian, Nasim; Alizadeh, Amir Hossein; Mohammadpour, Rahele; Ahmadi, Vahid; Alizadeh, Abdolali

2016-08-09

A simple and practical approach is introduced for the deposition of CuI as an inexpensive inorganic hole-transport material (HTM) for the fabrication of low cost perovskite solar cells (PSCs) by gas-solid phase transformation of Cu to CuI. The method provides a uniform and well-controlled CuI layer with large grains and good compactness that prevents the direct connection between the contact electrodes. Solar cells prepared with CuI as the HTM with Au electrodes displays an exceptionally high short-circuit current density of 32 mA cm(-2) , owing to an interfacial species formed between the perovskite and the Cu resulting in a long wavelength contribution to the incident photon-to-electron conversion efficiency (IPCE), and an overall power conversion efficiency (PCE) of 7.4 %. The growth of crystalline and uniform CuI on a low roughness perovskite layer leads to remarkably high charge extraction in the cells, which originates from the high hole mobility of CuI in addition to a large number of contact points between CuI and the perovskite layer. In addition, the solvent-free method has no damaging side effect on the perovskite layer, which makes it an appropriate method for large scale applications of CuI in perovskite solar cells. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Züfle, Simon; Altazin, Stéphane; Hofmann, Alexander; Jäger, Lars; Neukom, Martin T.; Schmidt, Tobias D.; Brütting, Wolfgang; Ruhstaller, Beat

2017-05-01

We demonstrate the application of the CELIV (charge carrier extraction by linearly increasing voltage) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (α-NPD). In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility. In fully operating devices, however, bipolar carrier transport and recombination complicate the analysis of CELIV transients as well as the assignment of the extracted mobility value to one charge carrier species. This has motivated a new approach of fabricating dedicated metal-insulator-semiconductor (MIS) devices, where the extraction current contains signatures of only one charge carrier type. In this work, we show that the MIS-CELIV concept can be employed in bilayer polar OLEDs as well, which are easy to fabricate using most common electron transport layers (ETLs), like Tris-(8-hydroxyquinoline)aluminum (Alq3). Due to the macroscopic polarization of the ETL, holes are already injected into the hole transport layer below the built-in voltage and accumulate at the internal interface with the ETL. This way, by a standard CELIV experiment only holes will be extracted, allowing us to determine their mobility. The approach can be established as a powerful way of selectively measuring charge mobilities in new materials in a standard device configuration.

Hole transporting material 5, 10, 15-tribenzyl-5H-diindolo[3, 2-a:3‧, 2‧-c]-carbazole for efficient optoelectronic applications as an active layer

NASA Astrophysics Data System (ADS)

Zheng, Yan-Qiong; J. Potscavage, William, Jr.; Zhang, Jian-Hua; Wei, Bin; Huang, Rong-Juan

2015-02-01

In order to explore the novel application of the transparent hole-transporting material 5,10,15-tribenzyl-5H-diindolo[3,2-a:3‧,2‧-c]-carbazole (TBDI), in this article TBDI is used as an active layer but not a buffer layer in a photodetector (PD), organic light-emitting diode (OLED), and organic photovoltaic cell (OPV) for the first time. Firstly, the absorption and emission spectra of a blend layer comprised of TBDI and electron-transporting material bis-(2-methyl-8-quinolinate) 4-phenylphenolate (BAlq) are investigated. Based on the absorption properties, an organic PD with a peak absorption at 320 nm is fabricated, and a relatively-high detectivity of 2.44 × 1011 cm·Hz1/2/W under 320-nm illumination is obtained. The TBDI/tris (8-hydroxyquinoline) aluminum (Alq3) OLED device exhibits a comparable external quantum efficiency and current efficiency to a traditional 4, 4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD)/Alq3 OLED. A C70-based Schottky junction with 5 wt%-TBDI yields a power conversion efficiency of 5.0%, which is much higher than 1.7% for an α-NPD-based junction in the same configuration. These results suggest that TBDI has some promising properties which are in favor of the hole-transporting in Schottky junctions with a low-concentration donor. Project supported by the Funding Program for World-Leading Innovative R & D on Science and Technology (FIRST) from JSPS, the Fund from the Science and Technology Commission of Shanghai Municipality, China (Grant Nos. 14DZ2280900 and 14XD1401800), and the Natural Science Foundation of Shanghai (Grant No. 15ZR1416600).

Polymers Containing Diphenylvinyl-Substituted Indole Rings as Charge-Transporting Materials for OLEDs

NASA Astrophysics Data System (ADS)

Grigalevicius, S.; Zostautiene, R.; Sipaviciute, D.; Stulpinaite, B.; Volyniuk, D.; Grazulevicius, J. V.; Liu, L.; Xie, Z.; Zhang, B.

2016-02-01

Monomers and polymers containing electronically isolated diphenylvinyl-substituted indole rings were synthesized and characterized by nuclear magnetic resonance (NMR) and mass spectroscopies as well as by gel permeation chromatography. The polymers represent amorphous materials with glass transition temperatures of 91-109°C and thermal decomposition starting above 307°C. Electron photoemission spectra of thin films of the synthesized polymers revealed ionization potentials of 5.54-5.58 eV. The synthesized polymers were tested as hole-transporting materials in simple electroluminescent organic light-emitting diode (OLED) devices with tris(quinolin-8-olato)aluminium (Alq3) as an emitter as well as an electron-transporting layer. A green OLED device containing a hole-transporting layer of poly[1-(2,3-epithiopropyl)-2-methyl-3-(2,2-diphenylvinyl)índole] exhibited the best overall performance with a driving voltage of 4.0 V, maximum photometric efficiency of 2.8 cd/A and maximum brightness of about 4200 cd/m2.

A numerical study on the charge transport in TPD/Alq3-based organic light emitting diodes.

PubMed

Kim, K S; Hwang, Y W; Lee, H G; Won, T Y

2014-08-01

We report our simulation study on the charge transport characteristic of the multi-layer structure for organic light emitting diodes (OLEDs). We performed a numerical simulation on a multilayer structure comprising a hole transport layer (HTL), an emission layer (EML), and an electron transport layer (ETL) between both electrodes. The material of the HTL is TPD (N,N'-Bis (3-methylphenyl)-N,N'-bis(phenyl) benzidine), and the ETL includes Alq3 (Tris (8-hyroxyquinolinato) aluminium). Here, we investigated the parameters such as recombination rates which influence the efficiency of the charge transport between layers in bilayer OLEDs. We also analyzed a transient response during the turn on/off period and the carrier transport in accordance with the variation of the injection barrier and applied voltage. In addition, our numerical simulation revealed that the insertion of the EML affects the photonic characteristics in bilayer structure and also the efficiency due to the difference in the internal barrier height.

Manipulation and control of the interfacial polarization in organic light-emitting diodes by dipolar doping

NASA Astrophysics Data System (ADS)

Jäger, Lars; Schmidt, Tobias D.; Brütting, Wolfgang

2016-09-01

Most of the commonly used electron transporting materials in organic light-emitting diodes exhibit interfacial polarization resulting from partially aligned permanent dipole moments of the molecules. This property modifies the internal electric field distribution of the device and therefore enables an earlier flat band condition for the hole transporting side, leading to improved charge carrier injection. Recently, this phenomenon was studied with regard to different materials and degradation effects, however, so far the influence of dilution has not been investigated. In this paper we focus on dipolar doping of the hole transporting material 4,4-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) with the polar electron transporting material tris-(8-hydroxyquinolate) aluminum (Alq3). Impedance spectroscopy reveals that changes of the hole injection voltage do not scale in a simple linear fashion with the effective thickness of the doped layer. In fact, the measured interfacial polarization reaches a maximum value for a 1:1 blend. Taking the permanent dipole moment of Alq3 into account, an increasing degree of dipole alignment is found for decreasing Alq3 concentration. This observation can be explained by the competition between dipole-dipole interactions leading to dimerization and the driving force for vertical orientation of Alq3 dipoles at the surface of the NPB layer.

Fabrication of Semi-quasi Solid DSSC using Spiro Material as Hole Transport Material

NASA Astrophysics Data System (ADS)

Safriani, L.; Primawati, W. P.; Mulyana, C.; Susilawati, T.; Aprilia, A.

2017-05-01

Dye Sensitized Solar Cells (DSSC) has been emerging a promising development in recent years. DSSC is a low-cost solar cell belonging to the third generation of solar cells. However, the conversion efficiency of DSSC is still far behind compared to silicon based solar cells. To produce long stability of DSSC, the used of solid state electrolyte is recommended instead of liquid electrolyte, though solid state DSSC also has problem relating to a lack of pore-filling hole transport material into mesoporous TiO2. In this work an attempt to improve performance of DSSC has been done by adding hole transport material into mesoporous TiO2 layer and optimizing fabrication method. In the first part of the work, we used low Tg material spiro-TAD and spiro-TPD as hole transport material with mosalyte and hybrid polymer as gel electrolyte to obtain a semi-quasi solid DSSC. In the second part, we modified fabrication method by annealing process before spin-coated spiro material into dye-coated TiO2 substrate. Current-voltage measurement of semi-quasi solid DSSC was performed using halogen lamp. We found that the used of spiro-TPD as hole transport give the best power conversion efficiency η = 2.03% of semi-quasi solid DSSC.

Phosphorescent organic light emitting diodes with high efficiency and brightness

DOEpatents

Forrest, Stephen R; Zhang, Yifan

2015-11-12

An organic light emitting device including a) an anode; b) a cathode; and c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising an organic host compound and a phosphorescent compound exhibiting a Stokes Shift overlap greater than 0.3 eV. The organic light emitting device may further include a hole transport layer disposed between the emissive layer and the anode; and an electron transport layer disposed between the emissive layer and the cathode. In some embodiments, the phosphorescent compound exhibits a phosphorescent lifetime of less than 10 .mu.s. In some embodiments, the concentration of the phosphorescent compound ranges from 0.5 wt. % to 10 wt. %.

Undoped GaAs bilayers for exciton condensation experiments

NASA Astrophysics Data System (ADS)

Lilly, M. P.

2005-03-01

Experimental progress in transport studies of exciton condensation of in electron and hole bilayers at high magnetic fields [1,2] has shown this novel physics can be observed. Fabrication of the bipolar electron-hole bilayers for zero field studies of exciton condensation still remains elusive. We describe a series of experiments on undoped GaAs/AlGaAs heterostructures with the motivation of making electron-hole bilayers. In these undoped devices, external electric fields induce carriers rather than the traditional doping techniques. Single layer electron (or hole) devices demonstrate a high mobility over a wide range of density. More recently, fully undoped bilayers have been made where the density in each layer is independently controlled with gates on the top and bottom of the bilayer. In this talk we present high field transport of undoped electron-electron bilayers, and describe recent progress towards extending the fabrication techniques to creating electron-hole bilayers for exciton condensation studies at zero magnetic field. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. 1. M. Kellogg, J. P. Eisenstein, L. N. Pfeiffer, and K. W. West, Phys. Rev. Lett. 93 036801 (2004). 2. E. Tutoc, M. Shayegan, and D. A. Huse, Phys. Rev. Lett. 93, 036802 (2004).

Effect of Nonionic Surfactant Additive in PEDOT:PSS on PFO Emission Layer in Organic-Inorganic Hybrid Light-Emitting Diode.

PubMed

Cho, Seong Rae; Porte, Yoann; Kim, Yun Cheol; Myoung, Jae-Min

2018-03-21

Poly(9,9-dioctylfluorene) (PFO) has attracted significant interests owing to its versatility in electronic devices. However, changes in its optical properties caused by its various phases and the formation of oxidation defects limit the application of PFO in light-emitting diodes (LEDs). We investigated the effects of the addition of Triton X-100 (hereinafter shortened as TX) in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to induce interlayer diffusion between PEDOT:PSS and PFO to enhance the stability of the PFO phase and suppress its oxidation. Photoluminescence (PL) measurement on PFO/TX-mixed PEDOT:PSS layers revealed that, upon increasing the concentration of TX in the PEDOT:PSS layer, the β phase of PFO could be suppressed in favor of the glassy phase and the wide PL emission centered at 535 nm caused by ketone defects formed by oxidation was decreased considerably. LEDs were then fabricated using PFO as an emission layer, TX-mixed PEDOT:PSS as hole-transport layer, and zinc oxide (ZnO) nanorods as electron-transport layer. As the TX concentration reached 3 wt %, the devices exhibited dramatic increases in current densities, which were attributed to the enhanced hole injection due to TX addition, along with a shift in the dominant emission wavelength from a green electroluminescence (EL) emission centered at 518 nm to a blue EL emission centered at 448 nm. The addition of TX in PEDOT:PSS induced a better hole injection in the PFO layer, and through interlayer diffusion, stabilized the glassy phase of PFO and limited the formation of oxidation defects.

Controlling charge balance and exciton recombination by bipolar host in single-layer organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Qiao, Xianfeng; Tao, Youtian; Wang, Qiang; Ma, Dongge; Yang, Chuluo; Wang, Lixiang; Qin, Jingui; Wang, Fosong

2010-08-01

Highly efficient single-layer organic light-emitting diodes with reduced efficiency roll-off are demonstrated by using a bipolar host material of 2,5-bis(2-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o-CzOXD) doped with iridium complexes as the emissive layer. For example, the green single-layer device, employing fac-tris(2-phenylpyridine)iridium Ir(ppy)3 as dopant, shows a peak current efficiency of 45.57 cd A-1, corresponding to external quantum efficiency (EQE) of 12.42%, and still exhibits efficiencies of 45.26 cd A-1 and 40.42 cd A-1 at luminance of 1000 and 10 000 cd m-2, respectively. In addition, the yellow and red single-layer devices, with bis(2-(9,9- diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N ,C3)iridium(acetylacetonate) (fbi)2Ir(acac) and bis(1-phenylisoquinolinolato-C2,N)iridium(acetylacetonate) (piq)2Ir(acac) as emitter, also show high EQE of 7.04% and 7.28%, respectively. The transport properties of o-CzOXD film are well investigated by current-voltage measurement, from which both hole and electron mobility are determined. It is found that the o-CzOXD shows appealing bipolar transport character, which is favor for the balanced charge distribution in the whole doped zone. More importantly, the multifunctional role of hole trapping and electron transporting of the iridium complex in o-CzOXD further balances the charge carriers and broadens the recombination zone. As a result, the recombination of electrons and holes is significantly improved and the triplet-triplet annihilation and triplet-polaron quenching processes are effectively suppressed, eventually leading to the high efficiency as well as the reduced efficiency roll-off.

Bifacial Modified Charge Transport Materials for Highly Efficient and Stable Inverted Perovskite Solar Cells.

PubMed

Li, Xin; Zhao, Xingyue; Hao, Feng; Yin, Xuewen; Yao, Zhibo; Zhou, Yu; Shen, Heping; Lin, Hong

2018-05-30

Significant efforts have been devoted to enhancing both the performance and long-term stability of lead halide perovskite solar cells (PSCs) to promote their practical application. In this context, a self-assembled monolayer composed of a dye molecule is demonstrated for the first time to be efficient in passivating the surface of the hole transport layer, NiO x , in the p-i-n PSCs through multiple functions, including the minimization of energy-level offset, reducing surface trap states, and enhancing wetting between NiO x and perovskite layers coupled with increasing perovskite crystallinity. Consequently, the dye monolayer has sufficiently improved the hole extraction efficiency and suppressed the charge recombination, validated by steady and transient photoluminescence measurements and the electrochemical impedance analysis. Concurrently, a mixed layer of BaSnO 3 nanoparticles and [6,6]-phenyl-C 61 -butyric acid methyl (PCBM) (barium stannate (BSO)/PCBM) was exploited as an efficient electron transport layer, resulting in superior electron transport properties and correspondingly excellent device stability. By incorporating these bifacial modifications, the device performance of the inverted PSC was propelled to 16.2%, compared with 14.0% for that without any interfacial and compositional engineering. Benefiting from the excellent crystallinity of the perovskite through dye passivation and the blocking of moisture, oxygen, and ion migration by using the hybrid BSO/PCBM layer, over 90% of the initial power conversion efficiency has been preserved for the device after exposure to ambient air for 650 h.

Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%

NASA Astrophysics Data System (ADS)

Arora, Neha; Dar, M. Ibrahim; Hinderhofer, Alexander; Pellet, Norman; Schreiber, Frank; Zakeeruddin, Shaik Mohammed; Grätzel, Michael

2017-11-01

Perovskite solar cells (PSCs) with efficiencies greater than 20% have been realized only with expensive organic hole-transporting materials. We demonstrate PSCs that achieve stabilized efficiencies exceeding 20% with copper(I) thiocyanate (CuSCN) as the hole extraction layer. A fast solvent removal method enabled the creation of compact, highly conformal CuSCN layers that facilitate rapid carrier extraction and collection. The PSCs showed high thermal stability under long-term heating, although their operational stability was poor. This instability originated from potential-induced degradation of the CuSCN/Au contact. The addition of a conductive reduced graphene oxide spacer layer between CuSCN and gold allowed PSCs to retain >95% of their initial efficiency after aging at a maximum power point for 1000 hours under full solar intensity at 60°C. Under both continuous full-sun illumination and thermal stress, CuSCN-based devices surpassed the stability of spiro-OMeTAD-based PSCs.

The x-ray time of flight method for investigation of ghosting in amorphous selenium-based flat panel medical x-ray imagers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rau, A.W.; Bakueva, L.; Rowlands, J.A.

2005-10-15

Amorphous selenium (a-Se) based real-time flat-panel imagers (FPIs) are finding their way into the digital radiology department because they offer the practical advantages of digital x-ray imaging combined with an image quality that equals or outperforms that of conventional systems. The temporal imaging characteristics of FPIs can be affected by ghosting (i.e., radiation-induced changes of sensitivity) when the dose to the detector is high (e.g., portal imaging and mammography) or the images are acquired at a high frame rate (e.g., fluoroscopy). In this paper, the x-ray time-of-flight (TOF) method is introduced as a tool for the investigation of ghosting inmore » a-Se photoconductor layers. The method consists of irradiating layers of a-Se with short x-ray pulses. From the current generated in the a-Se layer, ghosting is quantified and the ghosting parameters (charge carrier generation rate and carrier lifetimes and mobilities) are assessed. The x-ray TOF method is novel in that (1) x-ray sensitivity (S) and ghosting parameters can be measured simultaneously (2) the transport of both holes and electrons can be isolated, and (3) the method is applicable to the practical a-Se layer structure with blocking contacts used in FPIs. The x-ray TOF method was applied to an analysis of ghosting in a-Se photoconductor layers under portal imaging conditions, i.e., 1 mm thick a-Se layers, biased at 5 V/{mu}m, were irradiated using a 6 MV LINAC x-ray beam to a total dose (ghosting dose) of 30 Gy. The initial sensitivity (S{sub 0}) of the a-Se layers was 63{+-}2 nC cm{sup -2} cGy{sup -1}. It was found that S decreases to 30% of S{sub 0} after a ghosting dose of 5 Gy and to 21% after 30 Gy at which point no further change in S occurs. At an x-ray intensity of 22 Gy/s (instantaneous dose rate during a LINAC x-ray pulse), the charge carrier generation rate was 1.25{+-}0.1x10{sup 22} ehp m{sup -3} s{sup -1} and, to a first approximation, independent of the ghosting dose. However, both hole and electron transport showed a strong dependence on the ghosting dose: hole transport decreased by 61%, electron transport by up to {approx}80%. Therefore, degradation of both hole and electron transport due to the recombination of mobile charge carriers with trapped carriers (of opposite polarity) were identified as the main cause of ghosting in this study.« less

Charge transport in quantum dot organic solar cells with Si quantum dots sandwiched between poly(3-hexylthiophene) (P3HT) absorber and bathocuproine (BCP) transport layers

NASA Astrophysics Data System (ADS)

Verma, Upendra Kumar; Kumar, Brijesh

2017-10-01

We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC).

Post-Treatment-Free Solution-Processed Reduced Phosphomolybdic Acid Containing Molybdenum Oxide Units for Efficient Hole-Injection Layers in Organic Light-Emitting Devices.

PubMed

Ohisa, Satoru; Endo, Kohei; Kasuga, Kosuke; Suzuki, Michinori; Chiba, Takayuki; Pu, Yong-Jin; Kido, Junji

2018-02-19

We report the development of solution-processed reduced phosphomolybdic acid (rPMA) containing molybdenum oxide units for post-treatment-free hole-injection layers (HILs) in organic light-emitting devices (OLEDs). The physical and chemical properties of rPMA, including its structure, solubility in several solvents, film surface roughness, work function, and valence states, were investigated. The formation of gap states just below the Fermi level of rPMA was observed. Without any post-treatment after the formation of rPMA films, OLEDs employing rPMA as an HIL exhibited a very low driving voltage and a high luminous efficiency. The low driving voltage was attributed to the energy level alignment between the gap states formed by reduction and the HOMO level of the hole-transport layer material N,N'-bis(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine.

Efficient Planar Perovskite Solar Cells Using Passivated Tin Oxide as an Electron Transport Layer.

PubMed

Lee, Yonghui; Lee, Seunghwan; Seo, Gabseok; Paek, Sanghyun; Cho, Kyung Taek; Huckaba, Aron J; Calizzi, Marco; Choi, Dong-Won; Park, Jin-Seong; Lee, Dongwook; Lee, Hyo Joong; Asiri, Abdullah M; Nazeeruddin, Mohammad Khaja

2018-06-01

Planar perovskite solar cells using low-temperature atomic layer deposition (ALD) of the SnO 2 electron transporting layer (ETL), with excellent electron extraction and hole-blocking ability, offer significant advantages compared with high-temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO 2 layer and its influence on the device performance are investigated. It is found that surface passivation of SnO 2 is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.

Novel Flexible Plastic-Based Solar Cells

DTIC Science & Technology

2012-10-19

Fabrication of newly designed hybrid solar cells that are composed of a electron transport layer ( TiO2 ), a light sensitizing layer (NCs), and a hole...coating and spraying techniques, to produce broad-band light harvesting hybrid solar cells with bulk and layered heterojunction of inorganic...fabrication of hybrid bulk heterojunction photovoltaic cell using a blend film of polymer-inorganic NCs, 2) Fabrication of newly designed hybrid solar

A way for studying the impact of PEDOT:PSS interface layer on carrier transport in PCDTBT:PC71BM bulk hetero junction solar cells by electric field induced optical second harmonic generation measurement

NASA Astrophysics Data System (ADS)

Ahmad, Zubair; Abdullah, Shahino Mah; Taguchi, Dai; Sulaiman, Khaulah; Iwamoto, Mitsumasa

2015-04-01

Electric-field-induced optical second-harmonic generation (EFISHG) measurement was employed to study the impact of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) interface layer on the carrier transport mechanism of the PCDTBT:PC71BM bulk heterojunction (BHJ) organic solar cells (OSCs). We revealed that the electric fields in the PCDTBT and PC71BM were allowed to be measured individually by choosing fundamental laser wavelengths of 1000 nm and 1060 nm, respectively, in dark and under illumination. The results showed that the direction of the internal electric fields in the PCDTBT:PC71BM BHJ layer is reversed by introducing the PEDOT:PSS layer, and this results in longer electron transport time in the BHJ layer. We conclude that TR-EFISHG can be used as a novel way for studying the impact of interfacial layer on the transport of electrons and holes in the bulk-heterojunction OSCs.

Recent Advances in Interface Engineering for Planar Heterojunction Perovskite Solar Cells.

PubMed

Yin, Wei; Pan, Lijia; Yang, Tingbin; Liang, Yongye

2016-06-25

Organic-inorganic hybrid perovskite solar cells are considered as one of the most promising next-generation solar cells due to their advantages of low-cost precursors, high power conversion efficiency (PCE) and easy of processing. In the past few years, the PCEs have climbed from a few to over 20% for perovskite solar cells. Recent developments demonstrate that perovskite exhibits ambipolar semiconducting characteristics, which allows for the construction of planar heterojunction (PHJ) perovskite solar cells. PHJ perovskite solar cells can avoid the use of high-temperature sintered mesoporous metal oxides, enabling simple processing and the fabrication of flexible and tandem perovskite solar cells. In planar heterojunction materials, hole/electron transport layers are introduced between a perovskite film and the anode/cathode. The hole and electron transporting layers are expected to enhance exciton separation, charge transportation and collection. Further, the supporting layer for the perovskite film not only plays an important role in energy-level alignment, but also affects perovskite film morphology, which have a great effect on device performance. In addition, interfacial layers also affect device stability. In this review, recent progress in interfacial engineering for PHJ perovskite solar cells will be reviewed, especially with the molecular interfacial materials. The supporting interfacial layers for the optimization of perovskite films will be systematically reviewed. Finally, the challenges remaining in perovskite solar cells research will be discussed.

CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%.

PubMed

Ye, Senyun; Sun, Weihai; Li, Yunlong; Yan, Weibo; Peng, Haitao; Bian, Zuqiang; Liu, Zhiwei; Huang, Chunhui

2015-06-10

Although inorganic hole-transport materials usually possess high chemical stability, hole mobility, and low cost, the efficiency of most of inorganic hole conductor-based perovskite solar cells is still much lower than that of the traditional organic hole conductor-based cells. Here, we have successfully fabricated high quality CH3NH3PbI3 films on top of a CuSCN layer by utilizing a one-step fast deposition-crystallization method, which have lower surface roughness and smaller interface contact resistance between the perovskite layer and the selective contacts in comparison with the films prepared by a conventional two-step sequential deposition process. The average efficiency of the CuSCN-based inverted planar CH3NH3PbI3 solar cells has been improved to 15.6% with a highest PCE of 16.6%, which is comparable to that of the traditional organic hole conductor-based cells, and may promote wider application of the inexpensive inorganic materials in perovskite solar cells.

Effect of organic small-molecule hole injection materials on the performance of inverted organic solar cells

NASA Astrophysics Data System (ADS)

Li, Jie; Zheng, Yifan; Zheng, Ding; Yu, Junsheng

2016-07-01

In this study, the influence of small-molecule organic hole injection materials on the performance of organic solar cells (OSCs) as the hole transport layer (HTL) with an architecture of ITO/ZnO/P3HT:PC71BM/HTL/Ag has been investigated. A significant enhancement on the performance of OSCs from 1.06% to 2.63% is obtained by using N, N‧-bis(1-naphthalenyl)-N, N‧-bis-phenyl-(1, 1‧-biphenyl)-4, 4‧-diamine (NPB) HTL. Through the resistance simulation and space-charge limited current analysis, we found that NPB HTL cannot merely improve the hole mobility of the device but also form the Ohmic contact between the active layer and anode. Besides, when we apply mix HTL by depositing the NPB on the surface of molybdenum oxide, the power conversion efficiency of OSC are able to be further improved to 2.96%.

Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer

NASA Astrophysics Data System (ADS)

Ikai, Masamichi; Tokito, Shizuo; Sakamoto, Youichi; Suzuki, Toshiyasu; Taga, Yasunori

2001-07-01

One of the keys to highly efficient phosphorescent emission in organic light-emitting devices is to confine triplet excitons generated within the emitting layer. We employ "starburst" perfluorinated phenylenes (C60F42) as a both hole- and exciton-block layer, and a hole-transport material 4,4',4″-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer. A maximum external quantum efficiency reaches to 19.2%, and keeps over 15% even at high current densities of 10-20 mA/cm2, providing several times the brightness of fluorescent tubes for lighting. The onset voltage of the electroluminescence is as low as 2.4 V and the peak power efficiency is 70-72 lm/W, promising for low-power display devices.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure

PubMed Central

Marchal, Wouter; Verboven, Inge; Kesters, Jurgen; Moeremans, Boaz; De Dobbelaere, Christopher; Bonneux, Gilles; Elen, Ken; Conings, Bert; Maes, Wouter; Boyen, Hans Gerd; Deferme, Wim; Van Bael, Marlies; Hardy, An

2017-01-01

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs. PMID:28772483

[Performance dependence of organic light-emitting devices on the thickness of Alq3 emitting layer].

PubMed

Lian, Jia-rong; Liao, Qiao-sheng; Yang, Rui-bo; Zheng, Wei; Zeng, Peng-ju

2010-10-01

The dependence of opto-electronical characteristics in organic light-emitting devices on the thickness of Alq3 emitter layer was studied, where MoO3, NPB, and Alq3 were used as hole injector, hole transporter, and emitter/electron transporter, respectively. By increasing the thickness of Alq3 layer from 20 to 100 nm, the device current decreased gradually, and the EL spectra of devices performed a little red shift with an obvious broadening in long wavelength range but a little decrease in intensity of short wavelength range. The authors simulated the EL spectra using the photoluminescence (PL) spectra of Alq3 as Alq3 intrinsic emission, which coincided with the experimental EL spectra well. The simulated results suggested that the effect of interference takes the major role in broadening the long wavelength range of EL spectra, and the distribution of emission zone largely affects the profile of EL spectra in short wavelength range.

Improved efficiency in blue phosphorescent organic light-emitting diodes by the stepwise doping structure

NASA Astrophysics Data System (ADS)

Yang, Liping; Wang, Xiaoping; Kou, Zhiqi; Ji, Changyan

2017-04-01

The electro-optical properties of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be affected by the stepwise doping structure in the emitting layer (EML). A series of multi-EML devices with different doping concentration of blue dopant (FIrpic) are fabricated. The effect of the stepwise doping structure close to the electron transport layer is more obvious than that close to the hole transport layer. When the doping concentration increases gradually from the hole injection side to the electron injection side, the maximum values of the luminance, current and power efficiency can reach to 9745 cd/m2 (at 9 V), 32.0 cd/A and 25.1 lm/W in the device with the asymmetric tri-EML structure, which is improved by about 10% compared with that in the bi-EML device. When the number of the EML is four, the performance of the device becomes worse because of the interface effect resulting from different concentration of dopant.

Highly-efficient and low-temperature perovskite solar cells by employing a Bi-hole transport layer consisting of vanadium oxide and copper phthalocyanine.

PubMed

Lei, Ting; Dong, Hua; Xi, Jun; Niu, Yong; Xu, Jie; Yuan, Fang; Jiao, Bo; Zhang, Wenwen; Hou, Xun; Wu, Zhaoxin

2018-06-12

In this article, an inorganic-organic bilayer hole transport layer (B-HTL) is designed and utilized in planar perovskite solar cells. Here the B-HTL consists of an inorganic VOx matrix and a copper phthalocyanine (CuPc) buffer layer, providing excellent resistance to moisture as well as the alignment of the interfacial energy level. Benefiting from this typical HTL, an enlarged built-in potential and charge extraction can be achieved in PSCs simultaneously. Correspondingly, a champion device with a B-HTL shows a 16.85% efficiency with negligible hysteresis, which is superior to that of a PSC based on a PEDOT:PSS HTL. Meanwhile, significantly prolonged stability of the PSC with the B-HTL can be observed, exhibiting only a 10% efficiency loss after 350 hours in ambient air. Moreover, such an entirely low-temperature (≤60 °C) fabrication process of this typical PSC exhibits its successful application in flexible devices.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure.

PubMed

Marchal, Wouter; Verboven, Inge; Kesters, Jurgen; Moeremans, Boaz; De Dobbelaere, Christopher; Bonneux, Gilles; Elen, Ken; Conings, Bert; Maes, Wouter; Boyen, Hans Gerd; Deferme, Wim; Van Bael, Marlies; Hardy, An

2017-01-30

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs.

Charge-Retraction Time-of-Flight Measurement for Organic Charge Transport Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wallace, J.U.; Young, R.H.; Tang, C.W.

This describes an all-electrical technique, charge-retraction time-of-flight (CR-TOF), to measure charge carrier mobility through an organic layer. Carriers are injected and accumulated at a blocking interface, then retracted. The retraction current transient is nearly indistinguishable from a traditional time-of-flight photocurrent. The CR-TOF technique is validated by measurement of the hole mobility of two well-known compounds, 4,4',4"-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine and 4,4'-bis[N-1-napthyl)-N-phenylamino]biphenyl, utilizing 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene as a hole-blocking layer.

The role of the hole-extraction layer in determining the operational stability of a polycarbazole:fullerene bulk-heterojunction photovoltaic device

NASA Astrophysics Data System (ADS)

Bovill, E.; Scarratt, N.; Griffin, J.; Yi, H.; Iraqi, A.; Buckley, A. R.; Kingsley, J. W.; Lidzey, D. G.

2015-02-01

We have made a comparative study of the relative operational stability of bulk-heterojunction organic photovoltaic (OPV) devices utilising different hole transport layers (HTLs). OPV devices were fabricated based on a blend of the polymer PCDTBT with the fullerene PC70BM, and incorporated the different HTL materials PEDOT:PSS, MoOx and V2O5. Following 620 h of irradiation by light from a solar simulator, we find that devices using the PEDOT:PSS HTL retained the highest efficiency, having a projected T80 lifetime of 14 500 h.

Covalent organic nanosheets for effective charge transport layers in planar-type perovskite solar cells.

PubMed

Park, Soyun; Kim, Min-Sung; Jang, Woongsik; Park, Jin Kuen; Wang, Dong Hwan

2018-03-08

Herein, solvent-treated bandgap-tunable covalent organic nanosheets (CONs) were prepared via the Stille cross-coupling reaction. These materials are considered useful as interlayers in photovoltaic devices upon the alignment of energy levels between other components. Among various types of solar cells, according to the organic-interlayer study, inverted planar perovskite solar cells (PSCs) are mostly demanded to effectively transport and collect charge carriers due to their high performance. At first, the C-V analysis proved the energy levels of the frontier orbitals for CON-10 and CON-16 nanosheets; this verified the suitability of these nanosheets as hole transport layers (HTLs) with the PEDOT:PSS upon casting both films from DMSO. It became evident, however, that the hole transport property of the PEDOT:PSS on the CON-16 layer was unfavorable with the increasing UPS-proven hole injection barrier. In addition, both CONs induced a rough surface morphology; however, CON-10 showed a relatively smooth surface as compared to CON-16 based on the Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) profiles; furthermore, their surface properties influenced both the PEDOT:PSS layers and the perovskite layers. Especially, the XRD profiles presented an enhanced crystallinity of the perovskite layers with CON-10. All these aspects indicate that CON-10 is a more effective HTL material, and several versions of perovskite solar cells (PSCs) have been fabricated with/without CON-10 and CON-16 together with the PEDOT:PSS to determine the more-HTL-suitable CON. As a result, the power conversion efficiencies (PCEs) of the optimized devices with CON-10 exhibited a value of 10.2%, which represented a 1% increase over those of the reference devices without the CONs and was 4% higher than that of the CON-16 devices. Moreover, the devices with CON-10 were further optimized with TiO x using Al electrodes, leading to a PCE increase of these devices that became slightly higher than the PCEs of the device with CON-10 and without TiO x . This tendency was supported by photoluminescence (PL) spectroscopy, photocurrent density (J ph ), and space-charge-limited current (SCLC) mobility results.

Highly Efficient p-i-n Perovskite Solar Cells Utilizing Novel Low-Temperature Solution-Processed Hole Transport Materials with Linear π-Conjugated Structure.

PubMed

Li, Yang; Xu, Zheng; Zhao, Suling; Qiao, Bo; Huang, Di; Zhao, Ling; Zhao, Jiao; Wang, Peng; Zhu, Youqin; Li, Xianggao; Liu, Xicheng; Xu, Xurong

2016-09-01

Alternative low-temperature solution-processed hole-transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π-conjugated structure, 4,4'-bis(4-(di-p-toyl)aminostyryl)biphenyl (TPASBP) and 1,4'-bis(4-(di-p-toyl)aminostyryl)benzene (TPASB), are applied as hole-transporting layer (HTL) by low-temperature (sub-100 °C) solution-processed method in p-i-n PSCs. Compared with standard poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH 3 NH 3 PbI 3 ) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH 3 NH 3 PbI 3 interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Determination of the Width of the Carrier Recombination Zone in Organic Light-Emitting Diodes

DTIC Science & Technology

2003-09-18

biphenyl-4,48-diamine ~TPD!/tris-~8-hydroxyquinolinato! aluminum III ( Alq3 )/ Mg:Ag. In addition, an independent evaluation of the light output coupling...5 min. TPD, obtained from H. W. Sands, was used as the hole transport layer and Alq3 , ob- tained from TCI America, was used as the emitting/electron...transport layer. TPD was used as received while Alq3 was purified by train sublimation. A 100 nm thick Mg:Ag film,4 © 2003 American Institute of

Copper thiocyanate: An attractive hole transport/extraction layer for use in organic photovoltaic cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Treat, Neil D., E-mail: neil.treat@imperial.ac.uk, E-mail: t.anthopoulos@imperial.ac.uk; Stingelin, Natalie; Yaacobi-Gross, Nir

2015-07-06

We report the advantageous properties of the inorganic molecular semiconductor copper(I) thiocyanate (CuSCN) for use as a hole collection/transport layer (HTL) in organic photovoltaic (OPV) cells. CuSCN possesses desirable HTL energy levels [i.e., valence band at −5.35 eV, 0.35 eV deeper than poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)], which produces a 17% increase in power conversion efficiency (PCE) relative to PEDOT:PSS-based devices. In addition, a two-fold increase in shunt resistance for the solar cells measured in dark conditions is achieved. Ultimately, CuSCN enables polymer:fullerene based OPV cells to achieve PCE > 8%. CuSCN continues to offer promise as a chemically stable and straightforward replacement for the commonly usedmore » PEDOT:PSS.« less

Graphene oxide hole transport layers for large area, high efficiency organic solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Chris T. G.; Rhodes, Rhys W.; Beliatis, Michail J.

2014-08-18

Graphene oxide (GO) is becoming increasingly popular for organic electronic applications. We present large active area (0.64 cm{sup 2}), solution processable, poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1, 3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-Phenyl C{sub 71} butyric acid methyl ester (PCDTBT:PC{sub 70}BM) organic photovoltaic (OPV) solar cells, incorporating GO hole transport layers (HTL). The power conversion efficiency (PCE) of ∼5% is the highest reported for OPV using this architecture. A comparative study of solution-processable devices has been undertaken to benchmark GO OPV performance with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) HTL devices, confirming the viability of GO devices, with comparable PCEs, suitable as high chemical and thermal stability replacements for PEDOT:PSS in OPV.

Stable and null current hysteresis perovskite solar cells based nitrogen doped graphene oxide nanoribbons hole transport layer

PubMed Central

Kim, Jeongmo; Mat Teridi, Mohd Asri; Mohd Yusoff, Abd. Rashid bin; Jang, Jin

2016-01-01

Perovskite solar cells are becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequently used component poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has several shortcomings, such as an easily corroded indium-tin-oxide (ITO) interface at elevated temperatures and induced electrical inhomogeneity. Herein, we propose solution-processed nitrogen-doped graphene oxide nanoribbons (NGONRs) as a hole transport layer (HTL) in perovskite solar cells, replacing the conducting polymer PEDOT:PSS. The conversion efficiency of NGONR-based perovskite solar cells has outperformed a control device constructed using PEDOT:PSS. Moreover, our proposed NGONR-based devices also demonstrate a negligible current hysteresis along with improved stability. This work provides an effective route for substituting PEDOT:PSS as the effective HTL. PMID:27277388

Degradation of Bilayer Organic Light-Emitting Diodes Studied by Impedance Spectroscopy.

PubMed

Sato, Shuri; Takata, Masashi; Takada, Makoto; Naito, Hiroyoshi

2016-04-01

The degradation of bilayer organic light-emitting diodes (OLEDs) with a device structure of N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) (hole transport layer) and tris-(8-hydroxyquinolate)aluminum (Alq3) (emissive layer and electron transport layer) has been studied by impedance spectroscopy and device simulation. Two modulus peaks are found in the modulus spectra of the OLEDs below the electroluminescence threshold. After aging of the OLEDs, the intensity of electroluminescence is degraded and the modulus peak due to the Alq3 layer is shifted to lower frequency, indicating that the resistance of the Alq3 layer is increased. Device simulation reveals that the increase in the resistance of the Alq3 layer is due to the decrease in the electron mobility in the Alq3 layer.

Rational Strategies for Efficient Perovskite Solar Cells.

PubMed

Seo, Jangwon; Noh, Jun Hong; Seok, Sang Il

2016-03-15

A long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic-organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pillared architecture of a three-dimensional nanocomposite of perovskites fully infiltrating mesoporous TiO2, resulting in the formation of continuous phases and perovskite domains overlaid with a polymeric hole conductor. Since then, the PCE of our PSCs has been rapidly increased from 3% to over 20% certified efficiency. The unprecedented increase in the PCE can be attributed to the effective integration of the advantageous attributes of the refined bicontinuous architecture, deposition process, and composition of perovskite materials. Specifically, the bicontinuous architectures used in the high efficiency comprise a layer of perovskite sandwiched between mesoporous metal-oxide layer, which is a very thinner than that of used in conventional dye-sensitized solar cells, and hole-conducting contact materials with a metal back contact. The mesoporous scaffold can affect the hysteresis under different scan direction in measurements of PSCs. The hysteresis also greatly depends on the cell architecture and perovskite composition. In this Account, we will describe what we do with major aspects including (1) the film morphology through the development of intermediate chemistry retarding the rapid reaction between methylammonium or formamidinium iodide and lead halide (PbI2) for improved perovskite film formation; (2) the phase stability and band gap tuning of the perovskite layer through the materials engineering; (3) the development of electron and hole transporting materials for carrier-selective contacting layers; and (4) the adoption of p-i-n and n-i-p architectures depending on the position of the electron or hole conducting layer in front of incident light. Finally, we will summarize the recent incredible achievements in PSCs, and finally provide challenges facing the future development and commercialization of PSCs.

Low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene

NASA Astrophysics Data System (ADS)

Hu, Bo

2015-08-01

Based on semiclassical Boltzamnn transport theory in random phase approximation, we develop a theoretical model to investigate low-temperature carrier transport properties in relatively high doped bilayer graphene. In the presence of both electron-hole puddles and band gap induced by charged impurities, we calculate low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene. Our calculated conductivity results are in excellent agreement with published experimental data in all compensated gate voltage regime of study by using potential fluctuation parameter as only one free fitting parameter, indicating that both electron-hole puddles and band gap induced by charged impurities play an important role in carrier transport. More importantly, we also find that the conductivity not only depends strongly on the total charged impurity density, but also on the top layer charged impurity density, which is different from that obtained by neglecting the opening of band gap, especially for bilayer graphene with high top layer charged impurity density.

Highly efficient red fluorescent organic light-emitting diodes by sorbitol-doped PEDOT:PSS

NASA Astrophysics Data System (ADS)

Zheng, Yan-Qiong; Yu, Jun-Le; Wang, Chao; Yang, Fang; Wei, Bin; Zhang, Jian-Hua; Zeng, Cheng-Hui; Yang, Yang

2018-06-01

This work shows a promising approach to improve device performance by optimizing the electron transport and hole injection layers for tetraphenyldibenzoperiflanthene (DBP):rubrene-based red fluorescent organic light-emitting diodes (OLEDs). We compared the effect of two electron transport layers (ETLs), and found that the rubrene/bathophenanthroline (Bphen) ETL-based OLED showed a much higher external quantum efficiency (EQE) (4.67%) than the Alq3 ETL-based OLED (EQE of 3.08%). The doping ratio of DBP in rubrene was tuned from 1.0 wt% to 4.5 wt%, and the 1.5 wt%-DBP:rubrene-based OLED demonstrated the highest EQE of 5.24% and lowest turn-on voltage of 2.2 V. Atomic force microscopy images indicated that 1.5 wt% DBP-doped rubrene film exhibited a regular strip shape, and this regular surface was favorable to the hole and electron recombination in the emitting layer. Finally, the sorbitol-doped poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used to further improve the EQE; doping with 6 wt% sorbitol achieved the highest current efficiency of 7.03 cd A‑1 and an EQE of 7.50%. The significantly enhanced performance implies that the hole injection is a limiting factor for DBP:rubrene-based red fluorescent OLEDs.

Designing Two-Dimensional Dirac Heterointerfaces of Few-Layer Graphene and Tetradymite-Type Sb2Te3 for Thermoelectric Applications.

PubMed

Jang, Woosun; Lee, Jiwoo; In, Chihun; Choi, Hyunyong; Soon, Aloysius

2017-12-06

Despite the ubiquitous nature of the Peltier effect in low-dimensional thermoelectric devices, the influence of finite temperature on the electronic structure and transport in the Dirac heterointerfaces of the few-layer graphene and layered tetradymite, Sb 2 Te 3 (which coincidently have excellent thermoelectric properties) are not well understood. In this work, using the first-principles density-functional theory calculations, we investigate the detailed atomic and electronic structure of these Dirac heterointerfaces of graphene and Sb 2 Te 3 and further re-examine the effect of finite temperature on the electronic band structures using a phenomenological temperature-broadening model based on Fermi-Dirac statistics. We then proceed to understand the underlying charge redistribution process in this Dirac heterointerfaces and through solving the Boltzmann transport equation, we present the theoretical evidence of electron-hole asymmetry in its electrical conductivity as a consequence of this charge redistribution mechanism. We finally propose that the hexagonal-stacked Dirac heterointerfaces are useful as efficient p-n junction building blocks in the next-generation thermoelectric devices where the electron-hole asymmetry promotes the thermoelectric transport by "hot" excited charge carriers.

Architecture, development and implementation of a SWIR to visible integrated up-conversion imaging device

NASA Astrophysics Data System (ADS)

Sarusi, Gabby; Templeman, Tzvi; Hechster, Elad; Nissim, Nimrod; Vitenberg, Vladimir; Maman, Nitzan; Tal, Amir; Solodar, Assi; Makov, Guy; Abdulhalim, Ibrahim; Visoly-Fisher, Iris; Golan, Yuval

2016-04-01

A new concept of short wavelength infrared (SWIR) to visible upconversion integrated imaging device is proposed, modeled and some initial measured results are presented. The device is a hybrid inorganic-organic device that comprises six nano-metric scale sub-layers grown on n-type GaAs substrates. The first layer is a ~300nm thick PbSe nano-columnar absorber layer grown in (111) orientation to the substrate plan (100), with a diameter of 8- 10nm and therefore exhibit quantum confinement effects parallel to the substrate and bulk properties perpendicular to it. The advantage of this structure is the high oscillator strength and hence absorption to incoming SWIR photons while maintaining the high bulk mobility of photo-excited charges along the columns. The top of the PbSe absorber layer is coated with 20nm thick metal layer that serves as a dual sided mirror, as well as a potentially surface plasmon enhanced absorption in the PbSe nano-columns layer. The photo-excited charges (holes and electrons in opposite directions) are drifted under an external applied field to the OLED section (that is composed of a hole transport layer, an emission layer and an electron transport layer) where they recombine with injected electron from the transparent cathode and emit visible light through this cathode. Due to the high absorption and enhanced transport properties this architecture has the potential of high quantum efficiency, low cost and easy implementation in any optical system. As a bench-mark, alternative concept where InGaAs/InP heterojunction couple to liquid crystal optical spatial light modulator (OSLM) structure was built that shows a full upconversion to visible of 1550nm laser light.

Toward Edge-Defined Holey Boron Nitride Nanosheets

NASA Technical Reports Server (NTRS)

Lin, Yi; Liao, Yunlong; Chen, Zhongfan; Connell, John W.

2015-01-01

"Holey" two-dimensional (2D) nanosheets with well-defined holy morphology and edge chemistry are highly desirable for applications such as energy storage, catalysis, sensing, transistors, and molecular transport/separation. For example, holey grapheme is currently under extensive investigation for energy storage applications because of the improvement in ion transport due to through the thickness pathways provided by the holes. Without the holes, the 2D materials have significant limitations for such applications in which efficient ion transport is important. As part of an effort to apply this approach to other 2D nanomaterials, a method to etch geometrically defined pits or holes on the basal plane surface of hexagonal boron nitride (h-BN) nanosheets has been developed. The etching, conducted via heating in ambient air using metal nanoparticles as catalysts, was facile, controllable, and scalable. Starting h-BN layered crystals were etched and subsequently exfoliated into boron nitride nanosheets (BNNSs). The as-etched and exfoliated h-BN nanosheets possessed defined pit and hole shapes that were comprised of regulated nanostructures at the edges. The current finding are the first step toward the bulk preparation of holey BNNSs with defined holes and edges.

Improved fill factor in inverted planar perovskite solar cells with zirconium acetate as the hole-and-ion-blocking layer.

PubMed

Zhang, Xuewen; Liang, Chunjun; Sun, Mengjie; Zhang, Huimin; Ji, Chao; Guo, Zebang; Xu, Yajun; Sun, Fulin; Song, Qi; He, Zhiqun

2018-03-14

Planar perovskite solar cells (PSCs) have gained great interest due to their low-temperature solution preparation and simple process. In inverted planar PSCs, an additional buffer layer is usually needed on the top of the PCBM electron-transport layer (ETL) to enhance the device performance. In this work, we used a new buffer layer, zirconium acetate (Zr(Ac) 4 ). The inclusion of the Zr(Ac) 4 buffer layer leads to the increase of FF from ∼68% to ∼79% and PCE from ∼14% to ∼17% in the planar PSCs. The UPS measurement indicates that the Zr(Ac) 4 layer has a low HOMO level of -8.2 eV, indicating that the buffer layer can act as a hole-blocking layer. Surface morphology and surface chemistry investigations reveal that the elements I, MA and Pb can diffuse across the PCBM ETL, damaging the device performance. The covering Zr(Ac) 4 molecules fill in the pinholes of the PCBM layer and effectively block the ions/molecules of the perovskite from diffusion across the ETL. The resulting more robust PCBM/Zr(Ac) 4 ETL leads to weaker ionic charge accumulation and lower diode leakage current. The double role of hole-and-ion blocking of the Zr(Ac) 4 layer explains the improved FF and PCE in the PSCs.

Hybrid UV-Ozone-Treated rGO-PEDOT:PSS as an Efficient Hole Transport Material in Inverted Planar Perovskite Solar Cells

NASA Astrophysics Data System (ADS)

Wang, Shuying; Huang, Xiaona; Sun, Haoxuan; Wu, Chunyang

2017-12-01

Inverted planar perovskite solar cells (PSCs), which are regarded as promising devices for new generation of photovoltaic systems, show many advantages, such as low-temperature film formation, low-cost fabrication, and smaller hysteresis compared with those of traditional n-i-p PSCs. As an important carrier transport layer in PSCs, the hole transport layer (HTL) considerably affects the device performance. Therefore, HTL modification becomes one of the most critical issues in improving the performance of PSCs. In this paper, we report an effective and environmentally friendly UV-ozone treatment method to enhance the hydrophilia of reduced graphene oxide (rGO) with its excellent electrical performance. The treated rGO was applied to doped poly(3,4-ethylenedioxythiophene) poly(styrene-sulfonate) (PEDOT:PSS) as HTL material of PSCs. Consequently, the performance of rGO/PEDOT:PSS-doped PSCs was improved significantly, with power conversion efficiency (PCE) of 10.7%, Jsc of 16.75 mA/cm2, Voc of 0.87 V, and FF of 75%. The PCE of this doped PSCs was 27% higher than that of the PSCs with pristine PEDOT:PSS as HTL. This performance was attributed to the excellent surface morphology and optimized hole mobility of the solution-processable rGO-modified PEDOT:PSS.

Stable Organic Radicals as Hole Injection Dopants for Efficient Optoelectronics.

PubMed

Bin, Zhengyang; Guo, Haoqing; Liu, Ziyang; Li, Feng; Duan, Lian

2018-02-07

Precursors of reactive organic radicals have been widely used as n-dopants in electron-transporting materials to improve electron conductivity and enhance electron injection. However, the utilization of organic radicals in hole counterparts has been ignored. In this work, stable organic radicals have been proved for the first time to be efficient dopants to enhance hole injection. From the absorbance spectra and the ultraviolet photoelectron spectra, we could observe an efficient electron transfer between the organic radical, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz), and the widely used hole injection material, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN). When the unpaired electron of TTM-1Cz is transferred to HAT-CN, it would be oxidized to a TTM-1Cz cation with a newly formed lowest unoccupied molecular orbital which is quite close to the highest occupied molecular orbital (HOMO) of the hole-transporting material (HTM). In this way, the TTM-1Cz cation would promote the electron extraction from the HOMO of the HTM and improve hole injection. Using TTM-1Cz-doped HAT-CN as the hole injection layer, efficient organic light-emitting diodes with extremely low voltages can be attained.

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands.

PubMed

Kaplunov, Mikhail G; Krasnikova, Svetlana S; Nikitenko, Sergey L; Sermakasheva, Natalia L; Yakushchenko, Igor K

2012-04-03

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material.

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands

PubMed Central

2012-01-01

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material. PMID:22471942

Mn concentration and quantum size effects on spin-polarized transport through CdMnTe based magnetic resonant tunneling diode.

PubMed

Mnasri, S; Abdi-Ben Nasrallahl, S; Sfina, N; Lazzari, J L; Saïd, M

2012-11-01

Theoretical studies on spin-dependent transport in magnetic tunneling diodes with giant Zeeman splitting of the valence band are carried out. The studied structure consists of two nonmagnetic layers CdMgTe separated by a diluted magnetic semiconductor barrier CdMnTe, the hole is surrounded by two p-doped CdTe layers. Based on the parabolic valence band effective mass approximation and the transfer matrix method, the magnetization and the current densities for holes with spin-up and spin-down are studied in terms of the Mn concentration, the well and barrier thicknesses as well as the voltage. It is found that, the current densities depend strongly on these parameters and by choosing suitable values; this structure can be a good spin filter. Such behaviors are originated from the enhancement and suppression in the spin-dependent resonant states.

Polymers containing isolated phenylvinyl substituted carbazole rings as electroactive materials for OLEDs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griniene, Raimonda; Tavgeniene, Daiva, E-mail: daiva.tavgen@gmail.com; Grigalevičius, Saulius

2016-05-18

Polymers containing pendent 3-(2-phenylvinyl)carbazole moieties have been synthesized by the multi-step synthetic route. The polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 370 °C. The glass transition temperatures of the amorphous materials were in the rage of 56–65 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of about 5.6 eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq 3 as the green emitter. The device containing hole-transporting layers of poly{9-[6-(3-methyloxetan-3-ylmethoxy)hexyl]-3-(2-phenylvinyl)carbazole} exhibited the best overall performance with a maximum photometricmore » efficiency of about 4.0 cd/A and maximum brightness exceeding 6430 cd/m{sup 2}.« less

Perovskite Solar Cells with Inorganic Electron- and Hole-Transport Layers Exhibiting Long-Term (≈500 h) Stability at 85 °C under Continuous 1 Sun Illumination in Ambient Air.

PubMed

Seo, Seongrok; Jeong, Seonghwa; Bae, Changdeuck; Park, Nam-Gyu; Shin, Hyunjung

2018-05-22

Despite the high power conversion efficiency (PCE) of perovskite solar cells (PSCs), poor long-term stability is one of the main obstacles preventing their commercialization. Several approaches to enhance the stability of PSCs have been proposed. However, an accelerating stability test of PSCs at high temperature under the operating conditions in ambient air remains still to be demonstrated. Herein, interface-engineered stable PSCs with inorganic charge-transport layers are shown. The highly conductive Al-doped ZnO films act as efficient electron-transporting layers as well as dense passivation layers. This layer prevents underneath perovskite from moisture contact, evaporation of components, and reaction with a metal electrode. Finally, inverted-type PSCs with inorganic charge-transport layers exhibit a PCE of 18.45% and retain 86.7% of the initial efficiency for 500 h under continuous 1 Sun illumination at 85 °C in ambient air with electrical biases (at maximum power point tracking). © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nondispersive hole transport in a spin-coated dendrimer film measured by the charge-generation-layer time-of-flight method

NASA Astrophysics Data System (ADS)

Markham, Jonathan P. J.; Anthopoulos, Thomas D.; Samuel, Ifor D. W.; Richards, Gary J.; Burn, Paul L.; Im, Chan; Bassler, Heinz

2002-10-01

Measurements of the mobility of a first-generation (G1) bis-fluorene cored dendrimer have been performed on spin-coated samples of 500 nm thickness using the charge-generation-layer time-of-flight (TOF) technique. A 10 nm perylene charge generation layer was excited by the 532 nm line of a Q-switched Nd:YAG laser and the generated carriers swept through the dendrimer film under an applied field. We observe nondispersive hole transport in the dendrimer layer with a room-temperature mobility mu=2.0 x10-4 cm2/V s at a field of 0.55 MV/cm. There is a weak field dependence of the mobility and it increases from mu=1.6 x10-4 cm2/V s at 0.2 MV/cm to mu=3.0 x10-4 cm2/V s at 1.4 MV/cm. These results suggest that the measurement of mobility by TOF in spin-coated samples on thickness scales relevant to organic light-emitting diodes can yield valuable information, and that dendrimers are promising materials for device applications.

A comprehensive device modelling of perovskite solar cell with inorganic copper iodide as hole transport material

NASA Astrophysics Data System (ADS)

Zulqarnain Haider, Syed; Anwar, Hafeez; Wang, Mingqing

2018-03-01

Hole transport material (HTM) plays an important role in the efficiency and stability of perovskite solar cells (PSCs). Spiro-MeOTAD, the commonly used HTM, is costly and can be easily degraded by heat and moisture, thus offering hindrance to commercialize PSCs. There is dire need to find an alternate inorganic and stable HTM to exploit PSCs with their maximum capability. In this paper, a comprehensive device simulation is used to study various possible parameters that can influence the performance of perovskite solar cell with CuI as HTM. These include the effect of doping density, defect density and thickness of absorber layer, along with the influence of diffusion length of carriers as well as electron affinity of electron transport layer (ETM) and HTM on the performance of PSCs. In addition, hole mobility and doping density of HTM is also investigated. CuI is a p-type inorganic material with low cost and relatively high stability. It is found that concentration of dopant in absorber layer and HTM, the electron affinity of HTM and ETM affect the performance of solar cell minutely, while cell performance improves greatly with the reduction of defect density. Upon optimization of parameters, power conversion efficiency for this device is found to be 21.32%. The result shows that lead-based PSC with CuI as HTM is an efficient system. Enhancing the stability and reduction of defect density are critical factors for future research. These factors can be improved by better fabrication process and proper encapsulation of solar cell.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishi, Shohei; Taguchi, Dai; Manaka, Takaaki

By using electric-field-induced optical second-harmonic generation measurement coupled with the conventional current-voltage (I-V) measurement, we studied the carrier transport of organic double-layer diodes with a Au/pentacene/fluorine polymer (FP)/indium zinc oxide (IZO) structure. The rectifying I-V characteristics were converted into the I-E characteristics of the FP and pentacene layers. Results suggest a model in which Schottky-type electron injection from the IZO electrode to the FP layer governs the forward electrical conduction (V > 0), where the space charge electric field produced in the FP layer by accumulated holes at the pentacene/FP interface makes a significant contribution. On the other hand, Schottky-type injection bymore » accumulated interface electrons from the pentacene layer to the FP layer governs the backward electrical conduction (V < 0). The electroluminescence generated from the pentacene layer in the region V > 0 verifies the electron transport across the FP layer, and supports the above suggested model.« less

Performance enhancement of perovskite solar cells with Mg-doped TiO{sub 2} compact film as the hole-blocking layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jing; Qin, Minchao; Tao, Hong

2015-03-23

In this letter, we report perovskite solar cells with thin dense Mg-doped TiO{sub 2} as hole-blocking layers (HBLs), which outperform cells using TiO{sub 2} HBLs in several ways: higher open-circuit voltage (V{sub oc}) (1.08 V), power conversion efficiency (12.28%), short-circuit current, and fill factor. These properties improvements are attributed to the better properties of Mg-modulated TiO{sub 2} as compared to TiO{sub 2} such as better optical transmission properties, upshifted conduction band minimum (CBM) and downshifted valence band maximum (VBM), better hole-blocking effect, and higher electron life time. The higher-lying CBM due to the modulation with wider band gap MgO and themore » formation of magnesium oxide and magnesium hydroxides together resulted in an increment of V{sub oc}. In addition, the Mg-modulated TiO{sub 2} with lower VBM played a better role in the hole-blocking. The HBL with modulated band position provided better electron transport and hole blocking effects within the device.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyunbok; Lee, Jeihyun; Yi, Yeonjin, E-mail: yeonjin@yonsei.ac.kr

Metal phthalocyanines (MPcs) are well known as an efficient hole injection layer (HIL) in organic devices. They possess a low ionization energy, and so the low-lying highest occupied molecular orbital (HOMO) gives a small hole injection barrier from an anode in organic light-emitting diodes. However, in this study, we show that the hole injection characteristics of MPc are not only determined by the HOMO position but also significantly affected by the wave function distribution of the HOMO. We show that even with the HOMO level of a manganese phthalocyanine (MnPc) HIL located between the Fermi level of an indium tinmore » oxide anode and the HOMO level of a N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine hole transport layer the device performance with the MnPc HIL is rather deteriorated. This anomalous hole injection deterioration is due to the contracted HOMO wave function, which leads to small intermolecular electronic coupling. The origin of this contraction is the significant contribution of the Mn d-orbital to the MnPc HOMO.« less

Influence of the Preparation Method on Planar Perovskite CH3NH3PbI3-xClx Solar Cell Performance and Hysteresis

NASA Astrophysics Data System (ADS)

Ivanova, A.; Tokmakov, A.; Lebedeva, K.; Roze, M.; Kaulachs, I.

2017-08-01

Organometal halide perovskites are promising materials for lowcost, high-efficiency solar cells. The method of perovskite layer deposition and the interfacial layers play an important role in determining the efficiency of perovskite solar cells (PSCs). In the paper, we demonstrate inverted planar perovskite solar cells where perovskite layers are deposited by two-step modified interdiffusion and one-step methods. We also demonstrate how PSC parameters change by doping of charge transport layers (CTL). We used dimethylsupoxide (DMSO) as dopant for the hole transport layer (PEDOT:PSS) but for the electron transport layer [6,6]-phenyl C61 butyric acid methyl ester (PCBM)) we used N,N-dimethyl-N-octadecyl(3-aminopropyl)trimethoxysilyl chloride (DMOAP). The highest main PSC parameters (PCE, EQE, VOC) were obtained for cells prepared by the one-step method with fast crystallization and doped CTLs but higher fill factor (FF) and shunt resistance (Rsh) values were obtained for cells prepared by the two-step method with undoped CTLs.

Enhanced interfacial electron transfer of inverted perovskite solar cells by introduction of CoSe into the electron-transporting-layer

NASA Astrophysics Data System (ADS)

Chen, Shanshan; Yang, Songwang; Sun, Hong; Zhang, Lu; Peng, Jiajun; Liang, Ziqi; Wang, Zhong-Sheng

2017-06-01

To improve the electron transfer at the interface between the perovskite film and the electron-transporting-material (ETM) layer, CoSe doped [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is employed as the ETM layer for the inverted planar perovskite solar cell with NiO as the hole-transporting-material layer. Introduction of CoSe (5.8 wt%) into the PCBM layer improves the conductivity of the ETM layer and decreases the photoluminescence intensity, thus enhancing the interfacial electron extraction and reducing the electron transfer resistance at the perovskite/ETM interface. As a consequence, the power conversion efficiency is enhanced from 11.43% to 14.91% by 30% due to the noted increases in short-circuit current density from 17.95 mA cm-2 to 19.85 mA cm-2 and fill factor from 0.60 to 0.70. This work provides a new strategy to improve the performance of inverted perovskite solar cells.

Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe 2: Enabling nanoscale direct write homo-junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanford, Michael; Noh, Joo Hyon; Koehler, Michael R.

Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe 2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe 2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe 2more » thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe 2 is degraded more severely relative to electron transport after helium ion irradiation. Moreover, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe 2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.« less

Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe 2: Enabling nanoscale direct write homo-junctions

DOE PAGES

Stanford, Michael; Noh, Joo Hyon; Koehler, Michael R.; ...

2016-06-06

Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe 2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe 2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe 2more » thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe 2 is degraded more severely relative to electron transport after helium ion irradiation. Moreover, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe 2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.« less

Interfacial Passivation of the p-Doped Hole-Transporting Layer Using General Insulating Polymers for High-Performance Inverted Perovskite Solar Cells.

PubMed

Zhang, Fan; Song, Jun; Hu, Rui; Xiang, Yuren; He, Junjie; Hao, Yuying; Lian, Jiarong; Zhang, Bin; Zeng, Pengju; Qu, Junle

2018-05-01

Organic-inorganic lead halide perovskite solar cells (PVSCs), as a competing technology with traditional inorganic solar cells, have now realized a high power conversion efficiency (PCE) of 22.1%. In PVSCs, interfacial carrier recombination is one of the dominant energy-loss mechanisms, which also results in the simultaneous loss of potential efficiency. In this work, for planar inverted PVSCs, the carrier recombination is dominated by the dopant concentration in the p-doped hole transport layers (HTLs), since the F4-TCNQ dopant induces more charge traps and electronic transmission channels, thus leading to a decrease in open-circuit voltages (V OC ). This issue is efficiently overcome by inserting a thin insulating polymer layer (poly(methyl methacrylate) or polystyrene) as a passivation layer with an appropriate thickness, which allows for increases in the V OC without significantly sacrificing the fill factor. It is believed that the passivation layer attributes to the passivation of interfacial recombination and the suppression of current leakage at the perovskite/HTL interface. By manipulating this interfacial passivation technique, a high PCE of 20.3% is achieved without hysteresis. Consequently, this versatile interfacial passivation methodology is highly useful for further improving the performance of planar inverted PVSCs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reversible Conversion of Dominant Polarity in Ambipolar Polymer/Graphene Oxide Hybrids

PubMed Central

Zhou, Ye; Han, Su-Ting; Sonar, Prashant; Ma, Xinlei; Chen, Jihua; Zheng, Zijian; Roy, V. A. L.

2015-01-01

The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. This hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits. PMID:25801827

Suppressing spontaneous polarization of p-GaN by graphene oxide passivation: Augmented light output of GaN UV-LED

PubMed Central

Jeong, Hyun; Jeong, Seung Yol; Park, Doo Jae; Jeong, Hyeon Jun; Jeong, Sooyeon; Han, Joong Tark; Jeong, Hee Jin; Yang, Sunhye; Kim, Ho Young; Baeg, Kang-Jun; Park, Sae June; Ahn, Yeong Hwan; Suh, Eun-Kyung; Lee, Geon-Woong; Lee, Young Hee; Jeong, Mun Seok

2015-01-01

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage. However, one notorious issue is low hole injection rate in p-type transport layer due to poorly activated holes and spontaneous polarization, giving rise to insufficient light emission efficiency. Therefore, improving hole injection rate is a key step towards high performance UV-LEDs. Here, we report a new method of suppressing spontaneous polarization in p-type region to augment light output of UV-LEDs. This was achieved by simply passivating graphene oxide (GO) on top of the fully fabricated LED. The dipole layer formed by the passivated GO enhanced hole injection rate by suppressing spontaneous polarization in p-type region. The homogeneity of electroluminescence intensity in active layers was improved due to band filling effect. As a consequence, the light output was enhanced by 60% in linear current region. Our simple approach of suppressing spontaneous polarization of p-GaN using GO passivation disrupts the current state of the art technology and will be useful for high-efficiency UV-LED technology. PMID:25586148

Suppressing spontaneous polarization of p-GaN by graphene oxide passivation: augmented light output of GaN UV-LED.

PubMed

Jeong, Hyun; Jeong, Seung Yol; Park, Doo Jae; Jeong, Hyeon Jun; Jeong, Sooyeon; Han, Joong Tark; Jeong, Hee Jin; Yang, Sunhye; Kim, Ho Young; Baeg, Kang-Jun; Park, Sae June; Ahn, Yeong Hwan; Suh, Eun-Kyung; Lee, Geon-Woong; Lee, Young Hee; Jeong, Mun Seok

2015-01-14

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage. However, one notorious issue is low hole injection rate in p-type transport layer due to poorly activated holes and spontaneous polarization, giving rise to insufficient light emission efficiency. Therefore, improving hole injection rate is a key step towards high performance UV-LEDs. Here, we report a new method of suppressing spontaneous polarization in p-type region to augment light output of UV-LEDs. This was achieved by simply passivating graphene oxide (GO) on top of the fully fabricated LED. The dipole layer formed by the passivated GO enhanced hole injection rate by suppressing spontaneous polarization in p-type region. The homogeneity of electroluminescence intensity in active layers was improved due to band filling effect. As a consequence, the light output was enhanced by 60% in linear current region. Our simple approach of suppressing spontaneous polarization of p-GaN using GO passivation disrupts the current state of the art technology and will be useful for high-efficiency UV-LED technology.

Use of laser drilling in the manufacture of organic inverter circuits.

PubMed

Iba, Shingo; Kato, Yusaku; Sekitani, Tsuyoshi; Kawaguchi, Hiroshi; Sakurai, Takayasu; Someya, Takao

2006-01-01

Inverter circuits have been made by connecting two high-quality pentacene field-effect transistors. A uniform and pinhole-free 900 nm thick polyimide gate-insulating layer was formed on a flexible polyimide film with gold gate electrodes and partially removed by using a CO2 laser drilling machine to make via holes and contact holes. Subsequent evaporation of the gold layer results in good electrical connection with a gold gate layer underneath the gate-insulating layer. By optimization of the settings of the CO2 laser drilling machine, contact resistance can be reduced to as low as 3 ohms for 180 microm square electrodes. No degradation of the transport properties of the organic transistors was observed after the laser-drilling process. This study demonstrates the feasibility of using the laser drilling process for implementation of organic transistors in integrated circuits on flexible polymer films.

Sol-gel-processed yttrium-doped NiO as hole transport layer in inverted perovskite solar cells for enhanced performance

NASA Astrophysics Data System (ADS)

Hu, Zijun; Chen, Da; Yang, Pan; Yang, Lijun; Qin, Laishun; Huang, Yuexiang; Zhao, Xiaochong

2018-05-01

In this work, high-performance inverted planar perovskite solar cells (PSCs) using sol-gel processed Y-doped NiO thin films as hole transport layer (HTL) were demonstrated. Y-doped NiO thin films containing different Y doping concentrations were successfully prepared through a simple sol-gel process. The Y doping could significantly improve the electrical conductivity of NiO thin film, and the photovoltaic performance of Y-doped NiO HTL-based PSC devices outperformed that of the pristine NiO HTL-based device. Notably, the PSC using a 5%Y-NiO HTL exhibited the champion performance with an open-circuit voltage (Voc) of 1.00 V, a short circuit current density (Jsc) of 23.82 mA cm-2, a fill factor (FF) of 68% and a power conversion efficiency (PCE) of 16.31%, resulting in a 27.62% enhancement in PCE in comparison with the NiO device. The enhanced performance of the Y-doped NiO device could be attributed to the improved hole mobility, the high quality compact active layer morphology, the more efficient charge extraction from perovskite absorber as well as the lower recombination probability of charge carriers. Thus, this work provides a simple and effective approach to improve the electrical conductivity of p-type NiO thin films for use as a promising HTL in high performance PSCs.

Improved Efficiency of Polymer Solar Cells by means of Coating Hole Transporting Layer as Double Layer Deposition

NASA Astrophysics Data System (ADS)

Chonsut, T.; Kayunkid, N.; Rahong, S.; Rangkasikorn, A.; Wirunchit, S.; Kaewprajak, A.; Kumnorkaew, P.; Nukeaw, J.

2017-09-01

Polymer solar cells is one of the promising technologies that gain tremendous attentions in the field of renewable energy. Optimization of thickness for each layer is an important factor determining the efficiency of the solar cells. In this work, the optimum thickness of Poly(3,4-ethylenedioxythione): poly(styrenesulfonate) (PEDOT:PSS), a famous polymer widely used as hole transporting layer in polymer solar cells, is determined through the analyzing of device’s photovoltaic parameters, e.g. short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) as well as power conversion efficiency (PCE). The solar cells were prepared with multilayer of ITO/PEDOT:PSS/PCDTBT:PC70BM/TiOx/Al by rapid convective deposition. In such preparation technique, the thickness of the thin film is controlled by the deposition speed. The faster deposition speed is used, the thicker film is obtained. Furthermore, double layer deposition of PEDOT:PSS was introduced as an approach to improve solar cell efficiency. The results obviously reveal that, with the increase of PEDOT:PSS thickness, the increments of Jsc and FF play the important role to improve PCE from 3.21% to 4.03%. Interestingly, using double layer deposition of PEDOT:PSS shows the ability to enhance the performance of the solar cells to 6.12% under simulated AM 1.5G illumination of 100 mW/cm2.

Hole-Transport Materials for Perovskite Solar Cells.

PubMed

Calió, Laura; Kazim, Samrana; Grätzel, Michael; Ahmad, Shahzada

2016-11-14

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this level of performance. The use of a hole transport material (HTM) remains indispensable in perovskite solar cells. Perovskites can conduct holes, but they are present at low levels, and for efficient charge extraction a HTM layer is a prerequisite. Herein we provide an overview of the diverse types of HTM available, from organic to inorganic, in the hope of encouraging further research and the optimization of these materials. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning emission color of electroluminescence from two organic interfacial exciplexes by modulating the thickness of middle gadolinium complex layer

NASA Astrophysics Data System (ADS)

Li, Mingtao; Li, Wenlian; Chen, Lili; Kong, Zhiguo; Chu, Bei; Li, Bin; Hu, Zhizhi; Zhang, Zhiqiang

2006-02-01

Electroluminescent colors of organic light-emitting diodes (OLEDs) can be tuned by modulating the thickness of gadolinium (Gd) complex layer sandwiched between an electron-transporting layer (ETL) and a hole-transporting layer (HTL). The emission colors, which originate from the two interfacial exciplexes simultaneously, can be tuned from green to orange by increasing the thickness of the Gd-complex layer. The atom force microscope images have proved that there are many gaps in the thinner Gd-complex layers. Therefore, besides the exciplex formation between Gd complex and HTL, the exciplex between ETL and HTL is also formed. The results demonstrate that a simple way of color tuning can be realized by inserting a thin layer of color tuning material between HTL with lower ionization potentials and ETL with higher electron affinities. Moreover, photovoltaic device and white OLED based on the two exciplexes are also discussed.

Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating

NASA Astrophysics Data System (ADS)

Jin, Kui; Hu, Wei; Zhu, Beiyi; Kim, Dohun; Yuan, Jie; Sun, Yujie; Xiang, Tao; Fuhrer, Michael S.; Takeuchi, Ichiro; Greene, Richard. L.

2016-05-01

The occurrence of electrons and holes in n-type copper oxides has been achieved by chemical doping, pressure, and/or deoxygenation. However, the observed electronic properties are blurred by the concomitant effects such as change of lattice structure, disorder, etc. Here, we report on successful tuning the electronic band structure of n-type Pr2-xCexCuO4 (x = 0.15) ultrathin films, via the electric double layer transistor technique. Abnormal transport properties, such as multiple sign reversals of Hall resistivity in normal and mixed states, have been revealed within an electrostatic field in range of -2 V to + 2 V, as well as varying the temperature and magnetic field. In the mixed state, the intrinsic anomalous Hall conductivity invokes the contribution of both electron and hole-bands as well as the energy dependent density of states near the Fermi level. The two-band model can also describe the normal state transport properties well, whereas the carrier concentrations of electrons and holes are always enhanced or depressed simultaneously in electric fields. This is in contrast to the scenario of Fermi surface reconstruction by antiferromagnetism, where an anti-correlation is commonly expected.

Polyaniline as a new type of hole-transporting material to significantly increase the solar water splitting performance of BiVO4 photoanodes

NASA Astrophysics Data System (ADS)

Wang, Xiaojun; Ye, Kai-Hang; Yu, Xiang; Zhu, Jiaqian; Zhu, Yi; Zhang, Yuanming

2018-07-01

Polyaniline (PANI), with its low cost, chemical stability and high conductivity, is used as a hole transporting layer to fabricate NiOOH/PANI/BiVO4 (NPB) photoanode, of which the photoelectrochemical (PEC) water splitting performance is significantly enhanced. The remarkable water oxidation photocurrent of NPB photoanode achieves 3.31 mA cm-2 at 1.23 V vs. RHE under AM 1.5G solar light irradiation, which is greatly increased compared with that of pristine BiVO4 (0.89 mA cm-2 under the same condition). The maximal incident photon-to-current conversion efficiency achieves 83.3% at 430 nm at 1.23 V vs. RHE and the maximal applied bias photo-to-current efficiency reaches 1.20% at 0.68 V vs. RHE, which are nearly five and ten times higher than that of pristine BiVO4 photoanode, respectively. This NPB photoanode exhibits excellent stability with about 97.22% Faraday efficiency after PEC water splitting for 3 h. The exciting results demonstrate that PANI shows great potential as a hole-transporting layer for photoanode and NPB is an efficient and stable photoanode material with a great potential application in PEC water splitting. Overall, this work provides an excellent reference on designing and fabricating photoanode materials for the future.

Emergence of high-mobility minority holes in the electrical transport of the Ba (Fe1 -xMnxAs )2 iron pnictides

NASA Astrophysics Data System (ADS)

Urata, T.; Tanabe, Y.; Huynh, K. K.; Heguri, S.; Oguro, H.; Watanabe, K.; Tanigaki, K.

2015-05-01

In Fe pnictide (Pn) superconducting materials, neither Mn nor Cr doping to the Fe site induces superconductivity, even though hole carriers are generated. This is in strong contrast with the superconductivity appearing when holes are introduced by alkali-metal substitution on the insulating blocking layers. We investigate in detail the effects of Mn doping on magnetotransport properties in Ba (Fe1 -xMnxAs )2 for elucidating the intrinsic reason. The negative Hall coefficient for x =0 estimated in the low magnetic field (B ) regime gradually increases as x increases, and its sign changes to a positive one at x =0.020 . Hall resistivities as well as simultaneous interpretation using the magnetoconductivity tensor including both longitudinal and transverse transport components clarify that minority holes with high mobility are generated by the Mn doping via spin-density wave transition at low temperatures, while original majority electrons and holes residing in the paraboliclike Fermi surfaces of the semimetallic Ba (FeAs )2 are negligibly affected. Present results indicate that the mechanism of hole doping in Ba (Fe1 -xMnxAs )2 is greatly different from that of the other superconducting FePn family.

Polyaniline Nanofibers as the Hole Transport Medium in an Inverse Dye-Sensitized Solar Cell

NASA Astrophysics Data System (ADS)

Hesselsweet, Ian Brock

In order to become a viable alternative to silicon photovoltaics, dye-sensitized solar cells must overcome several issues primarily resulting from their use of a liquid electrolyte. Much research has gone into correcting these shortcomings by replacing the liquid electrolyte with solid-state hole-transport media. Using these solid-state materials brings new difficulties, such as completely filling the pores in the TiO2 nanostructure, and achieving good adhesion with the dye-coated TiO2. A novel approach to addressing these difficulties is the inverse dye-sensitized solar cell design. In this method the devices are constructed in reverse order, with the solidstate hole-transport medium providing the nanostructure instead of the TiO2. This allows new materials and methods to be used which may better address these issues. In this project, inverse dye-sensitized solar cells using polyaniline nanofibers as the hole transport medium were prepared and characterized. The devices were prepared on fluorine-doped tin oxide (FTO) coated glass electrodes. The first component was a dense spin-coated polyaniline blocking layer, to help prevent short circuiting of the devices. The second layer was a thin film of drop cast polyaniline nanofibers which acted as the hole transport medium and provided high surface area for the dye attachment. The dye used was 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), which was covalently attached to the nanofibers using a Friedel-Crafts acylation. Titania gel was then deposited into the pores of the nanofiber film by controlled hydrolysis of a titanium complex (Tyzor LA). A back electrode of TiO2 nanoparticles sintered on FTO was pressed on top to complete the devices. A typical device generated an open circuit voltage of 0.17 V and a closed circuit current of 5.7 nA/cm2 while the highest open circuit voltage recorded for any variation on a device was 0.31 V and the highest short circuit current was 52 nA/cm2 under AM 1.5 simulated solar spectrum at 100 mW/cm2. Initially prepared devices did not generate a measureable photocurrent due to two materials flaws. The first was traced to the poorly developed conduction band of the titania gel, as deposited from Tyzor LA hydrolysis, resulting in poor electron conduction. This prevented the titania gel from efficiently functioning as the electron transport medium. A remedy was found in adding a layer of sintered anatase TiO2 nanoparticles on the back electrode to serve as the electron transport medium. However, this remedy does not address the issue of the inability of titania gel to efficiently transport electrons photogenerated deep in the nanofiber film to the back electrode. The second flaw was found to originate from fast recombination kinetics between electrons in TiO2 and holes in polyaniline. However, a positive feature was that the titania gel intended to be used as the electron transport medium was found to sufficiently insulate the interface such that the recombination rate slowed enough to allow generation of a measureable photocurrent. Electronic insulation was further enhanced by co-attaching decanoic acid onto the polyaniline nanofibers to fill in pinholes between the dye molecules. While these solutions were not ideal, they were intended to be diagnostic in nature and supplied critical information about the weak links in the device design, thus pointing the way toward improving device performance. Significant enhancements can be expected by addressing these issues in further detail.

Numerical study on exciton transport and light emission for organic light emitting diodes with an emission layer.

PubMed

Kim, K S; Hwang, Y W; Won, T Y

2013-12-01

This paper reports the results of a numerical study on carrier injection and exciton transport in an organic light emitting diode (OLED) structure based on tris (8-hydroxyquinolinato) aluminum (Alq3). Because charge accumulation at the interfaces between the emission layer (EML) and transport layer are believed to increase the recombination rate, which also increases the exciton density, a numerical study was performed on the effect of inserting an EML in the bilayer structure. In the first case considered, the lowest unoccupied molecular orbital (LUMO) of the EML was aligned with the LUMO of the hole transport layer (HTL), whereas the highest occupied molecular orbital (HOMO) of the EML was aligned with the HOMO of the electron transport layer (ETL). In the second case, the LUMO of the EML was aligned with the LUMO of the ETL and the HOMO of the EML was aligned with the HOMO of the HTL. In case of a charge-blocking device, most of the recombination appeared to occur at both edges of the EML because the electric field exhibited a peak in these areas. On the other hand, in the case of the charge-confining device, the electric field was confined at the interface between the EML and ETL. This paper also discussed the effect of the insertion of a doping layer as transport layer.

Charge transport model in solid-state avalanche amorphous selenium and defect suppression design

NASA Astrophysics Data System (ADS)

Scheuermann, James R.; Miranda, Yesenia; Liu, Hongyu; Zhao, Wei

2016-01-01

Avalanche amorphous selenium (a-Se) in a layer of High Gain Avalanche Rushing Photoconductor (HARP) is being investigated for its use in large area medical imagers. Avalanche multiplication of photogenerated charge requires electric fields greater than 70 V μm-1. For a-Se to withstand this high electric field, blocking layers are used to prevent the injection of charge carriers from the electrodes. Blocking layers must have a high injection barrier and deep trapping states to reduce the electric field at the interface. In the presence of a defect in the blocking layer, a distributed resistive layer (DRL) must be included into the structure to build up space charge and reduce the electric field in a-Se and the defect. A numerical charge transport model has been developed to optimize the properties of blocking layers used in various HARP structures. The model shows the incorporation of a DRL functionality into the p-layer can reduce dark current at a point defect by two orders of magnitude by reducing the field in a-Se to the avalanche threshold. Hole mobility in a DRL of ˜10-8 cm2 V-1 s-1 at 100 V μm-1 as demonstrated by the model can be achieved experimentally by varying the hole mobility of p-type organic or inorganic semiconductors through doping, e.g., using Poly(9-vinylcarbozole) doped with 1%-3% (by weight) of poly(3-hexylthiopene).

A charge inverter for III-nitride light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zi-Hui, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn; Zhang, Yonghui; Bi, Wengang, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO{sub 2} insulator layer on the p{sup +}-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p{sup +}-GaN and SiO{sub 2} insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constantmore » of the thin SiO{sub 2} layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p{sup +}-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm{sup 2} LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.« less

Reversible conversion of dominant polarity in ambipolar polymer/graphene oxide hybrids

DOE PAGES

Zhou, Ye; Han, Su -Ting; Sonar, Prashant; ...

2015-03-24

The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. Wemore » conclude that this hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits.« less

Acquisition of an X-Ray Scattering System with Solid-Gas Reactor Chamber and Ultrafast Detection Capabilities for Research and Instruction in Science and Engineering

DTIC Science & Technology

2015-05-18

solar   cell  based  on  the  PEDOT:     PSS  hole  transport  layer  and  PCBM  electron  transport  layer...of  a   solar   cell                       10     X-­‐ray  diffraction  patterns  collected  in...the  UTEP  facility  on   hybrid  samples  of     CeO2/porous

Concepts for the material development of phosphorescent organic materials processable from solution and their application in OLEDs

NASA Astrophysics Data System (ADS)

Janietz, S.; Krueger, H.; Thesen, M.; Salert, B.; Wedel, A.

2014-10-01

One example of organic electronics is the application of polymer based light emitting devices (PLEDs). PLEDs are very attractive for large area and fine-pixel displays, lighting and signage. The polymers are more amenable to solution processing by printing techniques which are favourable for low cost production in large areas. With phosphorescent emitters like Ir-complexes higher quantum efficiencies were obtained than with fluorescent systems, especially if multilayer stack systems with separated charge transport and emitting layers were applied in the case of small molecules. Polymers exhibit the ability to integrate all the active components like the hole-, electron-transport and phosphorescent molecules in only one layer. Here, the active components of a phosphorescent system - triplet emitter, hole- and electron transport molecules - can be linked as a side group to a polystyrene main chain. By varying the molecular structures of the side groups as well as the composition of the side chains with respect to the triplet emitter, hole- and electron transport structure, and by blending with suitable glass-forming, so-called small molecules, brightness, efficiency and lifetime of the produced OLEDs can be optimized. By choosing the triplet emitter, such as iridium complexes, different emission colors can be specially set. Different substituted triazine molecules were introduced as side chain into a polystyrene backbone and applied as electron transport material in PLED blend systems. The influence of alkyl chain lengths of the performance will be discussed. For an optimized blend system with a green emitting phosphorescent Ir-complex efficiencies of 60 cd/A and an lifetime improvement of 66.000 h @ 1000 cd/m2 were achieved.

Balancing high gain and bandwidth in multilayer organic photodetectors with tailored carrier blocking layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammond, William T.; Mudrick, John P.; Xue, Jiangeng, E-mail: jxue@mse.ufl.edu

2014-12-07

We present detailed studies of the high photocurrent gain behavior in multilayer organic photodiodes containing tailored carrier blocking layers we reported earlier in a Letter [W. T. Hammond and J. Xue, Appl. Phys. Lett. 97, 073302 (2010)], in which a high photocurrent gain of up to 500 was attributed to the accumulation of photogenerated holes at the anode/organic active layer interface and the subsequent drastic increase in secondary electron injection from the anode. Here, we show that both the hole-blocking layer structure and layer thickness strongly influence the magnitude of the photocurrent gain. Temporal studies revealed that the frequency responsemore » of such devices is limited by three different processes with lifetimes of 10 μs, 202 μs, and 2.72 ms for the removal of confined holes, which limit the 3 dB bandwidth of these devices to 1.4 kHz. Furthermore, the composition in the mixed organic donor-acceptor photoactive layer affects both gain and bandwidth, which is attributed to the varying charge transport characteristics, and the optimal gain-bandwidth product is achieved with approximately 30% donor content. Finally, these devices show a high dynamic range of more than seven orders of magnitude, although the photocurrent shows a sublinear dependence on the incident optical power.« less

Molecular dynamics simulations reveal that water diffusion between graphene oxide layers is slow

DOE PAGES

Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; ...

2016-07-08

Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of a molecular dynamics simulation study of water intercalated between GO layers that have a C/O ratio of 4. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in spacing from about 0.7 nm to 0.8 nm and an increase in mass ofmore » about 14% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. As a result, slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.« less

Permanent polarization and charge distribution in organic light-emitting diodes (OLEDs): Insights from near-infrared charge-modulation spectroscopy of an operating OLED

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchetti, Alfred P.; Haskins, Terri L.; Young, Ralph H.

2014-03-21

Vapor-deposited Alq{sub 3} layers typically possess a strong permanent electrical polarization, whereas NPB layers do not. (Alq{sub 3} is tris(8-quinolinolato)aluminum(III); NPB is 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl.) The cause is a net orientation of the Alq{sub 3} molecules with their large dipole moments. Here we report on consequences for an organic light-emitting diode (OLED) with an NPB hole-transport layer and Alq{sub 3} electron-transport layer. The discontinuous polarization at the NPB|Alq{sub 3} interface has the same effect as a sheet of immobile negative charge there. It is more than compensated by a large concentration of injected holes (NPB{sup +}) when the OLED is running. Wemore » discuss the implications and consequences for the quantum efficiency and the drive voltage of this OLED and others. We also speculate on possible consequences of permanent polarization in organic photovoltaic devices. The concentration of NPB{sup +} was measured by charge-modulation spectroscopy (CMS) in the near infrared, where the NPB{sup +} has a strong absorption band, supplemented by differential-capacitance and current-voltage measurements. Unlike CMS in the visible, this method avoids complications from modulation of the electroluminescence and electroabsorption.« less

DNA bases thymine and adenine in bio-organic light emitting diodes.

PubMed

Gomez, Eliot F; Venkatraman, Vishak; Grote, James G; Steckl, Andrew J

2014-11-24

We report on the use of nucleic acid bases (NBs) in organic light emitting diodes (OLEDs). NBs are small molecules that are the basic building blocks of the larger DNA polymer. NBs readily thermally evaporate and integrate well into the vacuum deposited OLED fabrication. Adenine (A) and thymine (T) were deposited as electron-blocking/hole-transport layers (EBL/HTL) that resulted in increases in performance over the reference OLED containing the standard EBL material NPB. A-based OLEDs reached a peak current efficiency and luminance performance of 48 cd/A and 93,000 cd/m(2), respectively, while T-based OLEDs had a maximum of 76 cd/A and 132,000 cd/m(2). By comparison, the reference OLED yielded 37 cd/A and 113,000 cd/m(2). The enhanced performance of T-based devices is attributed to a combination of energy levels and structured surface morphology that causes more efficient and controlled hole current transport to the emitting layer.

TiO2 reinforced PMMA-TiO2 nanocomposite for its application in organic light emitting diode (OLED) as electron transport layer material

NASA Astrophysics Data System (ADS)

Kandulna, R.; Choudhary, R. B.; Singh, R.

2018-04-01

PMMA, TiO2 and PMMA-TiO2 nanocomposite were successfully synthesized in the laboratory via free radical polymerization process. The formation of PMMA corresponding change in the nanostructure with the embodiment of TiO2 nanofillers was confirmed by X-ray diffraction technique (XRD) analysis. Irregular tetragonal bipyramidal arrangement of TiO2 was formed within the spherical type structure of PMMA polymeric matrix, as examined by the surface morphological image. Relatively higher electron-hole non-radiative recombination of PMMA-TiO2 nanocomposite corresponded to blue-violet band, blue band, and green band was examined from PL spectra. An enhanced current density ˜ 165 % was observed with significantly improved p-type conductivity for PMMA-TiO2 nanocomposite. The improved specific capacitance with high dielectric constant and high electron-hole recombination rate confirmed that it can possibly use as electron transport layer material in the OLED devices fabrication.

Improvement in lifetime of green organic light-emitting device

NASA Astrophysics Data System (ADS)

Ki, Hyun Chul; Kim, Seon Hoon; Kim, Doo Gun; Kim, Hyun Jin; Ko, Hang Ju; Han, Myung-Soo; Kim, Hwe Jong; Hong, Kyung Jin

2010-02-01

We have proposed a novel encapsulation method with simple process in comparison with conventional encapsulation technique. Here, the encapsulation film of silicon dioxide is steady for external environment because this can be designed to cover the emitting organic material from air. Silicon dioxide of 220 nm was deposited by plasma enhanced chemical vapor deposition and etched by reactive ion etching system. Then, Alq3 was used as a material to emitting layer in the green (organic light emitting device) OLED and TPD in the hole transportation layer was used for the harmonious transportation of hole. Luminance was measured with 40 hour intervals at the air-exposed condition. After 400, 1,000, 1,600, and 2,000 hours, luminance of green OLED were 7,366, 7,200, 6,210, and 5,100 cd/m2, respectively. Luminance of green OLED doesn't decrease until 2,000 hours. As a results, proposed encapsulation technique can increase the life time of green OLED.

Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell.

PubMed

Bergmann, Victor W; Weber, Stefan A L; Javier Ramos, F; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Li, Dan; Domanski, Anna L; Lieberwirth, Ingo; Ahmad, Shahzada; Berger, Rüdiger

2014-09-22

Perovskite-sensitized solar cells have reached power conversion efficiencies comparable to commercially available solar cells used for example in solar farms. In contrast to silicon solar cells, perovskite-sensitized solar cells can be made by solution processes from inexpensive materials. The power conversion efficiency of these cells depends substantially on the charge transfer at interfaces. Here we use Kelvin probe force microscopy to study the real-space cross-sectional distribution of the internal potential within high efficiency mesoscopic methylammonium lead tri-iodide solar cells. We show that the electric field is homogeneous through these devices, similar to that of a p-i-n type junction. On illumination under short-circuit conditions, holes accumulate in front of the hole-transport layer as a consequence of unbalanced charge transport in the device. After light illumination, we find that trapped charges remain inside the active device layers. Removing these traps and the unbalanced charge injection could enable further improvements in performance of perovskite-sensitized solar cells.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Zhenyu, E-mail: jiangzhenyu1201@hotmail.com, E-mail: jianxu@engr.psu.edu; Liu, Yan; Mo, Chen

In an attempt to suppress the dark current, the barrier layer engineer for solution-processed PbSe colloidal quantum-dot (CQD) photodetectors has been investigated in the present study. It was found that the dark current can be significantly suppressed by implementing two types of carrier blocking layers, namely, hole blocking layer and electron blocking layer, sandwiched in between two active PbSe CQD layers. Meanwhile no adverse impact has been observed for the photo current. Our study suggests that this improvement resides on the transport pathway created via carrier recombination at intermediate layer, which provides wide implications for the suppression of dark currentmore » for infrared photodetectors.« less

Quantitative description of charge-carrier transport in a white organic light-emitting diode

NASA Astrophysics Data System (ADS)

Schober, M.; Anderson, M.; Thomschke, M.; Widmer, J.; Furno, M.; Scholz, R.; Lüssem, B.; Leo, K.

2011-10-01

We present a simulation model for the analysis of charge-carrier transport in organic thin-film devices, and apply it to a three-color white hybrid organic light-emitting diode (OLED) with fluorescent blue and phosphorescent red and green emission. We simulate a series of single-carrier devices, which reconstruct the OLED layer sequence step by step. Thereby, we determine the energy profiles for hole and electron transport, show how to discern bulk from interface limitation, and identify trap states.

Organic solar cells with graphene electrodes and vapor printed poly(3,4-ethylenedioxythiophene) as the hole transporting layers.

PubMed

Park, Hyesung; Howden, Rachel M; Barr, Miles C; Bulović, Vladimir; Gleason, Karen; Kong, Jing

2012-07-24

For the successful integration of graphene as a transparent conducting electrode in organic solar cells, proper energy level alignment at the interface between the graphene and the adjacent organic layer is critical. The role of a hole transporting layer (HTL) thus becomes more significant due to the generally lower work function of graphene compared to ITO. A commonly used HTL material with ITO anodes is poly(3,4-ethylenedioxythiophene) (PEDOT) with poly(styrenesulfonate) (PSS) as the solid-state dopant. However, graphene's hydrophobic surface renders uniform coverage of PEDOT:PSS (aqueous solution) by spin-casting very challenging. Here, we introduce a novel, yet simple, vapor printing method for creating patterned HTL PEDOT layers directly onto the graphene surface. Vapor printing represents the implementation of shadow masking in combination with oxidative chemical vapor deposition (oCVD). The oCVD method was developed for the formation of blanket (i.e., unpatterened) layers of pure PEDOT (i.e., no PSS) with systematically variable work function. In the unmasked regions, vapor printing produces complete, uniform, smooth layers of pure PEDOT over graphene. Graphene electrodes were synthesized under low-pressure chemical vapor deposition (LPCVD) using a copper catalyst. The use of another electron donor material, tetraphenyldibenzoperiflanthene, instead of copper phthalocyanine in the organic solar cells also improves the power conversion efficiency. With the vapor printed HTL, the devices using graphene electrodes yield comparable performances to the ITO reference devices (η(p,LPCVD) = 3.01%, and η(p,ITO) = 3.20%).

Facile Approach to Preparing a Vanadium Oxide Hydrate Layer as a Hole-Transport Layer for High-Performance Polymer Solar Cells.

PubMed

Cong, Hailin; Han, Dongwei; Sun, Bingbing; Zhou, Dongying; Wang, Chen; Liu, Ping; Feng, Lai

2017-05-31

We demonstrate a facile and green approach to preparing a vanadium oxide hydrate (VO x ·nH 2 O) layer to serve as the hole-transport layer (HTL) in high-performance polymer solar cells (PSCs). The VO x ·nH 2 O layer was in situ prepared by a combined H 2 O 2 and ultraviolet-ozone (UVO) processing on a VO x layer. The as-prepared VO x ·nH 2 O layer featured a work function of 5.0 ± 0.1 eV, high transmittance, and better interface properties compared to those of the generally prepared VO x (UVO or thermal annealing) layers. PSCs based on poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]/[6,6]-phenyl-C 71 -butyric acid methyl ester using the VO x ·nH 2 O layer as the HTL yielded high power conversion efficiencies (PCEs) up to 8.11%, outperforming the devices with VO x layers (PCE of 6.79% for the UVO-processed VO x layer and 6.10% for the thermally annealed VO x layer) and conventional polyethylenedioxythiophene-polystyrenesulfonate (PEDOT:PSS) layers (PCE of 7.67%). The improved PCE was attributed to the enhanced J SC and/or fill factor, which mainly correlate to the improved interfacial contact between the photoactive layer and the indium tin oxide/HTL or cathode when using the VO x ·nH 2 O layer as the HTL. A similar improvement in the PCE was also observed for the PSCs based on poly(3-hexylthiophene)/[6,6]-phenyl-C 61 -butyric acid methyl ester. In addition, PSCs with a VO x ·nH 2 O layer as the HTL showed a higher stability than that of those with a PEDOT:PSS layer. Hence, it would be possible to use this simply and in situ prepared VO x ·nH 2 O layer as an inexpensive HTL for high-performance PSCs.

Link between hopping models and percolation scaling laws for charge transport in mixtures of small molecules

DOE PAGES

Ha, Dong -Gwang; Kim, Jang -Joo; Baldo, Marc A.

2016-04-29

Mixed host compositions that combine charge transport materials with luminescent dyes offer superior control over exciton formation and charge transport in organic light emitting devices (OLEDs). Two approaches are typically used to optimize the fraction of charge transport materials in a mixed host composition: either an empirical percolative model, or a hopping transport model. We show that these two commonly-employed models are linked by an analytic expression which relates the localization length to the percolation threshold and critical exponent. The relation is confirmed both numerically and experimentally through measurements of the relative conductivity of Tris(4-carbazoyl-9-ylphenyl) amine (TCTA) :1,3-bis(3,5-dipyrid-3-yl-phenyl) benzene (BmPyPb)more » mixtures with different concentrations, where the TCTA plays a role as hole conductor and the BmPyPb as hole insulator. Furthermore, the analytic relation may allow the rational design of mixed layers of small molecules for high-performance OLEDs.« less

Link between hopping models and percolation scaling laws for charge transport in mixtures of small molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ha, Dong-Gwang; Kim, Jang-Joo; Baldo, Marc A.

2016-04-01

Mixed host compositions that combine charge transport materials with luminescent dyes offer superior control over exciton formation and charge transport in organic light emitting devices (OLEDs). Two approaches are typically used to optimize the fraction of charge transport materials in a mixed host composition: either an empirical percolative model, or a hopping transport model. We show that these two commonly-employed models are linked by an analytic expression which relates the localization length to the percolation threshold and critical exponent. The relation is confirmed both numerically and experimentally through measurements of the relative conductivity of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) :1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPb) mixtures withmore » different concentrations, where the TCTA plays a role as hole conductor and the BmPyPb as hole insulator. The analytic relation may allow the rational design of mixed layers of small molecules for high-performance OLEDs.« less

Investigation of p-type depletion doping for InGaN/GaN-based light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Yiping; Zhang, Zi-Hui; Tan, Swee Tiam; Hernandez-Martinez, Pedro Ludwig; Zhu, Binbin; Lu, Shunpeng; Kang, Xue Jun; Sun, Xiao Wei; Demir, Hilmi Volkan

2017-01-01

Due to the limitation of the hole injection, p-type doping is essential to improve the performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs). In this work, we propose and show a depletion-region Mg-doping method. Here we systematically analyze the effectiveness of different Mg-doping profiles ranging from the electron blocking layer to the active region. Numerical computations show that the Mg-doping decreases the valence band barrier for holes and thus enhances the hole transportation. The proposed depletion-region Mg-doping approach also increases the barrier height for electrons, which leads to a reduced electron overflow, while increasing the hole concentration in the p-GaN layer. Experimentally measured external quantum efficiency indicates that Mg-doping position is vitally important. The doping in or adjacent to the quantum well degrades the LED performance due to Mg diffusion, increasing the corresponding nonradiative recombination, which is well supported by the measured carrier lifetimes. The experimental results are well numerically reproduced by modifying the nonradiative recombination lifetimes, which further validate the effectiveness of our approach.

Novel Solid-State Solar Cell Based on Hole-Conducting MOF-Sensitizer Demonstrating Power Conversion Efficiency of 2.1.

PubMed

Ahn, Do Young; Lee, Deok Yeon; Shin, Chan Yong; Bui, Hoa Thi; Shrestha, Nabeen K; Giebeler, Lars; Noh, Yong-Young; Han, Sung-Hwan

2017-04-19

This work reports on designing of first successful MOF-sensitizer based solid-state photovoltaic device, perticularly with a meaningful output power conversion efficiency. In this study, an intrinsically conductive cobalt-based MOFs (Co-DAPV) formed by the coordination between Co (II) ions and a redox active di(3-diaminopropyl)-viologen (i.e., DAPV) ligand is investigated as sensitizer. Hall-effect measurement shows p-type conductivity of the Co-DAPV film with hole mobility of 0.017 cm 2 V -1 s -1 , suggesting its potential application as hole transporting sensitizer. Further, the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Co-DAPV are well-matched to be suitably employed for sensitizing TiO 2 . Thus, by layer-by-layer deposition of hole conducting MOF-sensitizer onto mesoporous TiO 2 film, a power conversion efficiency of as high as 2.1% is achieved, which exceeds the highest efficiency values of MOF-sensitized liquid-junction solar cells reported so far.

Prospects of e-beam evaporated molybdenum oxide as a hole transport layer for perovskite solar cells

NASA Astrophysics Data System (ADS)

Ali, F.; Khoshsirat, N.; Duffin, J. L.; Wang, H.; Ostrikov, K.; Bell, J. M.; Tesfamichael, T.

2017-09-01

Perovskite solar cells have emerged as one of the most efficient and low cost technologies for delivering of solar electricity due to their exceptional optical and electrical properties. Commercialization of the perovskite solar cells is, however, limited because of the higher cost and environmentally sensitive organic hole transport materials such as spiro-OMETAD and PEDOT:PSS. In this study, an empirical simulation was performed using the Solar Cell Capacitance Simulator software to explore the MoOx thin film as an alternative hole transport material for perovskite solar cells. In the simulation, properties of MoOx thin films deposited by the electron beam evaporation technique from high purity (99.99%) MoO3 pellets at different substrate temperatures (room temperature, 100 °C and 200 °C) were used as input parameters. The films were highly transparent (>80%) and have low surface roughness (≤2 nm) with bandgap energy ranging between 3.75 eV and 3.45 eV. Device simulation has shown that the MoOx deposited at room temperature can work in both the regular and inverted structures of the perovskite solar cell with a promising efficiency of 18.25%. Manufacturing of the full device is planned in order to utilize the MoOx as an alternative hole transport material for improved performance, good stability, and low cost of the perovskite solar cell.

Comparison and characterization of different tunnel layers, suitable for passivated contact formation

NASA Astrophysics Data System (ADS)

Ling, Zhi Peng; Xin, Zheng; Ke, Cangming; Jammaal Buatis, Kitz; Duttagupta, Shubham; Lee, Jae Sung; Lai, Archon; Hsu, Adam; Rostan, Johannes; Stangl, Rolf

2017-08-01

Passivated contacts for solar cells can be realized using a variety of differently formed ultra-thin tunnel oxide layers. Assessing their interface properties is important for optimization purposes. In this work, we demonstrate the ability to measure the interface defect density distribution D it(E) and the fixed interface charge density Q f for ultra-thin passivation layers operating within the tunnel regime (<2 nm). Various promising tunnel layer candidates [i.e., wet chemically formed SiO x , UV photo-oxidized SiO x , and atomic layer deposited (ALD) AlO x ] are investigated for their potential application forming electron or hole selective tunnel layer passivated contacts. In particular, ALD AlO x is identified as a promising tunnel layer candidate for hole-extracting passivated contact formation, stemming from its high (negative) fixed interface charge density in the order of -6 × 1012 cm-2. This is an order of magnitude higher compared to wet chemically or UV photo-oxidized formed silicon oxide tunnel layers, while keeping the density of interface defect states D it at a similar level (in the order of ˜2 × 1012 cm-2 eV-1). This leads to additional field effect passivation and therefore to significantly higher measured effective carrier lifetimes (˜2 orders of magnitude). A surface recombination velocity of ˜40 cm/s has been achieved for a 1.5 nm thin ALD AlO x tunnel layer prior to capping by an additional hole transport material, like p-doped poly-Si or PEDOT:PSS.

Room-Temperature and Solution-Processable Cu-Doped Nickel Oxide Nanoparticles for Efficient Hole-Transport Layers of Flexible Large-Area Perovskite Solar Cells.

PubMed

He, Qiqi; Yao, Kai; Wang, Xiaofeng; Xia, Xuefeng; Leng, Shifeng; Li, Fan

2017-12-06

Flexible perovskite solar cells (PSCs) using plastic substrates have become one of the most attractive points in the field of thin-film solar cells. Low-temperature and solution-processable nanoparticles (NPs) enable the fabrication of semiconductor thin films in a simple and low-cost approach to function as charge-selective layers in flexible PSCs. Here, we synthesized phase-pure p-type Cu-doped NiO x NPs with good electrical properties, which can be processed to smooth, pinhole-free, and efficient hole transport layers (HTLs) with large-area uniformity over a wide range of film thickness using a room-temperature solution-processing technique. Such a high-quality inorganic HTL allows for the fabrication of flexible PSCs with an active area >1 cm 2 , which have a power conversion efficiency over 15.01% without hysteresis. Moreover, the Cu/NiO x NP-based flexible devices also demonstrate excellent air stability and mechanical stability compared to their counterpart fabricated on the pristine NiO x films. This work will contribute to the evolution of upscaling flexible PSCs with a simple fabrication process and high device performances.

High-efficiency red electroluminescent device based on multishelled InP quantum dots.

PubMed

Jo, Jung-Ho; Kim, Jong-Hoon; Lee, Ki-Heon; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun

2016-09-01

We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4^'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849  cd/m², a current efficiency of 4.2  cd/A, and an external quantum efficiency of 2.5%.

Effect of tunneling layers on the performances of floating-gate based organic thin-film transistor nonvolatile memories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wei, E-mail: wwei99@jlu.edu.cn; Han, Jinhua; Ying, Jun

2014-09-22

Two types of floating-gate based organic thin-film transistor nonvolatile memories (FG-OTFT-NVMs) were demonstrated, with poly(methyl methacrylate co glycidyl methacrylate) (P(MMA-GMA)) and tetratetracontane (TTC) as the tunneling layer, respectively. Their device performances were measured and compared. In the memory with a P(MMA-GMA) tunneling layer, typical unipolar hole transport was obtained with a relatively small mobility of 0.16 cm{sup 2}/V s. The unidirectional shift of turn-on voltage (V{sub on}) due to only holes trapped/detrapped in/from the floating gate resulted in a small memory window of 12.5 V at programming/erasing voltages (V{sub P}/V{sub E}) of ±100 V and a nonzero reading voltage. Benefited from the well-ordered moleculemore » orientation and the trap-free surface of TTC layer, a considerably high hole mobility of 1.7 cm{sup 2}/V s and a visible feature of electrons accumulated in channel and trapped in floating-gate were achieved in the memory with a TTC tunneling layer. High hole mobility resulted in a high on current and a large memory on/off ratio of 600 at the V{sub P}/V{sub E} of ±100 V. Both holes and electrons were injected into floating-gate and overwritten each other, which resulted in a bidirectional V{sub on} shift. As a result, an enlarged memory window of 28.6 V at the V{sub P}/V{sub E} of ±100 V and a zero reading voltage were achieved. Based on our results, a strategy is proposed to optimize FG-OTFT-NVMs by choosing a right tunneling layer to improve the majority carrier mobility and realize ambipolar carriers injecting and trapping in the floating-gate.« less

Ultrathin nondoped emissive layers for efficient and simple monochrome and white organic light-emitting diodes.

PubMed

Zhao, Yongbiao; Chen, Jiangshan; Ma, Dongge

2013-02-01

In this paper, highly efficient and simple monochrome blue, green, orange, and red organic light emitting diodes (OLEDs) based on ultrathin nondoped emissive layers (EMLs) have been reported. The ultrathin nondoped EML was constructed by introducing a 0.1 nm thin layer of pure phosphorescent dyes between a hole transporting layer and an electron transporting layer. The maximum external quantum efficiencies (EQEs) reached 17.1%, 20.9%, 17.3%, and 19.2% for blue, green, orange, and red monochrome OLEDs, respectively, indicating the universality of the ultrathin nondoped EML for most phosphorescent dyes. On the basis of this, simple white OLED structures are also demonstrated. The demonstrated complementary blue/orange, three primary blue/green/red, and four color blue/green/orange/red white OLEDs show high efficiency and good white emission, indicating the advantage of ultrathin nondoped EMLs on constructing simple and efficient white OLEDs.

A charge carrier transport model for donor-acceptor blend layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, Janine, E-mail: janine.fischer@iapp.de; Widmer, Johannes; Koerner, Christian

2015-01-28

Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for themore » characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.« less

Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, C., E-mail: c.morrison.2@warwick.ac.uk; Casteleiro, C.; Leadley, D. R.

The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm{sup 2}/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m{sub 0}. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour,more » analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.« less

Ab initio modeling of steady-state and time-dependent charge transport in hole-only α-NPD devices

NASA Astrophysics Data System (ADS)

Liu, Feilong; Massé, Andrea; Friederich, Pascal; Symalla, Franz; Nitsche, Robert; Wenzel, Wolfgang; Coehoorn, Reinder; Bobbert, Peter A.

2016-12-01

We present an ab initio modeling study of steady-state and time-dependent charge transport in hole-only devices of the amorphous molecular semiconductor α-NPD [N ,N'-Di(1 -naphthyl)-N ,N'-diphenyl-(1 ,1'-biphenyl)-4 ,4'-diamine] . The study is based on the microscopic information obtained from atomistic simulations of the morphology and density functional theory calculations of the molecular hole energies, reorganization energies, and transfer integrals. Using stochastic approaches, the microscopic information obtained in simulation boxes at a length scale of ˜10 nm is expanded and employed in one-dimensional (1D) and three-dimensional (3D) master-equation modeling of the charge transport at the device scale of ˜100 nm. Without any fit parameter, predicted current density-voltage and impedance spectroscopy data obtained with the 3D modeling are in very good agreement with measured data on devices with different α-NPD layer thicknesses in a wide range of temperatures, bias voltages, and frequencies. Similarly good results are obtained with the computationally much more efficient 1D modeling after optimizing a hopping prefactor.

DFT/TDDFT investigation on the photophysical properties of a series of phosphorescent cyclometalated complexes based on the benchmark complex FIrpic

NASA Astrophysics Data System (ADS)

Han, Deming; Gong, Ping; Lv, Shuhui; Zhao, Lihui; Zhao, Henan

2018-05-01

The photophysical properties of four Ir(III) complexes have been investigated by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). The effect of the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption and phosphorescent properties has been studied. The theoretical calculation shows that the lowest-lying singlet absorptions for complexes 1-4 are located at 387, 385, 418 and 386 nm, respectively. For 1-4, the phosphorescence at 465, 485, 494 and 478 nm is mainly attributed to the LUMO → HOMO and LUMO → HOMO-1 transition configurations characteristics. In addition, ionisation potential (IP), electron affinities (EAs) and reorganisation energy have been investigated to evaluate the charge transfer and balance properties between hole and electron. The balance of the reorganisation energies for complex 3 is better than others. The difference between hole transport and electron transport for complex 3 is the smallest among these complexes, which is beneficial to achieve the hole and electron transfer balance in emitting layer.

Inverted Planar Perovskite Solar Cells with a High Fill Factor and Negligible Hysteresis by the Dual Effect of NaCl-Doped PEDOT:PSS.

PubMed

Hu, Lijun; Sun, Kuan; Wang, Ming; Chen, Wei; Yang, Bo; Fu, Jiehao; Xiong, Zhuang; Li, Xinyi; Tang, Xiaosheng; Zang, Zhigang; Zhang, Shupeng; Sun, Lidong; Li, Meng

2017-12-20

The performance of inverted perovskite solar cells is highly dependent on hole extraction and surface properties of hole transport layers. To highlight the important role of hole transport layers, a facile and simple method is developed by adding sodium chloride (NaCl) into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The average power conversion efficiency of the perovskite solar cells prepared on NaCl-doped PEDOT:PSS is 17.1% with negligible hysteresis, compared favorably to the control devices (15.1%). Particularly, they exhibit markedly improved V oc and fill factor (FF), with the best FF as high as 81.9%. The enhancement of photovoltaic performance is ascribed to two effects. Better conductivity and hole extraction of PEDOT:PSS are observed after NaCl doping. More intriguingly, the perovskite polycrystalline film shows a preferred orientation along the (001) direction on NaCl-doped PEDOT:PSS, leading to a more uniform thin film. The comparison of the crystal structure between NaCl and MAPbCl 3 indicates a lattice constant mismatch less than 2% and a matched chlorine atom arrangement on the (001) surface, which implies that the NaCl crystallites on the top surface of PEDOT:PSS might serve as seeds guiding the growth of perovskite crystals. This simple method is fully compatible with printing technologies to mass-produce perovskite solar cells with high efficiency and tunable crystal orientations.

Fully printable transparent monolithic solid-state dye-sensitized solar cell with mesoscopic indium tin oxide counter electrode.

PubMed

Yang, Ying; Ri, Kwangho; Rong, Yaoguang; Liu, Linfeng; Liu, Tongfa; Hu, Min; Li, Xiong; Han, Hongwei

2014-09-07

We present a new transparent monolithic mesoscopic solid-state dye-sensitized solar cell based on trilamellar films of mesoscopic TiO2 nanocrystalline photoanode, a ZrO2 insulating layer and an indium tin oxide counter electrode (ITO-CE), which were screen-printed layer by layer on a single substrate. When the thickness of the ITO-CE was optimized to 2.1 μm, this very simple and fully printable solid-state DSSC with D102 dye and spiro-OMeTAD hole transport materials presents efficiencies of 1.73% when irradiated from the front side and 1.06% when irradiated from the rear side under a standard simulated sunlight condition (AM 1.5 Global, 100 mW cm(-2)). Higher parameters could be expected with a better transparent mesoscopic counter electrode and hole conductor for the printable monolithic mesoscopic solid-state DSSC.

Organic-Inorganic Hybrid Interfacial Layer for High-Performance Planar Perovskite Solar Cells.

PubMed

Yang, Hao; Cong, Shan; Lou, Yanhui; Han, Liang; Zhao, Jie; Sun, Yinghui; Zou, Guifu

2017-09-20

4,7-Diphenyl-1,10-phenanthroline (Bphen) is an efficient electron transport and hole blocking material in organic photoelectric devices. Here, we report cesium carbonate (Cs 2 CO 3 ) doped Bphen as cathode interfacial layer in CH 3 NH 3 PbI 3-x Cl x based planar perovskite solar cells (PSCs). Investigation finds that introducing Cs 2 CO 3 suppresses the crystallization of Bphen and benefits a smooth interface contact between the perovskite and electrode, resulting in the decrease in carrier recombination and the perovskite degradation. In addition, the matching energy level of Bphen film in the PSCs effectively blocks the holes diffusion to cathode. The resultant power conversion efficiency (PCE) achieves as high as 17.03% in comparison with 12.67% of reference device without doping. Besides, experiments also demonstrate the stability of PSCs have large improvement because the suppressed crystallization of Bphen by doping Cs 2 CO 3 as a superior barrier layer blocks the Ag atom and surrounding moisture access to the vulnerable perovskite layer.

Design of p-type cladding layers for tunnel-injected UV-A light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuewei; Krishnamoorthy, Sriram; Akyol, Fatih

Here, we discuss the engineering of p-AlGaN cladding layers for achieving efficient tunnel-injected III-Nitride ultraviolet light emitting diodes (UV LEDs) in the UV-A spectral range. We show that the capacitance-voltage measurements can be used to estimate the compensation and doping in the p-AlGaN layers located between the multi-quantum well region and the tunnel junction layer. By increasing the p-type doping concentration to overcome the background compensation, on-wafer external quantum efficiency and wall-plug efficiency of 3.37% and 1.62%, respectively, were achieved for the tunnel-injected UV LEDs emitting at 325 nm. We also show that interband tunneling hole injection can be usedmore » to realize UV LEDs without any acceptor doping. The work discussed here provides new understanding of hole doping and transport in AlGaN-based UV LEDs and demonstrates the excellent performance of tunnel-injected LEDs for the UV-A wavelength range.« less

Design of p-type cladding layers for tunnel-injected UV-A light emitting diodes

DOE PAGES

Zhang, Yuewei; Krishnamoorthy, Sriram; Akyol, Fatih; ...

2016-11-09

Here, we discuss the engineering of p-AlGaN cladding layers for achieving efficient tunnel-injected III-Nitride ultraviolet light emitting diodes (UV LEDs) in the UV-A spectral range. We show that the capacitance-voltage measurements can be used to estimate the compensation and doping in the p-AlGaN layers located between the multi-quantum well region and the tunnel junction layer. By increasing the p-type doping concentration to overcome the background compensation, on-wafer external quantum efficiency and wall-plug efficiency of 3.37% and 1.62%, respectively, were achieved for the tunnel-injected UV LEDs emitting at 325 nm. We also show that interband tunneling hole injection can be usedmore » to realize UV LEDs without any acceptor doping. The work discussed here provides new understanding of hole doping and transport in AlGaN-based UV LEDs and demonstrates the excellent performance of tunnel-injected LEDs for the UV-A wavelength range.« less

Anisotropic carrier mobility in single- and bi-layer C3N sheets

NASA Astrophysics Data System (ADS)

Wang, Xueyan; Li, Qingfang; Wang, Haifeng; Gao, Yan; Hou, Juan; Shao, Jianxin

2018-05-01

Based on the density functional theory combined with the Boltzmann transport equation with relaxation time approximation, we investigate the electronic structure and predict the carrier mobility of single- and bi-layer newly fabricated 2D carbon nitrides C3N. Although C3N sheets possess graphene-like planar hexagonal structure, the calculated carrier mobility is remarkably anisotropic, which is found mainly induced by the anisotropic effective masses and deformation potential constants. Importantly, we find that both the electron and hole mobilities are considerable high, for example, the hole mobility along the armchair direction of single-layer C3N sheets can arrive as high as 1.08 ×104 cm2 V-1 s-1, greatly larger than that of C2N-h2D and many other typical 2D materials. Owing to the high and anisotropic carrier mobility and appropriate band gap, single- and bi-layer semiconducting C3N sheets may have great potential applications in high performance electronic and optoelectronic devices.

Improving the efficiency and environmental stability of inverted planar perovskite solar cells via silver-doped nickel oxide hole-transporting layer

NASA Astrophysics Data System (ADS)

Wei, Ying; Yao, Kai; Wang, Xiaofeng; Jiang, Yihua; Liu, Xueyuan; Zhou, Naigen; Li, Fan

2018-01-01

In this paper, we demonstrate the high-performance inverted planar heterojunction perovskite solar cells (PeSCs) based on the novel inorganic hole-transporting layer (HTL) of silver (Ag)-doped NiOx (Ag:NiOx). Density-functional theory (DFT) calculation reveals that Ag prefers to occupy the substitutional Ni site (AgNi) and behaves as an acceptor in NiO lattice. Compared with the pristine NiOx films, appropriate Ag doping can increase the optical transparency, work function, electrical conductivity and hole mobility of NiOx films. Moreover, the CH3NH3PbI3 perovskite films grown on Ag:NiOx exhibit better crystallinity, higher coverage and smoother surface with densely packed larger grains than those grown on the pristine NiOx film. Consequently, the Ag:NiOx HTL boosts the efficiency of the inverted planar heterojunction PeSCs from 13.46% (for the pristine NiOx-based device) to 16.86% (for the 2 at.% Ag:NiOx-based device). Furthermore, the environmental stability of PeSCs based on Ag:NiOx HTL is dramatically improved compared to devices based on organic HTLs and pristine NiOx HTLs. This work provides a simple and effective HTL material system for high-efficient and stable PeSCs.

Transport properties of ultrathin black phosphorus on hexagonal boron nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doganov, Rostislav A.; Özyilmaz, Barbaros; Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore

2015-02-23

Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO{sub 2} substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explainmore » the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400 K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO{sub 2} substrates and reduces the hysteresis at room temperature.« less

Electron Doping of Ultrathin Black Phosphorus with Cu Adatoms.

PubMed

Koenig, Steven P; Doganov, Rostislav A; Seixas, Leandro; Carvalho, Alexandra; Tan, Jun You; Watanabe, Kenji; Taniguchi, Takashi; Yakovlev, Nikolai; Castro Neto, Antonio H; Özyilmaz, Barbaros

2016-04-13

Few-layer black phosphorus is a monatomic two-dimensional crystal with a direct band gap that has high carrier mobility for both holes and electrons. Similarly to other layered atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is sensitive to surface impurities, adsorbates, and adatoms. Here we study the effect of Cu adatoms onto few-layer black phosphorus by characterizing few-layer black phosphorus field effect devices and by performing first-principles calculations. We find that the addition of Cu adatoms can be used to controllably n-dope few layer black phosphorus, thereby lowering the threshold voltage for n-type conduction without degrading the transport properties. We demonstrate a scalable 2D material-based complementary inverter which utilizes a boron nitride gate dielectric, a graphite gate, and a single bP crystal for both the p- and n-channels. The inverter operates at matched input and output voltages, exhibits a gain of 46, and does not require different contact metals or local electrostatic gating.

Reversing an S-kink effect caused by interface degradation in organic solar cells through gold ion implantation in the PEDOT:PSS layer

NASA Astrophysics Data System (ADS)

Brenes-Badilla, D.; Coutinho, D. J.; Amorim, D. R. B.; Faria, R. M.; Salvadori, M. C.

2018-04-01

In this work, we performed a study on the recovery of the photovoltaic performance of an ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al solar cell after the hole transport layer (PEDOT:PSS) had been degraded by contact with the environment. A device that was fully built in an inert environment exhibited a fill factor (FF) of 0.64, while the device whose hole transport layer was exposed to air presented a FF equal to 0.2. In addition, the J-V characteristic curve of the degraded device did not follow the photovoltaic pattern exhibiting the degenerate S shape. However, the elimination of the deleterious effect was achieved by bombarding gold ions on the contaminated surface of PEDOT:PSS by means of the Metal Plasma Immersion Ion Implantation technique. Due to the low energy of the ionic beam of gold, the implanted gold atoms were located at few nanometers off the surface, forming nanometric clusters, that is, gold nanoparticles. Most probably, the degradation of the J-V photovoltaic curve, represented by the S-kink effect, was caused by the appearance of a potential barrier at PEDOT:PSS/P3HT:PCBM interface, which was demolished by the gold nanoparticles that have work function close to HOMO of P3HT. This S-kink effect was also simulated by using an equivalent circuit model constituted by a two-diode circuit, one of which plays the role of the undesirable potential barrier formed at the PEDOT:PSS/P3HT:PCBM interface. Our analysis shows that deposition of gold nanoparticles next to the interface recovers the good hole injection condition from the PEDOT:PSS into the active layer, restoring the fill factor and the device efficiency.

High-performance ultraviolet detection and visible-blind photodetector based on Cu{sub 2}O/ZnO nanorods with poly-(N-vinylcarbazole) intermediate layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perng, Dung-Ching, E-mail: dcperng@ee.ncku.edu.tw; Center for Micro/Nano Science and Technology, National Cheng Kung University, One University Road, Tainan 701, Taiwan; Lin, Hsueh-Pin

This study reports a high-performance hybrid ultraviolet (UV) photodetector with visible-blind sensitivity fabricated by inserting a poly-(N-vinylcarbazole) (PVK) intermediate layer between low-cost processed Cu{sub 2}O film and ZnO nanorods (NRs). The PVK layer acts as an electron-blocking/hole-transporting layer between the n-ZnO and p-Cu{sub 2}O films. The Cu{sub 2}O/PVK/ZnO NR photodetector exhibited a responsivity of 13.28 A/W at 360 nm, a high detectivity of 1.03 × 10{sup 13} Jones at a low bias of −0.1 V under a low UV light intensity of 24.9 μW/cm{sup 2}. The photo-to-dark current ratios of the photodetector with and without the PVK intermediate layer at a bias of −0.5 V are 1.34 × 10{supmore » 2} and 3.99, respectively. The UV-to-visible rejection ratios (R{sub 360 nm}/R{sub 450 nm}) are 350 and 1.735, respectively. Several features are demonstrated: (a) UV photo-generated holes at the ZnO NRs can effectively be transported through the PVK layer to the p-Cu{sub 2}O layer; (b) the insertion of a PVK buffer layer significantly minimizes the reverse-bias leakage current, which leads to a larger amplification of the photocurrent; and (c) the PVK buffer layer greatly improves the UV-to-visible responsivity ratio, allowing the device to achieve high UV detection sensitivity at a low bias voltage using a very low light intensity.« less

Stacking dependence of carrier transport properties in multilayered black phosphorous

NASA Astrophysics Data System (ADS)

Sengupta, A.; Audiffred, M.; Heine, T.; Niehaus, T. A.

2016-02-01

We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green’s function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous.

Architecture of the Interface between the Perovskite and Hole-Transport Layers in Perovskite Solar Cells.

PubMed

Moriya, Masahiro; Hirotani, Daisuke; Ohta, Tsuyoshi; Ogomi, Yuhei; Shen, Qing; Ripolles, Teresa S; Yoshino, Kenji; Toyoda, Taro; Minemoto, Takashi; Hayase, Shuzi

2016-09-22

The interface between the perovskite (PVK, CH 3 NH 3 PbI 3 ) and hole-transport layers in perovskite solar cells is discussed. The device architecture studied is as follows: F-doped tin oxide (FTO)-coated glass/compact TiO 2 /mesoporous TiO 2 /PVK/2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-MeOTAD)/Au. After a thin layer of 4,4,4-trifluorobutylammonium iodide (TFBA) was inserted at the interface between PVK and Spiro-MeOTAD, the photovoltaic efficiency increased from 11.6-14.5 % to 15.1-17.6 %. TFBA (10 ppm) was added in the PVK solution before coating. Owing to the low surface tension of TFBA, TFBA rose to the surface of the PVK layer spontaneously during spin-coating to make a thin organic layer. The PVK grain boundaries also seemed to be passivated with the addition of TFBA. However, large differences in Urbach energies and valence band energy level were not observed for the PVK layer with and without the addition of TFBA. The charge recombination time constant between the PVK and the Spiro-MeOTAD became slower (from 8.4 to 280 μsec) after 10 ppm of TFBA was added in the PVK. The experimental results using TFBA conclude that insertion of a very thin layer at the interface between PVK and Spiro-MeOTAD is effective for suppressing charge recombination and increasing photovoltaic performances. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Well-Defined Nanostructured, Single-Crystalline TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells.

PubMed

Choi, Jongmin; Song, Seulki; Hörantner, Maximilian T; Snaith, Henry J; Park, Taiho

2016-06-28

An electron transporting layer (ETL) plays an important role in extracting electrons from a perovskite layer and blocking recombination between electrons in the fluorine-doped tin oxide (FTO) and holes in the perovskite layers, especially in planar perovskite solar cells. Dense TiO2 ETLs prepared by a solution-processed spin-coating method (S-TiO2) are mainly used in devices due to their ease of fabrication. Herein, we found that fatal morphological defects at the S-TiO2 interface due to a rough FTO surface, including an irregular film thickness, discontinuous areas, and poor physical contact between the S-TiO2 and the FTO layers, were inevitable and lowered the charge transport properties through the planar perovskite solar cells. The effects of the morphological defects were mitigated in this work using a TiO2 ETL produced from sputtering and anodization. This method produced a well-defined nanostructured TiO2 ETL with an excellent transmittance, single-crystalline properties, a uniform film thickness, a large effective area, and defect-free physical contact with a rough substrate that provided outstanding electron extraction and hole blocking in a planar perovskite solar cell. In planar perovskite devices, anodized TiO2 ETL (A-TiO2) increased the power conversion efficiency by 22% (from 12.5 to 15.2%), and the stabilized maximum power output efficiency increased by 44% (from 8.9 to 12.8%) compared with S-TiO2. This work highlights the importance of the ETL geometry for maximizing device performance and provides insights into achieving ideal ETL morphologies that remedy the drawbacks observed in conventional spin-coated ETLs.

Tunable Electron and Hole Injection Enabled by Atomically Thin Tunneling Layer for Improved Contact Resistance and Dual Channel Transport in MoS2/WSe2 van der Waals Heterostructure.

PubMed

Khan, Muhammad Atif; Rathi, Servin; Lee, Changhee; Lim, Dongsuk; Kim, Yunseob; Yun, Sun Jin; Youn, Doo Hyeb; Kim, Gil-Ho

2018-06-25

Two-dimensional (2D) materials based heterostructures provide a unique platform where interaction between stacked 2D layers can enhance the electrical and opto-electrical properties as well as give rise to interesting new phenomena. Here, operation of a van der Waals heterostructure device comprising of vertically stacked bi-layer MoS 2 and few layered WSe 2 has been demonstrated in which atomically thin MoS 2 layer has been employed as a tunneling layer to the underlying WSe 2 layer. In this way, simultaneous contacts to both MoS 2 and WSe 2 2D layers have been established by forming direct MS (metal semiconductor) to MoS 2 and tunneling based MIS (metal insulator semiconductor) contacts to WSe 2 , respectively. The use of MoS 2 as a dielectric tunneling layer results in improved contact resistance (80 kΩ-µm) for WSe 2 contact, which is attributed to reduction in effective Schottky barrier height and is also confirmed from the temperature dependent measurement. Further, this unique contact engineering and type II band alignment between MoS 2 and WSe 2 enables a selective and independent carrier transport across the respective layers. This contact engineered dual channel heterostructure exhibits an excellent gate control and both channel current and carrier types can be modulated by the vertical electric field of the gate electrode, which is also reflected in on/off ratio of 10 4 for both electrons (MoS 2 ) and holes (WSe 2 ) channels. Moreover, the charge transfer at the heterointerface is studied quantitatively from the shift in the threshold voltage of the pristine MoS 2 and heterostructure device, which agrees with the carrier recombination induced optical quenching as observed in the Raman spectra of the pristine and heterostructure layers. This observation of dual channel ambipolar transport enabled by the hybrid tunneling contacts and strong interlayer coupling can be utilized for high performance opto-electrical devices and applications.

Improved performances of organic light-emitting diodes with mixed layer and metal oxide as anode buffer

NASA Astrophysics Data System (ADS)

Xue, Qin; Liu, Shouyin; Zhang, Shiming; Chen, Ping; Zhao, Yi; Liu, Shiyong

2013-01-01

We fabricated organic light-emitting devices (OLEDs) employing 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN) as hole-transport material (HTM) instead of commonly used N,N'-bis-(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB). After inserting a 0.9 nm thick molybdenum oxide (MoOx) layer at the indium tin oxide (ITO)/MADN interface and a 5 nm thick mixed layer at the organic/organic heterojunction interface, the power conversion efficiency of the device can be increased by 4-fold.

Ultrathin Lutetium Oxide Film as an Epitaxial Hole-Blocking Layer for Crystalline Bismuth Vanadate Water Splitting Photoanodes

DOE PAGES

Zhang, Wenrui; Yan, Danhua; Tong, Xiao; ...

2018-01-08

Here a novel ultrathin lutetium oxide (Lu 2O 3) interlayer is integrated with crystalline bismuth vanadate (BiVO4) thin film photoanodes to facilitate carrier transport through atomic-scale interface control. The epitaxial Lu 2O 32O 3

Energy resolution in semiconductor gamma radiation detectors using heterojunctions and methods of use and preparation thereof

DOEpatents

Nikolic, Rebecca J.; Conway, Adam M.; Nelson, Art J.; Payne, Stephen A.

2012-09-04

In one embodiment, a system comprises a semiconductor gamma detector material and a hole blocking layer adjacent the gamma detector material, the hole blocking layer resisting passage of holes therethrough. In another embodiment, a system comprises a semiconductor gamma detector material, and an electron blocking layer adjacent the gamma detector material, the electron blocking layer resisting passage of electrons therethrough, wherein the electron blocking layer comprises undoped HgCdTe. In another embodiment, a method comprises forming a hole blocking layer adjacent a semiconductor gamma detector material, the hole blocking layer resisting passage of holes therethrough. Additional systems and methods are also presented.

Design, synthesis, thin film deposition and characterization of new indium tin oxide anode functionalization/hole transport organic materials and their application to high performance organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Huang, Qinglan

The primary goals of this dissertation were to understand the physical and chemical aspects of organic light-emitting diode (OLED) fundamentals, develop new materials as well as device structures, and enhance OLED electroluminescent (EL) response. Accordingly, this dissertation analyzes the relative effects of indium tin oxide (ITO) anode-hole transporting layer (HTL) contact vs. the intrinsic HTL material properties on OLED EL response. Two siloxane-based HTL materials, 4,4'-bis[(4″ -trichlorosilylpropyl-1″-naphthylphenylamino)biphenyl (NPB-Si2) and 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2) have thereby been designed, synthesized and covalently bound to ITO surface. They afford a 250% increase in luminance and ˜50% reduction in turn-on voltage vs. comparable 4,4'-bis(1-naphthylphenylamino)biphenyl (NPB) HTL-based devices. These results suggest new strategies for developing OLED HTL structures, with focus on the anode-HTL contact. Furthermore, archetypical OLED device structures have been refined by simultaneously incorporating the TPD-Si2 layer and a hole- and exciton-blocking/electron transport layer (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) in tris(8-hydroxyquinolato)aluminum(III) and tetrakis(2-methyl-8-hydroxyquinolinato)borate-based OLEDs. The refined device structures lead to high performance OLEDs such as green-emitting OLEDs with maximum luminance (Lmax) ˜ 85,000 cd/m2, power and forward external quantum efficiencies (eta p and etaext) as high as 15.2 lm/W and 4.4 +/- 0.5%, respectively, and blue-emitting OLEDs with Lmax 30,000 cd/m 2, and ˜5.0 lm/W and 1.6 +/- 0.2% etap and eta ext, respectively. The high performance is attributed to synergistically enhanced hole/electron injection and recombination efficiency. In addition, molecule-scale structure effects at ITO anode-HTL interfaces have been systematically probed via a self-assembly approach. A series of silyltriarylamine precursors differing in aryl group and linker density have been designed and synthesized for this purpose. These precursors form conformal and largely pin-hole free self-assembled monolayers (SAMs) on the anode surface with A-level thickness control. Followed by deposition of a HTL on top of the SAMs, the probe molecules are placed precisely at the anode-HTL interface, resulting in varied hole injection magnitude and OLED response. The large interfacial molecular structure effects afford an approach to tuning OLED hole injection flux over one to two orders of magnitude, resulting in up to 3 fold variation in OLED brightness at identical bias and up to a 2 V driving voltage modulation at identical brightness.

Interface Engineering Based on Liquid Metal for Compact-Layer-free, Fully Printable Mesoscopic Perovskite Solar Cells.

PubMed

Zhang, Yumin; Zhao, Jianhong; Zhang, Jin; Jiang, Xixi; Zhu, Zhongqi; Liu, Qingju

2018-05-09

A printing process for the fabrication of perovskite solar cells (PSCs) exhibits promising future application in the photovoltaic industry due to its low-cost and eco-friendly preparation. In mesoscopic carbon-based PSCs, however, compared to conventional ones, the hole-transport-layer-free PSCs often lead to inefficient hole extraction. Here, we used liquid metal (LM, Galinstan) as an interface modifier material in combination with a carbon electrode. Considering the high conductivity and room-temperature fluidity, it is found that LMs are superior in improving hole extraction and, more importantly, LMs tend to be reserved at the interface between ZrO 2 and carbon for enhancing the contact property. Correspondingly, the carrier transfer resistance was decreased at the carbon/perovskite interface. As optimized content, the triple mesoscopic PSCs based on mixed-cation perovskite with a power conversion efficiency of 13.51% was achieved, involving a 26% increase compared to those without LMs. This work opens new techniques for LMs in optoelectronics and printing.

Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in BaMnBi 2

DOE PAGES

Li, Lijun; Wang, Kefeng; Graf, D.; ...

2016-03-28

Here, we report two-dimensional quantum transport and Dirac fermions in BaMnBi 2 single crystals. BaMnBi 2 is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotron mass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.

Few-layer 1T‧ MoTe2 as gapless semimetal with thickness dependent carrier transport

NASA Astrophysics Data System (ADS)

Song, Peng; Hsu, Chuanghan; Zhao, Meng; Zhao, Xiaoxu; Chang, Tay-Rong; Teng, Jinghua; Lin, Hsin; Loh, Kian Ping

2018-07-01

Semimetal MoTe2 can be a type II Weyl semimetal in the bulk, but monolayer of this material is predicted to be quantum spin hall insulators. This dramatic change in electronic properties with number of layers is an excellent example of the dimensional effects of quantum transport. However, a detailed experimental study of the carrier transport and band structure of ultrathin semimetal MoTe2 is lacking so far. We performed magneto-transport measurements to study the conduction behavior and quantum phase coherence of 1T‧ MoTe2 as a function of its thickness. We show that due to a unique two-band transport mechanism (synergetic contribution from electron conduction and hole conduction), the conduction behavior of 1T‧ MoTe2 changes from metallic to p-type unipolar, and finally to ambipolar as the thickness decreases, suggesting that this effect can be used in devices by effectively controlling the thickness. Our transport studies, optical measurements and first-principles electronic structure calculations reveal that 1T‧ MoTe2 remains gapless down to a few (~2–3) layers. Despite being gapless, 1T‧ MoTe2 exhibits metal-insulator transition at 3-layer thickness, due to enhanced carrier localization effect.

A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect

NASA Astrophysics Data System (ADS)

Sha, Wei E. I.; Zhu, Hugh L.; Chen, Luzhou; Chew, Weng Cho; Choy, Wallace C. H.

2015-02-01

It is well known that transport paths of photocarriers (electrons and holes) before collected by electrodes strongly affect bulk recombination and thus electrical properties of solar cells, including open-circuit voltage and fill factor. For boosting device performance, a general design rule, tailored to arbitrary electron to hole mobility ratio, is proposed to decide the transport paths of photocarriers. Due to a unique ability to localize and concentrate light, plasmonics is explored to manipulate photocarrier transport through spatially redistributing light absorption at the active layer of devices. Without changing the active materials, we conceive a plasmonic-electrical concept, which tunes electrical properties of solar cells via the plasmon-modified optical field distribution, to realize the design rule. Incorporating spectrally and spatially configurable metallic nanostructures, thin-film solar cells are theoretically modelled and experimentally fabricated to validate the design rule and verify the plasmonic-tunable electrical properties. The general design rule, together with the plasmonic-electrical effect, contributes to the evolution of emerging photovoltaics.

A hole modulator for InGaN/GaN light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

2015-02-01

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ˜332 meV to ˜294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.

Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seif, Johannes Peter; Menda, Deneb; Descoeudres, Antoine

Here, amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers -- inserted between substrate and (front or rear) contacts -- since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. Asmore » a consequence, device implementation of such films as window layers -- without degraded carrier collection -- demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.« less

Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

DOE PAGES

Seif, Johannes Peter; Menda, Deneb; Descoeudres, Antoine; ...

2016-08-01

Here, amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers -- inserted between substrate and (front or rear) contacts -- since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. Asmore » a consequence, device implementation of such films as window layers -- without degraded carrier collection -- demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.« less

Study of interface chemistry between the carrier-transporting layers and their influences on the stability and performance of organic solar cells

NASA Astrophysics Data System (ADS)

Hilal, Muhammad; Han, Jeong In

2018-06-01

This is the first study that described how the interface interactions of graphene oxide (GO) with poly(3-hexylthiophene): 3'H-cyclopropa [8,25] [5,6] fullerene-C60-D5h(6)-3'-butanoic acid 3'-phenyl methyl ester (PCBM) and with poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) are influencing the stability and performance of poly(3-hexylthiophene): poly(3-hexylthiophene) (P3HT) (P3HT:PCBM)-based organic solar cell. The interface functionalization of these carrier-transporting layers was confirmed by XRD pattern, XPS analysis, and Raman spectroscopy. These interfaces chemical bond formation helped to firmly attach the GO layer with PCBM and PEDOT:PSS layers, forming a strong barrier against water molecule absorption and also provided an easy pathway for fast transfer of free carriers between P3HT:PCBM layer and metal electrodes via the backbone of the conjugated GO sheets. Because of these interface interactions, the device fabricated with PCBM/GO composite as an electron transport layer and GO/PEDOT:PSS composite as hole transport layer demonstrated a remarkable improvement in the value of power conversion efficiency (5.34%) and reproducibility with a high degree of control over the environmental stability (600 h). This study is paving a way for a new technique to further improve the stability and PCE for the commercialization of OSCs.

Dopant-Free Tetrakis-Triphenylamine Hole Transporting Material for Efficient Tin-Based Perovskite Solar Cells.

PubMed

Ke, Weijun; Priyanka, Pragya; Vegiraju, Sureshraju; Stoumpos, Constantinos C; Spanopoulos, Ioannis; Soe, Chan Myae Myae; Marks, Tobin J; Chen, Ming-Chou; Kanatzidis, Mercouri G

2018-01-10

Developing dopant-free hole transporting layers (HTLs) is critical in achieving high-performance and robust state-of-the-art perovskite photovoltaics, especially for the air-sensitive tin-based perovskite systems. The commonly used HTLs require hygroscopic dopants and additives for optimal performance, which adds extra cost to manufacturing and limits long-term device stability. Here we demonstrate the use of a novel tetrakis-triphenylamine (TPE) small molecule prepared by a facile synthetic route as a superior dopant-free HTL for lead-free tin-based perovskite solar cells. The best-performing tin iodide perovskite cells employing the novel mixed-cation ethylenediammonium/formamidinium with the dopant-free TPE HTL achieve a power conversion efficiency as high as 7.23%, ascribed to the HTL's suitable band alignment and excellent hole extraction/collection properties. This efficiency is one of the highest reported so far for tin halide perovskite systems, highlighting potential application of TPE HTL material in low-cost high-performance tin-based perovskite solar cells.

Fast Fabrication of a Stable Perovskite Solar Cell with an Ultrathin Effective Novel Inorganic Hole Transport Layer.

PubMed

Huang, Aibin; Lei, Lei; Zhu, Jingting; Yu, Yu; Liu, Yan; Yang, Songwang; Bao, Shanhu; Cao, Xun; Jin, Ping

2017-04-18

With the aim of fabricating simple, reproducible, and scalable perovskite solar cells (PSCs) with least time consumption, a novel CoO x hole transport layer (HTL) was first proposed and introduced in this work. The CoO x HTL thickness was minimized to about 10 nm with complete coverage on the FTO substrate (F-doped SnO 2 ) by direct current magnetron sputtering. The ultrathin HTL could minimize the incident light loss caused by cobalt ion absorption and reduce the carrier transport loss by shortening the transport path. Copper was incorporated into the CoO x lattice to address the low conductivity of the CoO x film and the energy-level mismatch between CoO x and the perovskite material. On the basis of cobalt-copper binary oxide (Co 1-y Cu y O x ), the highest power conversion efficiency (PCE) of about 10% was achieved, which was acceptable for mass production. Moreover, the deposition of such Co 1-y Cu y O x films takes only 2 min without size limitation of substrates. A well-functioned device based on the Co 1-y Cu y O x HTL could hence be fabricated within 100 min. Excellent stability was demonstrated as well, with over 90% of the initial PCE remaining after being stored in a dark and humid environment (relative humidity 60%) for 12 days.

Perovskite solar cells in N-I-P structure with four slot-die-coated layers

PubMed Central

Burkitt, Daniel; Searle, Justin

2018-01-01

The fabrication of perovskite solar cells in an N-I-P structure with compact titanium dioxide blocking, mesoporous titanium dioxide scaffold, single-step perovskite and hole-transport layers deposited using the slot-die coating technique is reported. Devices on fluorine-doped tin oxide-coated glass substrates with evaporated gold top contacts and four slot-die-coated layers are demonstrated, and best cells reach stabilized power conversion efficiencies of 7%. This work demonstrates the suitability of slot-die coating for the production of layers within this perovskite solar cell stack and the potential to transfer to large area and roll-to-roll manufacturing processes. PMID:29892402

Comparative Aging Study of Organic Solar Cells Utilizing Polyaniline and PEDOT:PSS as Hole Transport Layers.

PubMed

Abdulrazzaq, Omar; Bourdo, Shawn E; Woo, Myungwu; Saini, Viney; Berry, Brian C; Ghosh, Anindya; Biris, Alexandru S

2015-12-23

The aging effect on P3HT:PCBM organic solar cells was investigated with camphorsulfonic doped polyaniline (PANI:CSA) or poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PSS) used as the hole transport layer (HTL). The cells were encapsulated and exposed to a continuous normal atmosphere on a dark shelf and then characterized intermittently for more than two years. The photovoltaic results revealed that the cells with PSS HTL showed better initial results than the cells with PANI:CSA HTL. Over time, PSS-based cells exhibited faster degradation than PANI:CSA-based cells, where the average efficiency of six cells dropped to zero in less than one and a half years. On the other hand, PANI:CSA-based cells exhibited a much more stable performance with an average efficiency drop of only 15% of their initial values after one and a half years and 63% after two years. A single-diode model was utilized to fit the experimental data with the theoretical curve to extract the diode parameters, such as the ideality factor, to explain the effect of aging on the diode's performance.

Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS₂ thin film.

PubMed

Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

2015-09-14

Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.

Ultrathin efficient perovskite solar cells employing a periodic structure of a composite hole conductor for elevated plasmonic light harvesting and hole collection

NASA Astrophysics Data System (ADS)

Long, Mingzhu; Chen, Zefeng; Zhang, Tiankai; Xiao, Yubin; Zeng, Xiaoliang; Chen, Jian; Yan, Keyou; Xu, Jianbin

2016-03-01

We developed a molecule/polymer composite hole transporting material (HTM) with a periodic microstructure for morphology replication of a corrugated Au electrode, which in combination plays a dual role in the optical and electronic enhancement of high performance perovskite solar cells (PSCs). The electro-optics revealed that perovskite couldn't readily extinct the red light even though the thickness increased to 370 nm, but we found that the quasi periodic microstructure composite (PMC) HTM in combination with the conformal Au electrode could promote the absorption through the enhanced cavity effects, leading to comparable absorption even using much thinner perovskite (240 nm). We identified that the cavity was the combination of Fabry-Pérot interferometer and surface plasmonic resonance, with light harvesting enhancement through surface plasmon polariton or waveguide modes that propagate in the plane of the perovskite layer. On the other hand, the PMC HTM increased hole conductivity by one order of magnitude with respect to standard spiro-OMeTAD HTM due to molecular packing and self-assembly, embodying traceable hole mobility and density elevation up to 3 times, and thus the hysteresis was greatly avoided. Owing to dual optical and electronic enhancement, the PMC PSC afforded high efficiency PSC using as thin as 240 nm perovskite layer, delivering a Voc of 1.05 V, Jsc of 22.9 mA cm-2, FF of 0.736, and efficiency amounting to 17.7% PCE, the highest efficiency with ultrathin perovskite layer.We developed a molecule/polymer composite hole transporting material (HTM) with a periodic microstructure for morphology replication of a corrugated Au electrode, which in combination plays a dual role in the optical and electronic enhancement of high performance perovskite solar cells (PSCs). The electro-optics revealed that perovskite couldn't readily extinct the red light even though the thickness increased to 370 nm, but we found that the quasi periodic microstructure composite (PMC) HTM in combination with the conformal Au electrode could promote the absorption through the enhanced cavity effects, leading to comparable absorption even using much thinner perovskite (240 nm). We identified that the cavity was the combination of Fabry-Pérot interferometer and surface plasmonic resonance, with light harvesting enhancement through surface plasmon polariton or waveguide modes that propagate in the plane of the perovskite layer. On the other hand, the PMC HTM increased hole conductivity by one order of magnitude with respect to standard spiro-OMeTAD HTM due to molecular packing and self-assembly, embodying traceable hole mobility and density elevation up to 3 times, and thus the hysteresis was greatly avoided. Owing to dual optical and electronic enhancement, the PMC PSC afforded high efficiency PSC using as thin as 240 nm perovskite layer, delivering a Voc of 1.05 V, Jsc of 22.9 mA cm-2, FF of 0.736, and efficiency amounting to 17.7% PCE, the highest efficiency with ultrathin perovskite layer. Electronic supplementary information (ESI) available: XRD patterns corresponding to the perovskite; AFM images of 3D PMC HTM perovskite solar cells; performance statistics for 3D PMC HTM; ultraviolet photoelectron spectra (UPS) of HTMs on FTO. See DOI: 10.1039/c5nr05042a

Investigation of the Charge Balance in Green Phosphorescent Organic Light-Emitting Diodes by Controlling the Mixed Host Emission Layer.

PubMed

Lee, Jeonghyun; Choi, Pyungho; Kim, Minsoo; Lim, Kiwon; Hyeon, Younghwan; Kim, Soonkon; Koo, Kwangjun; Kim, Sangsoo; Choi, Byoungdeog

2018-09-01

In this paper, we investigated the use of a mixed host emission layer (MH-EML) in green phosphorescent organic light-emitting diodes (OLEDs). The hole transport type (p-type) material (4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP)) and electron transport type (N-type) material (2,2',2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)) were mixed with different ratios. The electrons were easily injected through the lowest unoccupied molecular orbital (LUMO) of TPBi in the mixed host system. Also, holes were confined in the EML because of the deep highest occupied molecular orbital (HOMO) level of TPBi (6.7 eV). These results indicate that excitons were formed effectively and the recombination zone became wider under a high electric field in MH-EML devices. For these reasons, the lifetime of the MH-OLED device was 1.36 times higher than that of a single host emission layer (SH-EML) device and showed a reduction in Joule heating. Finally, the external quantum efficiency (EQE) roll-off ratio from 1 mA/cm2 to 100 mA/cm2 in the optimized device (30.46%) was 18.12%p lower than that of the SH-EML (48.58%).

Development of organic-inorganic double hole-transporting material for high performance perovskite solar cells

NASA Astrophysics Data System (ADS)

Jo, Jea Woong; Seo, Myung-Seok; Jung, Jae Woong; Park, Joon-Suh; Sohn, Byeong-Hyeok; Ko, Min Jae; Son, Hae Jung

2018-02-01

The control of the optoelectronic properties of the interlayers of perovskite solar cells (PSCs) is crucial for achieving high photovoltaic performances. Of the solution-processable interlayer candidates, NiOx is considered one of the best inorganic hole-transporting layer (HTL) materials. However, the power conversion efficiencies (PCEs) of NiOx-based PSCs are limited by the unfavorable contact between perovskite layers and NiOx HTLs, the high density of surface trap sites, and the inefficient charge extraction from perovskite photoactive layers to anodes. Here, we introduce a new organic-inorganic double HTL consisting of a Cu:NiOx thin film passivated by a conjugated polyelectrolyte (PhNa-1T) film. This double HTL has a significantly lower pinhole density and forms better contact with perovskite films, which results in enhanced charge extraction. As a result, the PCEs of PSCs fabricated with the double HTL are impressively improved up to 17.0%, which is more than 25% higher than that of the corresponding PSC with a Cu:NiOx HTL. Moreover, PSCs with the double HTLs exhibit similar stabilities under ambient conditions to devices using inorganic Cu:NiOx. Therefore, this organic-inorganic double HTL is a promising interlayer material for high performance PSCs with high air stability.

Quantum Transmission Conditions for Diffusive Transport in Graphene with Steep Potentials

NASA Astrophysics Data System (ADS)

Barletti, Luigi; Negulescu, Claudia

2018-05-01

We present a formal derivation of a drift-diffusion model for stationary electron transport in graphene, in presence of sharp potential profiles, such as barriers and steps. Assuming the electric potential to have steep variations within a strip of vanishing width on a macroscopic scale, such strip is viewed as a quantum interface that couples the classical regions at its left and right sides. In the two classical regions, where the potential is assumed to be smooth, electron and hole transport is described in terms of semiclassical kinetic equations. The diffusive limit of the kinetic model is derived by means of a Hilbert expansion and a boundary layer analysis, and consists of drift-diffusion equations in the classical regions, coupled by quantum diffusive transmission conditions through the interface. The boundary layer analysis leads to the discussion of a four-fold Milne (half-space, half-range) transport problem.

Influence of different TiO2 blocking films on the photovoltaic performance of perovskite solar cells

NASA Astrophysics Data System (ADS)

Zhang, Chenxi; Luo, Yudan; Chen, Xiaohong; Ou-Yang, Wei; Chen, Yiwei; Sun, Zhuo; Huang, Sumei

2016-12-01

Organolead trihalide perovskite materials have been successfully used as light absorbers in efficient photovoltaic (PV) cells. Cell structures based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive and brisk advances, holding great potential to grow into a mature PV technology. High power conversion efficiency (PCE) values have been obtained from the mesoscopic configuration in which a few hundred nano-meter thick mesoporous scaffold (e.g. TiO2 or Al2O3) infiltrated by perovskite absorber was sandwiched between the electron and hole transport layers. A uniform and compact hole-blocking layer is necessary for high efficient perovskite-based thin film solar cells. In this study, we investigated the characteristics of TiO2 compact layer using various methods and its effects on the PV performance of perovskite solar cells. TiO2 compact layer was prepared by a sol-gel method based on titanium isopropoxide and HCl, spin-coating of titanium diisopropoxide bis (acetylacetonate), screen-printing of Dyesol's bocking layer titania paste, and a chemical bath deposition (CBD) technique via hydrolysis of TiCl4, respectively. The morphological and micro-structural properties of the formed compact TiO2 layers were characterized by scanning electronic microscopy and X-ray diffraction. The analyses of devices performance characteristics showed that surface morphologies of TiO2 compact films played a critical role in affecting the efficiencies. The nanocrystalline TiO2 film deposited via the CBD route acts as the most efficient hole-blocking layer and achieves the best performance in perovskite solar cells. The CBD-based TiO2 compact and dense layer offers a small series resistance and a large recombination resistance inside the device, and makes it possible to achieve a high power conversion efficiency of 12.80%.

Multipositional silica-coated silver nanoparticles for high-performance polymer solar cells.

PubMed

Choi, Hyosung; Lee, Jung-Pil; Ko, Seo-Jin; Jung, Jae-Woo; Park, Hyungmin; Yoo, Seungmin; Park, Okji; Jeong, Jong-Ryul; Park, Soojin; Kim, Jin Young

2013-05-08

We demonstrate high-performance polymer solar cells using the plasmonic effect of multipositional silica-coated silver nanoparticles. The location of the nanoparticles is critical for increasing light absorption and scattering via enhanced electric field distribution. The device incorporating nanoparticles between the hole transport layer and the active layer achieves a power conversion efficiency of 8.92% with an external quantum efficiency of 81.5%. These device efficiencies are the highest values reported to date for plasmonic polymer solar cells using metal nanoparticles.

White organic light-emitting diodes with Zn-complexes.

PubMed

Kim, Dong-Eun; Shin, Hoon-Kyu; Kim, Nam-Kyu; Lee, Burm-Jong; Kwon, Young-Soo

2014-02-01

This paper reviews OLEDs fabricated using Zn-complexes. Zn(HPB)2, Zn(HPB)q, and Zn(phen)q were synthesized as new electroluminescence materials. The electron affinity (EA) and ionization potential (IP) of Zn complexes were also determined and devices were characterized. Zn complexes such as Zn(HPB)2, Zn(HPB)q, and Zn(phen)q were found to exhibit blue and yellow emissions with wavelengths of 455, 532, and 535 nm, respectively. On the other hand, Zn(HPB)2 and Zn(HPB)q were applied as hole-blocking materials. As a result, the OLED efficiency by using Zn(HPB)2 as a hole-blocking material was improved. In particular, the OLED property of Zn(HPB)2 was found to be better than that of Zn(HPB)q. Moreover, Zn(phen)q was used as an electron-transporting material and compared with Alq3. The performance of the device with Zn(phen)q as an electron-transporting material was improved compared with Alq3-based devices. The Zn complexes can possibly be used as hole-blocking and electron-transporting materials in OLED devices. A white emission was ultimately realized from the OLED devices using Zn-complexes as inter-layer components.

Graphene oxide/PEDOT:PSS composite hole transport layer for efficient and stable planar heterojunction perovskite solar cells.

PubMed

Lee, Da-Young; Na, Seok-In; Kim, Seok-Soon

2016-01-21

We investigated a graphene oxide (GO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ( PSS) composite as a promising candidate for the practical application of a 2-D carbonaceous hole transport layer (HTL) to planar heterojunction perovskite solar cells (PeSCs) consisting of a transparent electrode/HTL/perovskite/fullerene/metal electrode. Both the insulating properties of GO and the non-uniform coating of the transparent electrode with GO cause the poor morphology of perovskite induced low power conversion efficiency (PCE) of 6.4%. On the other hand, PeSCs with a GO/PEDOT:PSS composite HTL, exhibited a higher PCE of 9.7% than that of a device fabricated with conventional PSS showing a PCE of 8.2%. The higher performance is attributed to the decreased series resistance (RS) and increased shunt resistance (RSh). The well-matched work-function between GO (4.9 eV) and PSS (5.1 eV) probably results in more efficient charge transport and an overall decrease in RS. The existence of GO with a large bandgap of ∼3.6 eV might induce the effective blocking of electrons, leading to an increase of RSh. Moreover, improvement in the long-term stability under atmospheric conditions was observed.

Semitransparent Flexible Organic Solar Cells Employing Doped-Graphene Layers as Anode and Cathode Electrodes.

PubMed

Shin, Dong Hee; Jang, Chan Wook; Lee, Ha Seung; Seo, Sang Woo; Choi, Suk-Ho

2018-01-31

Semitransparent flexible photovoltaic cells are advantageous for effective use of solar energy in many areas such as building-integrated solar-power generation and portable photovoltaic chargers. We report semitransparent and flexible organic solar cells (FOSCs) with high aperture, composed of doped graphene layers, ZnO, P3HT:PCBM, and PEDOT:PSS as anode/cathode transparent conductive electrodes (TCEs), electron transport layer, photoactive layer, and hole transport layer, respectively, fabricated based on simple solution processing. The FOSCs do not only harvest solar energy from ultraviolet-visible region but are also less sensitive to near-infrared photons, indicating semitransparency. For the anode/cathode TCEs, graphene is doped with bis(trifluoromethanesulfonyl)-amide or triethylene tetramine, respectively. Power conversion efficiency (PCE) of 3.12% is obtained from the fundamental FOSC structure, and the PCE is further enhanced to 4.23% by adding an Al reflective mirror on the top or bottom side of the FOSCs. The FOSCs also exhibit remarkable mechanical flexibilities through bending tests for various curvature radii.

Defective TiO 2 with high photoconductive gain for efficient and stable planar heterojunction perovskite solar cells

DOE PAGES

Li, Yanbo; Cooper, Jason K.; Liu, Wenjun; ...

2016-08-18

Formation of planar heterojunction perovskite solar cells exhibiting both high efficiency and stability under continuous operation remains a challenge. Here, we show this can be achieved by using a defective TiO 2 thin film as the electron transport layer. TiO 2 layers with native defects are deposited by electron beam evaporation in an oxygen-deficient environment. Deep-level hole traps are introduced in the TiO 2 layers and contribute to a high photoconductive gain and reduced photocatalytic activity. The high photoconductivity of the TiO 2 electron transport layer leads to improved efficiency for the fabricated planar devices. A maximum power conversion efficiencymore » of 19.0% and an average PCE of 17.5% are achieved. In addition, the reduced photocatalytic activity of the TiO 2 layer leads to enhanced long-Term stability for the planar devices. Under continuous operation near the maximum power point, an efficiency of over 15.4% is demonstrated for 100 h.« less

Fulleropyrrolidinium Iodide As an Efficient Electron Transport Layer for Air-Stable Planar Perovskite Solar Cells.

PubMed

Huang, Jiabin; Yu, Xuegong; Xie, Jiangsheng; Li, Chang-Zhi; Zhang, Yunhai; Xu, Dikai; Tang, Zeguo; Cui, Can; Yang, Deren

2016-12-21

Organic-inorganic halide perovskite solar cells have attracted great attention in recent years. But there are still a lot of unresolved issues related to the perovskite solar cells such as the phenomenon of anomalous hysteresis characteristics and long-term stability of the devices. Here, we developed a simple three-layered efficient perovskite device by replacing the commonly employed PCBM electrical transport layer with an ultrathin fulleropyrrolidinium iodide (C 60 -bis) in an inverted p-i-n architecture. The devices with an ultrathin C 60 -bis electronic transport layer yield an average power conversion efficiency of 13.5% and a maximum efficiency of 15.15%. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements show that the high performance is attributed to the efficient blocking of holes and high extraction efficiency of electrons by C 60 -bis, due to a favorable energy level alignment between the CH 3 NH 3 PbI 3 and the Ag electrodes. The hysteresis effect and stability of our perovskite solar cells with C 60 -bis become better under indoor humidity conditions.

Enhancing Perovskite Solar Cell Performance by Interface Engineering Using CH3NH3PbBr0.9I2.1 Quantum Dots.

PubMed

Cha, Mingyang; Da, Peimei; Wang, Jun; Wang, Weiyi; Chen, Zhanghai; Xiu, Faxian; Zheng, Gengfeng; Wang, Zhong-Sheng

2016-07-13

To improve the interfacial charge transfer that is crucial to the performance of perovskite solar cells, the interface engineering in a device should be rationally designed. Here we have developed an interface engineering method to tune the photovoltaic performance of planar-heterojunction perovskite solar cells by incorporating MAPbBr3-xIx (MA = CH3NH3) quantum dots (QDs) between the MAPbI3 perovskite film and the hole-transporting material (HTM) layer. By adjustment of the Br:I ratio, the as-synthesized MAPbBr3-xIx QDs show tunable fluorescence and band edge positions. When the valence band (VB) edge of MAPbBr3-xIx QDs is located below that of the MAPbI3 perovskite, the hole transfer from the MAPbI3 perovskite film to the HTM layer is hindered, and hence, the power conversion efficiency decreases. In contrast, when the VB edge of MAPbBr3-xIx QDs is located between the VB edge of the MAPbI3 perovskite film and the highest occupied molecular orbital of the HTM layer, the hole transfer from the MAPbI3 perovskite film to the HTM layer is well-facilitated, resulting in significant improvements in the fill factor, short-circuit photocurrent, and power conversion efficiency.

Improved hole-injection and power efficiency of organic light-emitting diodes using an ultrathin cerium fluoride buffer layer

NASA Astrophysics Data System (ADS)

Lu, Hsin-Wei; Kao, Po-Ching; Chu, Sheng-Yuan

2016-09-01

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3 film as an ultra-thin buffer layer between the ITO and NPB hole transport layer, with the structure configuration ITO/CeF3 (1 nm)/NPB (40 nm)/Alq3 (60 nm)/LiF (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The work function increased from 4.8 eV (standard ITO electrode) to 5.2 eV (1-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The turn-on voltage decreased from 4.2 V to 4.0 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 10820 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.5 cd/A when the 1-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

On the hole accelerator for III-nitride light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zi-Hui, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn; Zhang, Yonghui; Bi, Wengang, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn

2016-04-11

In this work, we systematically conduct parametric studies revealing the sensitivity of the hole injection on the hole accelerator (a hole accelerator is made of the polarization mismatched p-electron blocking layer (EBL)/p-GaN/p-Al{sub x}Ga{sub 1−x}N heterojunction) with different designs, including the AlN composition in the p-Al{sub x}Ga{sub 1−x}N layer, and the thickness for the p-GaN layer and the p-Al{sub x}Ga{sub 1−x}N layer. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-Al{sub x}Ga{sub 1−x}N layer increases. Meanwhile, with p-GaN layer or p-Al{sub x}Ga{sub 1−x}N layer thickening, the energy that themore » holes gain increases and then reaches a saturation level. Thus, the hole injection efficiency and the device efficiency are very sensitive to the p-EBL/p-GaN/p-Al{sub x}Ga{sub 1−x}N design, and the hole accelerator can effectively increase the hole injection if properly designed.« less

A hole modulator for InGaN/GaN light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei

2015-02-09

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall holemore » concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm{sup 2} and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.« less

Correlation of Pliocene and Pleistocene tephra layers between the Turkana Basin of East Africa and the Gulf of Aden

USGS Publications Warehouse

Brown, F.H.; Sarna-Wojcicki, A. M.; Meyer, C.E.; Haileab, B.

1992-01-01

Electron-microprobe analyses of glass shards from volcanic ash in Pliocene and Pleistocene deep-sea sediments in the Gulf of Aden and the Somali Basin demonstrate that most of the tephra layers correlate with tephra layers known on land in the Turkana Basin of northern Kenya and southern Ethiopia. Previous correlations are reviewed, and new correlations proposed. Together these data provide correlations between the deep-sea cores, and to the land-based sections at eight levels ranging in age from about 4 to 0.7 Ma. Specifically, we correlate the Moiti Tuff (???4.1 Ma) with a tephra layer at 188.6 m depth in DSDP hole 231 and with a tephra layer at 150 m depth in DSDP hole 241, the Wargolo Tuff with a tephra layer at 179.7 m in DSDP Hole 231 and with a tephra layer at 155.3 m depth in DSDP Hole 232, the Lomogol Tuff (defined here) with a tephra layer at 165 m in DSDP Hole 232A, the Lokochot Tuff with a tephra layer at 140.1 m depth in DSDP Hole 232, the Tulu Bor Tuff with a tephra layer at 160.8 m depth in DSDP Hole 231, the Kokiselei Tuff with a tephra layer at 120 m depth in DSDP Hole 231 and with a tephra layer at 90.3 m depth in DSDP Hole 232, the Silbo Tuff (0.74 Ma) with a tephra layer at 35.5 m depth in DSDP Hole 231 and possibly with a tephra layer at 10.9 m depth in DSDP Hole 241. We also present analyses of other tephra from the deep sea cores for which correlative units on land are not yet known. The correlated tephra layers provide eight chronostratigraphic horizons that make it possible to temporally correlate paleoecological and paleoclimatic data between the terrestrial and deep-sea sites. Such correlations may make it possible to interpret faunal evolution in the Lake Turkana basin and other sites in East Africa within a broader regional or global paleoclimatic context. ?? 1992.

Solution-processed small molecules as mixed host for highly efficient blue and white phosphorescent organic light-emitting diodes.

PubMed

Fu, Qiang; Chen, Jiangshan; Shi, Changsheng; Ma, Dongge

2012-12-01

The widely used hole-transporting host 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA) blended with either a hole-transporting or an electron-transporting small-molecule material as a mixed-host was investigated in the phosphorescent organic light-emitting diodes (OLEDs) fabricated by the low-cost solution-process. The performance of the solution-processed OLEDs was found to be very sensitive to the composition of the mixed-host systems. The incorporation of the hole-transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) into TCTA as the mixed-host was demonstrated to greatly reduce the driving voltage and thus enhance the efficiency due to the improvement of hole injection and transport. On the basis of the mixed-host of TCTA:TAPC, we successfully fabricated low driving voltage and high efficiency blue and white phosphorescent OLEDs. A maximum forward viewing current efficiency of 32.0 cd/A and power efficiency of 25.9 lm/W were obtained in the optimized mixed-host blue OLED, which remained at 29.6 cd/A and 19.1 lm/W at the luminance of 1000 cd/m(2) with a driving voltage as low as 4.9 V. The maximum efficiencies of 37.1 cd/A and 32.1 lm/W were achieved in a single emissive layer white OLED based on the TCTA:TAPC mixed-host. Even at 1000 cd/m(2), the efficiencies still reach 34.2 cd/A and 23.3 lm/W and the driving voltage is only 4.6 V, which is comparable to those reported from the state-of-the-art vacuum-evaporation deposited white OLEDs.

Role of 4- tert -Butylpyridine as a Hole Transport Layer Morphological Controller in Perovskite Solar Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shen; Sina, Mahsa; Parikh, Pritesh

2016-09-14

Hybrid organic-inorganic materials for high efficiency, low cost photovoltaic devices have seen rapid progress since the introduction of lead based perovskites and solid-state hole transport layers. Although majority of the materials used for perovskite solar cells (PSC) are introduced from dye-sensitized solar cells (DSSCs), the presence of a perovskite capping layer as opposed to a single dye molecule (in DSSCs) changes the interactions between the various layers in perovskite solar cells. 4-tert-butylpyridine (tBP), commonly used in PSCs, is assumed to function as a charge recombination inhibitor, similar to DSSCs. However, the presence of a perovskite capping layer calls for amore » re-evaluation of its function in PSCs. Using TEM (transmission electron microscopy), we first confirm the role of tBP as a HTL morphology controller in PSCs. Our observations suggest that tBP significantly improves the uniformity of the HTL and avoids accumulation of Li salt. We also study degradation pathways by using FTIR (Fourier transform infrared spectroscopy) and APT (atom probe tomography) to investigate and visualize in 3-dimensions the moisture content associated with the Li salt. Long term effects, over 1000 hours, due to evaporation of tBP have also been studied. Based on our findings, a PSC failure mechanism associated with the morphological change of the HTL is proposed. tBP, the morphology controller in HTL, plays a key role in this process and thus this study highlights the need for additive materials with higher boiling points for consistent long term performance of PSCs.« less

Role of 4-tert-Butylpyridine as a Hole Transport Layer Morphological Controller in Perovskite Solar Cells.

PubMed

Wang, Shen; Sina, Mahsa; Parikh, Pritesh; Uekert, Taylor; Shahbazian, Brian; Devaraj, Arun; Meng, Ying Shirley

2016-09-14

Hybrid organic-inorganic materials for high-efficiency, low-cost photovoltaic devices have seen rapid progress since the introduction of lead based perovskites and solid-state hole transport layers. Although majority of the materials used for perovskite solar cells (PSC) are introduced from dye-sensitized solar cells (DSSCs), the presence of a perovskite capping layer as opposed to a single dye molecule (in DSSCs) changes the interactions between the various layers in perovskite solar cells. 4-tert-Butylpyridine (tBP), commonly used in PSCs, is assumed to function as a charge recombination inhibitor, similar to DSSCs. However, the presence of a perovskite capping layer calls for a re-evaluation of its function in PSCs. Using TEM (transmission electron microscopy), we first confirm the role of tBP as a HTL morphology controller in PSCs. Our observations suggest that tBP significantly improves the uniformity of the HTL and avoids accumulation of Li salt. We also study degradation pathways by using FTIR (Fourier transform infrared spectroscopy) and APT (atom probe tomography) to investigate and visualize in 3-dimensions the moisture content associated with the Li salt. Long-term effects, over 1000 h, due to evaporation of tBP have also been studied. Based on our findings, a PSC failure mechanism associated with the morphological change of the HTL is proposed. tBP, the morphology controller in HTL, plays a key role in this process, and thus this study highlights the need for additive materials with higher boiling points for consistent long-term performance of PSCs.

Photo-induced surface modification to improve the performance of lead sulfide quantum dot solar cell.

PubMed

Tulsani, Srikanth Reddy; Rath, Arup Kumar

2018-07-15

The solution-processed quantum dot (QD) solar cell technology has seen significant advancements in recent past to emerge as a potential contender for the next generation photovoltaic technology. In the development of high performance QD solar cell, the surface ligand chemistry has played the important role in controlling the doping type and doping density of QD solids. For instance, lead sulfide (PbS) QDs which is at the forefront of QD solar cell technology, can be made n-type or p-type respectively by using iodine or thiol as the surfactant. The advancements in surface ligand chemistry enable the formation of p-n homojunction of PbS QDs layers to attain high solar cell performances. It is shown here, however, that poor Fermi level alignment of thiol passivated p-type PbS QD hole transport layer with the n-type PbS QD light absorbing layer has rendered the photovoltaic devices from realizing their full potential. Here we develop a control surface oxidation technique using facile ultraviolet ozone treatment to increase the p-doping density in a controlled fashion for the thiol passivated PbS QD layer. This subtle surface modification tunes the Fermi energy level of the hole transport layer to deeper values to facilitate the carrier extraction and voltage generation in photovoltaic devices. In photovoltaic devices, the ultraviolet ozone treatment resulted in the average gain of 18% in the power conversion efficiency with the highest recorded efficiency of 8.98%. Copyright © 2018 Elsevier Inc. All rights reserved.

Graded Heterojunction Engineering for Hole-Conductor-Free Perovskite Solar Cells with High Hole Extraction Efficiency and Conductivity.

PubMed

Li, Bo; Zhang, Yanan; Zhang, Luyuan; Yin, Longwei

2017-10-01

Despite great progress in the photovoltaic conversion efficiency (PCE) of inorganic-organic hybrid perovskite solar cells (PSCs), the large-scale application of PSCs still faces serious challenges due to the poor-stability and high-cost of the spiro-OMeTAD hole transport layer (HTL). It is of great fundamental importance to rationally address the issues of hole extraction and transfer arising from HTL-free PSCs. Herein, a brand-new PSC architecture is designed by introducing multigraded-heterojunction (GHJ) inorganic perovskite CsPbBr x I 3- x layers as an efficient HTL. The grade adjustment can be achieved by precisely tuning the halide proportion and distribution in the CsPbBr x I 3- x film to reach an optimal energy alignment of the valance and conduction band between MAPbI 3 and CsPbBr x I 3- x . The CsPbBr x I 3- x GHJ as an efficient HTL can induce an electric field where a valance/conduction band edge is leveraged to bend at the heterojunction interface, boosting the interfacial electron-hole splitting and photoelectron extraction. The GHJ architecture enhances the hole extraction and conduction efficiency from the MAPbI 3 to the counter electrode, decreases the recombination loss during the hole transfer, and benefits in increasing the open-circuit voltage. The optimized HTL-free PCS based on the GHJ architecture demonstrates an outstanding thermal stability and a significantly improved PCE of 11.33%, nearly 40% increase compared with 8.16% for pure HTL-free devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Substrate misorientation induced strong increase in the hole concentration in Mg doped GaN grown by metalorganic vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suski, T.; Litwin-Staszewska, E.; Piotrzkowski, R.

We demonstrate that relatively small GaN substrate misorientation can strongly change hole carrier concentration in Mg doped GaN layers grown by metalorganic vapor phase epitaxy. In this work intentionally misoriented GaN substrates (up to 2 deg. with respect to ideal <0001> plane) were employed. An increase in the hole carrier concentration to the level above 10{sup 18} cm{sup -3} and a decrease in GaN:Mg resistivity below 1 {omega} cm were achieved. Using secondary ion mass spectroscopy we found that Mg incorporation does not change with varying misorientation angle. This finding suggests that the compensation rate, i.e., a decrease in unintentionalmore » donor density, is responsible for the observed increase in the hole concentration. Analysis of the temperature dependence of electrical transport confirms this interpretation.« less

Carrier mobility and scattering lifetime in electric double-layer gated few-layer graphene

NASA Astrophysics Data System (ADS)

Piatti, E.; Galasso, S.; Tortello, M.; Nair, J. R.; Gerbaldi, C.; Bruna, M.; Borini, S.; Daghero, D.; Gonnelli, R. S.

2017-02-01

We fabricate electric double-layer field-effect transistor (EDL-FET) devices on mechanically exfoliated few-layer graphene. We exploit the large capacitance of a polymeric electrolyte to study the transport properties of three, four and five-layer samples under a large induced surface charge density both above and below the glass transition temperature of the polymer. We find that the carrier mobility shows a strong asymmetry between the hole and electron doping regime. We then employ ab initio density functional theory (DFT) calculations to determine the average scattering lifetime from the experimental data. We explain its peculiar dependence on the carrier density in terms of the specific properties of the electrolyte we used in our experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhi, Ting; Tao, Tao; Liu, Bin, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn

Through investigating the temperature dependent current-voltage (T-I-V) properties of GaN based blue and green LEDs in this study, we propose an asymmetric tunneling model to understand the leakage current below turn-on voltage (V < 3.2 V): At the forward bias within 1.5 V ∼ 2.1 V (region 1), the leakage current is main attributed to electrons tunneling from the conduction band of n-type GaN layer to the valence band of p-type GaN layer via defect states in space-charge region (SCR); While, at the forward bias within 2 V ∼ 2.4 V (region 2), heavy holes tunneling gradually becomes dominant atmore » low temperature (T < 200K) as long as they can overcome the energy barrier height. The tunneling barrier for heavy holes is estimated to be lower than that for electrons, indicating the heavy holes might only tunnel to the defect states. This asymmetric tunneling model shows a novel carrier transport process, which provides better understanding of the leakage characteristics and is vital for future device improvements.« less

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

PubMed Central

Yin, Zhigang; Wei, Jiajun

2016-01-01

Organic solar cells (OSCs) have shown great promise as low‐cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single‐junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single‐junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small‐molecules, metals and metal salts/complexes, carbon‐based materials, organic‐inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron‐transporting and hole‐transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure–property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research. PMID:27812480

Effect of the electric field during annealing of organic light emitting diodes for improving its on/off ratio.

PubMed

Sharma, Rahul K; Katiyar, Monica; Rao, I V Kameshwar; Unni, K N Narayanan; Deepak

2016-01-28

If an organic light emitting diode is to be used as part of a matrix addressed array, it should exhibit low reverse leakage current. In this paper we present a method to improve the on/off ratio of such a diode by simultaneous application of heat and electric field post device fabrication. A green OLED with excellent current efficiency was seen to be suffering from a poor on/off ratio of 10(2). After examining several combinations of annealing along with the application of a reverse bias voltage, the on/off ratio of the same device could be increased by three orders of magnitude, specifically when the device was annealed at 80 °C under reverse bias (-15 V) followed by slow cooling also under the same bias. Simultaneously, the forward characteristics of the device were relatively unaffected. The reverse leakage in the OLED is mainly due to the injection of minority carriers in the hole transport layer (HTL) and the electron transport layer (ETL), in this case, of holes in tris-(8-hydroxyquinoline)aluminum(Alq3) and electrons in 4,4',4''-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA). Hence, to investigate these layers adjacent to the electrodes, we fabricated their single layer devices. The possibility of bulk traps present adjacent to electrodes providing states for injection was ruled out after estimating the trap density both before and after the reverse biased annealing. The temperature independent current in reverse bias ruled out the possibility of thermionic injection. The origin of the reverse bias current is attributed to the availability of interfacial hole levels in Alq3 at the cathode work function level in the as-fabricated device; the suppression of the same being attributed to the fact that these levels in Alq3 are partly removed after annealing under an electric field.

Probing Exciton Diffusion and Dissociation in Single-Walled Carbon Nanotube-C60 Heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dowgiallo, Anne-Marie; Mistry, Kevin S.; Johnson, Justin C.

The efficiency of thin-film organic photovoltaic (OPV) devices relies heavily upon the transport of excitons to type-II heterojunction interfaces, where there is sufficient driving force for exciton dissociation and ultimately the formation of charge carriers. Semiconducting single-walled carbon nanotubes (SWCNTs) are strong near-infrared absorbers that form type-II heterojunctions with fullerenes such as C60. Although the efficiencies of SWCNT-fullerene OPV devices have climbed over the past few years, questions remain regarding the fundamental factors that currently limit their performance. In this study, we determine the exciton diffusion length in the C60 layer of SWCNT-C60 bilayer active layers using femtosecond transient absorptionmore » measurements. We demonstrate that hole transfer from photoexcited C60 molecules to SWCNTs can be tracked by the growth of narrow spectroscopic signatures of holes in the SWCNT 'reporter layer'. In bilayers with thick C60 layers, the SWCNT charge-related signatures display a slow rise over hundreds of picoseconds, reflecting exciton diffusion through the C60 layer to the interface. A model based on exciton diffusion with a Beer-Lambert excitation profile, as well as Monte Carlo simulations, gives the best fit to the data as a function of C60 layer thickness using an exciton diffusion length of approximately 5 nm.« less

Probing Exciton Diffusion and Dissociation in Single-Walled Carbon Nanotube-C(60) Heterojunctions.

PubMed

Dowgiallo, Anne-Marie; Mistry, Kevin S; Johnson, Justin C; Reid, Obadiah G; Blackburn, Jeffrey L

2016-05-19

The efficiency of thin-film organic photovoltaic (OPV) devices relies heavily upon the transport of excitons to type-II heterojunction interfaces, where there is sufficient driving force for exciton dissociation and ultimately the formation of charge carriers. Semiconducting single-walled carbon nanotubes (SWCNTs) are strong near-infrared absorbers that form type-II heterojunctions with fullerenes such as C60. Although the efficiencies of SWCNT-fullerene OPV devices have climbed over the past few years, questions remain regarding the fundamental factors that currently limit their performance. In this study, we determine the exciton diffusion length in the C60 layer of SWCNT-C60 bilayer active layers using femtosecond transient absorption measurements. We demonstrate that hole transfer from photoexcited C60 molecules to SWCNTs can be tracked by the growth of narrow spectroscopic signatures of holes in the SWCNT "reporter layer". In bilayers with thick C60 layers, the SWCNT charge-related signatures display a slow rise over hundreds of picoseconds, reflecting exciton diffusion through the C60 layer to the interface. A model based on exciton diffusion with a Beer-Lambert excitation profile, as well as Monte Carlo simulations, gives the best fit to the data as a function of C60 layer thickness using an exciton diffusion length of approximately 5 nm.

Spinel Co3O4 nanomaterials for efficient and stable large area carbon-based printed perovskite solar cells.

PubMed

Bashir, Amna; Shukla, Sudhanshu; Lew, Jia Haur; Shukla, Shashwat; Bruno, Annalisa; Gupta, Disha; Baikie, Tom; Patidar, Rahul; Akhter, Zareen; Priyadarshi, Anish; Mathews, Nripan; Mhaisalkar, Subodh G

2018-02-01

Carbon based perovskite solar cells (PSCs) are fabricated through easily scalable screen printing techniques, using abundant and cheap carbon to replace the hole transport material (HTM) and the gold electrode further reduces costs, and carbon acts as a moisture repellent that helps in maintaining the stability of the underlying perovskite active layer. An inorganic interlayer of spinel cobaltite oxides (Co 3 O 4 ) can greatly enhance the carbon based PSC performance by suppressing charge recombination and extracting holes efficiently. The main focus of this research work is to investigate the effectiveness of Co 3 O 4 spinel oxide as the hole transporting interlayer for carbon based perovskite solar cells (PSCs). In these types of PSCs, the power conversion efficiency (PCE) is restricted by the charge carrier transport and recombination processes at the carbon-perovskite interface. The spinel Co 3 O 4 nanoparticles are synthesized using the chemical precipitation method, and characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV-Vis spectroscopy. A screen printed thin layer of p-type inorganic spinel Co 3 O 4 in carbon PSCs provides a better-energy level matching, superior efficiency, and stability. Compared to standard carbon PSCs (PCE of 11.25%) an improved PCE of 13.27% with long-term stability, up to 2500 hours under ambient conditions, is achieved. Finally, the fabrication of a monolithic perovskite module is demonstrated, having an active area of 70 cm 2 and showing a power conversion efficiency of >11% with virtually no hysteresis. This indicates that Co 3 O 4 is a promising interlayer for efficient and stable large area carbon PSCs.

Flexible Mechanical Conveyors for Regolith Extraction and Transport

NASA Technical Reports Server (NTRS)

Walton, Otis R.; Vollmer, Hubert J.

2013-01-01

A report describes flexible mechanical conveying systems for transporting fine cohesive regolith under microgravity and vacuum conditions. They are totally enclosed, virtually dust-free, and can include enough flexibility in the conveying path to enable an expanded range of extraction and transport scenarios, including nonlinear drill-holes and excavation of enlarged subsurface openings without large entry holes. The design of the conveyors is a modification of conventional screw conveyors such that the central screw-shaft and the outer housing or conveyingtube have a degree of bending flexibility, allowing the conveyors to become nonlinear conveying systems that can convey around gentle bends. The central flexible shaft is similar to those used in common tools like a weed whacker, consisting of multiple layers of tightly wound wires around a central wire core. Utilization of compliant components (screw blade or outer wall) increases the robustness of the conveying, allowing an occasional oversized particle to pass hough the conveyor without causing a jam or stoppage

Electro-active polymers containing pendent 2,7-diarylfluorene fragments as materials for OLEDs

NASA Astrophysics Data System (ADS)

Krucaite, G.; Tavgeniene, D.; Peciulyte, L.; Buika, G.; Liu, L.; Zhang, B.; Xie, Z.; Grigalevicius, S.

2016-05-01

Poly[2-phenyl-7-(4-vinylphenyl)-9,9-diethylfluorene)], poly[2-(1-naphtyl)-7-(4-vinylphenyl)-9,9-diethylfluorene)] and poly[2-(4-biphenyl)-7-(4-vinylphenyl)-9,9-diethylfluorene)] were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The derivatives represent materials of high thermal stability with initial thermal destruction temperatures from 390°C to 400 °C. The glass transition temperatures of the amorphous materials were 182 °C, 151 °C and 159 °C respectively. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting material. The device containing hole-transporting layers of polymer with 2-(4-biphenyl)-7-(4-vinylphenyl)-9,9-diethylfluorene moieties exhibited the best overall performance with turn on voltage of 3.6 V, a maximum photometric efficiency of 3.1 cd/A and maximum brightness of about 5300 cd/m2.

Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

NASA Astrophysics Data System (ADS)

Paradzah, Alexander T.; Diale, Mmantsae; Maabong, Kelebogile; Krüger, Tjaart P. J.

2018-04-01

Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.

Effects of electron transport material on blue organ light-emitting diode with fluorescent dopant of BCzVBi.

PubMed

Meng, Mei; Song, Wook; Kim, You-Hyun; Lee, Sang-Youn; Jhun, Chul-Gyu; Zhu, Fu Rong; Ryu, Dae Hyun; Kim, Woo-Young

2013-01-01

High efficiency blue organic light emitting diodes (OLEDs), based on 2-me-thyl-9,10-di(2-naphthyl) anthracene (MADN) doped with 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi), were fabricated using two different electron transport layers (ETLs) of tris(8-hydroxyquinolino)-aluminum (Alq3) and 4,7-di-phenyl-1,10-phenanthroline (Bphen). Bphen ETL layers favored the efficient hole-electron recombination in the emissive layer of the BCzVBi-doped blue OLEDs, leading to high luminous efficiency and quantum efficiency of 8.34 cd/A at 100 mA/cm2 and 5.73% at 100 cd/m2, respectively. Maximum luminance of blue OLED with Bphen ETL and Alq3 ETL were 10670 cd/m2, and CIExy coordinates of blue OLEDs were (0.180, 0279) and (0.155, 0.212) at 100 cd/m2.

A series connection architecture for large-area organic photovoltaic modules with a 7.5% module efficiency.

PubMed

Hong, Soonil; Kang, Hongkyu; Kim, Geunjin; Lee, Seongyu; Kim, Seok; Lee, Jong-Hoon; Lee, Jinho; Yi, Minjin; Kim, Junghwan; Back, Hyungcheol; Kim, Jae-Ryoung; Lee, Kwanghee

2016-01-05

The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned subcells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called aperture loss in series connection regions. Herein we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron- and hole-transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm(2).

2D black phosphorous nanosheets as a hole transporting material in perovskite solar cells

NASA Astrophysics Data System (ADS)

Muduli, Subas Kumar; Varrla, Eswaraiah; Kulkarni, Sneha Avinash; Han, Guifang; Thirumal, Krishnamoorthy; Lev, Ovadia; Mhaisalkar, Subodh; Mathews, Nripan

2017-12-01

We demonstrate for the first-time liquid exfoliated few layers of 2D Black phosphorus (BP) nanosheets as a hole transporting material (HTM) for perovskite based solar cells. The photoelectron spectroscopy in air (PESA) measurements confirm the low laying valence band level of BP nanosheets (-5.2 eV) favourable for hole injection from CH3NH3PbI3 (MAPbI3). Our results show that ∼25% improvement in power conversion efficiency (PCE) of η = 16.4% for BP nanosheets + Spiro-OMeTAD as an HTM as compared to spiro-OMeTAD (η = 13.1%). When BP nanosheets are exclusively utilised as an HTM, a PCE of η = 7.88% is noted, an improvement over the 4% PCE values observed for HTM free devices. Photoluminescence (PL) quenching of MAPbI3 and impedance measurements further confirm the charge extraction ability of BP nanosheets. The structural and optical characterization of liquid exfoliated BP nanosheets is discussed in detail with the aid of transmission electron microscopy, Raman spectroscopy, absorption spectroscopy and photo-electron spectroscopy.

Organic Solar Cells Based on Electrodeposited Polyaniline Films

NASA Astrophysics Data System (ADS)

Inoue, Kei; Akiyama, Tsuyoshi; Suzuki, Atsushi; Oku, Takeo

2012-04-01

Polyaniline thin films as hole transporting layers were fabricated on transparent indium-tin-oxide electrodes by electrodeposition of aniline in an aqueous H2SO4 electrolyte solution. Emerald-green polyaniline films were obtained, which showed stable redox waves. A mixed solution of polythiophene and fullerene derivative was spin-coated onto the electrodeposited polyaniline film. After the modification of titanium oxide film on the surface of the polythiophene/fullerene layer, an aluminum electrode was fabricated by vacuum deposition. The obtained solar cells generated stable photocurrent and photovoltage under light illumination.

An organic surface modifier to produce a high work function transparent electrode for high performance polymer solar cells.

PubMed

Choi, Hyosung; Kim, Hak-Beom; Ko, Seo-Jin; Kim, Jin Young; Heeger, Alan J

2015-02-04

Modification of an ITO electrode with small-molecule organic surface modifier, 4-chloro-benzoic acid (CBA), via a simple spin-coating method produces a high-work-function electrode with high transparency and a hydrophobic surface. As an alternative to PEDOT:PSS, CBA modification achieves efficiency enhancement up to 8.5%, which is attributed to enhanced light absorption within the active layer and smooth hole transport from the active layer to the anode. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dual functions of a new n-type conjugated dendrimer: light-emitting material and additive for polymer electroluminescent devices

NASA Astrophysics Data System (ADS)

Hyeok Park, Jong; Kim, Chulhee; Kim, Young Chul

2009-02-01

We demonstrate a novel light-emitting diode (LED) of a graded bilayer structure that comprises poly(N-vinylcarbazole) (PVK) with good hole transport ability as the energy donor and a new distyrylanthracene-triazine-based dendrimer with enhanced electron transport ability as the light-emitting molecule. The device contains a graded bilayer structure of the PVK film covered with the dendrimer film prepared by sequential spin-casting of the dendrimer layer from a solvent that only swells the PVK layer. The bilayer device demonstrated a significantly enhanced electoluminescence quantum efficiency compared with the dendrimer single layer device or the PVK : dendrimer blend device with optimized composition. We also prepared composite LEDs with an MEH-PPV : emissive dendrimer blend. By doping the electron-deficient MEH-PPV layer with a small amount of the distyrylanthracene-triazine-based dendrimer, we could not only enhance the device performance but also depress the long-wavelength emission of MEH-PPV.

Bimetallic nanocomposite as hole transport co-buffer layer in organic solar cell

NASA Astrophysics Data System (ADS)

Mola, Genene Tessema; Arbab, Elhadi A. A.

2017-12-01

Silver-zinc bimetallic nanocomposite (Ag:Zn BiM-NPs) was used as an inter-facial buffer layer in the preparation of thin film organic solar cell (TFOSC). The current investigation focuses on the effect of bimetallic nanoparticles on the performance of TFOSC. A number experiments were conducted by employing Ag:Zn nanocomposite buffer layer of thickness 1 nm at various positions of the device structure. In all cases, we found significant improvement on the power conversion efficiency of the solar cells. It is also noted that the open circuit voltage of the devices are decreasing when Ag:Zn form direct contact with the ITO electrode and without the inclusion of PEDOT:PSS. However, all results show that the introduction of Ag:Zn nanocomposite layer close to PEDOT:PSS could be beneficial to improve the charge transport processes in the preparation of thin film organic solar cell. The Ag:Zn BiM-NPs and the device properties were presented and discussed in terms of optical, electrical and film morphologies of the devices.

Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered ZnO as electron transport layer [Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered inorganic electron transport layer

DOE PAGES

Subbiah, Anand S.; Agarwal, Sumanshu; Mahuli, Neha; ...

2017-02-10

Here, radio-frequency magnetron sputtering is demonstrated as an effective tool to deposit highly crystalline thin zinc oxide (ZnO) layer directly on perovskite absorber as an electron transport layer (ETL). As an absorber, formamidinium lead tribromide (FAPbBr 3) is fabricated through a modified single-step solution process using hydrogen bromide (HBr) as an additive resulting in complete surface coverage and highly crystalline material. A planar p-i-n device architecture with spin-coated poly-(3,4-ethylenedioxythiophene):poly-styrenesulfonic acid (PEDOT:PSS) as hole transport material (HTM) and sputtered ZnO as ETL results in a short circuit current density of 9.5 mA cm -2 and an open circuit potential of 1.19more » V. Numerical simulations are performed to validate the underlying loss mechanisms. The use of phenyl C 60 butyric acid methyl ester (PCBM) interface layer between FAPbBr 3 and sputter-coated ZnO offers shielding from potential plasma-related interface damage. The modified interface results in a better device efficiency of 8.3% with an open circuit potential of 1.35 V. Such devices offer better stability under continuous illumination under ambient conditions in comparison with the conventional organic ETL (PCBM)-based devices.« less

Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered ZnO as electron transport layer [Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered inorganic electron transport layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subbiah, Anand S.; Agarwal, Sumanshu; Mahuli, Neha

Here, radio-frequency magnetron sputtering is demonstrated as an effective tool to deposit highly crystalline thin zinc oxide (ZnO) layer directly on perovskite absorber as an electron transport layer (ETL). As an absorber, formamidinium lead tribromide (FAPbBr 3) is fabricated through a modified single-step solution process using hydrogen bromide (HBr) as an additive resulting in complete surface coverage and highly crystalline material. A planar p-i-n device architecture with spin-coated poly-(3,4-ethylenedioxythiophene):poly-styrenesulfonic acid (PEDOT:PSS) as hole transport material (HTM) and sputtered ZnO as ETL results in a short circuit current density of 9.5 mA cm -2 and an open circuit potential of 1.19more » V. Numerical simulations are performed to validate the underlying loss mechanisms. The use of phenyl C 60 butyric acid methyl ester (PCBM) interface layer between FAPbBr 3 and sputter-coated ZnO offers shielding from potential plasma-related interface damage. The modified interface results in a better device efficiency of 8.3% with an open circuit potential of 1.35 V. Such devices offer better stability under continuous illumination under ambient conditions in comparison with the conventional organic ETL (PCBM)-based devices.« less

Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nie, Wanyi; Tsai, Hsinhan; Blancon, Jean -Christophe

Hybrid perovskites are on a trajectory toward realizing the most efficient single-junction, solution-processed photovoltaic devices. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grownmore » on poly(3,4-ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near-ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10-Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. Here, these results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high-performance and photostable optoelectronic devices.« less

Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide.

PubMed

Nie, Wanyi; Tsai, Hsinhan; Blancon, Jean-Christophe; Liu, Fangze; Stoumpos, Costas C; Traore, Boubacar; Kepenekian, Mikael; Durand, Olivier; Katan, Claudine; Tretiak, Sergei; Crochet, Jared; Ajayan, Pulickel M; Kanatzidis, MercouriG; Even, Jacky; Mohite, Aditya D

2018-02-01

Hybrid perovskites are on a trajectory toward realizing the most efficient single-junction, solution-processed photovoltaic devices. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grown on poly(3,4-ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near-ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10-Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. These results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high-performance and photostable optoelectronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide

DOE PAGES

Nie, Wanyi; Tsai, Hsinhan; Blancon, Jean -Christophe; ...

2017-12-11

Hybrid perovskites are on a trajectory toward realizing the most efficient single-junction, solution-processed photovoltaic devices. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grownmore » on poly(3,4-ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near-ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10-Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. Here, these results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high-performance and photostable optoelectronic devices.« less

A simple model for remineralization of subsurface lesions in tooth enamel

NASA Astrophysics Data System (ADS)

Christoffersen, J.; Christoffersen, M. R.; Arends, J.

1982-12-01

A model for remineralization of subsurface lesions in tooth enamel is presented. The important assumption on which the model is based is that the rate-controlling process is the crystal surface process by which ions are incorporated in the crystallites; that is, the transport of ions through small holes in the so-called intact surface layer does not influence the rate of mineral uptake at the crystal surface. Further, the density of mineral in the lesion is assumed to increase down the lesion, when the remineralization process is started. It is shown that the dimension of the initial holes in the enamel surface layer must be larger than the dimension of the individual crystallites in order to prevent the formation of arrested lesions. Theoretical expressions for the progress of remineralization are given. The suggested model emphasizes the need for measurements of mineral densities in the lesion, prior to, and during the lesion repair.

Electronic transport properties of Ti-impurity band in Si

NASA Astrophysics Data System (ADS)

Olea, J.; González-Díaz, G.; Pastor, D.; Mártil, I.

2009-04-01

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures.

PubMed

Gamucci, A; Spirito, D; Carrega, M; Karmakar, B; Lombardo, A; Bruna, M; Pfeiffer, L N; West, K W; Ferrari, A C; Polini, M; Pellegrini, V

2014-12-19

Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures <5-10 K. The low-temperature data follow a logarithmic law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

Interfacial electronic structures revealed at the rubrene/CH3NH3PbI3 interface.

PubMed

Ji, Gengwu; Zheng, Guanhaojie; Zhao, Bin; Song, Fei; Zhang, Xiaonan; Shen, Kongchao; Yang, Yingguo; Xiong, Yimin; Gao, Xingyu; Cao, Liang; Qi, Dong-Chen

2017-03-01

The electronic structures of rubrene films deposited on CH 3 NH 3 PbI 3 perovskite have been investigated using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was found that rubrene molecules interacted weakly with the perovskite substrate. Due to charge redistribution at their interface, a downward 'band bending'-like energy shift of ∼0.3 eV and an upward band bending of ∼0.1 eV were identified at the upper rubrene side and the CH 3 NH 3 PbI 3 substrate side, respectively. After the energy level alignment was established at the rubrene/CH 3 NH 3 PbI 3 interface, its highest occupied molecular orbital (HOMO)-valence band maximum (VBM) offset was found to be as low as ∼0.1 eV favoring the hole extraction with its lowest unoccupied molecular orbital (LUMO)-conduction band minimum (CBM) offset as large as ∼1.4 eV effectively blocking the undesired electron transfer from perovskite to rubrene. As a demonstration, simple inverted planar solar cell devices incorporating rubrene and rubrene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layers (HTLs) were fabricated in this work and yielded a champion power conversion efficiency of 8.76% and 13.52%, respectively. Thus, the present work suggests that a rubrene thin film could serve as a promising hole transport layer for efficient perovskite-based solar cells.

Charge transport properties of intrinsic layer in diamond vertical pin diode

NASA Astrophysics Data System (ADS)

Shimaoka, Takehiro; Kuwabara, Daisuke; Hara, Asuka; Makino, Toshiharu; Tanaka, Manobu; Koizumi, Satoshi

2017-05-01

Diamond is hoped to be utilized in ultimate power electronic devices exhibiting ultra-high blocking voltages. For practical device formation, it is important to characterize the electric properties to precisely simulate carrier transport and to practically design optimum device structures. In this study, we experimentally evaluated the charge transport properties of intrinsic layers in diamond vertical pin diodes using alpha-particle induced charge distribution measurements. The charge collection efficiencies were 98.1 ± 0.6% for a {111} pin diode and 96.9 ± 0.6% for a {100} pin diode, which means that almost all generated charges are collected accordingly equivalent to conventional Silicon pin photodiodes. Mobility-lifetime (μτ) products of holes were (2.2 ± 0.3) × 10-6 cm2/V for {111} and (1.8 ± 0.1) × 10-5 cm2/V for {100} diamond pin diodes.

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer

PubMed Central

Rafique, Saqib; Abdullah, Shahino Mah; Shahid, Muhammad Mehmood; Ansari, Mohammad Omaish; Sulaiman, Khaulah

2017-01-01

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC71BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability. PMID:28084304

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer.

PubMed

Rafique, Saqib; Abdullah, Shahino Mah; Shahid, Muhammad Mehmood; Ansari, Mohammad Omaish; Sulaiman, Khaulah

2017-01-13

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC 71 BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer

NASA Astrophysics Data System (ADS)

Rafique, Saqib; Abdullah, Shahino Mah; Shahid, Muhammad Mehmood; Ansari, Mohammad Omaish; Sulaiman, Khaulah

2017-01-01

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC71BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Liping; Chen, Jiangshan; Ma, Dongge, E-mail: mdg1014@ciac.ac.cn

2015-11-07

We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency,more » and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.« less

A white organic light emitting diode based on anthracene-triphenylamine derivatives

NASA Astrophysics Data System (ADS)

Jiang, Quan; Qu, Jianjun; Yu, Junsheng; Tao, Silu; Gan, Yuanyuan; Jiang, Yadong

2010-10-01

White organic lighting-diode (WOLED) can be used as flat light sources, backlights for liquid crystal displays and full color displays. Recently, a research mainstream of white OLED is to develop the novel materials and optimize the structure of devices. In this work a WOLED with a structure of ITO/NPB/PAA/Alq3: x% rubrene/Alq3/Mg: Ag, was fabricated. The device has two light-emitting layers. NPB is used as a hole transport layer, PAA as a blue emitting layer, Alq3: rubrene host-guest system as a yellow emitting layer, and Alq3 close to the cathode as an electron transport layer. In the experiment, the doping concentration of rubrene was optimized. WOLED 1 with 4% rubrene achieved a maximum luminous efficiency of 1.80 lm/W, a maximum luminance of 3926 cd/m2 and CIE coordinates of (0.374, 0.341) .WOLED 2 with 2% rubrene achieved a maximum luminous efficiency of 0.65 lm/W, a maximum luminance of 7495cd/m2 and CIE coordinates of (0.365,0.365).

Enhancement of Photovoltaic Performance by Utilizing Readily Accessible Hole Transporting Layer of Vanadium(V) Oxide Hydrate in a Polymer-Fullerene Blend Solar Cell.

PubMed

Jiang, Youyu; Xiao, Shengqiang; Xu, Biao; Zhan, Chun; Mai, Liqiang; Lu, Xinhui; You, Wei

2016-05-11

Herein, a successful application of V2O5·nH2O film as hole transporting layer (HTL) instead of PSS in polymer solar cells is demonstrated. The V2O5·nH2O layer was spin-coated from V2O5·nH2O sol made from melting-quenching sol-gel method by directly using vanadium oxide powder, which is readily accessible and cost-effective. V2O5·nH2O (n ≈ 1) HTL is found to have comparable work function and smooth surface to that of PSS. For the solar cell containing V2O5·nH2O HTL and the active layer of the blend of a novel polymer donor (PBDSe-DT2PyT) and the acceptor of PC71BM, the PCE was significantly improved to 5.87% with a 30% increase over 4.55% attained with PSS HTL. Incorporation of V2O5·nH2O as HTL in the polymer solar cell was found to enhance the crystallinity of the active layer, electron-blocking at the anode and the light-harvest in the wavelength range of 400-550 nm in the cell. V2O5·nH2O HTL improves the charge generation and collection and suppress the charge recombination within the PBDSe-DT2PyT:PC71BM solar cell, leading to a simultaneous enhancement in Voc, Jsc, and FF. The V2O5·nH2O HTL proposed in this work is envisioned to be of great potential to fabricate highly efficient PSCs with low-cost and massive production.

Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seif, Johannes Peter, E-mail: johannes.seif@alumni.epfl.ch; Ballif, Christophe; De Wolf, Stefaan

Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers—inserted between substrate and (front or rear) contacts—since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation ofmore » such films as window layers—without degraded carrier collection—demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.« less

New PCBM/carbon based electron transport layer for perovskite solar cells.

PubMed

Mamun, Abdullah Al; Ava, Tanzila Tasnim; Zhang, Kai; Baumgart, Helmut; Namkoong, Gon

2017-07-21

Carbon is inherently abundant in nature and relatively inexpensive, which can potentially reduce the manufacturing cost of solar cells. In recent years, carbon has been used as a hole transport layer or counter electrode in perovskite solar cells. Herein, we demonstrate that carbon can also be used as a charge transport layer capable of enhancing the energy conversion efficiency of a CH 3 NH 3 PbI 3-x Cl x solar cell when carbon is combined with PCBM. Particularly, we have been able to deposit an ultra-flat carbon layer using an e-beam irradiation method, which exhibited much better conductivity than the competitive PCBM/C60 layer. In addition, quantitative analysis of interfacial charge dynamics shows that the quenching efficiency of PCBM/carbon is comparable to that of PCBM/C60 but better interface defect passivation and improved series and shunt resistances were observed when PCBM/carbon was employed. For the photovoltaic performance, the reference perovskite solar cell fabricated from the widely used PCBM/C60 has a power conversion efficiency (PCE) of 14% while the perovskite solar cell with PCBM/carbon has an increased PCE of 16%. Our results demonstrate the potential of the use of cost-effective carbon for perovskite solar cells, which could reduce production costs.

Charge transfer through amino groups-small molecules interface improving the performance of electroluminescent devices

NASA Astrophysics Data System (ADS)

Havare, Ali Kemal; Can, Mustafa; Tozlu, Cem; Kus, Mahmut; Okur, Salih; Demic, Şerafettin; Demirak, Kadir; Kurt, Mustafa; Icli, Sıddık

2016-05-01

A carboxylic group functioned charge transporting was synthesized and self-assembled on an indium tin oxide (ITO) anode. A typical electroluminescent device [modified ITO/TPD (50 nm)/Alq3 (60 nm)/LiF (2 nm)/(120 nm)] was fabricated to investigate the effect of the amino groups-small molecules interface on the characteristics of the device. The increase in the surface work function of ITO is expected to facilitate the hole injection from the ITO anode to the Hole Transport Layer (HTL) in electroluminescence. The modified electroluminescent device could endure a higher current and showed a much higher luminance than the nonmodified one. For the produced electroluminescent devices, the I-V characteristics, optical characterization and quantum yields were performed. The external quantum efficiency of the modified electroluminescent device is improved as the result of the presence of the amino groups-small molecules interface.

Toward High-Efficiency Solution-Processed Planar Heterojunction Sb2S3 Solar Cells.

PubMed

Zimmermann, Eugen; Pfadler, Thomas; Kalb, Julian; Dorman, James A; Sommer, Daniel; Hahn, Giso; Weickert, Jonas; Schmidt-Mende, Lukas

2015-05-01

Low-cost hybrid solar cells have made tremendous steps forward during the past decade owing to the implementation of extremely thin inorganic coatings as absorber layers, typically in combination with organic hole transporters. Using only extremely thin films of these absorbers reduces the requirement of single crystalline high-quality materials and paves the way for low-cost solution processing compatible with roll-to-roll fabrication processes. To date, the most efficient absorber material, except for the recently introduced organic-inorganic lead halide perovskites, has been Sb 2 S 3 , which can be implemented in hybrid photovoltaics using a simple chemical bath deposition. Current high-efficiency Sb 2 S 3 devices utilize absorber coatings on nanostructured TiO 2 electrodes in combination with polymeric hole transporters. This geometry has so far been the state of the art, even though flat junction devices would be conceptually simpler with the additional potential of higher open circuit voltages due to reduced charge carrier recombination. Besides, the role of the hole transporter is not completely clarified yet. In particular, additional photocurrent contribution from the polymers has not been directly shown, which points toward detrimental parasitic light absorption in the polymers. This study presents a fine-tuned chemical bath deposition method that allows fabricating solution-processed low-cost flat junction Sb 2 S 3 solar cells with the highest open circuit voltage reported so far for chemical bath devices and efficiencies exceeding 4%. Characterization of back-illuminated solar cells in combination with transfer matrix-based simulations further allows to address the issue of absorption losses in the hole transport material and outline a pathway toward more efficient future devices.

Investigation of cross-linking characteristics of novel hole-transporting materials for solution-processed phosphorescent OLEDs

NASA Astrophysics Data System (ADS)

Lee, Jaemin; Ameen, Shahid; Lee, Changjin

2016-04-01

After the success of commercialization of the vacuum-evaporated organic light-emitting diodes (OLEDs), solutionprocessing or printing of OLEDs are currently attracting much research interests. However, contrary to various kinds of readily available vacuum-evaporable OLED materials, the solution-processable OLED materials are still relatively rare. Hole-transporting layer (HTL) materials for solution-processed OLEDs are especially limited, because they need additional characteristics such as cross-linking to realize multilayer structures in solution-processed OLEDs, as well as their own electrically hole-transporting characteristics. The presence of such cross-linking characteristics of solutionprocessable HTL materials therefore makes them more challenging in the development stage, and also makes them essence of solution-processable OLED materials. In this work, the structure-property relationships of thermally crosslinkable HTL materials were systematically investigated by changing styrene-based cross-linking functionalities and modifying the carbazole-based hole-transporting core structures. The temperature dependency of the cross-linking characteristics of the HTL materials was systematically investigated by the UV-vis. absorption spectroscopy. The new HTL materials were also applied to green phosphorescent OLEDs, and their device characteristics were also investigated based on the chemical structures of the HTL materials. The device configuration was [ITO / PEDOT:PSS / HTL / EML / ETL / CsF / Al]. We found out that the chemical structures of the cross-linking functionalities greatly affect not only the cross-linking characteristics of the resultant HTL materials, but also the resultant OLED device characteristics. The increase of the maximum luminance and efficiency of OLEDs was evident as the cross-linking temperature decreases from higher than 200°C to at around 150°C.

Interfacial engineering with ultrathin poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) layer for high efficient perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Lin, Chunyan; Chen, Ping; Xiong, ZiYang; Liu, Debei; Wang, Gang; Meng, Yan; Song, Qunliang

2018-02-01

Organic-inorganic hybrid perovskites have attracted great attention in the field of lighting and display due to their very high color purity and low-cost solution-process. Researchers have done a lot of work in realizing high performance electroluminescent devices. However, the current efficiency (CE) of methyl-ammonium lead halide perovskite light-emitting diodes (PeLEDs) still needs to be improved. Herein, we demonstrate the enhanced performance of PeLEDs through introducing an ultrathin poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) buffer layer between poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and CH3NH3PbBr3 perovskite. Compared to the reference device without PFO, the optimal device luminous intensity, the maximum CE, and the maximum external quantum efficiency increases from 8139 cd m-2 to 30 150 cd m-2, from 7.20 cd A-1 (at 6.8 V) to 10.05 cd A-1 (at 6.6 V), and from 1.73% to 2.44%, respectively. The ultrathin PFO layer not only reduces the exciton quenching at the interface between the hole-transport layer and emission layer, but also passivates the shallow-trap ensure increasing hole injection, as well as increases the coverage of perovskite film.

I. Hole-transporting dendrimers and their use in organic light-emitting devices (OLEDs) and II. Novel layered catalysts containing bipyridinium and zero-valent metal species

NASA Astrophysics Data System (ADS)

Koene, Shannon Carol

A series of polyaromatic ether/ester dendrimers containing a hole transporting naphthylphenylbenzyl amine at the periphery and a variety of fluorescent dyes at the core has been studied in an effort to observe energy transfer in these species. The dyes incorporated in these dendrimers include 1,4-dihydroxyanthraquinone (quinizarin), Coumarin 343, and a benzopentathiophene. These dendrimers have been incorporated into both single layer and heterostructure organic light emitting devices (OLEDs). In the case of first generation dendrimer OLEDs, excimer/exciplex formation was predominant. In third generation dendrimers, complete energy transfer from the periphery to the dye at the core was observed both in photoluminescence spectra and electroluminescence in OLEDs. Dendrimers containing different dye cores can be combined to achieve color mixing/tuning. In addition, layered catalysts were prepared via both covalent and electrostatic means to achieve the catalytic production of hydrogen peroxide from hydrogen and oxygen. Covalent catalysts were prepared by first growing layers of zirconium and a bipyridinium containing bisphosphonate onto silica particles. Palladium and/or platinum was ion-exchanged into the structure and reduced to the zero valent metal by hydrogen gas. A second set of catalysts was prepared by electrostatically depositing polycations/polyanions onto carboxylate or amine functionalized polystyrene microspheres. Anionic colloidal particles were adsorbed to the polycationic surface. An octacationic viologen oligomer was used in an attempt to increase the affinity of adsorption of the Pd particles to the surface of the microspheres. Catalytic studies of both types of catalysts are herein reported.

Fabrication of PDMS through-holes using the MIMIC method and the surface treatment by atmospheric-pressure CH4/He RF plasma

NASA Astrophysics Data System (ADS)

Choi, Jongchan; Lee, Kyeong-Hwan; Yang, Sung

2011-09-01

This note presents a simple fabrication process for patterning micro through-holes in a PDMS layer by a combination of the micromolding in capillaries (MIMIC) method and the surface treatment by atmospheric-pressure CH4/He RF plasma. The fabrication process is confirmed by forming micro through-holes with various shapes including circle, C-shape, open microfluidic channel and hemisphere. All micro through-holes of various shapes in a wide range of diameters and heights are well fabricated by the proposed method. Also, a 3D micromixer containing a PDMS micro through-hole layer formed by the proposed method is built and its performance is tested as another practical demonstration of the proposed fabrication method. Therefore, we believe that the proposed fabrication process will build a PDMS micro through-hole layer in a simple and easy way and will contribute to developing highly efficient multi-layered microfluidic systems, which may require PDMS micro through-hole layers.

Interface architecture between TiO2/perovskite, perovskite/hole transport layer, and perovskite grain boundary(Conference Presentation)

NASA Astrophysics Data System (ADS)

Hayase, Shuzi; Hirotani, Daisuke; Moriya, Masahiro; Ogomi, Yuhei; Shen, Qing; Yoshino, Kenji; Toyoda, Taro

2016-09-01

In order to examine the interface structure of TiO2/perovskite layer, quartz crystal microbalance sensor (QCM) was used. On the QCM sensor, TiO2 layer was fabricated and the PbI2 solution in Dimethylformamide (DMF) was passed on the QCM sensor to estimate the adsorption density of the PbI2 on the titania2. The amount of PbI2 adsorption on TiO2 surface increased as the adsorption time and leveled off at a certain time. PbI2 still remained even after the solvent only (DMF) was passed on the TiO2 layer on QCM (namely rinsing with DMF), suggesting that the PbI2 was tightly bonded on the TiO2 surface. The bonding structure was found to be Ti-O-Pb linkage by XPS analysis. We concluded that the Ti-OH on the surface of TiO2 reacts with I-Pb-I to form Ti-O-Pb-I and HI (Fig.1 B). The surface trap density was measured by thermally stimulated current (TSC) method. Before the PbI2 passivation, the trap density of TiO2 was 1019 cm3. The trap density decreased to 1016/cm3 after the PbI2 passivation, suggesting that the TiO2 surface trap was passivated with I-Pb-I. The passivation density was tuned by the concentration of PbI2 in DMF, by which TiO2 layer was passivated. Perovskite solar cells were fabricated on the passivated TiO2 layer with various PbI2 passivation densities by one step process (mixture of PbI2 + MAI in DMF). It was found that Jsc increased with an increase in the Ti-O-Pb density. We concluded that the interface between TiO2 and perovskite layer has passivation structure consisting of Ti-O-Pb-I which decreases the trap density of the interfaces and supresses charge recombination. The effect of Cl anion on high efficiency is still controversial when perovskite layer is prepared by one step method from the mixture of MAI and PbCl2. It was found that adsorption density of PbCl2 on TiO2 surface was much higher than that of PbI2 from the experiment using QCM sensor. After the surface was washed with DMF, Cl and Pb were detected. These results suggest that the TiO2 surface was much more passivated by PbCl2 than by PbI2. This may explain partially the high efficiency when the perovskite layer was fabricated by one step process consisting of MAI and PbCl2 solution. We also observed that the crystal size increased with an increase in the amount of Cl anion which of course one of the explanation of the high efficiency. The interface of hole transport layer/perovskite layer, and between perovskite layer /perovskite layer (grain boundary) was passivated with organic amines. The passivation was also effective for increasing Voc and Jsc. This was explained by the results of transient absorption spectroscopy that the charge recombination time between hole transport payer/perovskite layer increased from 0.3 μsec to 60 μsec.

Facile preparation of porous alumina through-hole masks for sputtering by two-layer anodization

NASA Astrophysics Data System (ADS)

Yanagishita, Takashi; Masuda, Hideki

2016-08-01

Highly ordered porous alumina through-hole masks were fabricated on a substrate by combining two-layer anodization with subsequent through-holing by selective etching. This process allowed the fabrication of porous alumina masks without an increase in pore size during the etching performed for through-holing. Additionally, the process contributed to improved operability in the setting of the masks on substrates because the second anodizing layer acts as a supporting layer for the handling of the mask. The fabrication of ordered Au nanodot arrays was demonstrated as an example application of the through-hole masks obtained by the present process.

Numerical analysis of drilling hole work-hardening effects in hole-drilling residual stress measurement

NASA Astrophysics Data System (ADS)

Li, H.; Liu, Y. H.

2008-11-01

The hole-drilling strain gage method is an effective semi-destructive technique for determining residual stresses in the component. As a mechanical technique, a work-hardening layer will be formed on the surface of the hole after drilling, and affect the strain relaxation. By increasing Young's modulus of the material near the hole, the work-hardening layer is simplified as a heterogeneous annulus. As an example, two finite rectangular plates submitted to different initial stresses are treated, and the relieved strains are measured by finite element simulation. The accuracy of the measurement is estimated by comparing the simulated residual stresses with the given initial ones. The results are shown for various hardness of work-hardening layer. The influence of the relative position of the gages compared with the thickness of the work-hardening layer, and the effect of the ratio of hole diameter to work-hardening layer thickness are analyzed as well.

P-doped organic semiconductor: Potential replacement for PEDOT:PSS in organic photodetectors

NASA Astrophysics Data System (ADS)

Herrbach, J.; Revaux, A.; Vuillaume, D.; Kahn, A.

2016-08-01

In this work, we present an alternative to the use of PEDOT:PSS as hole transport and electron blocking layers in organic photodetectors processed by solution. As Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is known to be sensitive to humidity, oxygen, and UV, removing this layer is essential for lifetime improvements. As a first step to achieving this goal, we need to find an alternative layer that fulfills the same role in order to obtain a working diode with similar or better performance. As a replacement, a layer of poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b')dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-c) p-doped with the dopant tris-[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-COCF3)3) is used. This p-doped layer effectively lowers the hole injection barrier, and the low electron affinity of the polymer prevents the injection of electrons into the active layer. We show similar device performance under light and the improvements of detection performance with the doped layer in comparison with PEDOT:PSS, leading to a detectivity of 1.9 × 1013 cm (Hz)1/2 (W)-1, competitive with silicon diodes used in imaging applications. Moreover, contrary to PEDOT:PSS, no localization of the p-doped layer is needed, leading to a diode active area defined by the patterned electrodes.

Cu/Cu2O nanocomposite films as a p-type modified layer for efficient perovskite solar cells.

PubMed

Chen, You-Jyun; Li, Ming-Hsien; Huang, Jung-Chun-Andrew; Chen, Peter

2018-05-16

Cu/Cu 2 O films grown by ion beam sputtering were used as p-type modified layers to improve the efficiency and stability of perovskite solar cells (PSCs) with an n-i-p heterojunction structure. The ratio of Cu to Cu 2 O in the films can be tuned by the oxygen flow ratio (O 2 /(O 2  + Ar)) during the sputtering of copper. Auger electron spectroscopy was performed to determine the elemental composition and chemical state of Cu in the films. Ultraviolet photoelectron spectroscopy and photoluminescence spectroscopy revealed that the valence band maximum of the p-type Cu/Cu 2 O matches well with the perovskite. The Cu/Cu 2 O film not only acts as a p-type modified layer but also plays the role of an electron blocking buffer layer. By introducing the p-type Cu/Cu 2 O films between the low-mobility hole transport material, spiro-OMeTAD, and the Ag electrode in the PSCs, the device durability and power conversion efficiency (PCE) were effectively improved as compared to the reference devices without the Cu/Cu 2 O interlayer. The enhanced PCE is mainly attributed to the high hole mobility of the p-type Cu/Cu 2 O film. Additionally, the Cu/Cu 2 O film serves as a protective layer against the penetration of humidity and Ag into the perovskite active layer.

Structure-driven turbulence in ``No man's Land''

NASA Astrophysics Data System (ADS)

Kosuga, Yusuke; Diamond, Patrick

2012-10-01

Structures are often observed in many physical systems. In tokamaks, for example, such structures are observed as density blobs and holes. Such density blobs and holes are generated at the tokamak edge, where strong gradient perturbations generate an outgoing blob and an incoming hole. Since density holes can propagate from the edge to the core, such structures may play an important role in understanding the phenomenology of the edge-core coupling region, so-called ``No Man's Land.'' In this work, we discuss the dynamics of such structures in real space. In particular, we consider the dynamics of density blobs and holes in the Hasegawa-Wakatani system. Specific questions addressed here include: i) how these structures extract free energy and enhance transport? how different is the relaxation driven by such structures from that driven by linear drift waves? ii) how these structures interact with shear flows? In particular, how these structures interact with a shear layer, which can absorb structures resonantly? iii) how can we calculate the coupled evolution of structures and shear flows? Implications for edge-core coupling problem are discussed as well.

Efficiency enhancement of solution-processed inverted organic solar cells with a carbon-nanotube-doped active layer

NASA Astrophysics Data System (ADS)

Lin, Wen-Kai; Su, Shui-Hsiang; Yeh, Meng-Cheng; Huang, Yang-Chan; Yokoyama, Meiso

2016-01-01

Solution-processed titanium-doped ZnO (TZO) is synthesized by the sol-gel method to be the electron-transporting layer (ETL) in an inverted organic solar cell (IOSC). Carbon nanotubes (CNTs) are doped into an active layer of poly(3-hexylthiophene):[6,6]-phenyl C 61 butyric acid methyl ester (P3HT:PCBM). The addition of CNTs in the P3HT:PCBM composite increases the conjugation length of P3HT:PCBM:CNTs, which simultaneously enhances the capacity of the composite to absorb solar energy radiation. Vanadium oxide (V2O5) was spin-coated onto the active layer to be a hole-transporting layer (HTL). The power conversion efficiency (PCE) results indicate that the V2O5 nanobelt structure possesses better phase separation and provides a more efficient surface area for the P3HT:PCBM:CNT active layer to increase photocurrent. The optimized IOSCs exhibited an open circuit voltage (Voc), a short-circuit current density (Jsc), a fill factor (FF), and a PCE of 0.55 V, 6.50 mA/cm2, 58.34%, and 2.20%, respectively, under simulated AM1.5G illumination of 100 mW/cm2.

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

NASA Astrophysics Data System (ADS)

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob

2015-07-01

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq)2(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq)2(acac). The lifetime of device (t95: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

Management of light absorption in extraordinary optical transmission based ultra-thin-film tandem solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mashooq, Kishwar; Talukder, Muhammad Anisuzzaman, E-mail: anis@eee.buet.ac.bd

2016-05-21

Although ultra-thin-film solar cells can be attractive in reducing the cost, they suffer from low absorption as the thickness of the active layer is usually much smaller than the wavelength of incident light. Different nano-photonic techniques, including plasmonic structures, are being explored to increase the light absorption in ultra-thin-film solar cells. More than one layer of active materials with different energy bandgaps can be used in tandem to increase the light absorption as well. However, due to different amount of light absorption in different active layers, photo-generated currents in different active layers will not be the same. The current mismatchmore » between the tandem layers makes them ineffective in increasing the efficiency. In this work, we investigate the light absorption properties of tandem solar cells with two ultra-thin active layers working as two subcells and a metal layer with periodically perforated holes in-between the two subcells. While the metal layer helps to overcome the current mismatch, the periodic holes increase the absorption of incident light by helping extraordinary optical transmission of the incident light from the top to the bottom subcell, and by coupling the incident light to plasmonic and photonic modes within ultra-thin active layers. We extensively study the effects of the geometry of holes in the intermediate metal layer on the light absorption properties of tandem solar cells with ultra-thin active layers. We also study how different metals in the intermediate layer affect the light absorption; how the geometry of holes in the intermediate layer affects the absorption when the active layer materials are changed; and how the intermediate metal layer affects the collection of photo-generated electron-hole pairs at the terminals. We find that in a solar cell with 6,6-phenyl C61-butyric acid methyl ester top subcell and copper indium gallium selenide bottom subcell, if the periodic holes in the metal layer are square or polygon, total absorption remains approximately the same. However, the total absorption suffers significantly if the holes are triangle. The transmission spectra of incident light into the bottom subcell, and hence the absorption, change significantly for square and circle holes if the active materials change to cadmium selenide (CdSe) and cadmium telluride (CdTe) in the top and bottom subcells, respectively. Although the intermediate metal layer may induce electron-hole pair recombination due to surface defects, the short-circuit current density of an ultra-thin plasmonic solar cell with an intermediate metal layer with two-dimensional hole array is >9% of that of a structure without the intermediate metal layer.« less

Helical edge states and fractional quantum Hall effect in a graphene electron-hole bilayer

NASA Astrophysics Data System (ADS)

Sanchez-Yamagishi, Javier D.; Luo, Jason Y.; Young, Andrea F.; Hunt, Benjamin M.; Watanabe, Kenji; Taniguchi, Takashi; Ashoori, Raymond C.; Jarillo-Herrero, Pablo

2017-02-01

Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.

Using a compositionally step graded hole reservoir layer with hole accelerating ability for reducing efficiency droop in GaN-based LEDs

NASA Astrophysics Data System (ADS)

Ye, Daqian; Zhang, Dongyan; Wu, Chaoyu; Wang, Duxiang; Xu, Chenke; Zhang, Jie; Huang, Meichun

2017-05-01

We presented a compositionally graded hole reservoir layers(HRL) - an AlGaN/GaN super lattice hole reservoir layer with Al mole fraction multi-step gradient from high to low (GSL-HRL) in this paper. The designed LED with compositionally step graded HRL shows comparable low operating voltage and less efficiency droop. Simulation results reveal that this graded HRL could reserve the hole effectively and the hole in HRL can be energized by the strong electric field due to the polarization caused by different Al contents AlxGa1-xN layers. Such a design makes hole travel across the p-type EBL and inject into the MQWs more efficiently and smoothly. The novel structure of HRL improves the performance of the LED significantly and gives a promising application in high power GaN-based LED in the future.

Synthesis of Ferrite Nickel Nano-particles and Its Role as a p-Dopant in the Improvement of Hole Injection of an Organic Light-Emitting Diode

NASA Astrophysics Data System (ADS)

Noori, Maryam; Jafari, Mohammad Reza; Hosseini, Sayed Mohsen; Shahedi, Zahra

2017-07-01

We fabricated an organometallic complex based on zinc ions using zinc complex as a fluorescent in organic light-emitting diodes (OLEDs). Also, the nano-particles of ferrite nickel were produced in a simple aqueous system prepared by mixing Ni (NO3)2, Fe (NO3)3 and deionized water solutions. The synthesized zinc bis (8-hydroxyquinoline) (Znq2) complex and NiFe2O4 nano-particles were characterized by using x-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) as well as photoluminescence spectroscopy analysis. Their energy level was also determined by some cyclic voltammetry (CV) measurements. The maximum green photoluminescence was observed at 565 nm. The nano-particles of ferrite nickel were utilized in preparation of OLEDs by blending of the magnetic nano-particles with PEDOT:PSS and Zn-complex solutions. The electrical and optical performance of prepared OLEDs with/without doped nano-particle was studied. The samples were configured into two structures: (1) Indium Tin Oxide (ITO)/ poly(3,4-ethylenedi-oxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Znq2/(2-4-biphenylyl)-5-phenyl-oxadiazole (PBD)/aluminum (Al) and (2) ITO/PEDOT:PSS:NiFe2O4(NPs)/Znq2/PBD/Al. Obtained results showed that the current density and electroluminescence efficiency were increased and the turn-on voltage decreased (about 3 V) by using nano-particles into a PEDOT:PSS layer (Hole transport layer). Also, the electroluminescence efficiency was decreased by incorporating magnetic nano-particles into a Zn-complex layer (emissive layer). It was found that utilizing NiFe2O4 nano-particles caused an increase of hole-injection layer conductivity effectively and a decrease of the turn-on voltage.

Stability of excitons in double quantum well: Through electron and holes transmission probabilities

NASA Astrophysics Data System (ADS)

Vignesh, G.; Nithiananthi, P.

2017-05-01

Stability of excitons has been analyzed using the transmission probability of its constituent particles in GaAs/Al0.3Ga0.7As Double Quantum Well (DQW) structure by varying well and barrier layer thickness. The effective mass approximation is used and anisotropy in material properties are also considered to get realistic situations. It is observed that tuning barrier layer avails many resonance peaks for the transmission and tuning well width admits maximum transmission at narrow well widths. Every saddle point of the observed transmission coefficients decides the formation, strength and transportation of excitons in DQW.

Theoretical insights into the effect of a conjugated core on the hole transport properties of hole-transporting materials for perovskite solar cells.

PubMed

Zhang, Zemin; Hu, Weixia; Cui, Jianyu; He, Rongxing; Shen, Wei; Li, Ming

2017-09-20

Conjugated bifluorenylidene and naphthalene central cores are introduced into hole-transporting materials DT1 and DT2 to replace the spiro-core of the reported, highly efficient FDT. The effects of the conjugated core on the geometrics, electronic properties and hole transport properties are investigated by using density functional theory coupled with Marcus theory and the Einstein relation. The calculated results show that DT1 (-5.21 eV) and DT2 (-5.23 eV) have lower HOMO levels than FDT (-5.15 eV), which indicates that the perovskite solar cells with conjugated hole-transporting materials can have higher open-circuit voltages. The introduction of the conjugated core is beneficial to the more efficient face-to-face packing pattern of the dimer, resulting in a larger intermolecular electronic coupling. Importantly, it is found that DT1 (1.6 × 10 -3 cm 2 V -1 s -1 ) and DT2 (2.7 × 10 -2 cm 2 V -1 s -1 ) exhibit relatively higher hole mobilities than FDT (1.3 × 10 -4 cm 2 V -1 s -1 ) owing to the larger electronic coupling. Therefore, enhanced hole transport ability can be achieved by switching from the spiro-core to the conjugated core. The present work provides a new strategy to improve the hole transport properties of hole-transporting materials, which will contribute to the development of conjugated small molecules as hole-transporting materials in efficient perovskite solar cells.

Imaging the Anomalous Charge Distribution Inside CsPbBr3 Perovskite Quantum Dots Sensitized Solar Cells.

PubMed

Panigrahi, Shrabani; Jana, Santanu; Calmeiro, Tomás; Nunes, Daniela; Martins, Rodrigo; Fortunato, Elvira

2017-10-24

Highly luminescent CsPbBr 3 perovskite quantum dots (QDs) have gained huge attention in research due to their various applications in optoelectronics, including as a light absorber in photovoltaic solar cells. To improve the performances of such devices, it requires a deeper knowledge on the charge transport dynamics inside the solar cell, which are related to its power-conversion efficiency. Here, we report the successful fabrication of an all-inorganic CsPbBr 3 perovskite QD sensitized solar cell and the imaging of anomalous electrical potential distribution across the layers of the cell under different illuminations using Kelvin probe force microscopy. Carrier generation, separation, and transport capacity inside the cells are dependent on the light illumination. Large differences in surface potential between electron and hole transport layers with unbalanced carrier separation at the junction have been observed under white light (full solar spectrum) illumination. However, under monochromatic light (single wavelength of solar spectrum) illumination, poor charge transport occurred across the junction as a consequence of less difference in surface potential between the active layers. The outcome of this study provides a clear idea on the carrier dynamic processes inside the cells and corresponding surface potential across the layers under the illumination of different wavelengths of light to understand the functioning of the solar cells and ultimately for the improvement of their photovoltaic performances.

New oligomers containing pendant 4-aryl-7-phenylfluorene units as efficient charge transporting materials for OLEDs

NASA Astrophysics Data System (ADS)

Krucaite, G.; Baranauskyte, U.; Tavgeniene, D.; Andruleviciute, V.; Sutkuviene, S.; Yao, B.; Xie, Z.; Zhang, B.; Grigalevicius, S.

2017-10-01

Monomers and oligomers containing electronically isolated 4-aryl-7-phenylfluorene fragments have been synthesized by the multi-step synthetic route. The materials were characterized by thermo-gravimetric analysis, differential scanning calorimetry and electron photoemission technique. The oligomers represent materials of very high thermal stability having initial thermal degradation temperatures in the range of 402-412 °C. The glass transition temperatures of the amorphous oligomers were in the rage of 97-129 °C. The electron photoemission spectra of thin layers of the oligomeric materials showed ionization potentials in the range of 5.7-6.1 eV. Hole injecting/transporting properties of the electroactive oligomers were tested in the structures of organic light emitting diodes with tris(quinolin-8-olato)aluminium as a green emitter. The device containing hole-transporting material with 4-biphenyl-7-phenylfluorene electrophores exhibited the best overall performance with low turn on voltage of 4.4 V, high current efficiency exceeding 3.6 cd/A and maximum brightness exceeding 3200 cd/m2.

High-Efficiency Selective Electron Tunnelling in a Heterostructure Photovoltaic Diode.

PubMed

Jia, Chuancheng; Ma, Wei; Gu, Chunhui; Chen, Hongliang; Yu, Haomiao; Li, Xinxi; Zhang, Fan; Gu, Lin; Xia, Andong; Hou, Xiaoyuan; Meng, Sheng; Guo, Xuefeng

2016-06-08

A heterostructure photovoltaic diode featuring an all-solid-state TiO2/graphene/dye ternary interface with high-efficiency photogenerated charge separation/transport is described here. Light absorption is accomplished by dye molecules deposited on the outside surface of graphene as photoreceptors to produce photoexcited electron-hole pairs. Unlike conventional photovoltaic conversion, in this heterostructure both photoexcited electrons and holes tunnel along the same direction into graphene, but only electrons display efficient ballistic transport toward the TiO2 transport layer, thus leading to effective photon-to-electricity conversion. On the basis of this ipsilateral selective electron tunnelling (ISET) mechanism, a model monolayer photovoltaic device (PVD) possessing a TiO2/graphene/acridine orange ternary interface showed ∼86.8% interfacial separation/collection efficiency, which guaranteed an ultrahigh absorbed photon-to-current efficiency (APCE, ∼80%). Such an ISET-based PVD may become a fundamental device architecture for photovoltaic solar cells, photoelectric detectors, and other novel optoelectronic applications with obvious advantages, such as high efficiency, easy fabrication, scalability, and universal availability of cost-effective materials.

Expansible apparatus for removing the surface layer from a concrete object

DOEpatents

Allen, Charles H.

1979-01-01

A method and apparatus for removing the surface layer from a concrete object. The method consists of providing a hole having a circular wall in the surface layer of the object, the hole being at least as deep as the thickness of the surface layer to be removed, and applying an outward wedging pressure on the wall of the hole sufficient to spall the surface layer around the hole. By the proper spacing of an appropriate number of holes, it is possible to remove the entire surface layer from an object. The apparatus consists of an elongated tubular-shaped body having a relatively short handle with a solid wall at one end, the wall of the remainder of the body containing a plurality of evenly spaced longitudinal cuts to form a relatively long expandable section, the outer end of the expandable section having an expandable, wedge-shaped spalling edge extending from the outer surface of the wall, perpendicular to the longitudinal axis of the body, and expanding means in the body for outwardly expanding the expandable section and forcing the spalling edge into the wall of a hole with sufficient outward pressure to spall away the surface layer of concrete. The method and apparatus are particularly suitable for removing surface layers of concrete which are radioactively contaminated.

Diverse carrier mobility of monolayer BNC_x: A combined density functional theory and Boltzmann transport theory study.

PubMed

Wu, Tao; Deng, Kaiming; Deng, Wei-Qiao; Lu, Ruifeng

2017-09-19

BNCX monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNCX (x=1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC2-1 is a material with very small band gap (0.02 eV) among all the structures while other BNCX monolayers are semiconductors with band gap ranging from 0.51 to 1.32 eV. The carrier mobility of BNCX varies considerably from tens to millions of cm2 V-1 s-1. For BNC2-1, the hole mobility and electron mobility along both x and y directions can reach 105 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNCX monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC4, its hole mobility along y direction and electron mobility along x direction unexpectedly reach 106 orders of magnitude, even higher than that of graphene. Our findings suggest that BNCX layered materials with proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices. © 2017 IOP Publishing Ltd.

Improved Carrier Transport in Perovskite Solar Cells Probed by Femtosecond Transient Absorption Spectroscopy.

PubMed

Serpetzoglou, Efthymis; Konidakis, Ioannis; Kakavelakis, George; Maksudov, Temur; Kymakis, Emmanuel; Stratakis, Emmanuel

2017-12-20

CH 3 NH 3 PbI 3 perovskite thin films have been deposited on glass/indium tin oxide/hole transport layer (HTL) substrates, utilizing two different materials as the HTLs. In the first configuration, the super hydrophilic polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), known as PEDOT:PSS, was employed as the HTL material, whereas in the second case, the nonwetting poly(triarylamine) semiconductor polymer, known as PTAA, was used. It was found that when PTAA is used as the HTL material, the averaged power conversion efficiency (PCE) of the perovskite solar cells (PSCs) remarkably increases from 12.60 to 15.67%. To explore the mechanism behind this enhancement, the aforementioned perovskite/HTL arrangements were investigated by time-resolved transient absorption spectroscopy (TAS) performed under inert conditions. By means of TAS, the charge transfer, carrier trapping, and hole injection dynamics from the photoexcited perovskite layers to the HTL can be directly monitored via the characteristic bleaching profile of the perovskite at ∼750 nm. TAS studies revealed faster relaxation times and decay dynamics when the PTAA polymer is employed, which potentially account for the enhanced PCE observed. The TAS results are correlated with the structure and crystalline quality of the corresponding perovskite films, investigated by scanning electron microscopy, X-ray diffraction, atomic force microscopy, micro-photoluminescence, and transmittance spectroscopy. It is concluded that TAS is a benchmark technique for the understanding of the carrier transport mechanisms in PSCs and constitutes a figure-of-merit tool toward their efficiency improvement.

Astrophysical and Geophysical Flows as Dynamical Systems. 1998 Summer Study Program in Geophysical Fluid Dynamics

DTIC Science & Technology

1999-01-01

Jerusalem, ISRAEL University of Miami Woods Hole Oceanographic Institution Brown University University of Chicago University Politecnica de Catalunya...University Politecnica de Catalunya, SPAIN - Resonant Mode Interactions in Rayleigh-Benard Convection 2:30 pm Ian Melbourne, University of Houston... Transport in a Porous Layer 2:30 pm Michael Proctor, University of Cambridge, UK - Noise Sensitivity in Travelling-Wave Instabilities Week of July

An organic p-type dopant with high thermal stability for an organic semiconductor.

PubMed

Gao, Zhi Qiang; Mi, Bao Xiu; Xu, Gui Zhen; Wan, Yi Qian; Gong, Meng Lian; Cheah, Kok Wai; Chen, Chin H

2008-01-07

To overcome the thermal instability of a p-doped organic hole transporting layer using the state-of-the-art p-type dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, a potent electron accepter, 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane, has been found to possess superior thermal stability and proved to be an excellent p-type dopant.

Screening of inorganic wide-bandgap p-type semiconductors for high performance hole transport layers in organic photovoltaic devices

NASA Astrophysics Data System (ADS)

Ginley, David; Zakutayev, Andriy; Garcia, Andreas; Widjonarko, Nicodemus; Ndione, Paul; Sigdel, Ajaya; Parilla, Phillip; Olson, Dana; Perkins, John; Berry, Joseph

2011-03-01

We will report on the development of novel inorganic hole transport layers (HTL) for organic photovoltaics (OPV). All the studied materials belong to the general class of wide-bandgap p-type oxide semiconductors. Potential candidates suitable for HTL applications include SnO, NiO, Cu2O (and related CuAlO2, CuCrO2, SrCu2O4 etc) and Co3O4 (and related ZnCo2O4, NiCo2O4, MgCo2O4 etc.). Materials have been optimized by high-throughput combinatorial approaches. The thin films were deposited by RF sputtering and pulsed laser deposition at ambient and elevated temperatures. Performance of the inorganic HTLs and that of the reference organic PEDOT:PSS HTL were compared by measuring the power conversion efficiencies and spectral responses of the P3HT/PCBM- and PCDTBT/PCBM-based OPV devices. Preliminary results indicate that Co3O4-based HTLs have performance comparable to that of our previously reported NiOs and PEDOT:PSS HTLs, leading to a power conversion efficiency of about 4 percent. The effect of composition and work function of the ternary materials on their performance in OPV devices is under investigation.

Highly Efficient Perovskite Solar Modules by Scalable Fabrication and Interconnection Optimization

DOE PAGES

Yang, Mengjin; Kim, Dong Hoe; Klein, Talysa R.; ...

2018-01-02

To push perovskite solar cell (PSC) technology toward practical applications, large-area perovskite solar modules with multiple subcells need to be developed by fully scalable deposition approaches. Here, we demonstrate a deposition scheme for perovskite module fabrication with spray coating of a TiO2 electron transport layer (ETL) and blade coating of both a perovskite absorber layer and a spiro-OMeTAD-based hole transport layer (HTL). The TiO2 ETL remaining in the interconnection between subcells significantly affects the module performance. Reducing the TiO2 thickness changes the interconnection contact from a Schottky diode to ohmic behavior. Owing to interconnection resistance reduction, the perovskite modules withmore » a 10 nm TiO2 layer show enhanced performance mainly associated with an improved fill factor. Finally, we demonstrate a four-cell MA0.7FA0.3PbI3 perovskite module with a stabilized power conversion efficiency (PCE) of 15.6% measured from an aperture area of ~10.36 cm2, corresponding to an active-area module PCE of 17.9% with a geometric fill factor of ~87.3%.« less

Highly Efficient Perovskite Solar Modules by Scalable Fabrication and Interconnection Optimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Mengjin; Kim, Dong Hoe; Klein, Talysa R.

To push perovskite solar cell (PSC) technology toward practical applications, large-area perovskite solar modules with multiple subcells need to be developed by fully scalable deposition approaches. Here, we demonstrate a deposition scheme for perovskite module fabrication with spray coating of a TiO2 electron transport layer (ETL) and blade coating of both a perovskite absorber layer and a spiro-OMeTAD-based hole transport layer (HTL). The TiO2 ETL remaining in the interconnection between subcells significantly affects the module performance. Reducing the TiO2 thickness changes the interconnection contact from a Schottky diode to ohmic behavior. Owing to interconnection resistance reduction, the perovskite modules withmore » a 10 nm TiO2 layer show enhanced performance mainly associated with an improved fill factor. Finally, we demonstrate a four-cell MA0.7FA0.3PbI3 perovskite module with a stabilized power conversion efficiency (PCE) of 15.6% measured from an aperture area of ~10.36 cm2, corresponding to an active-area module PCE of 17.9% with a geometric fill factor of ~87.3%.« less

Opto-electro-modulated transient photovoltage and photocurrent system for investigation of charge transport and recombination in solar cells.

PubMed

Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Wu, Huijue; Meng, Qingbo

2016-12-01

An opto-electro-modulated transient photovoltage/photocurrent system has been developed to probe microscopic charge processes of a solar cell in its adjustable operating conditions. The reliability of this system is carefully determined by electric circuit simulations and experimental measurements. Using this system, the charge transport, recombination and storage properties of a conventional multicrystalline silicon solar cell under different steady-state bias voltages, and light illumination intensities are investigated. This system has also been applied to study the influence of the hole transport material layer on charge extraction and the microscopic charge processes behind the widely considered photoelectric hysteresis in perovskite solar cells.

Novel hole transport materials for organic light emitting devices

NASA Astrophysics Data System (ADS)

Shi, Jianmin; Forsythe, Eric; Morton, David

2008-08-01

Organic electronic devices generally have a layered structure with organic materials sandwiched between an anode and a cathode, such organic electronic devices of organic light-emitting diode (OLED), organic photovoltaic (OPV), organic thin-film transistor (OTFT). There are many advantages of these organic electronic devices as compared to silicon-based devices. However, one of key challenge for an organic electronic device is to minimize the charge injection barrier from electrodes to organic materials and improve the charge transport mobility. In order to overcome these circumstances, there are many approaches including, designing organic materials with minimum energy barriers and improving charge transport mobility. Ideally organic materials or complex with Ohmic contact will be the most desired.

Effect of multiple deposition of NiO layer on the performance of inverted type organic solar cell based on ZnO/P3HT:PCBM

NASA Astrophysics Data System (ADS)

Sabri, Nasehah Syamin; Lim, Eng Liang; Yap, Chi Chin; Yahaya, Muhammad; Salleh, Muhamad Mat; Jumali, Mohammad Hafizuddin Haji

2017-05-01

In this work, the effect of multiple deposition of nickel oxide (NiO) hole transport layer (HTL) on the performance of inverted type organic solar cell with a configuration of fluorine tin oxide (FTO)/zinc oxide (ZnO) nanorods/ poly(3-hexylthiopene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/NiO/silver (Ag) was investigated. The NiO nanoparticles solution was spin-coated on top of the photoactive layer (P3HT:PCBM) prior to deposition of Ag electrode. Different numbers of NiO layers (1, 2, and 4) were deposited on the photoactive layer to obtain the optimum surface morphology of HTL. The device with 2 layers of NiO exhibited the optimum power conversion efficiency of 1.10%. It is believed that the optimum NiO deposition layer gives the complete coverage at photoactive layer and forms ohmic contact between the photoactive layer and Ag electrode.

Simple single-emitting layer hybrid white organic light emitting with high color stability

NASA Astrophysics Data System (ADS)

Nguyen, C.; Lu, Z. H.

2017-10-01

Simultaneously achieving a high efficiency and color quality at luminance levels required for solid-state lighting has been difficult for white organic light emitting diodes (OLEDs). Single-emitting layer (SEL) white OLEDs, in particular, exhibit a significant tradeoff between efficiency and color stability. Furthermore, despite the simplicity of SEL white OLEDs being its main advantage, the reported device structures are often complicated by the use of multiple blocking layers. In this paper, we report a highly simplified three-layered white OLED that achieves a low turn-on voltage of 2.7 V, an external quantum efficiency of 18.9% and power efficiency of 30 lm/W at 1000 cd/cm2. This simple white OLED also shows good color quality with a color rendering index of 75, CIE coordinates (0.42, 0.46), and little color shifting at high luminance. The device consists of a SEL sandwiched between a hole transport layer and an electron transport layer. The SEL comprises a thermally activated delayer fluorescent molecule having dual functions as a blue emitter and as a host for other lower energy emitters. The improved color stability and efficiency in such a simple device structure is explained as due to the elimination of significant energy barriers at various organic-organic interfaces in the traditional devices having multiple blocking layers.

Electrical response of electron selective atomic layer deposited TiO2‑x heterocontacts on crystalline silicon substrates

NASA Astrophysics Data System (ADS)

Ahiboz, Doğuşcan; Nasser, Hisham; Aygün, Ezgi; Bek, Alpan; Turan, Raşit

2018-04-01

Integration of oxygen deficient sub-stoichiometric titanium dioxide (TiO2‑x) thin films as the electron transporting-hole blocking layer in solar cell designs are expected to reduce fabrication costs by eliminating high temperature processes while maintaining high conversion efficiencies. In this paper, we conducted a study to reveal the electrical properties of TiO2‑x thin films grown on crystalline silicon (c-Si) substrates by atomic layer deposition (ALD) technique. Effect of ALD substrate temperature, post deposition annealing, and doping type of the c-Si substrate on the interface states and TiO2‑x bulk properties were extracted by performing admittance (C-V, G-V) and current-voltage (J-V) measurements. Moreover, the asymmetry in C-V and J-V measurements between the p-n type and n-n TiO2‑x-c-Si heterojunction types were examined and the electron transport selectivity of TiO2‑x was revealed.

A series connection architecture for large-area organic photovoltaic modules with a 7.5% module efficiency

PubMed Central

Hong, Soonil; Kang, Hongkyu; Kim, Geunjin; Lee, Seongyu; Kim, Seok; Lee, Jong-Hoon; Lee, Jinho; Yi, Minjin; Kim, Junghwan; Back, Hyungcheol; Kim, Jae-Ryoung; Lee, Kwanghee

2016-01-01

The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned subcells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called aperture loss in series connection regions. Herein we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron- and hole-transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm2. PMID:26728507

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Changlei; Xiao, Chuanxiao; Yu, Yue

Through detailed device characterization using cross-sectional Kelvin probe force microscopy (KPFM) and trap density of states measurements, we identify that the J-V hysteresis seen in planar organic-inorganic hybrid perovskite solar cells (PVSCs) using SnO 2 electron selective layers (ESLs) synthesized by low-temperature plasma-enhanced atomic-layer deposition (PEALD) method is mainly caused by the imbalanced charge transportation between the ESL/perovskite and the hole selective layer/perovskite interfaces. We find that this charge transportation imbalance is originated from the poor electrical conductivity of the low-temperature PEALD SnO 2 ESL. We further discover that a facile low-temperature thermal annealing of SnO 2 ESLs can effectivelymore » improve the electrical mobility of low-temperature PEALD SnO 2 ESLs and consequently significantly reduce or even eliminate the J-V hysteresis. With the reduction of J-V hysteresis and optimization of deposition process, planar PVSCs with stabilized output powers up to 20.3% are achieved. Here, the results of this study provide insights for further enhancing the efficiency of planar PVSCs.« less

Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol.

PubMed

Chipperfield, M P; Dhomse, S S; Feng, W; McKenzie, R L; Velders, G J M; Pyle, J A

2015-05-26

Chlorine- and bromine-containing ozone-depleting substances (ODSs) are controlled by the 1987 Montreal Protocol. In consequence, atmospheric equivalent chlorine peaked in 1993 and has been declining slowly since then. Consistent with this, models project a gradual increase in stratospheric ozone with the Antarctic ozone hole expected to disappear by ∼2050. However, we show that by 2013 the Montreal Protocol had already achieved significant benefits for the ozone layer. Using a 3D atmospheric chemistry transport model, we demonstrate that much larger ozone depletion than observed has been avoided by the protocol, with beneficial impacts on surface ultraviolet. A deep Arctic ozone hole, with column values <120 DU, would have occurred given meteorological conditions in 2011. The Antarctic ozone hole would have grown in size by 40% by 2013, with enhanced loss at subpolar latitudes. The decline over northern hemisphere middle latitudes would have continued, more than doubling to ∼15% by 2013.

Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol

NASA Astrophysics Data System (ADS)

Chipperfield, M. P.; Dhomse, S. S.; Feng, W.; McKenzie, R. L.; Velders, G. J. M.; Pyle, J. A.

2015-05-01

Chlorine- and bromine-containing ozone-depleting substances (ODSs) are controlled by the 1987 Montreal Protocol. In consequence, atmospheric equivalent chlorine peaked in 1993 and has been declining slowly since then. Consistent with this, models project a gradual increase in stratospheric ozone with the Antarctic ozone hole expected to disappear by ~2050. However, we show that by 2013 the Montreal Protocol had already achieved significant benefits for the ozone layer. Using a 3D atmospheric chemistry transport model, we demonstrate that much larger ozone depletion than observed has been avoided by the protocol, with beneficial impacts on surface ultraviolet. A deep Arctic ozone hole, with column values <120 DU, would have occurred given meteorological conditions in 2011. The Antarctic ozone hole would have grown in size by 40% by 2013, with enhanced loss at subpolar latitudes. The decline over northern hemisphere middle latitudes would have continued, more than doubling to ~15% by 2013.

Photoactivated and patternable charge transport materials and their use in organic light-emitting devices

NASA Astrophysics Data System (ADS)

Liu, Jie; Lewis, Larry N.; Duggal, Anil R.

2007-06-01

Organic light-emitting devices (OLEDs) usually employ at least one organic semiconductor layer that acts as a hole-injection material. The prototypical example is a conjugated polymer such as poly(3,4-ethylenedioxythiophene) heavily p doped with polystyrene sulfonic acid. Here, the authors describe a chemical doping strategy for hole injection material formulation that enables spatial patterning of the material conductivity through optical activation. The strategy utilizes an organic photoacid generator (PAG) dispersed in a polymeric organic semiconductor host. Upon UV irradiation, the PAG decomposes and generates a strong protonic acid that subsequently p dopes the host. The authors demonstrate an OLED made with such a light-activated hole-injection material and show that arbitrary emission patterning can be accomplished. This approach may provide a simple, low cost path toward specialty lighting and signage applications for OLED technology.

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus.

PubMed

Long, Gen; Maryenko, Denis; Shen, Junying; Xu, Shuigang; Hou, Jianqiang; Wu, Zefei; Wong, Wing Ki; Han, Tianyi; Lin, Jiangxiazi; Cai, Yuan; Lortz, Rolf; Wang, Ning

2016-12-14

We demonstrate that a field-effect transistor (FET) made of few-layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum exhibits a room-temperature hole mobility of 5200 cm 2 /(Vs), being limited just by the phonon scattering. At cryogenic temperatures, the FET mobility increases up to 45 000 cm 2 /(Vs), which is five times higher compared to the mobility obtained in earlier reports. The unprecedentedly clean h-BN-BP-h-BN heterostructure exhibits Shubnikov-de Haas oscillations and a quantum Hall effect with Landau level (LL) filling factors down to v = 2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass of m * = 0.26 m 0 is measured, and a Landé g-factor of g = 2.47 is reported. Furthermore, an indication for a distinct hole transport behavior with up- and down-spin orientations is found.

Superconductivity and valence state in layered single-crystal HfAs1.67Te0.12

NASA Astrophysics Data System (ADS)

Peng, Jian; Yu, Jia; Zhang, Shuai; Chen, Genfu

2018-01-01

We report a detailed study on single crystals of HfAs1.67Te0.12 within a PbFCl-type layered structure. The single crystals of the title compound were successfully grown using a chemical transport reaction. The temperature dependence of electrical resistivity ρ (T), AC magnetic susceptibility {χ }{AC}(T) and specific heat C(T) show a bulk superconductivity with transition temperature T c = 1.67 K. The jump of C/T at T c is comparable to the traditional BCS weak-coupling model. A full H-T phase diagram is established using the results of ρ (T,H) and C(T) under fields, suggesting a rather weak anisotropy [({H}c2\\parallel {ab}(0)/{H}c2\\parallel c(0)] of 1.8 in orbital limit dominated three-dimension-like superconducting system. The mixed-valence states of Hf and As observed in the binding energy from x-ray photoelectron spectroscopy are consistent with the single-crystal x-ray diffraction analysis, indicating that the As-Te disorder prefers to occur in the [HfAs] layer and a large amount of vacancies are present in tetragonal As layer. As compared to HfAs1.7Se0.2 (T c = 0.52 K), a positive-like vacancy effect on T c has been confirmed in HfAs1.67Te0.12. The analysis of the Hall coefficient implies that the hole-type carriers dominate the transport properties, which is in good agreement with the hole pockets at Fermi surface obtained in a band structure calculation. The detailed study of single-crystal HfAs1.67Te0.12 provides a possible candidate to discuss the non-magnetic Kondo effect.

Tracking Hole Transport in DNA Hairpins Using a Phenylethynylguanine Nucleobase.

PubMed

Brown, Kristen E; Singh, Arunoday P N; Wu, Yi-Lin; Mishra, Ashutosh Kumar; Zhou, Jiawang; Lewis, Frederick D; Young, Ryan M; Wasielewski, Michael R

2017-08-30

The hole transport dynamics of DNA hairpins possessing a stilbene electron acceptor and donor along with a modified guanine (G) nucleobase, specifically 8-(4'-phenylethynyl)deoxyguanosine, or EG, have been investigated. The nearly indistinguishable oxidation potentials of EG and G and unique spectroscopic characteristics of EG +• make it well-suited for directly observing transient hole occupation during charge transport between a stilbene electron donor and acceptor. In contrast to the cation radical G +• , EG +• possesses a strong absorption near 460 nm and has a distinct Raman-active ethynyl stretch. Both spectroscopic characteristics are easily distinguished from those of the stilbene donor/acceptor radical ion chromophores. Employing EG, we observe its role as a shallow hole trap, or as an intermediate hole transport site when a deeper trap state is present. Using a combination of ultrafast absorption and stimulated Raman spectroscopies, the hole-transport dynamics are observed to be similar in systems having EG vs G bases, with small perturbations to the charge transport rates and yields. These results show EG can be deployed at specified locations throughout the sequence to report on hole occupancy, thereby enabling detailed monitoring of the hole transport dynamics with base-site specificity.

Self-cleaning effect in high quality percussion ablating of cooling hole by picosecond ultra-short pulse laser

NASA Astrophysics Data System (ADS)

Zhao, Wanqin; Yu, Zhishui

2018-06-01

Comparing with the trepanning technology, cooling hole could be processed based on the percussion drilling with higher processing efficiency. However, it is widely believed that the ablating precision of hole is lower for percussion drilling than for trepanning, wherein, the melting spatter materials around the hole surface and the recast layer inside the hole are the two main issues for reducing the ablating precision of hole, especially for the recast layer, it can't be eliminated completely even through the trepanning technology. In this paper, the self-cleaning effect which is a particular property just for percussion ablating of holes has been presented in detail. In addition, the reasons inducing the self-cleaning effect have been discussed. At last, based on the self-cleaning effect of percussion drilling, high quality cooling hole without the melting spatter materials around the hole surface and recast layer inside the hole could be ablated in nickel-based superalloy by picosecond ultra-short pulse laser.

Children's and adults' knowledge and models of reasoning about the ozone layer and its depletion

NASA Astrophysics Data System (ADS)

Leighton, Jacqueline P.; Bisanz, Gay L.

2003-01-01

As environmental concepts, the ozone layer and ozone hole are important to understand because they can profoundly influence our health. In this paper, we examined: (a) children's and adults' knowledge of the ozone layer and its depletion, and whether this knowledge increases with age' and (b) how the 'ozone layer' and 'ozone hole' might be structured as scientific concepts. We generated a standardized set of questions and used it to interview 24 kindergarten students, 48 Grade 3 students, 24 Grade 5 students, and 24 adults in university, in Canada. An analysis of participants' responses revealed that adults have more knowledge than children about the ozone layer and ozone hole, but both adults and children exhibit little knowledge about protecting themselves from the ozone hole. Moreover, only some participants exhibited 'mental models' in their conceptual understanding of the ozone layer and ozone hole. The implications of these results for health professionals, educators, and scientists are discussed.

Si photoanode protected by a metal modified ITO layer with ultrathin NiO(x) for solar water oxidation.

PubMed

Sun, Ke; Shen, Shaohua; Cheung, Justin S; Pang, Xiaolu; Park, Namseok; Zhou, Jigang; Hu, Yongfeng; Sun, Zhelin; Noh, Sun Young; Riley, Conor T; Yu, Paul K L; Jin, Sungho; Wang, Deli

2014-03-14

We report an ultrathin NiOx catalyzed Si np(+) junction photoanode for a stable and efficient solar driven oxygen evolution reaction (OER) in water. A stable semi-transparent ITO/Au/ITO hole conducting oxide layer, sandwiched between the OER catalyst and the Si photoanode, is used to protect the Si from corrosion in an alkaline working environment, enhance the hole transportation, and provide a pre-activation contact to the NiOx catalyst. The NiOx catalyzed Si photoanode generates a photocurrent of 1.98 mA cm(-2) at the equilibrium water oxidation potential (EOER = 0.415 V vs. NHE in 1 M NaOH solution). A thermodynamic solar-to-oxygen conversion efficiency (SOCE) of 0.07% under 0.51-sun illumination is observed. The successful development of a low cost, highly efficient, and stable photoelectrochemical electrode based on earth abundant elements is essential for the realization of a large-scale practical solar fuel conversion.

Transition Metal-Oxide Free Perovskite Solar Cells Enabled by a New Organic Charge Transport Layer.

PubMed

Chang, Sehoon; Han, Ggoch Ddeul; Weis, Jonathan G; Park, Hyoungwon; Hentz, Olivia; Zhao, Zhibo; Swager, Timothy M; Gradečak, Silvija

2016-04-06

Various electron and hole transport layers have been used to develop high-efficiency perovskite solar cells. To achieve low-temperature solution processing of perovskite solar cells, organic n-type materials are employed to replace the metal oxide electron transport layer (ETL). Although PCBM (phenyl-C61-butyric acid methyl ester) has been widely used for this application, its morphological instability in films (i.e., aggregation) is detrimental. Herein, we demonstrate the synthesis of a new fullerene derivative (isobenzofulvene-C60-epoxide, IBF-Ep) that serves as an electron transporting material for methylammonium mixed lead halide-based perovskite (CH3NH3PbI(3-x)Cl(x)) solar cells, both in the normal and inverted device configurations. We demonstrate that IBF-Ep has superior morphological stability compared to the conventional acceptor, PCBM. IBF-Ep provides higher photovoltaic device performance as compared to PCBM (6.9% vs 2.5% in the normal and 9.0% vs 5.3% in the inverted device configuration). Moreover, IBF-Ep devices show superior tolerance to high humidity (90%) in air. By reaching power conversion efficiencies up to 9.0% for the inverted devices with IBF-Ep as the ETL, we demonstrate the potential of this new material as an alternative to metal oxides for perovskite solar cells processed in air.

Effects of the interfacial charge injection properties of silver nanowire transparent conductive electrodes on the performance of organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Kim, Jin-Hoon; Triambulo, Ross E.; Park, Jin-Woo

2017-03-01

We investigated the charge injection properties of silver nanowire networks (AgNWs) in a composite-like structure with poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS). The composite films acted as the anodes and hole transport layers (HTLs) in organic light-emitting diodes (OLEDs). The current density (J)-voltage (V)-luminance (L) characteristics and power efficiency (ɛ) of the OLEDs were measured to determine their electrical and optical properties. The charge injection properties of the AgNWs in the OLEDs during operation were characterized via impedance spectroscopy (IS) by determining the variations in the capacitances (C) of the devices with respect to the applied V and the corresponding frequency (f). All measured results were compared with results for OLEDs fabricated on indium tin oxide (ITO) anodes. The OLEDs on AgNWs showed lower L and ɛ values than the OLEDs on ITO. It was also observed that AgNWs exhibit excellent charge injection properties and that the interfaces between the AgNWs and the HTL have very small charge injection barriers, resulting in an absence of charge carrier traps when charges move across these interfaces. However, in the AgNW-based OLED, there was a large mismatch in the number of injected holes and electrons. Furthermore, the highly conductive electrical paths of the AgNWs in the composite-like AgNW and PEDOT:PSS structure allowed a large leakage current of holes that did not participate in radiative recombination with the electrons; consequently, a lower ɛ was observed for the AgNW-based OLEDs than for the ITO-based OLEDs. To match the injection of electrons by the electron transport layer (ETL) in the AgNW-based OLED with that of holes by the AgNW/PEDOT:PSS composite anode, the electron injection barrier of the ETL was decreased by using the low work function polyethylenimine ethoxylated (PEIE) doped with n-type cesium carbonate (Cs2CO3). With the doped-PEIE, the performance of the AgNW-based OLED was significantly enhanced through the balanced injection of holes and electrons, which clearly verified our analysis results by IS.

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob, E-mail: sy96.lee@samsung.com

2015-07-27

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq){sub 2}(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq){sub 2}(acac). The lifetime of device (t{sub 95}: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

Characterization of nitride hole lateral transport in a charge trap flash memory by using a random telegraph signal method

NASA Astrophysics Data System (ADS)

Liu, Yu-Heng; Jiang, Cheng-Min; Lin, Hsiao-Yi; Wang, Tahui; Tsai, Wen-Jer; Lu, Tao-Cheng; Chen, Kuang-Chao; Lu, Chih-Yuan

2017-07-01

We use a random telegraph signal method to investigate nitride trapped hole lateral transport in a charge trap flash memory. The concept of this method is to utilize an interface oxide trap and its associated random telegraph signal as an internal probe to detect a local channel potential change resulting from nitride charge lateral movement. We apply different voltages to the drain of a memory cell and vary a bake temperature in retention to study the electric field and temperature dependence of hole lateral movement in a nitride. Thermal energy absorption by trapped holes in lateral transport is characterized. Mechanisms of hole lateral transport in retention are investigated. From the measured and modeled results, we find that thermally assisted trap-to-band tunneling is a major trapped hole emission mechanism in nitride hole lateral transport.

Influence of hole shape on sound absorption of underwater anechoic layers

NASA Astrophysics Data System (ADS)

Ye, Changzheng; Liu, Xuewei; Xin, Fengxian; Lu, Tian Jian

2018-07-01

A theoretical model is established to evaluate the sound absorption performance of underwater anechoic layers containing periodically distributed axial holes. Based on the concept for homogenized equivalent layer and on the theory of wave propagation in viscoelastic cylindrical tubes, the transfer function method is used to obtain the absorption coefficient of the anechoic layer adhered on the rigid plate. Three different types of axial holes are considered, the cylindrical, the conical and the horn shaped one. Results obtained with full finite element simulations are used to validate the model predictions. For each hole type, the vibration characteristics of the anechoic layer as well as the propagation of longitudinal and transverse waves in the layer are analyzed in detail to explore the physical mechanisms underlying its absorption performance. Furthermore, a three-dimensional finite element model for oblique incidence is developed to study the effect of hole shape at different incidence angles. The results show that two new absorption peaks appear since the oblique incidence excites two horizontal modes. Among the three hole types, the horn one achieves the best absorption performance at relatively low frequencies both in normal incidence and in oblique incidence.

[The role of BCP in electroluminescence of multilayer organic light-emitting devices].

PubMed

Deng, Zhao-Ru; Yang, Sheng-Yi; Lou, Zhi-Dong; Meng, Ling-Chuan

2009-03-01

As a hole-blocking layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is usually used in blue and white light electroluminescent devices. The ability of blocking holes of BCP layer depends on its thickness, and basically holes can tunnel through thin BCP layer. In order to know the role of BCP layer in electroluminescence (EL) of multilayer organic light-emitting diodes (OLEDs), in the present paper, the authors designed a multilayer OLED ITO/NPB/BCP/Alq3 : DCJTB/Alq3/Al and investigated the influence of thickness of BCP on the EL spectra of multilayer OLEDs at different applied voltages. The experimental data show that thin BCP layer can block holes partially and tune the energy transfer between different emissive layers, and in this way, it is easy to obtain white emission, but its EL spectra will change with the applied voltages. The EL spectra of multilayer device will remain relatively stable when BCP layer is thick enough, and the holes can hardly tunnel through when the thickness of BCP layer is more than 15 nm. Furthermore, the stability of EL spectra of the multilayer OLED at different applied voltages was discussed.

Specific features of waveguide recombination in laser structures with asymmetric barrier layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polubavkina, Yu. S., E-mail: polubavkina@mail.ru; Zubov, F. I.; Moiseev, E. I.

2017-02-15

The spatial distribution of the intensity of the emission caused by recombination appearing at a high injection level (up to 30 kA/cm{sup 2}) in the waveguide layer of a GaAs/AlGaAs laser structure with GaInP and AlGaInAs asymmetric barrier layers is studied by means of near-field scanning optical microscopy. It is found that the waveguide luminescence in such a laser, which is on the whole less intense as compared to that observed in a similar laser without asymmetric barriers, is non-uniformly distributed in the waveguide, so that the distribution maximum is shifted closer to the p-type cladding layer. This can bemore » attributed to the ability of the GaInP barrier adjoining the quantum well on the side of the n-type cladding layer to suppress the hole transport.« less

Efficiency Enhancement of Hybrid Perovskite Solar Cells with MEH-PPV Hole-Transporting Layers

PubMed Central

Chen, Hsin-Wei; Huang, Tzu-Yen; Chang, Ting-Hsiang; Sanehira, Yoshitaka; Kung, Chung-Wei; Chu, Chih-Wei; Ikegami, Masashi; Miyasaka, Tsutomu; Ho, Kuo-Chuan

2016-01-01

In this study, hybrid perovskite solar cells are fabricated using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT) as dopant-free hole-transporting materials (HTMs), and two solution processes (one- and two-step methods, respectively) for preparing methylammonium lead iodide perovskite. By optimizing the concentrations and solvents of MEH-PPV solutions, a power conversion efficiency of 9.65% with hysteresis-less performance is achieved, while the device with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′spirobifluorene (Spiro-OMeTAD) doped with lithium salts and tert-butylpyridine (TBP) exhibits an efficiency of 13.38%. This result shows that non-doped MEH-PPV is a suitable, low-cost HTM for efficient polymer-based perovskite solar cells. The effect of different morphologies of methylammonium lead iodide perovskite on conversion efficiency is also investigated by incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectroscopy (EIS). PMID:27698464

Interplay between efficiency and device architecture for small molecule organic solar cells.

PubMed

Williams, Graeme; Sutty, Sibi; Aziz, Hany

2014-06-21

Small molecule organic solar cells (OSCs) have experienced a resurgence of interest over their polymer solar cell counterparts, owing to their improved batch-to-batch (thus, cell-to-cell) reliability. In this systematic study on OSC device architecture, we investigate five different small molecule OSC structures, including the simple planar heterojunction (PHJ) and bulk heterojunction (BHJ), as well as several planar-mixed structures. The different OSC structures are studied over a wide range of donor:acceptor mixing concentrations to gain a comprehensive understanding of their charge transport behavior. Transient photocurrent decay measurements provide crucial information regarding the interplay between charge sweep-out and charge recombination, and ultimately hint toward space charge effects in planar-mixed structures. Results show that the BHJ/acceptor architecture, comprising a BHJ layer with high C60 acceptor content, generates OSCs with the highest performance by balancing charge generation with charge collection. The performance of other device architectures is largely limited by hole transport, with associated hole accumulation and space charge effects.

Impact of Interfacial Layers in Perovskite Solar Cells.

PubMed

Cho, An-Na; Park, Nam-Gyu

2017-10-09

Perovskite solar cells (PCSs) are composed of organic-inorganic lead halide perovskite as the light harvester. Since the first report on a long-term-durable, 9.7 % efficient, solid-state perovskite solar cell, organic-inorganic halide perovskites have received considerable attention because of their excellent optoelectronic properties. As a result, a power conversion efficiency (PCE) exceeding 22 % was certified. Controlling the grain size, grain boundary, morphology, and defects of the perovskite layer is important for achieving high efficiency. In addition, interfacial engineering is equally or more important to further improve the PCE through better charge collection and a reduction in charge recombination. In this Review, the type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures. Four different interfaces of fluorine-doped tin oxide (FTO)/electron-transport layer (ETL), ETL/perovskite, perovskite/hole-transport layer (HTL), and HTL/metal are classified, and their roles are investigated. The effects of interfacial engineering with organic or inorganic materials on photovoltaic performance are described in detail. Grain-boundary engineering is also included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-voltage organic field effect transistors with a 2-tridecyl[1]benzothieno[3,2-b][1]benzothiophene semiconductor layer.

PubMed

Amin, Atefeh Y; Khassanov, Artoem; Reuter, Knud; Meyer-Friedrichsen, Timo; Halik, Marcus

2012-10-10

An asymmetric n-alkyl substitution pattern was realized in 2-tridecyl[1]benzothieno[3,2-b][1]benzothiophene (C(13)-BTBT) in order to improve the charge transport properties in organic thin-film transistors. We obtained large hole mobilities up to 17.2 cm(2)/(V·s) in low-voltage operating devices. The large mobility is related to densely packed layers of the BTBT π-systems at the channel interface dedicated to the substitution motif and confirmed by X-ray reflectivity measurements. The devices exhibit promising stability in continuous operation for several hours in ambient air.

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films.

PubMed

Moia, Davide; Szumska, Anna; Vaissier, Valérie; Planells, Miquel; Robertson, Neil; O'Regan, Brian C; Nelson, Jenny; Barnes, Piers R F

2016-10-12

Charge recombination between oxidized dyes attached to mesoporous TiO 2 and electrons in the TiO 2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modeled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO 2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.

Charge Transport in Metal Oxides: A Theoretical Study of Hematite α-Fe2O3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iordanova, Nellie I.; Dupuis, Michel; Rosso, Kevin M.

2005-04-08

Transport of conduction electrons and holes through the lattice of ??Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e. the reorganization energy and the electronic coupling matrix element that enter Marcus? theory. The calculation of the electronic couplingmore » followed the Generalized Mulliken-Hush approach using the complete active space self-consistent field (CASSCF) method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c-axis, in good accord with experimental data. The anisotropy arises from the slowness of both electron and hole mobility across basal oxygen planes relative to that within iron bi-layers between basal oxygen planes. Interestingly, for elementary reaction steps along either of the directions considered, there is only approximately one order of magnitude difference in mobility between electrons and holes, in contrast to accepted classical arguments. Our findings indicate that the most important quantity underlying mobility differences is the electronic coupling, albeit the reorganization energy contributes as well. The large values computed for the electronic coupling suggest that charge transport reactions in hematite are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Fe?Fe donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.« less

p-Type semiconducting nickel oxide as an efficiency-enhancing anode interfacial layer in polymer bulk-heterojunction solar cells

PubMed Central

Irwin, Michael D.; Buchholz, D. Bruce; Hains, Alexander W.; Chang, Robert P. H.; Marks, Tobin J.

2008-01-01

To minimize interfacial power losses, thin (5–80 nm) layers of NiO, a p-type oxide semiconductor, are inserted between the active organic layer, poly(3-hexylthiophene) (P3HT) + [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), and the ITO (tin-doped indium oxide) anode of bulk-heterojunction ITO/P3HT:PCBM/LiF/Al solar cells. The interfacial NiO layer is deposited by pulsed laser deposition directly onto cleaned ITO, and the active layer is subsequently deposited by spin-coating. Insertion of the NiO layer affords cell power conversion efficiencies as high as 5.2% and enhances the fill factor to 69% and the open-circuit voltage (Voc) to 638 mV versus an ITO/P3HT:PCBM/LiF/Al control device. The value of such hole-transporting/electron-blocking interfacial layers is clearly demonstrated and should be applicable to other organic photovoltaics.

MgO Nanoparticle Modified Anode for Highly Efficient SnO2-Based Planar Perovskite Solar Cells.

PubMed

Ma, Junjie; Yang, Guang; Qin, Minchao; Zheng, Xiaolu; Lei, Hongwei; Chen, Cong; Chen, Zhiliang; Guo, Yaxiong; Han, Hongwei; Zhao, Xingzhong; Fang, Guojia

2017-09-01

Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO 2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO 2 :F (FTO) electrode and SnO 2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO-modified FTO/SnO 2 as compared to FTO/SnO 2 , such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron-hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn-doped In 2 O 3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole-blocking layer exhibits a remarkable improvement of all J-V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO 2 ETL by transparent conductive electrode surface modification.

Graphene interfaced perovskite solar cells: Role of graphene flake size

NASA Astrophysics Data System (ADS)

Sakorikar, Tushar; Kavitha, M. K.; Tong, Shi Wun; Vayalamkuzhi, Pramitha; Loh, Kian Ping; Jaiswal, Manu

2018-04-01

Graphene interfaced inverted planar heterojunction perovskite solar cells are fabricated by facile solution method and studied its potential as hole conducting layer. Reduced graphene oxide (rGO) with small and large flake size and Polyethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) are utilized as hole conducting layers in different devices. For the solar cell employing PEDOT:PSS as hole conducting layer, 3.8 % photoconversion efficiency is achieved. In case of solar cells fabricated with rGO as hole conducting layer, the efficiency of the device is strongly dependent on flake size. With all other fabrication conditions kept constant, the efficiency of graphene-interfaced solar cell improves by a factor of 6, by changing the flake size of graphene oxide. We attribute this effect to uniform coverage of graphene layer and improved electrical percolation network.

Electrode quenching control for highly efficient CsPbBr3 perovskite light-emitting diodes via surface plasmon resonance and enhanced hole injection by Au nanoparticles.

PubMed

Meng, Yan; Wu, Xiaoyan; Xiong, Ziyang; Lin, Chunyan; Xiong, Zuhong; Blount, Ethan; Chen, Ping

2018-04-27

Compared to organic-inorganic hybrid metal halide perovskites, all-inorganic cesium lead halides (e.g, CsPbBr 3 ) hold greater promise in being emissive materials for light-emitting diodes owing to their superior optoelectronic properties as well as their higher stabilities. However, there is still considerable potential for breakthroughs in the current efficiency of CsPbBr 3 perovskite light-emitting diodes (PeLEDs). Electrode quenching is one of the main problems limiting the current efficiency of PeLEDs when poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is used as the hole injection layer. In this work, electrode quenching control was realized via incorporating Au NPs into PEDOT:PSS. As a result, the CsPbBr 3 PeLEDs realized an improvement in maximum luminescence ranging from ∼2348 to ∼7660 cd m -2 (∼226% enhancement) and current efficiency from 1.65 to 3.08 cd A -1 (∼86% enhancement). Such substantial enhancement of the electroluminescent performance can be attributed to effective electrode quenching control at the PEDOT:PSS/CsPbBr 3 perovskite interface via the combined effects of local surface plasma resonance coupling and enhanced hole transportation in the PEDOT:PSS layer by Au nanoparticles.

Electrode quenching control for highly efficient CsPbBr3 perovskite light-emitting diodes via surface plasmon resonance and enhanced hole injection by Au nanoparticles

NASA Astrophysics Data System (ADS)

Meng, Yan; Wu, Xiaoyan; Xiong, Ziyang; Lin, Chunyan; Xiong, Zuhong; Blount, Ethan; Chen, Ping

2018-04-01

Compared to organic-inorganic hybrid metal halide perovskites, all-inorganic cesium lead halides (e.g, CsPbBr3) hold greater promise in being emissive materials for light-emitting diodes owing to their superior optoelectronic properties as well as their higher stabilities. However, there is still considerable potential for breakthroughs in the current efficiency of CsPbBr3 perovskite light-emitting diodes (PeLEDs). Electrode quenching is one of the main problems limiting the current efficiency of PeLEDs when poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is used as the hole injection layer. In this work, electrode quenching control was realized via incorporating Au NPs into PEDOT:PSS. As a result, the CsPbBr3 PeLEDs realized an improvement in maximum luminescence ranging from ˜2348 to ˜7660 cd m-2 (˜226% enhancement) and current efficiency from 1.65 to 3.08 cd A-1 (˜86% enhancement). Such substantial enhancement of the electroluminescent performance can be attributed to effective electrode quenching control at the PEDOT:PSS/CsPbBr3 perovskite interface via the combined effects of local surface plasma resonance coupling and enhanced hole transportation in the PEDOT:PSS layer by Au nanoparticles.

Nonradiative recombination centers and electrical aging of organic light-emitting diodes: Direct connection between accumulation of trapped charge and luminance loss

NASA Astrophysics Data System (ADS)

Kondakov, D. Y.; Sandifer, J. R.; Tang, C. W.; Young, R. H.

2003-01-01

Organic light-emitting diodes (OLEDs) are attractive for display applications because of their high brightness, low driving voltage, and tunable color. Their operating lifetimes, hundreds or thousands of hours, are sufficient for only a limited range of applications. The luminance efficiency decreases gradually as the device is operated (electrically aged), for reasons that are poorly understood. A prototypical OLED has the structure anode|HTL|ETL|cathode, where the HTL and ETL are hole- and electron-transporting layers, and the recombination and emission occur at or near the HTL|ETL interface. We find that the decreasing luminance efficiency is linearly correlated with an accumulation of immobile positive charge at the HTL|ETL interface, and the magnitude of the charge is comparable to the total charge at that interface when an unaged device is operated. A natural explanation of the connection between the two phenomena is that electrical aging either generates hole traps (and trapped holes) or drives metal ions into the device, and that either species act as nonradiative recombination centers. To estimate the accumulating immobile charge and determine its location, we use a variant of a recently introduced capacitance versus voltage technique. In the prototypical OLEDs described here, the HTL is a ca. 1000 Å layer of NPB, and the ETL is a 300-1800 Å layer of Alq3. A device with an additional "emission layer" (EML) of an anthracene derivative between the HTL and ETL, in which the electroluminescence spectrum is characteristic of the EML, behaved similarly. We surmise that the phenomena reported here may be common to a wider variety of OLED structures and compositions.

How to regulate energy levels and hole mobility of spiro-type hole transport materials in perovskite solar cells.

PubMed

Chi, Wei-Jie; Sun, Ping-Ping; Li, Ze-Sheng

2016-10-21

Methoxyaniline-based organic small molecules with three-dimensional structure have been proven as the most promising hole conductor for state-of-the-art perovskite devices. A fundamental understanding of the electronic properties and hole transport behavior of spiro-CPDT analogues, which is dependent on the number and position of the -OCH 3 groups, is significant for their potential applications as hole transport materials of perovskite solar cells. Our results from density functional theory calculations indicate that meta-substitution is more beneficial to reduce the highest occupied molecular orbital (HOMO) levels of molecules compared with ortho- and para-substitution. Furthermore, the hole mobility can be improved by ortho-substitution or mixed ortho- and para-substitution. Most interestingly, it is found that the improvement in hole mobility is at the expense of raising the HOMO level of spiro-CPDT analogues. These results can be useful in the process of designing and synthesizing excellent hole transport materials with suitable HOMO levels and high hole mobility.

All Solution-processed Stable White Quantum Dot Light-emitting Diodes with Hybrid ZnO@TiO2 as Blue Emitters

PubMed Central

Chen, Jing; Zhao, Dewei; Li, Chi; Xu, Feng; Lei, Wei; Sun, Litao; Nathan, Arokia; Sun, Xiao Wei

2014-01-01

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. However, it is challenging to integrate various QD emitters into one device and also to obtain efficient blue QDs. Here, we report a simply solution-processed white QD-LED using a hybrid ZnO@TiO2 as electron injection layer and ZnCdSeS QD emitters. The white emission is obtained by integrating the yellow emission from QD emitters and the blue emission generated from hybrid ZnO@TiO2 layer. We show that the performance of white QD-LEDs can be adjusted by controlling the driving force for hole transport and electroluminescence recombination region via varying the thickness of hole transport layer. The device is demonstrated with a maximum luminance of 730 cd/m2 and power efficiency of 1.7 lm/W, exhibiting the Commission Internationale de l'Enclairage (CIE) coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 96 h at its initial luminance of 730 cd/m2, primarily due to the fact that the device with hybrid ZnO@TiO2 has low leakage current and is insensitive to the oxygen and the moisture. These results indicate that hybrid ZnO@TiO2 provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices. PMID:24522341

Efficient Long-Range Hole Transport Through G-Quadruplexes.

PubMed

Wu, Jingyuan; Meng, Zhenyu; Lu, Yunpeng; Shao, Fangwei

2017-10-09

DNA offers a means of long-range charge transport for biology and electric nanodevices. Here, a series of tetra-stranded G-quadruplexes were assembled within a dendritic DNA architecture to explore oxidative charge transport (hole transport) through the G-quadruplex. Efficient charge transport was achieved over 28 Å upon UV irradiation. Over a longer G-quadruplex bridge, hole transport was escalated to a higher efficiency, which resulted in a higher yield than that of the optimal duplex DNA for charge transport, that is, the adenine tract. Efficient long-range hole transport suggests tetra-stranded G-quadruplexes, instead of an oxidation hotspot, hold better potential as an electron conduit than duplex DNA. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanostructured Electron-Selective Interlayer for Efficient Inverted Organic Solar Cells.

PubMed

Song, Jiyun; Lim, Jaehoon; Lee, Donggu; Thambidurai, M; Kim, Jun Young; Park, Myeongjin; Song, Hyung-Jun; Lee, Seonghoon; Char, Kookheon; Lee, Changhee

2015-08-26

We report a unique nanostructured electron-selective interlayer comprising of In-doped ZnO (ZnO:In) and vertically aligned CdSe tetrapods (TPs) for inverted polymer:fullerene bulkheterojunction (BHJ) solar cells. With dimension-controlled CdSe TPs, the direct inorganic electron transport pathway is provided, resulting in the improvement of the short circuit current and fill factor of devices. We demonstrate that the enhancement is attributed to the roles of CdSe TPs that reduce the recombination losses between the active layer and buffer layer, improve the hole-blocking as well as electron-transporting properties, and simultaneously improve charge collection characteristics. As a result, the power conversion efficiency of PTB7:PC70BM based solar cell with nanostructured CdSe TPs increases to 7.55%. We expect this approach can be extended to a general platform for improving charge extraction in organic solar cells.

Development of Efficient and Stable Inverted Bulk Heterojunction (BHJ) Solar Cells Using Different Metal Oxide Interfaces

PubMed Central

Litzov, Ivan; Brabec, Christoph J.

2013-01-01

Solution-processed inverted bulk heterojunction (BHJ) solar cells have gained much more attention during the last decade, because of their significantly better environmental stability compared to the normal architecture BHJ solar cells. Transparent metal oxides (MeOx) play an important role as the dominant class for solution-processed interface materials in this development, due to their excellent optical transparency, their relatively high electrical conductivity and their tunable work function. This article reviews the advantages and disadvantages of the most common synthesis methods used for the wet chemical preparation of the most relevant n-type- and p-type-like MeOx interface materials consisting of binary compounds AxBy. Their performance for applications as electron transport/extraction layers (ETL/EEL) and as hole transport/extraction layers (HTL/HEL) in inverted BHJ solar cells will be reviewed and discussed. PMID:28788423

Investigation of Various Active Layers for Their Performance on Organic Solar Cells.

PubMed

Huang, Pao-Hsun; Wang, Yeong-Her; Ke, Jhong-Ciao; Huang, Chien-Jung

2016-08-09

The theoretical mechanism of open-circuit voltages (V OC ) in OSCs based on various small molecule organic materials is studied. The structure under investigation is simple planar heterojunction (PHJ) by thermal vacuum evaporation deposition. The various wide band gaps of small molecule organic materials are used to enhance the power conversion efficiency (PCE). The donor materials used in the device include: Alpha-sexithiophene (α-6T), Copper(II) phthalocyanine (CuPc), boron subnaphthalocyanine chloride (SubNc) and boron Subphthalocyanine chloride (SubPc). It is combined with fullerene or SubPc acceptor material to obtain a comprehensive understanding of the charge transport behavior. It is found that the V OC of the device is largely limited by charge transport. This was associated with the space charge effects and hole accumulation. These results are attributed to the improvement of surface roughness and work function after molybdenum trioxide (MoO₃) is inserted as an anode buffer layer.

Development of Efficient and Stable Inverted Bulk Heterojunction (BHJ) Solar Cells Using Different Metal Oxide Interfaces.

PubMed

Litzov, Ivan; Brabec, Christoph J

2013-12-10

Solution-processed inverted bulk heterojunction (BHJ) solar cells have gained much more attention during the last decade, because of their significantly better environmental stability compared to the normal architecture BHJ solar cells. Transparent metal oxides (MeO x ) play an important role as the dominant class for solution-processed interface materials in this development, due to their excellent optical transparency, their relatively high electrical conductivity and their tunable work function. This article reviews the advantages and disadvantages of the most common synthesis methods used for the wet chemical preparation of the most relevant n -type- and p -type-like MeO x interface materials consisting of binary compounds A x B y . Their performance for applications as electron transport/extraction layers (ETL/EEL) and as hole transport/extraction layers (HTL/HEL) in inverted BHJ solar cells will be reviewed and discussed.

Numerical Study on Recombination Efficiency at 4,4'-Bis(2,2'-diphenylvinyl)-1,1'-spirobiphenyl/Tris(8-quinolinolato)aluminium Interface in Organic Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Hwang, Young Wook; Kim, Kwang Sik; Won, Tae Young

2013-10-01

In this paper, we report our numerical study on the electrical and optical properties of the organic light emitting diodes (OLEDs) devices with n-doped layer, which is inserted for the purpose of reducing the interface barrier height between the cathode and the electron transport layer (ETL). We performed finite element method (FEM) simulation on OLEDs in order to understand the transport behavior of carriers, recombination kinetics, and emission property. Our model includes Poisson's equation, continuity equation to account for behavior of electrons and holes and exciton continuity/transfer equation to account for recombination of carriers. We employ the multilayer structure which consists of indium tin oxide (ITO); 2,2',7,7'-tetrakis(N,N-diphenylamine)-9,9'-spirobi-fluorene (S-TAD); 4,4'-bis(2,2'-diphenylvinyl)-1,1'-spirobiphenyl (S-DPVBi); tris(8-quinolinolato)aluminium (Alq3); calcium (Ca).

Enhanced hole transport in InGaN/GaN multiple quantum well light-emitting diodes with a p-type doped quantum barrier.

PubMed

Ji, Yun; Zhang, Zi-Hui; Tan, Swee Tiam; Ju, Zhen Gang; Kyaw, Zabu; Hasanov, Namig; Liu, Wei; Sun, Xiao Wei; Demir, Hilmi Volkan

2013-01-15

We study hole transport behavior of InGaN/GaN light-emitting diodes with the dual wavelength emission method. It is found that at low injection levels, light emission is mainly from quantum wells near p-GaN, indicating that hole transport depth is limited in the active region. Emission from deeper wells only occurs under high current injection. However, with Mg-doped quantum barriers, holes penetrate deeper within the active region even under low injection, increasing the radiative recombination. Moreover, the improved hole transport leads to reduced forward voltage and enhanced light generation. This is also verified by numerical analysis of hole distribution and energy band structure.

Universal optimal hole-doping concentration in single-layer high-temperature cuprate superconductors

NASA Astrophysics Data System (ADS)

Honma, T.; Hor, P. H.

2006-09-01

We argue that in cuprate physics there are two types, hole content per CuO2 plane (Ppl) and the corresponding hole content per unit volume (P3D), of hole-doping concentrations for addressing physical properties that are two dimensional (2D) and three dimensional (3D) in nature, respectively. We find that the superconducting transition temperature (Tc) varies systematically with P3D as a superconducting 'dome' with a universal optimal hole-doping concentration of P3Dopt = 1.6 × 1021 cm-3 for single-layer high-temperature superconductors. We suggest that P3Dopt determines the upper bound of the electronic energy of underdoped single-layer high-Tc cuprates.

The Hole in the Ozone Layer.

ERIC Educational Resources Information Center

Hamers, Jeanne S.; Jacob, Anthony T.

This document contains information on the hole in the ozone layer. Topics discussed include properties of ozone, ozone in the atmosphere, chlorofluorocarbons, stratospheric ozone depletion, effects of ozone depletion on life, regulation of substances that deplete the ozone layer, alternatives to CFCs and Halons, and the future of the ozone layer.…

Internal retinal layer thickness and macular migration after internal limiting membrane peeling in macular hole surgery.

PubMed

Faria, Mun Y; Ferreira, Nuno P; Mano, Sofia; Cristóvao, Diana M; Sousa, David C; Monteiro-Grillo, Manuel E

2018-05-01

To provide a spectral-domain optical coherence tomography (SD-OCT)-based analysis of retinal layers thickness and nasal displacement of closed macular hole after internal limiting membrane peeling in macular hole surgery. In this nonrandomized prospective interventional study, 36 eyes of 32 patients were subjected to pars plana vitrectomy and 3.5 mm diameter internal limiting membrane (ILM) peeling for idiopathic macular hole (IMH). Nasal and temporal internal retinal layer thickness were assessed with SD-OCT. Each scan included optic disc border so that distance between optic disc border and fovea were measured. Thirty-six eyes had a successful surgery with macular hole closure. Total nasal retinal thickening (p<0.001) and total temporal retinal thinning (p<0.0001) were observed. Outer retinal layers increased thickness after surgery (nasal p<0.05 and temporal p<0.01). Middle part of inner retinal layers (mIRL) had nasal thickening (p<0.001) and temporal thinning (p<0.05). The mIRL was obtained by deducting ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL) thickness from overall thickness of the inner retinal layer. Papillofoveal distance was shorter after ILM peeling in macular hole surgery (3,651 ± 323 μm preoperatively and 3,361 ± 279 μm at 6 months; p<0.0001). Internal limiting membrane peel is associated with important alteration in inner retinal layer architecture, with thickening of mIRL and shortening of papillofoveal distance. These factors may contribute to recovery of disrupted foveal photoreceptor and vision improvement after IMH closure.

Performance Enhancement of Organic Light-Emitting Diodes Using Electron-Injection Materials of Metal Carbonates

NASA Astrophysics Data System (ADS)

Shin, Jong-Yeol; Kim, Tae Wan; Kim, Gwi-Yeol; Lee, Su-Min; Shrestha, Bhanu; Hong, Jin-Woong

2016-05-01

Performance of organic light-emitting diodes was investigated depending on the electron-injection materials of metal carbonates (Li2CO3 and Cs2CO3 ); and number of layers. In order to improve the device efficiency, two types of devices were manufactured by using the hole-injection material (Teflon-amorphous fluoropolymer -AF) and electron-injection materials; one is a two-layer reference device ( ITO/Teflon-AF/Alq3/Al ) and the other is a three-layer device (ITO/Teflon-AF/Alq3/metal carbonate/Al). From the results of the efficiency for the devices with hole-injection layer and electron-injection layer, it was found that the electron-injection layer affects the electrical properties of the device more than the hole-injection layer. The external-quantum efficiency for the three-layer device with Li2CO3 and Cs2CO3 layer is improved by approximately six and eight times, respectively, compared with that of the two-layer reference device. It is thought that a use of electron-injection layer increases recombination rate of charge carriers by the active injection of electrons and the blocking of holes.

Diverse carrier mobility of monolayer BNC x : a combined density functional theory and Boltzmann transport theory study.

PubMed

Wu, Tao; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2017-10-19

BNC x monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC x (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC 2 -1 is a material with very small band gap (0.02 eV) among all the structures while other BNC x monolayers are semiconductors with band gap ranging from 0.51 eV to 1.32 eV. The carrier mobility of BNC x varies considerably from tens to millions of cm 2 V -1 s -1 . For BNC 2 -1, the hole mobility and electron mobility along both x and y directions can reach 10 5 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNC x monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC 4 , its hole mobility along the y direction and electron mobility along the x direction unexpectedly reach 10 6 orders of magnitude, even higher than that of graphene. Our findings suggest that BNC x layered materials with the proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices.

Diverse carrier mobility of monolayer BNC x : a combined density functional theory and Boltzmann transport theory study

NASA Astrophysics Data System (ADS)

Wu, Tao; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2017-11-01

BNC x monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC x (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC2-1 is a material with very small band gap (0.02 eV) among all the structures while other BNC x monolayers are semiconductors with band gap ranging from 0.51 eV to 1.32 eV. The carrier mobility of BNC x varies considerably from tens to millions of cm2 V-1 s-1. For BNC2-1, the hole mobility and electron mobility along both x and y directions can reach 105 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNC x monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC4, its hole mobility along the y direction and electron mobility along the x direction unexpectedly reach 106 orders of magnitude, even higher than that of graphene. Our findings suggest that BNC x layered materials with the proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices.

A Methoxydiphenylamine-Substituted Carbazole Twin Derivative: An Efficient Hole-Transporting Material for Perovskite Solar Cells.

PubMed

Gratia, Paul; Magomedov, Artiom; Malinauskas, Tadas; Daskeviciene, Maryte; Abate, Antonio; Ahmad, Shahzada; Grätzel, Michael; Getautis, Vytautas; Nazeeruddin, Mohammad Khaja

2015-09-21

The small-molecule-based hole-transporting material methoxydiphenylamine-substituted carbazole was synthesized and incorporated into a CH3NH3PbI3 perovskite solar cell, which displayed a power conversion efficiency of 16.91%, the second highest conversion efficiency after that of Spiro-OMeTAD. The investigated hole-transporting material was synthesized in two steps from commercially available and relatively inexpensive starting reagents. Various electro-optical measurements (UV/Vis, IV, thin-film conductivity, hole mobility, DSC, TGA, ionization potential) have been carried out to characterize the new hole-transporting material. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multifunctional Fischer Aminocarbene Complexes as Hole or Electron Transporting Layers in Organic Solar Cells.

PubMed

Vidal-García, Pablo; Sánchez-Vergara, María Elena; Corona-Sánchez, Ricardo; Jiménez-Sandoval, Omar; Mercado, Efraín Gutiérrez-Rivas; Toscano, Rubén A; Álvarez-Toledano, Cecilio

2018-03-24

A new series of Fischer carbenes have been synthetized and examined as hole-transporting or electron-transporting layers (HTLs or ETLs) in the fabrication of organic solar cells (OSCs). The synthesis of three Fischer aminocarbene complexes with the general formula [Cr(CO)₅{C(NHCH₂)Ar}] (Ar = 2-pyridyl ( 3a ), 3-pyridyl ( 3b ) and 4-pyridyl ( 3c )) is reported. The molecular structure of complex 3b has been confirmed by X-ray analysis. In order to study the possible applications of the three Fischer aminocarbenes in OSCs, thin films of these complexes were prepared using a vacuum deposition process. These organometallic films were chemically and morphologically characterized by IR spectroscopy, SEM, AFM and XRD. According to the IR and Tauc analysis, the vacuum deposition process generates thin films free of impurities with an activation energy of 4.0, 2.7 and 2.1 eV for 3a , 3b y 3c, respectively. The UV-vis spectra of the amorphous aminocarbene films show that they are practically transparent to the visible radiation of the electromagnetic spectrum. This is due to the fact that their absorption is located mainly in the ultraviolet range. Two OSCs with bulk-heterojunction configuration were manufactured in order to prove the use of the aminocarbenes as ETL o HTL. The aminocarbene [Cr(CO)₅{C(NHCH₂) 4-pyridyl}] ( 3c ) proved to be suitable as ETL with a fill factor (FF) of 0.23 and a short circuit current density ( J SC ) of 1.037 mA/cm².

Multiscale modeling for SiO2 atomic layer deposition for high-aspect-ratio hole patterns

NASA Astrophysics Data System (ADS)

Miyano, Yumiko; Narasaki, Ryota; Ichikawa, Takashi; Fukumoto, Atsushi; Aiso, Fumiki; Tamaoki, Naoki

2018-06-01

A multiscale simulation model is developed for optimizing the parameters of SiO2 plasma-enhanced atomic layer deposition of high-aspect-ratio hole patterns in three-dimensional (3D) stacked memory. This model takes into account the diffusion of a precursor in a reactor, that in holes, and the adsorption onto the wafer. It is found that the change in the aperture ratio of the holes on the wafer affects the concentration of the precursor near the top of the wafer surface, hence the deposition profile in the hole. The simulation results reproduced well the experimental results of the deposition thickness for the various hole aperture ratios. By this multiscale simulation, we can predict the deposition profile in a high-aspect-ratio hole pattern in 3D stacked memory. The atomic layer deposition parameters for conformal deposition such as precursor feeding time and partial pressure of precursor for wafers with various hole aperture ratios can be estimated.

Schottky diode behaviour with excellent photoresponse in NiO/FTO heterostructure

NASA Astrophysics Data System (ADS)

Saha, B.; Sarkar, K.; Bera, A.; Deb, K.; Thapa, R.

2017-10-01

Delocalization of charge carriers through formation of native defects in NiO, to achieve a good metal oxide hole transport layer was attemted in this work and thus a heterojunction of p-type NiO and n-type FTO have been prepared through sol-gel process on FTO coated glass substrate. The synthesis process was stimulated by imparting large number of OH- sites during nucleation of Ni(OH)2 on FTO, so that during oxidation through annealing Ni vacancies are introduced. The structural properties as observed from X-ray diffraction measurement indicate formation of well crystalline NiO nanoparticles. Uniform distribution of NiO nanoparticles has been observed in the images obtained from scanning electron microscope. The occurrence of p-type conductivity in the NiO film was stimulated through the formation of delocalized defect carriers originated from crystal defects like vacancies or interstitials in the lattice. Ni vacancy creates shallow levels with respect to the valance band maxima and they readily produce holes. Thus a native p-type conductivity of NiO originates from Ni vacancies. NiO was thus obtained as an auspicious hole transport medium, which creates an expedient heterojunction at the interface with FTO. Excellent rectifying behavior was observed in the electrical J-V plot obtained from the prepared heterojunction. The results are explained from the band energy diagram of the NiO/FTO heterojunction. Remarkable photoresponse has been observed in the reverse characteristics of the heterojunction caused by photon generated electron hole pairs.

Vertical Hole Transport and Carrier Localization in InAs /InAs1 -xSbx Type-II Superlattice Heterojunction Bipolar Transistors

NASA Astrophysics Data System (ADS)

Olson, B. V.; Klem, J. F.; Kadlec, E. A.; Kim, J. K.; Goldflam, M. D.; Hawkins, S. D.; Tauke-Pedretti, A.; Coon, W. T.; Fortune, T. R.; Shaner, E. A.; Flatté, M. E.

2017-02-01

Heterojunction bipolar transistors are used to measure vertical hole transport in narrow-band-gap InAs /InAs1 -xSbx type-II superlattices (T2SLs). Vertical hole mobilities (μh) are reported and found to decrease rapidly from 360 cm2/V s at 120 K to approximately 2 cm2/V s at 30 K, providing evidence that holes are confined to localized states near the T2SL valence-miniband edge at low temperatures. Four distinct transport regimes are identified: (1) pure miniband transport, (2) miniband transport degraded by temporary capture of holes in localized states, (3) hopping transport between localized states in a mobility edge, and (4) hopping transport through defect states near the T2SL valence-miniband edge. Region (2) is found to have a thermal activation energy of ɛ2=36 meV corresponding to the energy range of a mobility edge. Region (3) is found to have a thermal activation energy of ɛ3=16 meV corresponding to the hopping transport activation energy. This description of vertical hole transport is analogous to electronic transport observed in disordered amorphous semiconductors displaying Anderson localization. For the T2SL, we postulate that localized states are created by disorder in the group-V alloy of the InAs1 -xSbx hole well causing fluctuations in the T2SL valence-band energy.

Transport Properties of Thin Bismuth Films on InP (110) Surfaces by Scanning Tunneling Potentiometry

NASA Astrophysics Data System (ADS)

Feenstra, R. M.; Briner, B. G.; Chin, T. P.; Woodall, J. M.

1996-03-01

Charge transport in 20--30 Å thick Bi-films is studied by scanning tunneling potentiometry (STP) at room temperature. The Bi is deposited on cleaved InP(110) surfaces at temperatures near 140 K, yielding atomically flat films interspersed with 12 Å deep holes. The InP substrates contain conducting/insulating/conducting layers, which in cross-section are used to form contacts to the film, thus enabling lateral current densities as high as 8 × 10^6 A/cm^2 . Potential variations due to scattering of this lateral current is detected using STP, by locating the zero-crossing of current-voltage characteristics at each pixel in an image. Potential images reveal, on a coarse scale, a smooth ramp arising from the electric field due to phonon scattering in the film, from which an electron-phonon scattering length of >1000 Å is deduced. On a finer scale, potential steps 2--10 mV high are seen near surface holes and grain boundaries in the film. Detailed study of the ballistic scattering near the holes reveals a dipole shaped feature, which is identified as a residual resistivity dipole. *present address: Physics, Carnegie Mellon Univ., Pittsburgh PA 15213 **now at: Fritz-Haber-Institut, 14195 Berlin, briner@fhi-berlin.mpg.de

Efficient Carbon-Based CsPbBr3 Inorganic Perovskite Solar Cells by Using Cu-Phthalocyanine as Hole Transport Material

NASA Astrophysics Data System (ADS)

Liu, Zhiyong; Sun, Bo; Liu, Xingyue; Han, Jinghui; Ye, Haibo; Shi, Tielin; Tang, Zirong; Liao, Guanglan

2018-06-01

Metal halide perovskite solar cells (PSCs) have attracted extensive research interest for next-generation solution-processed photovoltaic devices because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication cost. Although the world's best PSC successfully achieves a considerable PCE of over 20% within a very limited timeframe after intensive efforts, the stability, high cost, and up-scaling of PSCs still remain issues. Recently, inorganic perovskite material, CsPbBr3, is emerging as a promising photo-sensitizer with excellent durability and thermal stability, but the efficiency is still embarrassing. In this work, we intend to address these issues by exploiting CsPbBr3 as light absorber, accompanied by using Cu-phthalocyanine (CuPc) as hole transport material (HTM) and carbon as counter electrode. The optimal device acquires a decent PCE of 6.21%, over 60% higher than those of the HTM-free devices. The systematic characterization and analysis reveal a more effective charge transfer process and a suppressed charge recombination in PSCs after introducing CuPc as hole transfer layer. More importantly, our devices exhibit an outstanding durability and a promising thermal stability, making it rather meaningful in future fabrication and application of PSCs.[Figure not available: see fulltext.

Thin film electronic devices with conductive and transparent gas and moisture permeation barriers

DOEpatents

Simpson, Lin Jay

2015-07-28

Thin film electronic devices (or stacks integrated with a substrate) that include a permeation barrier formed of a thin layer of metal that provides a light transmitting and electrically conductive layer, wherein the electrical conductive layer is formed on a surface of the substrate or device layer such as a transparent conducting material layer with pin holes or defects caused by manufacturing and the thin layer of metal is deposited on the conductive layer and formed from a self-healing metal that forms self-terminating oxides. A permeation plug or block is formed in or adjacent to the thin film of metal at or proximate to the pin holes to block further permeation of contaminants through the pin holes.

A Low-Temperature, Solution-Processable, Cu-Doped Nickel Oxide Hole-Transporting Layer via the Combustion Method for High-Performance Thin-Film Perovskite Solar Cells

DOE PAGES

Jung, Jae Woong; Chueh, Chu-Chen; Jen, Alex K. -Y.

2015-10-20

The promising photophysical properties of the emerging organometallic halide perovskites, such as intense broadband absorption, high charge carrier mobility, and long charge diffusion length, have enabled the rapid development in solar cells reaching over 20% power conversion effi ciency (PCE) recently. Especially, the low material cost and facile solution processability of perovskites are very attractive as next-generation photovoltaic materials for sustainable energy.

Enhancement of photoresponse property of perovskite solar cell by aluminium chloride (AlCl3)

NASA Astrophysics Data System (ADS)

Ghosh, S. S.; Sil, A.

2018-05-01

The fabrication of a three layer solar cell device is a new area of research. The formation of perovskite phase is evident from x-ray diffraction and its particle size is observed by microstructural analysis. A thin layer of gold coating over the device increases the surface conductivity. Direct contact between a SnCl2 or AlCl3 based perovskite with the gold coating increases the durability of the film but decreases the hole transport properties due to absence of an organic hole transport material. The absorbance spectroscopy analysis gives characteristic peaks showing the evidence of ITO, TiO2 (rutile) and Sn2+ complexes present in the Sn-perovskite film or Al3+ complexes present within the Al-perovskite cell. The desired absorbance near 550 nm due to Al3+ complexes causes a much higher flow of current on illumination and thus is also evidenced by the presence of comparatively high intensity PL spectra in the Al-perovskite system which occurred due to free exciton formation near band edge excitation. The fill factor of the devices is estimated as ∼0.83 and ∼0.65 for Sn-perovskite and Al-perovskite devices respectively. The PCE values of Sn-perovskite and Al-perovskite devices are calculated 0.39% and 0.96% respectively, which establish Al-perovskite film as a useful component for future solar cell device manufacturing.

Sediment erosion by Görtler vortices: the scour-hole problem

NASA Astrophysics Data System (ADS)

Hopfinger, E. J.; Kurniawan, A.; Graf, W. H.; Lemmin, U.

2004-12-01

Experimental results on sediment erosion (scour) by a plane turbulent wall jet, issuing from a sluice gate, are presented which show clearly it seems for the first time that the turbulent wall layer is destabilized by the concave curvature of the water/sediment interface. The streamwise Görtler vortices which emerge create sediment streaks or longitudinal sediment ridges. The analysis of the results in terms of Görtler instability of the wall layer indicates that the strength of these curvature-excited streamwise vortices is such that the sediment transport is primarily due to turbulence created by these vortices. Their contribution to the wall shear stress is taken to be of the same form as the normal turbulent wall shear stress. For this reason, the model developed by Hogg et al. (J. Fluid Mech. Vol. 338, 1997, p. 317) remains valid; only the numerical coefficients are affected. The logarithmic dependency of the time evolution of the scour-hole depth predicted by this model is shown to be in good agreement with experiments. New scaling laws for the quasi-steady state depth and the associated time, inspired by the Hogg et al. (1997) model are proposed. Furthermore, it is emphasized that at least two scouring regimes must be distinguished: a short-time regime after which a quasi-steady state is reached, followed by a long-time regime, leading to an asymptotic state of virtually no sediment transport.

Effects of interfacial stability between electron transporting layer and cathode on the degradation process of organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Chu, Ta-Ya; Lee, Yong-Han; Song, Ok-Keun

2007-11-01

The authors have demonstrated that the increase of electron injection barrier height between tris(8-hydroxyquinoline)aluminum (Alq3) and LiF /Al cathode is one of the most critical parameters to determine the reliability of organic light-emitting diode with the typical structure of indium tin oxide/N ,N'-bis(naphthalen-1-yl)-N ,N'-bis(phenyl) benzidine/Alq3/LiF /Al. The electrical properties of several devices (hole only, electron only, and integrated double-layered devices) have been measured in the function of operating time to analyze the bulk and interface property changes. Bulk properties of trap energy and mobility in an organic layer have been estimated by using trap-charge-limited currents and transient electroluminescence measurements.

Enhanced device performances of a new inverted top-emitting OLEDs with relatively thick Ag electrode.

PubMed

Park, So-Ra; Suh, Min Chul

2018-02-19

To improve the device performances of top-emitting organic light emitting diodes (TEOLEDs), we developed a new inverted TEOLEDs structure with silver (Ag) metal as a semi-transparent top electrode. Especially, we found that the use of relatively thick Ag electrode without using any carrier injection layer is beneficial to realize highly efficient device performances. Also, we could insert very thick overlying hole transport layer (HTL) on the emitting layer (EML) which could be very helpful to suppress the surface plasmon polariton (SPP) coupling if it is applied to the common bottom-emission OLEDs (BEOLEDs). As a result, we could realize noteworthy high current efficiency of approximately ~188.1 cd/A in our new inverted TEOLEDs with 25 nm thick Ag electrode.

Inverted polymer solar cell based on MEH-PPV/PC61BM coupled with ZnO nanoparticles as electron transport layer

NASA Astrophysics Data System (ADS)

Salem, A. M. S.; El-Sheikh, S. M.; Harraz, Farid A.; Ebrahim, S.; Soliman, M.; Hafez, H. S.; Ibrahim, I. A.; Abdel-Mottaleb, M. S. A.

2017-12-01

In this work, we demonstrate the use of annealed sol-gel derived ZnO nanoparticles acting as electron transport layer (ETL) in inverted bulk heterojunction (BHJ) polymer solar cells (PSCs). We have examined the photovoltaic performance of devices based on poly(2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV):(6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) blend system employing the ZnO nanoparticles as an ETL with CuI as hole transport layer (HTL) in comparison to the case of using the conventional HTL of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) sulfonic acid (PEDOT:PSS). The effect of the presence of another layer of ZnO macrospheres attached to the ZnO nanoparticles is also investigated. The highest power conversion efficiency (PCE) value of 1.35% was achieved for device: ITO/ZnO nanoparticles/MEH-PPV:PC61BM/CuI/Ag, which is 275% more the value obtained when CuI was replaced by PEDOT:PSS. The comprehensive analyses on structural and optical characteristics including SEM, XRD, FTIR, PL and UV-vis spectroscopy indicated that the use of the ZnO nanoparticles alone as ETL, together with the CuI as HTL could effectively reduce trap-assisted recombination and charge accumulation at the interface, which is beneficial for the enhanced device performance.

Tomographic Structural Changes of Retinal Layers after Internal Limiting Membrane Peeling for Macular Hole Surgery.

PubMed

Faria, Mun Yueh; Ferreira, Nuno P; Cristóvao, Diana M; Mano, Sofia; Sousa, David Cordeiro; Monteiro-Grillo, Manuel

2018-01-01

To highlight tomographic structural changes of retinal layers after internal limiting membrane (ILM) peeling in macular hole surgery. Nonrandomized prospective, interventional study in 38 eyes (34 patients) subjected to pars plana vitrectomy and ILM peeling for idiopathic macular hole. Retinal layers were assessed in nasal and temporal regions before and 6 months after surgery using spectral domain optical coherence tomography. Total retinal thickness increased in the nasal region and decreased in the temporal region. The retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and inner plexiform layer (IPL) showed thinning on both nasal and temporal sides of the fovea. The thickness of the outer plexiform layer (OPL) increased. The outer nuclear layer (ONL) and outer retinal layers (ORL) increased in thickness after surgery in both nasal and temporal regions. ILM peeling is associated with important alterations in the inner retinal layer architecture, with thinning of the RNFL-GCL-IPL complex and thickening of OPL, ONL, and ORL. These structural alterations can help explain functional outcome and could give indications regarding the extent of ILM peeling, even though peeling seems important for higher rate of hole closure. © 2017 S. Karger AG, Basel.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohite, Aditya; Blancon, Jean-Christophe

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are gaining an extra degree of freedom in designing and fabricating efficient optoelectronic devices based on 2D layered hybrid perovskites. Industrial applications could include low cost solar cells, LEDs, laser diodes, detectors, and other nano-optoelectronic devices. The 2D, near-single-crystalline “Ruddlesden-Popper” thin films have an out-of-plane orientation so that uninhibited charge transport occurs through the perovskite layers in planar devices. The new research finds the existence of “layer-edge-states” at the edges of the perovskite layers which are key to bothmore » high efficiency of solar cells (greater than 12 percent) and high fluorescence efficiency (a few tens of percent) for LEDs. The spontaneous conversion of excitons (bound electron-hole pairs) to free carriers via these layer-edge states appears to be the key to the improvement of the photovoltaic and light-emitting thin film layered materials.« less

Distinct oxygen hole doping in different layers of Sr₂CuO 4-δ/La₂CuO₄ superlattices

DOE PAGES

Smadici, S.; Lee, J. C. T.; Rusydi, A.; ...

2012-03-28

X-ray absorption in Sr₂CuO 4-δ/La₂CuO₄ (SCO/LCO) superlattices shows a variable occupation with doping of a hole state different from holes doped for x≲x optimal in bulk La 2-xSr xCuO₄ and suggests that this hole state is on apical oxygen atoms and polarized in the a-b plane. Considering the surface reflectivity gives a good qualitative description of the line shapes of resonant soft x-ray scattering. The interference between superlattice and surface reflections was used to distinguish between scatterers in the SCO and the LCO layers, with the two hole states maximized in different layers of the superlattice.

Dilute group III-V nitride intermediate band solar cells with contact blocking layers

DOEpatents

Walukiewicz, Wladyslaw; Yu, Kin Man

2015-02-24

An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

Dilute Group III-V nitride intermediate band solar cells with contact blocking layers

DOEpatents

Walukiewicz, Wladyslaw [Kensington, CA; Yu, Kin Man [Lafayette, CA

2012-07-31

An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

Understanding and Eliminating Hysteresis for Highly Efficient Planar Perovskite Solar Cells

DOE PAGES

Wang, Changlei; Xiao, Chuanxiao; Yu, Yue; ...

2017-05-11

Through detailed device characterization using cross-sectional Kelvin probe force microscopy (KPFM) and trap density of states measurements, we identify that the J-V hysteresis seen in planar organic-inorganic hybrid perovskite solar cells (PVSCs) using SnO 2 electron selective layers (ESLs) synthesized by low-temperature plasma-enhanced atomic-layer deposition (PEALD) method is mainly caused by the imbalanced charge transportation between the ESL/perovskite and the hole selective layer/perovskite interfaces. We find that this charge transportation imbalance is originated from the poor electrical conductivity of the low-temperature PEALD SnO 2 ESL. We further discover that a facile low-temperature thermal annealing of SnO 2 ESLs can effectivelymore » improve the electrical mobility of low-temperature PEALD SnO 2 ESLs and consequently significantly reduce or even eliminate the J-V hysteresis. With the reduction of J-V hysteresis and optimization of deposition process, planar PVSCs with stabilized output powers up to 20.3% are achieved. Here, the results of this study provide insights for further enhancing the efficiency of planar PVSCs.« less

Concentration history during pumping from a leaky aquifer with stratified initial concentration

USGS Publications Warehouse

Goode, Daniel J.; Hsieh, Paul A.; Shapiro, Allen M.; Wood, Warren W.; Kraemer, Thomas F.

1993-01-01

Analytical and numerical solutions are employed to examine the concentration history of a dissolved substance in water pumped from a leaky aquifer. Many aquifer systems are characterized by stratification, for example, a sandy layer overlain by a clay layer. To obtain information about separate hydrogeologic units, aquifer pumping tests are often conducted with a well penetrating only one of the layers. When the initial concentration distribution is also stratified (the concentration varies with elevation only), the concentration breakthrough in the pumped well may be interpreted to provide information on aquifer hydraulic and transport properties. To facilitate this interpretation, we present some simple analytical and numerical solutions for limiting cases and illustrate their application to a fractured bedrock/glacial drift aquifer system where the solute of interest is dissolved radon gas. In addition to qualitative information on water source, this method may yield estimates of effective porosity and saturated thickness (or fracture transport aperture) from a single-hole test. Little information about dispersivity is obtained because the measured concentration is not significantly affected by dispersion in the aquifer.

New cyclometalated Iridium(III) beta-dicetone complex as phosphorescent dopant in Organic light emitting devices

NASA Astrophysics Data System (ADS)

Ivanov, P.; Petrova, P.; Stanimirov, S.; Tomova, R.

2017-01-01

A new Bis[4-(benzothiazolato-N,C2‧-2-yl)-N,N-dimethylaniline]Iridium(III) acetylacetonate (Me2N-bt) 2Ir(acac) was synthesized and identified by 1H NMR and elemental analysis. The application of the new compound as a dopant in the hole transporting layer (HTL) of Organic light emitting diode (OLED) structure: HTL/EL/ETL, where HTL was N,N’-bis(3-methylphenyl)-N,N’-diphenylbenzidine (TPD), incorporated in Poly(N-vinylcarbazole) (PVK) matrix, EL - electroluminescent layer of Bis(8-hydroxy-2-methylquinoline)-(4-phenylpheno-xy)aluminum (BAlq) and ETL - electron-transporting layer of Tris-(8-hydroxyquinoline) aluminum (Alq3) or Bis[2-(2-benzothiazoly) phenolato]zinc (Zn(btz)2). We established that the electroluminescent spectra of OLEDs at different concentrations of the dopant were basically the sum of the greenish-blue emission of BAlq and yellowish-green emission of Ir complex. It was found that with increasing of the dopant concentration the relative electroluminescent intensity of Iridium complex emission increased and this of BAlq decreased and as a result the fine tuning of OLED color was observed.

Interaction of nanoparticles with lipid layers

NASA Astrophysics Data System (ADS)

Park, Jonghyun; Lu, Wei

2009-08-01

Poly (amidoamine) dendrimer nanoparticles are used extensively in diverse biological and medical applications. Examples include gene and drug delivery, where nanoparticles disrupt cell membranes to allow the transport of material into cells. The size and surface chemistry of these particles have a strong effect on their interaction with membranes. This paper proposes a three-dimensional phase-field model to investigate how the interaction drives deformation and morphological evolution of the membrane. Attention is focused on the hole-formation process in the membrane. The simulations have demonstrated that a larger amine-terminated generation 7 dendrimer, which has positive charges, causes the formation of a hole in the membrane. The displaced membrane molecules enclose the particle and form a dendrimer-filled membrane vesicle. The effect is significantly reduced for a smaller dendrimer. An acetamide-terminated dendrimer, which has a neutral charge at the surface, does not cause hole formation. These results agree with experimental observations from atomic force microscopy. The study will provide insight into the design of appropriate nanoparticle surface properties for medical applications.

Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol

PubMed Central

Chipperfield, M. P.; Dhomse, S. S.; Feng, W.; McKenzie, R. L.; Velders, G.J.M.; Pyle, J. A.

2015-01-01

Chlorine- and bromine-containing ozone-depleting substances (ODSs) are controlled by the 1987 Montreal Protocol. In consequence, atmospheric equivalent chlorine peaked in 1993 and has been declining slowly since then. Consistent with this, models project a gradual increase in stratospheric ozone with the Antarctic ozone hole expected to disappear by ∼2050. However, we show that by 2013 the Montreal Protocol had already achieved significant benefits for the ozone layer. Using a 3D atmospheric chemistry transport model, we demonstrate that much larger ozone depletion than observed has been avoided by the protocol, with beneficial impacts on surface ultraviolet. A deep Arctic ozone hole, with column values <120 DU, would have occurred given meteorological conditions in 2011. The Antarctic ozone hole would have grown in size by 40% by 2013, with enhanced loss at subpolar latitudes. The decline over northern hemisphere middle latitudes would have continued, more than doubling to ∼15% by 2013. PMID:26011106

Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layer.

PubMed

Schumann, T; Gotschke, T; Limbach, F; Stoica, T; Calarco, R

2011-03-04

GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth has been studied varying the substrate temperature, gallium beam equivalent pressure and patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes of the patterned oxide with complete suppression of the parasitic growth in between the holes. The occupation probability of a hole with a single or multiple NWs depends strongly on its diameter. The selectively grown GaN NWs have one common crystallographic orientation with respect to the Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based on the experimental data, we present a schematic model of the GaN NW formation in which a GaN pedestal is initially grown in the hole.

Transfer-printing of active layers to achieve high quality interfaces in sequentially deposited multilayer inverted polymer solar cells fabricated in air

PubMed Central

Vohra, Varun; Anzai, Takuya; Inaba, Shusei; Porzio, William; Barba, Luisa

2016-01-01

Abstract Polymer solar cells (PSCs) are greatly influenced by both the vertical concentration gradient in the active layer and the quality of the various interfaces. To achieve vertical concentration gradients in inverted PSCs, a sequential deposition approach is necessary. However, a direct approach to sequential deposition by spin-coating results in partial dissolution of the underlying layers which decreases the control over the process and results in not well-defined interfaces. Here, we demonstrate that by using a transfer-printing process based on polydimethylsiloxane (PDMS) stamps we can obtain increased control over the thickness of the various layers while at the same time increasing the quality of the interfaces and the overall concentration gradient within the active layer of PSCs prepared in air. To optimize the process and understand the influence of various interlayers, our approach is based on surface free energy, spreading parameters and work of adhesion calculations. The key parameter presented here is the insertion of high quality hole transporting and electron transporting layers, respectively above and underneath the active layer of the inverted structure PSC which not only facilitates the transfer process but also induces the adequate vertical concentration gradient in the device to facilitate charge extraction. The resulting non-encapsulated devices (active layer prepared in air) demonstrate over 40% increase in power conversion efficiency with respect to the reference spin-coated inverted PSCs. PMID:27877901

Inverted bulk-heterojunction solar cell with cross-linked hole-blocking layer

PubMed Central

Udum, Yasemin; Denk, Patrick; Adam, Getachew; Apaydin, Dogukan H.; Nevosad, Andreas; Teichert, Christian; S. White, Matthew.; S. Sariciftci, Niyazi.; Scharber, Markus C.

2014-01-01

We have developed a hole-blocking layer for bulk-heterojunction solar cells based on cross-linked polyethylenimine (PEI). We tested five different ether-based cross-linkers and found that all of them give comparable solar cell efficiencies. The initial idea that a cross-linked layer is more solvent resistant compared to a pristine PEI layer could not be confirmed. With and without cross-linking, the PEI layer sticks very well to the surface of the indium–tin–oxide electrode and cannot be removed by solvents used to process PEI or common organic semiconductors. The cross-linked PEI hole-blocking layer functions for multiple donor–acceptor blends. We found that using cross-linkers improves the reproducibility of the device fabrication process. PMID:24817837

Study of Exciton Hopping Transport in PbS Colloidal Quantum Dot Thin Films Using Frequency- and Temperature-Scanned Photocarrier Radiometry

NASA Astrophysics Data System (ADS)

Hu, Lilei; Mandelis, Andreas; Melnikov, Alexander; Lan, Xinzheng; Hoogland, Sjoerd; Sargent, Edward H.

2017-01-01

Solution-processed colloidal quantum dots (CQDs) are promising materials for realizing low-cost, large-area, and flexible photovoltaic devices. The study of charge carrier transport in quantum dot solids is essential for understanding energy conversion mechanisms. Recently, solution-processed two-layer oleic-acid-capped PbS CQD solar cells with one layer treated with tetrabutylammonium iodide (TBAI) serving as the main light-absorbing layer and the other treated with 1,2-ethanedithiol (EDT) acting as an electron-blocking/hole-extraction layer were reported. These solar cells demonstrated a significant improvement in power conversion efficiency of 8.55% and long-term air stability. Coupled with photocarrier radiometry measurements, this work used a new trap-state mediated exciton hopping transport model, specifically for CQD thin films, to unveil and quantify exciton transport mechanisms through the extraction of hopping transport parameters including exciton lifetimes, hopping diffusivity, exciton detrapping time, and trap-state density. It is shown that PbS-TBAI has higher trap-state density than PbS-EDT that results in higher PbS-EDT exciton lifetimes. Hopping diffusivities of both CQD thin film types show similar temperature dependence, particularly higher temperatures yield higher hopping diffusivity. The higher diffusivity of PbS-TBAI compared with PbS-EDT indicates that PbS-TBAI is a much better photovoltaic material than PbS-EDT. Furthermore, PCR temperature spectra and deep-level photothermal spectroscopy provided additional insights to CQD surface trap states: PbS-TBAI thin films exhibit a single dominant trap level, while PbS-EDT films with lower trap-state densities show multiple trap levels.

Graphene Oxide Derivatives as Hole- and Electron-Extraction Layers for High-Performance Polymer Solar Cells

DTIC Science & Technology

2013-11-20

Graphene oxide derivatives as hole- and electron- extraction layers for high-performance polymer solar cells Jun Liu,*a Michael Durstockb and Liming...oxide (GO) and its derivatives have been used as a new class of efficient hole- and electron-extraction materials in polymer solar cells (PSCs...new class of efficient hole- and electron-extraction materials in polymer solar cells (PSCs). Highly efficient and stable PSCs have been fabricated

Aluminum-nanodisc-induced collective lattice resonances: Controlling the light extraction in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Auer-Berger, Manuel; Tretnak, Veronika; Wenzl, Franz-Peter; Krenn, Joachim R.; List-Kratochvil, Emil J. W.

2017-10-01

We examine aluminum-nanodisc-induced collective lattice resonances as a means to enhance the efficiency of organic light emitting diodes. Thus, nanodisc arrays were embedded in the hole transporting layer of a solution-processed phosphorescent organic blue-light emitting diode. Through extinction spectroscopy, we confirm the emergence of array-induced collective lattice resonances within the organic light emitting diode. Through finite-difference time domain simulations, we show that the collective lattice resonances yield an enhancement of the electric field intensity within the emissive layer. The effectiveness for improving the light generation and light outcoupling is demonstrated by electro-optical characterization, realizing a gain in a current efficiency of 35%.

Enhanced Emission Efficiency in Organic Light-Emitting Diodes Using Deoxyribonucleic Acid Complex as an Electron Blocking Layer

DTIC Science & Technology

2006-04-28

1. Color online Photographs of EL emission from several devices: a green Alq3 baseline OLED at 25 V 707 mA/cm2—590 cd/m2, 0.35 cd/A; b green... Alq3 BioLED with DNA EBL at 25 V 308 mA/cm2—21 100 cd/m2, 6.56 cd/A; c blue NPB baseline OLED at 20 V 460 mA/cm2—700 cd/m2, 0.14 cd/A; d blue...al. Appl. Phys. Lett. 88, 171109 2006NPB N ,N-bisnaphthalene-1-yl-N ,N-bisphenyl benzi- dine hole transport layer HTL; Alq3 tris-8

All-inorganic large-area low-cost and durable flexible perovskite solar cells using copper foil as a substrate.

PubMed

Abdollahi Nejand, B; Nazari, P; Gharibzadeh, S; Ahmadi, V; Moshaii, A

2017-01-05

Here, a low-cost perovskite solar cell using CuI and ZnO as the respective inorganic hole and electron transport layers is introduced. Copper foil is chosen as a cheap and low-weight conductive substrate which has a similar work function to ITO. Besides, copper foil is an interesting copper atom source for the growth of the upper cuprous iodide layer on copper foil. A spray coating of a transparent silver nanowire electrode is used as a top contact. The prepared device shows a maximum power conversion efficiency of 12.80% and long-term durability providing an environmentally and market friendly perovskite solar cell.

Solution-Processed Metal Oxides as Efficient Carrier Transport Layers for Organic Photovoltaics.

PubMed

Choy, Wallace C H; Zhang, Di

2016-01-27

Carrier (electron and hole) transport layers (CTLs) are essential components for boosting the performance of various organic optoelectronic devices such as organic solar cells and organic light-emitting diodes. Considering the drawbacks of conventional CTLs (easily oxidized/unstable, demanding/costly fabrication, etc.), transition metal oxides with good carrier transport/extraction and superior stability have drawn extensive research interest as CTLs for next-generation devices. In recent years, many research efforts have been made toward the development of solution-based metal oxide CTLs with the focus on low- or even room-temperature processes, which can potentially be compatible with the deposition processes of organic materials and can significantly contribute to the low-cost and scale-up of organic devices. Here, the recent progress of different types of solution-processed metal oxide CTLs are systematically reviewed in the context of organic photovoltaics, from synthesis approaches to device performance. Different approaches for further enhancing the performance of solution-based metal oxide CTLs are also discussed, which may push the future development of this exciting field. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CFM technologies for space transportation: Multipurpose hydrogen testbed system definition and tank procurement

NASA Technical Reports Server (NTRS)

Fox, E. C.; Kiefel, E. R.; Mcintosh, G. L.; Sharpe, J. B.; Sheahan, D. R.; Wakefield, M. E.

1993-01-01

The development of a test bed tank and system for evaluating cryogenic fluid management technologies in a simulated upper stage liquid hydrogen tank is covered. The tank is 10 ft long and is 10 ft in diameter, and is an ASME certified tank constructed of 5083 aluminum. The tank is insulated with a combination of sprayed on foam insulation, covered by 45 layers of double aluminized mylar separated by dacron net. The mylar is applied by a continuous wrap system adapted from commercial applications, and incorporates variable spacing between the mylar to provide more space between those layers having a high delta temperature, which minimizes heat leak. It also incorporates a unique venting system which uses fewer large holes in the mylar rather than the multitude of small holes used conventionally. This significantly reduces radiation heat transfer. The test bed consists of an existing vacuum chamber at MSFC, the test bed tank and its thermal control system, and a thermal shroud (which may be heated) surrounding the tank. Provisions are made in the tank and chamber for inclusion of a variety of cryogenic fluid management experiments.

Tin doped indium oxide anodes with artificially controlled nano-scale roughness using segregated Ag nanoparticles for organic solar cells

NASA Astrophysics Data System (ADS)

Kim, Hyo-Joong; Ko, Eun-Hye; Noh, Yong-Jin; Na, Seok-In; Kim, Han-Ki

2016-09-01

Nano-scale surface roughness in transparent ITO films was artificially formed by sputtering a mixed Ag and ITO layer and wet etching of segregated Ag nanoparticles from the surface of the ITO film. Effective removal of self-segregated Ag particles from the grain boundaries and surface of the crystalline ITO film led to a change in only the nano-scale surface morphology of ITO film without changes in the sheet resistance and optical transmittance. A nano-scale rough surface of the ITO film led to an increase in contact area between the hole transport layer and the ITO anode, and eventually increased the hole extraction efficiency in the organic solar cells (OSCs). The heterojunction OSCs fabricated on the ITO anode with a nano-scale surface roughness exhibited a higher power conversion efficiency of 3.320%, than that (2.938%) of OSCs made with the reference ITO/glass. The results here introduce a new method to improve the performance of OSCs by simply modifying the surface morphology of the ITO anodes.

An organic water-gated ambipolar transistor with a bulk heterojunction active layer for stable and tunable photodetection

NASA Astrophysics Data System (ADS)

Xu, Haihua; Zhu, Qingqing; Wu, Tongyuan; Chen, Wenwen; Zhou, Guodong; Li, Jun; Zhang, Huisheng; Zhao, Ni

2016-11-01

Organic water-gated transistors (OWGTs) have emerged as promising sensing architectures for biomedical applications and environmental monitoring due to their ability of in-situ detection of biological substances with high sensitivity and low operation voltage, as well as compatibility with various read-out circuits. Tremendous progress has been made in the development of p-type OWGTs. However, achieving stable n-type operation in OWGTs due to the presence of solvated oxygen in water is still challenging. Here, we report an ambipolar OWGT based on a bulk heterojunction active layer, which exhibits a stable hole and electron transport when exposed to aqueous environment. The device can be used as a photodetector both in the hole and electron accumulation regions to yield a maximum responsivity of 0.87 A W-1. More importantly, the device exhibited stable static and dynamic photodetection even when operated in the n-type mode. These findings bring possibilities for the device to be adopted for future biosensing platforms, which are fully compatible with low-cost and low-power organic complementary circuits.

Tempo-spatially resolved dynamics of elec- trons and holes in bilayer MoS2 -WS2

NASA Astrophysics Data System (ADS)

Galicia-Hernandez, J. M.; Turkowski, V.; Hernandez-Cocoletzi, G.; Rahman, T. S.

We have performed a Density-Matrix Time-Dependent Density-Functional Theory analysis of the response of bilayer MoS2-WS2 to external laser-pulse perturbations. Time-resolved study of the dynamics of electrons and holes, including formation and dissociation of strongly-bound intra- and inter-layer excitonic states, shows that the experimentally observed ultrafast inter-layer MoS2 to WS2 migration of holes may be attributed to unusually large delocalization of the hole state which extends far into the inter-layer region. We also argue that the velocity of the hole transfer may be further enhanced by its interaction with transfer phonon modes. We analyze other possible consequences of the hole delocalization in the system, including reduction of the effects of the electron-electron and hole-hole repulsion in the trions and biexcitons as compared to that in the monolayers Work supported in part by DOE Grant No. DOE-DE-FG02-07ER46354 and by CONACYT Scholarship No. 23210 (J.M.G.H.).

Pin-Hole Free Perovskite Film for Solar Cells Application Prepared by Controlled Two-Step Spin-Coating Method

NASA Astrophysics Data System (ADS)

Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.

2017-05-01

Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.

Switching Oxide Traps

NASA Technical Reports Server (NTRS)

Oldham, Timothy R.

2003-01-01

We consider radiation-induced charge trapping in SiO2 dielectric layers, primarily from the point of view of CMOS devices. However, SiO2 insulators are used in many other ways, and the same defects occur in other contexts. The key studies, which determined the nature of the oxide charge traps, were done primarily on gate oxides in CMOS devices, because that was the main radiation problem in CMOS at one time. There are two major reviews of radiation-induced oxide charge trapping already in the literature, which discuss the subject in far greater detail than is possible here. The first of these was by McLean et al. in 1989, and the second, ten years later, was intended as an update, because of additional, new work that had been reported. Basically, the picture that has emerged is that ionizing radiation creates electron-hole pairs in the oxide, and the electrons have much higher mobility than the holes. Therefore, the electrons are swept out of the oxide very rapidly by any field that is present, leaving behind any holes that escape the initial recombination process. These holes then undergo a polaron hopping transport toward the Si/SiO2 interface (under positive bias). Near the interface, some fraction of them fall into deep, relatively stable, long-lived hole traps. The nature and annealing behavior of these hole traps is the main focus of this paper.

Recent Advances in the Inverted Planar Structure of Perovskite Solar Cells.

PubMed

Meng, Lei; You, Jingbi; Guo, Tzung-Fang; Yang, Yang

2016-01-19

Inorganic-organic hybrid perovskite solar cells research could be traced back to 2009, and initially showed 3.8% efficiency. After 6 years of efforts, the efficiency has been pushed to 20.1%. The pace of development was much faster than that of any type of solar cell technology. In addition to high efficiency, the device fabrication is a low-cost solution process. Due to these advantages, a large number of scientists have been immersed into this promising area. In the past 6 years, much of the research on perovskite solar cells has been focused on planar and mesoporous device structures employing an n-type TiO2 layer as the bottom electron transport layer. These architectures have achieved champion device efficiencies. However, they still possess unwanted features. Mesoporous structures require a high temperature (>450 °C) sintering process for the TiO2 scaffold, which will increase the cost and also not be compatible with flexible substrates. While the planar structures based on TiO2 (regular structure) usually suffer from a large degree of J-V hysteresis. Recently, another emerging structure, referred to as an "inverted" planar device structure (i.e., p-i-n), uses p-type and n-type materials as bottom and top charge transport layers, respectively. This structure derived from organic solar cells, and the charge transport layers used in organic photovoltaics were successfully transferred into perovskite solar cells. The p-i-n structure of perovskite solar cells has shown efficiencies as high as 18%, lower temperature processing, flexibility, and, furthermore, negligible J-V hysteresis effects. In this Account, we will provide a comprehensive comparison of the mesoporous and planar structures, and also the regular and inverted of planar structures. Later, we will focus the discussion on the development of the inverted planar structure of perovskite solar cells, including film growth, band alignment, stability, and hysteresis. In the film growth part, several methods for obtaining high quality perovskite films are reviewed. In the interface engineering parts, the effect of hole transport layer on subsequent perovskite film growth and their interface band alignment, and also the effect of electron transport layers on charge transport and interface contact will be discussed. As concerns stability, the role of charge transport layers especially the top electron transport layer in the devices stability will be concluded. In the hysteresis part, possible reasons for hysteresis free in inverted planar structure are provided. At the end of this Account, future development and possible solutions to the remaining challenges facing the commercialization of perovskite solar cells are discussed.

Highly efficient bilayer interface exciplex for yellow organic light-emitting diode.

PubMed

Hung, Wen-Yi; Fang, Guan-Cheng; Chang, Yuh-Chia; Kuo, Ting-Yi; Chou, Pi-Tai; Lin, Shih-Wei; Wong, Ken-Tsung

2013-08-14

A simple three-layer interfacial-type yellow emission exciplex device with an external quantum efficiency as high as 7.7% has been successfully achieved by combining conformation compatible C3-symmetric hole-transporting TCTA and electron-transporting 3P-T2T. The excellent and balanced charge-transporting properties of TCTA and 3P-T2T and the large energy-levels offset (0.8 eV) of TCTA/3P-T2T interface play important roles for the efficient exciplexes formation, which are effectively confined around the interfacial region due to the high triplet energies (2.85 eV) of TCTA and 3P-T2T. The high-performance OLED was believed to be from the effective harvest of exciplex triplet excitons via reverse intersystem crossing process.

Tetra-methyl substituted copper (II) phthalocyanine as a hole injection enhancer in organic light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yu-Long; Xu, Jia-Ju; Lin, Yi-Wei

2015-10-15

We have enhanced hole injection and lifetime in organic light-emitting diodes (OLEDs) by incorporating the isomeric metal phthalocyanine, CuMePc, as a hole injection enhancer. The OLED devices containing CuMePc as a hole injection layer (HIL) exhibited higher luminous efficiency and operational lifetime than those using a CuPc layer and without a HIL. The effect of CuMePc thickness on device performance was investigated. Atomic force microscope (AFM) studies revealed that the thin films were smooth and uniform because the mixture of CuMePc isomers depressed crystallization within the layer. This may have caused the observed enhanced hole injection, indicating that CuMePc ismore » a promising HIL material for highly efficient OLEDs.« less

Required Equipment for Photo-Switchable Donor-Acceptor (D-A) Dyad Interfacial Self-Assembled Monolayers for Organic Photovoltaic Cells

DTIC Science & Technology

2014-01-24

Interfacial Tuning via Electron-Blocking/Hole-Transport Layers and Indium Tin Oxide Surface Treatment in Bulk- Heterojunction Organic Photovoltaic Cells...devices Figure 3 shows the compounds we prepared to assemble on gold (Au) surfaces. Results of TPA-C60 dyads (1 and 2) self-assembled on Au electrodes...surface hydroxyl groups, respectively, we decided to prepare compounds 5-7 to attach as SAMs, see Figure 5. Difficulties and unexpected problems

Hot carrier-enhanced interlayer electron-hole pair multiplication in 2D semiconductor heterostructure photocells

NASA Astrophysics Data System (ADS)

Barati, Fatemeh; Grossnickle, Max; Su, Shanshan; Lake, Roger K.; Aji, Vivek; Gabor, Nathaniel M.

2017-12-01

Strong electronic interactions can result in novel particle-antiparticle (electron-hole, e-h) pair generation effects, which may be exploited to enhance the photoresponse of nanoscale optoelectronic devices. Highly efficient e-h pair multiplication has been demonstrated in several important nanoscale systems, including nanocrystal quantum dots, carbon nanotubes and graphene. The small Fermi velocity and nonlocal nature of the effective dielectric screening in ultrathin layers of transition-metal dichalcogenides (TMDs) indicates that e-h interactions are very strong, so high-efficiency generation of e-h pairs from hot electrons is expected. However, such e-h pair multiplication has not been observed in 2D TMD devices. Here, we report the highly efficient multiplication of interlayer e-h pairs in 2D semiconductor heterostructure photocells. Electronic transport measurements of the interlayer I-VSD characteristics indicate that layer-indirect e-h pairs are generated by hot-electron impact excitation at temperatures near T = 300 K. By exploiting this highly efficient interlayer e-h pair multiplication process, we demonstrate near-infrared optoelectronic devices that exhibit 350% enhancement of the optoelectronic responsivity at microwatt power levels. Our findings, which demonstrate efficient carrier multiplication in TMD-based optoelectronic devices, make 2D semiconductor heterostructures viable for a new class of ultra-efficient photodetectors based on layer-indirect e-h excitations.

Hole and electron extraction layers based on graphene oxide derivatives for high-performance bulk heterojunction solar cells.

PubMed

Liu, Jun; Xue, Yuhua; Gao, Yunxiang; Yu, Dingshan; Durstock, Michael; Dai, Liming

2012-05-02

By charge neutralization of carboxylic acid groups in graphene oxide (GO) with Cs(2)CO(3) to afford Cesium-neutralized GO (GO-Cs), GO derivatives with appropriate modification are used as both hole- and electron-extraction layers for bulk heterojunction (BHJ) solar cells. The normal and inverted devices based on GO hole- and GO-Cs electron-extraction layers both outperform the corresponding standard BHJ solar cells. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ionization chamber dosimeter

DOEpatents

Renner, Tim R.; Nyman, Mark A.; Stradtner, Ronald

1991-01-01

A method for fabricating an ion chamber dosimeter collecting array of the type utilizing plural discrete elements formed on a uniform collecting surface which includes forming a thin insulating layer over an aperture in a frame having surfaces, forming a predetermined pattern of through holes in the layer, plating both surfaces of the layer and simultaneously tilting and rotating the frame for uniform plate-through of the holes between surfaces. Aligned masking and patterned etching of the surfaces provides interconnects between the through holes and copper leads provided to external circuitry.

Micro-hole array fluorescent sensor based on AC-Dielectrophoresis (DEP) for simultaneous analysis of nano-molecules

NASA Astrophysics Data System (ADS)

Kim, Hye Jin; Kang, Dong-Hoon; Lee, Eunji; Hwang, Kyo Seon; Shin, Hyun-Joon; Kim, Jinsik

2018-02-01

We propose a simple fluorescent bio-chip based on two types of alternative current-dielectrophoretic (AC-DEP) force, attractive (positive DEP) and repulsive (negative DEP) force, for simultaneous nano-molecules analysis. Various radius of micro-holes on the bio-chip are designed to apply the different AC-DEP forces, and the nano-molecules are concentrated inside the micro-hole arrays according to the intensity of the DEP force. The bio-chip was fabricated by Micro Electro Mechanical system (MEMS) technique, and was composed of two layers; a SiO2 layer and Ta/Pt layer were accomplished for an insulation layer and a top electrode with micro-hole arrays to apply electric fields for DEP force, respectively. Each SiO2 and Ta/Pt layers were deposited by thermal oxidation and sputtering, and micro-hole arrays were fabricated with Inductively Coupled Plasma (ICP) etching process. For generation of each positive and negative DEP at micro-holes, we applied two types of sine-wave AC voltage with different frequency range alternately. The intensity of the DEP force was controlled by the radius of the micro-hole and size of nano-molecule, and calculated with COMSOL multi-physics. Three types of nano-molecules labelled with different fluorescent dye were used and the intensity of nano-molecules was examined by the fluorescent optical analysis after applying the DEP force. By analyzing the fluorescent intensities of the nano-molecules, we verify the various nano-molecules in analyte are located successfully inside corresponding micro-holes with different radius according to their size.

Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer

NASA Astrophysics Data System (ADS)

Jian-Feng, Li; Chuang, Zhao; Heng, Zhang; Jun-Feng, Tong; Peng, Zhang; Chun-Yan, Yang; Yang-Jun, Xia; Duo-Wang, Fan

2016-02-01

In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)) (PEDOT:PSS) and its influence on the performance of perovskite solar cells. . The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide (ITO)/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al, where PEDOT:PSS and PC61BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency (PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G (100 mW/cm2 illumination) after the buffer layer has been modified. Project supported by the National Natural Science Foundation of China (Grant Nos. 61264002, 61166002, 91333206, and 51463011), the Natural Science Foundation of Gansu Province, China (Grant No. 1308RJZA159), the New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0840), the Research Project of Graduate Teacher of Gansu Province, China (Grant No. 2014A-0042), and the Postdoctoral Science Foundation from Lanzhou Jiaotong University, China.

Demonstration of Hole Transport and Voltage Equilibration in Self-Assembled π-Conjugated Peptide Nanostructures Using Field-Effect Transistor Architectures.

PubMed

Besar, Kalpana; Ardoña, Herdeline Ann M; Tovar, John D; Katz, Howard E

2015-12-22

π-Conjugated peptide materials are attractive for bioelectronics due to their unique photophysical characteristics, biofunctional interfaces, and processability under aqueous conditions. In order to be relevant for electrical applications, these types of materials must be able to support the passage of current and the transmission of applied voltages. Presented herein is an investigation of both the current and voltage transmission activities of one-dimensional π-conjugated peptide nanostructures. Observations of the nanostructures as both semiconducting and gate layers in organic field-effect transistors (OFETs) were made, and the effect of systematic changes in amino acid composition on the semiconducting/conducting functionality of the nanostructures was investigated. These molecular variations directly impacted the hole mobility values observed for the nanomaterial active layers over 3 orders of magnitude (∼0.02 to 5 × 10(-5) cm(2) V(-1) s(-1)) when the nanostructures had quaterthiophene cores and the assembled peptide materials spanned source and drain electrodes. Peptides without the quaterthiophene core were used as controls and did not show field-effect currents, verifying that the transport properties of the nanostructures rely on the semiconducting behavior of the π-electron core and not just ionic rearrangements. We also showed that the nanomaterials could act as gate electrodes and assessed the effect of varying the gate dielectric layer thickness in devices where the conventional organic semiconductor pentacene spanned the source and drain electrodes in a top-contact OFET, showing an optimum performance with 35-40 nm dielectric thickness. This study shows that these peptides that self-assemble in aqueous environments can be used successfully to transmit electronic signals over biologically relevant distances.

CuI as Hole-Transport Channel for Enhancing Photoelectrocatalytic Activity by Constructing CuI/BiOI Heterojunction.

PubMed

Sun, Mingjuan; Hu, Jiayue; Zhai, Chunyang; Zhu, Mingshan; Pan, Jianguo

2017-04-19

In this paper, CuI, as a typical hole-transport channel, was used to construct a high-performance visible-light-driven CuI/BiOI heterostructure for photoelectrocatalytic applications. The heterostructure combines the broad visible absorption of BiOI and high hole mobility of CuI. Compared to pure BiOI, the CuI/BiOI heterostructure exhibited distinctly enhanced photoelectrocatalytic performance for the oxidation of methanol and organic pollutants under visible-light irradiation. The photogenerated electron-hole pairs of the excited BiOI can be separated efficiently through CuI, in which the CuI acts as a superior hole-transport channel to improve photoelectrocatalytic oxidization of methanol and organic pollutants. The outstanding photoelectrocatalytic activity shows that the p-type CuI works as a promising hole-transport channel to improve the photocatalytic performance of traditional semiconductors.

Magnetotransport of High Mobility Holes in Monolayer and Bilayer WSe2

NASA Astrophysics Data System (ADS)

Tutuc, Emanuel

Transition metal dichalcogenides have attracted significant interest because of their two-dimensional crystal structure, large band-gap, and strong spin-orbit interaction which leads to spin-valley locking. Recent advances in sample fabrication have allowed the experimental study of low temperature magneto-transport of high mobility holes in WSe2. We review here the main results of these studies which reveal clear quantum Hall states in mono- and bilayer WSe2. The data allows the extraction of an effective hole mass of m* = 0.45me (me is the bare electron mass) in both mono and bilayer WSe2. A systematic study of the carrier distribution in bilayer WSe2 determined from a Fourier analysis of the Shubnikov-de Haas oscillations indicates that the two layers are weakly coupled. The individual layer density dependence on gate bias shows negative compressibility, a signature of strong electron-electron interaction in these materials associated with the large effective mass. We discuss the interplay between cyclotron and Zeeman splitting using the dependence of the quantum Hall state sequence on carrier density, and the angle between the magnetic field and the WSe2 plane. Work done in collaboration with B. Fallahazad, H. C. P. Movva, K. Kim, S. K. Banerjee, T. Taniguchi, and K. Watanabe. This work supported by the Nanoelectronics Research Initiative SWAN center, Intel Corp., and National Science Foundation.

Organic electronic devices using phthalimide compounds

DOEpatents

Hassan, Azad M.; Thompson, Mark E.

2010-09-07

Organic electronic devices comprising a phthalimide compound. The phthalimide compounds disclosed herein are electron transporters with large HOMO-LUMO gaps, high triplet energies, large reduction potentials, and/or thermal and chemical stability. As such, these phthalimide compounds are suitable for use in any of various organic electronic devices, such as OLEDs and solar cells. In an OLED, the phthalimide compounds may serve various functions, such as a host in the emissive layer, as a hole blocking material, or as an electron transport material. In a solar cell, the phthalimide compounds may serve various functions, such as an exciton blocking material. Various examples of phthalimide compounds which may be suitable for use in the present invention are disclosed.

Organic electronic devices using phthalimide compounds

DOEpatents

Hassan, Azad M.; Thompson, Mark E.

2012-10-23

Organic electronic devices comprising a phthalimide compound. The phthalimide compounds disclosed herein are electron transporters with large HOMO-LUMO gaps, high triplet energies, large reduction potentials, and/or thermal and chemical stability. As such, these phthalimide compounds are suitable for use in any of various organic electronic devices, such as OLEDs and solar cells. In an OLED, the phthalimide compounds may serve various functions, such as a host in the emissive layer, as a hole blocking material, or as an electron transport material. In a solar cell, the phthalimide compounds may serve various functions, such as an exciton blocking material. Various examples of phthalimide compounds which may be suitable for use in the present invention are disclosed.

Organic electronic devices using phthalimide compounds

DOEpatents

Hassan, Azad M.; Thompson, Mark E.

2013-03-19

Organic electronic devices comprising a phthalimide compound. The phthalimide compounds disclosed herein are electron transporters with large HOMO-LUMO gaps, high triplet energies, large reduction potentials, and/or thermal and chemical stability. As such, these phthalimide compounds are suitable for use in any of various organic electronic devices, such as OLEDs and solar cells. In an OLED, the phthalimide compounds may serve various functions, such as a host in the emissive layer, as a hole blocking material, or as an electron transport material. In a solar cell, the phthalimide compounds may serve various functions, such as an exciton blocking material. Various examples of phthalimide compounds which may be suitable for use in the present invention are disclosed.

Use of XPS to clarify the Hall coefficient sign variation in thin niobium layers buried in silicon

NASA Astrophysics Data System (ADS)

Demchenko, Iraida N.; Lisowski, Wojciech; Syryanyy, Yevgen; Melikhov, Yevgen; Zaytseva, Iryna; Konstantynov, Pavlo; Chernyshova, Maryna; Cieplak, Marta Z.

2017-03-01

Si/Nb/Si trilayers formed with 9.5 and 1.3 nm thick niobium layer buried in amorphous silicon were prepared by magnetron sputtering and studied using XPS depth-profile techniques in order to investigate the change of Hall coefficient sign with thickness. The analysis of high-resolution (HR) XPS spectra revealed that the thicker layer sample has sharp top interface and metallic phase of niobium, thus holes dominate the transport. In contrast, the analysis indicates that the thinner layer sample has a Nb-rich mixed alloy formation at the top interface. The authors suggest that the main effect leading to a change of sign of the Hall coefficient for the thinner layer sample (which is negative contrary to the positive sign for the thicker layer sample) may be related to strong boundary scattering enhanced by the presence of silicon ions in the layer close to the interface/s. The depth-profile reconstruction was performed by SESSA software tool confirming that it can be reliably used for quantitative analysis/interpretation of experimental XPS data.

GPU based 3D feature profile simulation of high-aspect ratio contact hole etch process under fluorocarbon plasmas

NASA Astrophysics Data System (ADS)

Chun, Poo-Reum; Lee, Se-Ah; Yook, Yeong-Geun; Choi, Kwang-Sung; Cho, Deog-Geun; Yu, Dong-Hun; Chang, Won-Seok; Kwon, Deuk-Chul; Im, Yeon-Ho

2013-09-01

Although plasma etch profile simulation has been attracted much interest for developing reliable plasma etching, there still exist big gaps between current research status and predictable modeling due to the inherent complexity of plasma process. As an effort to address this issue, we present 3D feature profile simulation coupled with well-defined plasma-surface kinetic model for silicon dioxide etching process under fluorocarbon plasmas. To capture the realistic plasma surface reaction behaviors, a polymer layer based surface kinetic model was proposed to consider the simultaneous polymer deposition and oxide etching. Finally, the realistic plasma surface model was used for calculation of speed function for 3D topology simulation, which consists of multiple level set based moving algorithm, and ballistic transport module. In addition, the time consumable computations in the ballistic transport calculation were improved drastically by GPU based numerical computation, leading to the real time computation. Finally, we demonstrated that the surface kinetic model could be coupled successfully for 3D etch profile simulations in high-aspect ratio contact hole plasma etching.

Characterization of MgO Based Tunnel Barriers in Graphene Based Spin Valve Devices

NASA Astrophysics Data System (ADS)

Avsar, Ahmet; Balakrishnan, Jayakumar; Koon, Gavin; Ho, Yuda; Patra, Ajit; Bae, Sukang; Hong, Byung-Hee; Özyilmaz, Barbaros

2012-02-01

The low spin orbit coupling and hyperfine interaction in graphene allows a high spin relaxation length even at room temperature [1]. The demonstration of comparable spin transport properties in CVD synthesized single layer and bilayer graphene with its exfoliated counterparts raised hopes for the realization of possible room temperature spintronic applications [2]. To improve the spin transport properties of CVD Graphene based spin valves further, contact induced spin relaxation should be reduced by creating pin-hole free tunneling barriers. In this presentation, we will compare MgO barriers deposited under different conditions towards establishing pin-hole free barriers. We will discuss the effect of the substrate smoothness on the formation of high quality tunnel barriers by studying growth on different substrates. [4pt] [1] N. Tombros, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. van Wees, Nature 448, 571-574 (2007) [0pt] [2] A. Avsar, T. Yang, S. Bae, J. Balakrishnan, F. Volmer, M. Jaiswal, Z. Yi, S. R. Ali, G. Guntherodt, B. H. Hong, B. Beschoten, B. Ozyilmaz, Nano Lett. 10.10.1021/nl200714q (2011)

Characterization of few-layered graphene grown by carbon implantation

NASA Astrophysics Data System (ADS)

Lee, Kin Kiong; McCallum, Jeffrey C.; Jamieson, David N.

2014-02-01

Graphene is considered to be a very promising material for applications in nanotechnology. The properties of graphene are strongly dependent on defects that occur during growth and processing. These defects can be either detrimental or beneficial to device performance depending on defect type, location and device application. Here we present experimental results on formation of few-layered graphene by carbon ion implantation into nickel films and characteristics of graphene devices formed by graphene transfer and lithographic patterning. Micro-Raman spectroscopy was used to determine the number of graphene layers formed and identify defects arising from the device processing. The graphene films were cleaned by annealing in vacuum. Transport properties of cleaned graphene films were investigated by fabrication of back-gated field-effect transistors, which exhibited high hole and electron mobility of 1935 and 1905 cm2/Vs, respectively.

Dopant-Free Zinc Chlorophyll Aggregates as an Efficient Biocompatible Hole Transporter for Perovskite Solar Cells.

PubMed

Li, Mengzhen; Li, Yue; Sasaki, Shin-Ichi; Song, Jiaxing; Wang, Chen; Tamiaki, Hitoshi; Tian, Wenjing; Chen, Gang; Miyasaka, Tsutomu; Wang, Xiao-Feng

2016-10-06

Chlorophylls (Chls) are abundant, naturally occurring pigments that play key roles in light-harvesting and electron/energy transfer in natural photosynthetic apparatus. To demonstrate the idea that Chls are suitable hole transporters, we employed two Chl derivatives, Chl-1 and Chl-2, which self-assembled readily into π-stacking aggregates through a simple spincasting process, in perovskite solar cells (PSCs). The Chl aggregate films exhibit an ultra-smooth film surface, high hole mobility, appropriate energy levels, and efficient hole injection efficiencies that are all key characteristics for efficient hole transporters in PSCs. CH 3 NH 3 PbI 3-x Cl x -based PSCs with these Chls as hole transporters were fabricated and compared with P3HT as a standard hole transporter. PSCs based on Chl-1 and Chl-2 without the use of typical additives, such as 4-tert-butylpyridine and lithium bis(trifluoromethanesulfinyl)imide, gave power conversion efficiencies of 11.44 and 8.06 %, respectively. This research provides a unique way to incorporate low-cost and environmentally friendly natural photosynthetic materials in the development of highly efficient photovoltaic devices. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theory of the power characteristics of quantum-well lasers with asymmetric barrier layers: Inclusion of asymmetry in electron- and hole-state filling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asryan, L. V., E-mail: asryan@vt.edu; Zubov, F. I.; Kryzhanovskaya, N. V.

2016-10-15

The power characteristics of quantum-well lasers with asymmetric barrier layers, which represent a novel type of injection laser, are calculated on the basis of an extended model taking into account asymmetry in the filling of electron and hole states. The electron–hole asymmetry is shown to have no significant effect on the characteristics of these lasers. Even in the presence of intermediate layers (located between the quantum well and each of the two asymmetric barrier layers), where parasitic electron–hole recombination does occur, the internal differential quantum efficiency of such a laser exhibits only a weak dependence on the pump current andmore » remains close to unity; therefore, the light–current characteristic remains linear up to high pumping levels.« less

Transport anomalies of high-mobility Q-valley electrons in few-layer WS2 and MoS2

NASA Astrophysics Data System (ADS)

Wang, Ning

Atomically thin transition metal dichalcogenides (TMDCs) have opened new avenues for exploring physical property anomalies due to their large band gaps, strong spin-orbit couplings, and rich valley degrees of freedom. Although novel optical phenomena such as valley selective circular dichroism, opto-valley Hall effect, and valley Zeeman effect have been extensively studied in TMDCs, investigation of quantum transport properties has encountered a number of obstacles primarily due to the low carrier mobility and strong impurity scattering. Recently, we successfully fabricated ultrahigh-mobility few-layer TMDC field-effect transistors based on the boron nitride encapsulation method and observed a number of interesting transport properties, such as even-odd layer-dependent magnetotransport of Q-valley electrons in WS2 and MoS2 and unconventional quantum Hall transport of Γ-valley hole carriers in WSe2. In few-layer samples of these TMDCs, the conduction bands along the ΓK directions shift downward energetically in the presence of interlayer interactions, forming six Q-valleys related by three-fold rotational symmetry and time reversal symmetry. In even-layers the extra inversion symmetry requires all states to be Kramers degenerate, whereas in odd-layers the intrinsic inversion asymmetry dictates the Q-valleys to be spin-valley coupled. In this talk, I'll demonstrate the prominent Shubnikov-de Hass (SdH) oscillations and the observation of the onset of quantum Hall plateaus for the Q-valley electrons. Universally in the SdH oscillations, we observe a valley Zeeman effect in all odd-layer TMDC devices and a spin Zeeman effect in all even-layer TMDC devices. In addition, we observe a series of quantum Hall states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field in p-type few-layer TMDCs, indicating a large Zeeman energy associated with the carriers in the valence band at the Γ-valley. Financial supports from the Research Grants Council of Hong Kong (Project Nos. 16302215, HKU9/CRF/13G, 604112 and N-HKUST613/12) are hereby acknowledged.

Strategy to Boost the Efficiency of Mixed-Ion Perovskite Solar Cells: Changing Geometry of the Hole Transporting Material.

PubMed

Zhang, Jinbao; Xu, Bo; Johansson, Malin B; Vlachopoulos, Nick; Boschloo, Gerrit; Sun, Licheng; Johansson, Erik M J; Hagfeldt, Anders

2016-07-26

The hole transporting material (HTM) is an essential component in perovskite solar cells (PSCs) for efficient extraction and collection of the photoinduced charges. Triphenylamine- and carbazole-based derivatives have extensively been explored as alternative and economical HTMs for PSCs. However, the improvement of their power conversion efficiency (PCE), as well as further investigation of the relationship between the chemical structure of the HTMs and the photovoltaic performance, is imperatively needed. In this respect, a simple carbazole-based HTM X25 was designed on the basis of a reference HTM, triphenylamine-based X2, by simply linking two neighboring phenyl groups in a triphenylamine unit through a carbon-carbon single bond. It was found that a lowered highest occupied molecular orbital (HOMO) energy level was obtained for X25 compared to that of X2. Besides, the carbazole moiety in X25 improved the molecular planarity as well as conductivity property in comparison with the triphenylamine unit in X2. Utilizing the HTM X25 in a solar cell with mixed-ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3, a highest reported PCE of 17.4% at 1 sun (18.9% under 0.46 sun) for carbazole-based HTM in PSCs was achieved, in comparison of a PCE of 14.7% for triphenylamine-based HTM X2. From the steady-state photoluminescence and transient photocurrent/photovoltage measurements, we conclude that (1) the lowered HOMO level for X25 compared to X2 favored a higher open-circuit voltage (Voc) in PSCs; (2) a more uniform formation of X25 capping layer than X2 on the surface of perovskite resulted in more efficient hole transport and charge extraction in the devices. In addition, the long-term stability of PSCs with X25 is significantly enhanced compared to X2 due to its good uniformity of HTM layer and thus complete coverage on the perovskite. The results provide important information to further develop simple and efficient small molecular HTMs applied in solar cells.

Assessing the potential of group 13 and 14 metal/metalloid phthalocyanines as hole transport layers in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Plint, Trevor; Lessard, Benoît H.; Bender, Timothy P.

2016-04-01

In this study, we have assessed the potential application of group 13 and 14 metal and metalloid phthalocyanines ((X)n-MPcs) and their axially substituted derivatives as hole-transporting layers in organic light emitting diodes (OLEDs). OLEDs studied herein have the generic structure of glass/ITO/(N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB) or (X)n-MPc)(50 nm)/Alq3 (60 nm)/LiF (1 nm)/Al (80 nm), where X is an axial substituent group. OLEDs using chloro aluminum phthalocyanine (Cl-AlPc) showed good peak luminance values of 2620 ± 113 cd/m2 at 11 V. To our knowledge, Cl-AlPc has not previously been shown to work as a hole transport material (HTL) in OLEDs. Conversely, the di-chlorides of silicon, germanium, and tin phthalocyanine (Cl2-SiPc, Cl2-GePc, and Cl2-SnPc, respectively) showed poor performance compared to Cl-AlPc, having peak luminances of only 38 ± 4 cd/m2 (12 V), 23 ± 1 cd/m2 (8.5 V), and 59 ± 5 cd/m2 (13.5 V), respectively. However, by performing a simple axial substitution of the chloride groups of Cl2-SiPc with pentafluorophenoxy groups, the resulting bis(pentafluorophenoxy) silicon phthalocyanine (F10-SiPc) containing OLED had a peak luminance of 5141 ± 941 cd/m2 (10 V), a two order of magnitude increase over its chlorinated precursor. This material showed OLED characteristics approaching those of a baseline OLED based on the well-studied triarylamine NPB. Attempts to attach the pentafluorophenoxy axial group to both SnPc and GePc were hindered by synthetic difficulties and low thermal stability, respectively. In light of the performance improvements observed by simple axial substitution of SiPc in OLEDs, the use of axially substituted MPcs in organic electronic devices remains of continuing interest to us and potentially the field in general.

Enhancement of external quantum efficiency and reduction of roll-off in blue phosphorescent organic light emitt diodes using TCTA inter-layer

NASA Astrophysics Data System (ADS)

Kim, Ji Young; Kim, Nam Ho; Kim, Jin Wook; Kang, Jin Sung; Yoon, Ju-An; Yoo, Seung Il; Kim, Woo Young; Cheah, Kok Wai

2014-11-01

The improved external quantum efficiency (EQE) and reduced roll-off properties of blue phosphorescent organic light-emitting diodes (PHOLEDs), were fabricated with structure, ITO/NPB (400 Å)/TCTA (200 Å)/mCP:FIrpic (7%)(300 Å)/TPBi (300 Å)/Liq (20 Å)/Al (800 Å) by incorporating an 4,4‧,4‧‧-tris(carbazol-9-yl)-triphenylamine (TCTA) interlayer. We compared the properties of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) as the electron transport layer (ETL) with a typical structure of hole transport layer (HTL)/emissive layer (EML)/ETL in OLEDs and utilized inter-layer in the optimized structure to enhance EQE to 52% at 5.5 V, also stabilize the roll-off of 23%. The use of inter-layer in blue PHOLEDs exhibits a current efficiency of 10.04 cd/A, an EQE of 6.20% at 5.5 V and the highest luminance of 10310 cd/m2 at 9.5 V. We have identified the properties of electroluminescence through the inter-layer in blue PHOLEDs which can be divided into singlet excitons and triplet excitons which emit fluorescence of N,N‧-bis(1-naphthalenyl)-N,N‧-bis-phenyl-(1,1‧-biphenyl)-4,4‧-diamine (NPB) at 420 nm and phosphorescence of Iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2‧] picolinate (FIrpic) at 470 nm, 494 nm, respectively.

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, J. P.; Ye, G. Z.; Shahi, P.

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE PAGES

Sun, J. P.; Ye, G. Z.; Shahi, P.; ...

2017-04-07

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

Nanostructured organic/inorganic semicondutor photovoltaics: Investigation on morphology and optoelectronics performance

NASA Astrophysics Data System (ADS)

Wanninayake, Aruna Pushpa Kumara

Organic solar cell is a promising technology because of the versatility of organic materials in terms of tunability of their electrical and optical properties. In addition, their relative insensitivity to film imperfections potentially allows for very low-cost high-throughput roll-to-roll processing. However, the power conversion efficiency of organic solar cell is still limited and needs to be improved in order to be competitive with grid parity. This work is focused on the design and characterization of a new organic/inorganic hybrid device to enhance the efficiency factors of bilayer organic solar cells such as: light absorption, exciton diffusion, exciton dissociation, charge transportation and charge collection at the electrodes. In a hybrid solar cell operation, external quantum efficiency is determined by these five factors. The external quantum efficiency has linear relationship to the power conversation efficiency via short circuit current density. Bulk heterojunction (BHJ) PSCs benefit from a homogeneous donor-acceptor (D-A) contact interface compared to their inorganic counterpart. A homogenous D-A interface offers a longer free path for charge carriers, resulting in a longer diffusional pathway and a larger coulomb interaction between electrons and holes. This is triggered by the low dielectric constant of organic semiconductors. Among various conventional donor-acceptor structures, poly(3-hexylthiophene)/[6,6]-phenyl-C70-butyric acid methyl ester (P3HT/PCBM) mixture is the most promising and ideal donor-acceptor pair due to their unique properties. In order to take benefits from both organic and inorganic materials, inorganic nanoparticles are incorporated in this donor-acceptor polymer structure. Light trapping enhances light absorption and increases efficiencies with thinner device structure. In this study, copper oxide nanoparticles are used in the P3HT/PC70BM active layer to optimize the optical absorption properties in the blend. In addition, zinc oxide nanoparticles are used for tuning the conjugated polymer films due to their high electron accepting ability and optical absorption properties. In the zinc oxide structure, electrons exhibit higher mobility, which enhances the exciton dissociation efficiency. In addition, metal nanoparticles such as gold are added to the hole transport layer to enhance the overall hole transport ability. The optimum morphology of P3HT/PCBM films is described by two main features: 1) the molecular ordering within the donor or acceptor phase, which affects the photon absorption and carrier mobility; and 2) the scale of phase separation between the donor and the acceptor, which can directly influence the exciton dissociation and charge transport and/or collection processes. Hence, the molecular ordering and the phase separation between the donor and acceptor phases are crucial for solar cells with high efficiency. Optimization of the morphology of the organic/inorganic hybrid layers will be achieved via thermal annealing. The main goal of this work is to fabricate inorganic nanoparticles incorporated polymer PV devices with increased power conversion efficiency (PCE). This goal is achieved through four research objectives which are 1) enhancement of exciton generation and morphology by CuO NPs, 2) enhancement of exciton transportation and carrier diffusion by thermal annealing, 3) Improvement of exciton dissociation and electron mobility using ZnO NPs, and 4) improvement of hole collection ability using Au NPs. The key findings in this research can be applied to fabricate solar cells with higher power conversion efficiencies.

Effective Passivation and Tunneling Hybrid a-SiOx(In) Layer in ITO/n-Si Heterojunction Photovoltaic Device.

PubMed

Gao, Ming; Wan, Yazhou; Li, Yong; Han, Baichao; Song, Wenlei; Xu, Fei; Zhao, Lei; Ma, Zhongquan

2017-05-24

In this article, using controllable magnetron sputtering of indium tin oxide (ITO) materials on single crystal silicon at 100 °C, the optoelectronic heterojunction frame of ITO/a-SiO x (In)/n-Si is simply fabricated for the purpose of realizing passivation contact and hole tunneling. It is found that the gradation profile of indium (In) element together with silicon oxide (SiO x /In) within the ultrathin boundary zone between ITO and n-Si occurs and is characterized by X-ray photoelectron spectroscopy with the ion milling technique. The atomistic morphology and physical phase of the interfacial layer has been observed with a high-resolution transmission electron microscope. X-ray diffraction, Hall effect measurement, and optical transmittance with Tauc plot have been applied to the microstructure and property analyses of ITO thin films, respectively. The polycrystalline and amorphous phases have been verified for ITO films and SiO x (In) hybrid layer, respectively. For the quantum transport, both direct and defect-assisted tunneling of photogenerated holes through the a-SiO x (In) layer is confirmed. Besides, there is a gap state correlative to the indium composition and located at E v + 4.60 eV in the ternary hybrid a-SiO x (In) layer that is predicted by density functional theory of first-principles calculation, which acts as an "extended delocalized state" for direct tunneling of the photogenerated holes. The reasonable built-in potential (V bi = 0.66 V) and optimally controlled ternary hybrid a-SiO x (In) layer (about 1.4 nm) result in that the device exhibits excellent PV performance, with an open-circuit voltage of 0.540 V, a short-circuit current density of 30.5 mA/cm 2 , a high fill factor of 74.2%, and a conversion efficiency of 12.2%, under the AM 1.5 illumination. The work function difference between ITO (5.06 eV) and n-Si (4.31 eV) is determined by ultraviolet photoemission spectroscopy and ascribed to the essence of the built-in-field of the PV device. In addition, the strong inversion layer in the surface of the n-Si substrate is tentatively correlated to the a-SiO x (In) interface layer as well.

Diode and method of making the same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dickerson, Jeramy Ray; Wierer, Jr., Jonathan; Kaplar, Robert

2018-03-13

A diode includes a second semiconductor layer over a first semiconductor layer. The diode further includes a third semiconductor layer over the second semiconductor layer, where the third semiconductor layer includes a first semiconductor element over the second semiconductor layer. The third semiconductor layer additionally includes a second semiconductor element over the second semiconductor layer, wherein the second semiconductor element surrounds the first semiconductor element. Further, the third semiconductor layer includes a third semiconductor element over the second semiconductor element. Furthermore, a hole concentration of the second semiconductor element is less than a hole concentration of the first semiconductor element.

Solar cell contact formation using laser ablation

DOEpatents

Harley, Gabriel; Smith, David D.; Cousins, Peter John

2015-07-21

The formation of solar cell contacts using a laser is described. A method of fabricating a back-contact solar cell includes forming a poly-crystalline material layer above a single-crystalline substrate. The method also includes forming a dielectric material stack above the poly-crystalline material layer. The method also includes forming, by laser ablation, a plurality of contacts holes in the dielectric material stack, each of the contact holes exposing a portion of the poly-crystalline material layer; and forming conductive contacts in the plurality of contact holes.

Solar cell contact formation using laser ablation

DOEpatents

Harley, Gabriel; Smith, David; Cousins, Peter

2012-12-04

The formation of solar cell contacts using a laser is described. A method of fabricating a back-contact solar cell includes forming a poly-crystalline material layer above a single-crystalline substrate. The method also includes forming a dielectric material stack above the poly-crystalline material layer. The method also includes forming, by laser ablation, a plurality of contacts holes in the dielectric material stack, each of the contact holes exposing a portion of the poly-crystalline material layer; and forming conductive contacts in the plurality of contact holes.

Solar cell contact formation using laser ablation

DOEpatents

Harley, Gabriel; Smith, David D.; Cousins, Peter John

2014-07-22

The formation of solar cell contacts using a laser is described. A method of fabricating a back-contact solar cell includes forming a poly-crystalline material layer above a single-crystalline substrate. The method also includes forming a dielectric material stack above the poly-crystalline material layer. The method also includes forming, by laser ablation, a plurality of contacts holes in the dielectric material stack, each of the contact holes exposing a portion of the poly-crystalline materiat layer; and forming conductive contacts in the plurality of contact holes.

Design of Semiconducting Tetrahedral Mn 1-xZn xO Alloys and Their Application to Solar Water Splitting

DOE PAGES

Peng, Haowei; Ndione, Paul F.; Ginley, David S.; ...

2015-03-18

Transition metal oxides play important roles as contact and electrode materials, but their use as active layers in solar energy conversion requires achieving semiconducting properties akin to those of conventional semiconductors like Si or GaAs. In particular, efficient bipolar carrier transport is a challenge in these materials. Based on the prediction that a tetrahedral polymorph of MnO should have such desirable semiconducting properties, and the possibility to overcome thermodynamic solubility limits by nonequilibrium thin-film growth, we exploit both structure-property and composition-structure relationships to design and realize novel wurtzite-structure Mn 1₋xZn xO alloys. At Zn compositions above x≈0.3, thin films ofmore » these alloys assume the tetrahedral wurtzite structure instead of the octahedral rocksalt structure of MnO, thereby enabling semiconductor properties that are unique among transition metal oxides, i.e., a band gap within the visible spectrum, a band-transport mechanism for both electron and hole carriers, electron doping, and a band lineup suitable for solar hydrogen generation. In conclusion, a proof of principle is provided by initial photo-electrocatalytic device measurements, corroborating, in particular, the predicted favorable hole-transport properties of these alloys.« less

Lipid bilayers suspended on microfabricated supports

NASA Astrophysics Data System (ADS)

Ogier, Simon D.; Bushby, Richard J.; Cheng, Yaling; Cox, Tim I.; Evans, Stephen D.; Knowles, Peter F.; Miles, Robert E.; Pattison, Ian

2001-03-01

The plasma membrane, that exists as part of many animal and plant cells, is a regulator for the transport of ions and small molecules across cell boundaries. Two main components involved are the phospholipid bilayer and the transport proteins. This paper details the construction of a micromachined support for bilayers (MSB) as a first step towards the development of highly selective and highly sensitive ion-channel based biosensors. The device consists of a ~100 micrometer hole in a polymeric support above a cavity that can hold ~25 nL of electrolyte. Electrodes attached to the structure allow the resistance of the membranes to be measured using d.c. conductivity. The MSB is made in two halves, using SU8 ultra-thick resist, which are subsequently bonded together to make the final structure. A layer of gold, surrounding the aperture, enables self-assembled monolayers of alkanethiols to be used to make the polymeric structure biocompatible. Lipid membranes have been formed over these holes with resistances comparable with those of natural membranes >10 MOhmcm^2. The ion-channel gramicidin has successfully been incorporated into the bilayer and its activity monitored. It is proposed that this type of device could be used not only for studying membrane transport phenomena but also as part of an ion-channel based biosensor.

Gate dielectric surface treatments for performance improvement of poly(3-hexylthiophene-2,5-diyl) based organic field-effect transistors

NASA Astrophysics Data System (ADS)

Nawaz, Ali; de, Cristiane, , Col; Cruz-Cruz, Isidro; Kumar, Anshu; Kumar, Anil; Hümmelgen, Ivo A.

2015-08-01

We report on enhanced performance in poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic field effect transistors (OFETs) achieved by improvement in hole transport along the channel near the insulator/semiconductor (I/S) interface. The improvement in hole transport is demonstrated to occur very close to the I/S interface, after treatment of the insulator layer with sodium dodecyl sulfate (SDS). SDS is an anionic surfactant, with negatively charged heads, known for formation of micelles above critical micelle concentration (CMC), which contribute to the passivation of positively charged traps. Investigation of field-effect mobility (μFET) as a function of channel bottleneck thickness in OFETs reveals the favorable gate voltage regime where mobility is the highest. In addition, it shows that the gate dielectric surface treatment not only leads to an increase in mobility in that regime, but also displaces charge transport closer to the interface, hence pointing toward passivation of the charge traps at I/S interface. OFETs with SDS treatment were compared with untreated and vitamin C or hexadecyltrimethylammonium bromide (CTAB) treated OFETs. All the treatments resulted in significant improvements in specific dielectric capacitance, μFET, on/off current ratio and transconductance.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng

2018-04-01

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0-0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ˜17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm-3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Solution-processed multilayer polymer light-emitting diode without intermixing

NASA Astrophysics Data System (ADS)

Kasparek, C.; Blom, P. W. M.

2017-01-01

The intermixing of two emissive layers in a four-layer solution-processed polymeric light-emitting diode with a hole injection, two emissive layers, and one hole-blocking layer is investigated. The relative emission of both emissive layers is measured and compared to a calculated recombination profile across the device using drift-diffusion simulations. A good agreement between the measured and calculated relative emission was found, supporting that there is no intermixing in the two emissive materials.

Light illumination intensity dependence of photovoltaic parameter in polymer solar cells with ammonium heptamolybdate as hole extraction layer.

PubMed

Liu, Zhiyong; Niu, Shengli; Wang, Ning

2018-01-01

A low-temperature, solution-processed molybdenum oxide (MoO X ) layer and a facile method for polymer solar cells (PSCs) is developed. The PSCs based on a MoO X layer as the hole extraction layer (HEL) is a significant advance for achieving higher photovoltaic performance, especially under weaker light illumination intensity. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements show that the (NH 4 ) 6 Mo 7 O 24 molecule decomposes and forms the molybdenum oxide (MoO X ) molecule when undergoing thermal annealing treatment. In this study, PSCs with the MoO X layer as the HEL exhibited better photovoltaic performance, especially under weak light illumination intensity (from 100 to 10mWcm -2 ) compared to poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)-based PSCs. Analysis of the current density-voltage (J-V) characteristics at various light intensities provides information on the different recombination mechanisms in the PSCs with a MoO X and PEDOT:PSS layer as the HEL. That the slopes of the open-circuit voltage (V OC ) versus light illumination intensity plots are close to 1 unity (kT/q) reveals that bimolecular recombination is the dominant and weaker monomolecular recombination mechanism in open-circuit conditions. That the slopes of the short-circuit current density (J SC ) versus light illumination intensity plots are close to 1 reveals that the effective charge carrier transport and collection mechanism of the MoO X /indium tin oxide (ITO) anode is the weaker bimolecular recombination in short-circuit conditions. Our results indicate that MoO X is an alternative candidate for high-performance PSCs, especially under weak light illumination intensity. Copyright © 2017 Elsevier Inc. All rights reserved.

En face spectral domain optical coherence tomography analysis of lamellar macular holes.

PubMed

Clamp, Michael F; Wilkes, Geoff; Leis, Laura S; McDonald, H Richard; Johnson, Robert N; Jumper, J Michael; Fu, Arthur D; Cunningham, Emmett T; Stewart, Paul J; Haug, Sara J; Lujan, Brandon J

2014-07-01

To analyze the anatomical characteristics of lamellar macular holes using cross-sectional and en face spectral domain optical coherence tomography. Forty-two lamellar macular holes were retrospectively identified for analysis. The location, cross-sectional length, and area of lamellar holes were measured using B-scans and en face imaging. The presence of photoreceptor inner segment/outer segment disruption and the presence or absence of epiretinal membrane formation were recorded. Forty-two lamellar macular holes were identified. Intraretinal splitting occurred within the outer plexiform layer in 97.6% of eyes. The area of intraretinal splitting in lamellar holes did not correlate with visual acuity. Eyes with inner segment/outer segment disruption had significantly worse mean logMAR visual acuity (0.363 ± 0.169; Snellen = 20/46) than in eyes without inner segment/outer segment disruption (0.203 ± 0.124; Snellen = 20/32) (analysis of variance, P = 0.004). Epiretinal membrane was present in 34 of 42 eyes (81.0%). En face imaging allowed for consistent detection and quantification of intraretinal splitting within the outer plexiform layer in patients with lamellar macular holes, supporting the notion that an area of anatomical weakness exists within Henle's fiber layer, presumably at the synaptic connection of these fibers within the outer plexiform layer. However, the en face area of intraretinal splitting did not correlate with visual acuity, disruption of the inner segment/outer segment junction was associated with significantly worse visual acuity in patients with lamellar macular holes.

Ambipolar transport of silver nanoparticles decorated graphene oxide field effect transistors

NASA Astrophysics Data System (ADS)

Sarkar, Kalyan Jyoti; Sarkar, K.; Pal, B.; Kumar, Aparabal; Das, Anish; Banerji, P.

2018-05-01

In this article, we report ambipolar field effect transistor (FET) by using graphene oxide (GO) as a gate dielectric material for silver nanoparticles (AgNPs) decorated GO channel layer. GO was synthesized by Hummers' method. The AgNPs were prepared via photochemical reduction of silver nitrate solution by using monoethanolamine as a reducing agent. Morphological properties of channel layer were characterized by Field Effect Scanning Electron Microscopy (FESEM). Fourier Transform Infrared Spectroscopy (FTIR) was carried out to characterize GO thin film. For device fabrication gold (Au) was deposited as source-drain contact and aluminum (Al) was taken as bottom contact. Electrical measurements were performed by back gate configuration. Ambipolar transport behavior was explained from transfer characteristics. A maximum electron mobiliy of 6.65 cm2/Vs and a hole mobility of 2.46 cm2/Vs were extracted from the transfer characteristics. These results suggest that GO is a potential candidate as a gate dielectric material for thin film transistor applications and also provides new insights in GO based research.

Luminance mechanisms in green organic light-emitting devices fabricated utilizing tris(8-hydroxyquinoline)aluminum/4,7-diphenyl-1, 10-phenanthroline multiple heterostructures acting as an electron transport layer.

PubMed

Choo, Dong Chul; Seo, Su Yul; Kim, Tae Whan; Jin, You Young; Seo, Ji Hyun; Kim, Young Kwan

2010-05-01

The electrical and the optical properties in green organic light-emitting devices (OLEDs) fabricated utilizing tris(8-hydroxyquinoline)aluminum (Alq3)/4,7-diphenyl-1,10-phenanthroline (BPhen) multiple heterostructures acting as an electron transport layer (ETL) were investigated. The operating voltage of the OLEDs with a multiple heterostructure ETL increased with increasing the number of the Alq3/BPhen heterostructures because more electrons were accumulated at the Alq3/BPhen heterointerfaces. The number of the leakage holes existing in the multiple heterostructure ETL of the OLEDs at a low voltage range slightly increased due to an increase of the internal electric field generated from the accumulated electrons at the Alq3/BPhen heterointerface. The luminance efficiency of the OLEDs with a multiple heterostructure ETL at a high voltage range became stabilized because the increase of the number of the heterointerface decreased the quantity of electrons accumulated at each heterointerface.

Simplified Perovskite Solar Cell with 4.1% Efficiency Employing Inorganic CsPbBr3 as Light Absorber.

PubMed

Duan, Jialong; Zhao, Yuanyuan; He, Benlin; Tang, Qunwei

2018-05-01

Perovskite solar cells with cost-effectiveness, high power conversion efficiency, and improved stability are promising solutions to the energy crisis and environmental pollution. However, a wide-bandgap inorganic-semiconductor electron-transporting layer such as TiO 2 can harvest ultraviolet light to photodegrade perovskite halides, and the high cost of a state-of-the-art hole-transporting layer is an economic burden for commercialization. Here, the building of a simplified cesium lead bromide (CsPbBr 3 ) perovskite solar cell with fluorine-doped tin oxide (FTO)/CsPbBr 3 /carbon architecture by a multistep solution-processed deposition technology is demonstrated, achieving an efficiency as high as 4.1% and improved stability upon interfacial modification by graphene quantum dots and CsPbBrI 2 quantum dots. This work provides new opportunities of building next-generation solar cells with significantly simplified processes and reduced production costs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the AlGaInP-bulk and AlGaInP/GaAs-superlattice confinement effects for heterostructure-emitter bipolar transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Jung-Hui, E-mail: jhtsai@nknucc.nknu.edu.tw

2015-02-09

The confinement effect and electrical characteristics of heterostructure-emitter bipolar transistors with an AlGaInP bulk-confinement layer and an AlGaInP/GaAs superlattice-confinement layer are first demonstrated and compared by experimentally results. In the two devices, the relatively large valence band discontinuity at AlGaInP/GaAs heterojunction provides excellent confinement effect for holes to enhance current gain. As to the AlGaInP/GaAs superlattice-confinement device, part of thermionic-emission electrons will be trapped in the GaAs quantum wells of the superlattice. This will result in lower collector current and current gain as compared with the bulk-confinement device. Nevertheless, the superlattice-confinement device exhibits a larger current-gain cutoff frequency, which canmore » be attributed that the tunneling behavior is included in the carrier transportation and transporting time across the emitter region could be substantially reduced.« less

Comprehensive study of the electronic and optical behavior of highly degenerate p-type Mg-doped GaN and AlGaN

NASA Astrophysics Data System (ADS)

Gunning, Brendan P.; Fabien, Chloe A. M.; Merola, Joseph J.; Clinton, Evan A.; Doolittle, W. Alan; Wang, Shuo; Fischer, Alec M.; Ponce, Fernando A.

2015-01-01

The bulk and 2-dimensional (2D) electrical transport properties of heavily Mg-doped p-type GaN films grown on AlN buffer layers by Metal Modulated Epitaxy are explored. Distinctions are made between three primary p-type conduction mechanisms: traditional valence band conduction, impurity band conduction, and 2D conduction within a 2D hole gas at a hetero-interface. The bulk and 2D contributions to the overall carrier transport are identified and the relative contributions are found to vary strongly with growth conditions. Films grown with III/V ratio less than 1.5 exhibit high hole concentrations exceeding 2 × 1019 cm-3 with effective acceptor activation energies of 51 meV. Films with III/V ratios greater than 1.5 exhibit lower overall hole concentrations and significant contributions from 2D transport at the hetero-interface. Films grown with III/V ratio of 1.2 and Mg concentrations exceeding 2 × 1020 cm-3 show no detectable inversion domains or Mg precipitation. Highly Mg-doped p-GaN and p-AlGaN with Al fractions up to 27% similarly exhibit hole concentrations exceeding 2 × 1019 cm-3. The p-GaN and p-Al0.11Ga0.89N films show broad ultraviolet (UV) photoluminescence peaks, which intercept the valence band, supporting the presence of a Mg acceptor band. Finally, a multi-quantum-well light-emitting diode (LED) and p-i-n diode are grown, both of which demonstrate rectifying behavior with turn-on voltages of 3-3.5 V and series resistances of 6-10 Ω without the need for any post-metallization annealing. The LED exhibits violet-blue luminescence at 425 nm, while the p-i-n diode shows UV luminescence at 381 nm, and both devices still show substantial light emission even when submerged in liquid nitrogen at 77 K.

Band Transport and Trapping in Didodecyl[1]benzothieno[3,2-b][1]benzothiophene Probed by Terahertz Spectroscopy.

PubMed

Arend, Thomas R; Wimmer, Andreas; Schweicher, Guillaume; Chattopadhyay, Basab; Geerts, Yves H; Kersting, Roland

2017-11-02

Terahertz electromodulation spectroscopy provides insight into the material-inherent transport properties of charge carriers in organic semiconductors. Experiments on didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C 12 -BTBT-C 12 ) devices yield for holes an intraband mobility of 9 cm 2 V -1 s -1 . The short duration of the THz pulses advances the understanding of the hole transport on the molecular scale. The efficient screening of Coulomb potentials leads to a collective response of the hole gas to external fields, which can be well described by the Drude model. Bias stress of the devices generates deep traps that capture mobile holes. Although the resulting polarization across the device hinders the injection of mobile holes, the hole mobilities are not affected.

Polymer-based solar cells having an active area of 1.6 cm{sup 2} fabricated via spray coating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scarratt, N. W.; Griffin, J.; Zhang, Y.

We demonstrate the fabrication of polymer solar cells in which both a PEDOT:PSS hole transport and a PCDTBT:PC{sub 71}BM photoactive layer are deposited by spray-casting. Two device geometries are explored, with devices having a pixel area of 165 mm{sup 2} attaining a power conversion efficiency of 3.7%. Surface metrology indicates that the PEDOT:PSS and PCDTBT:PC{sub 71}BM layers have a roughness of 2.57 nm and 1.18 nm over an area of 100 μm{sup 2}. Light beam induced current mapping reveals fluctuations in current generation efficiency over length-scales of ∼2 mm, with the average photocurrent being 75% of its maximum value.

Universal intrinsic scale of the hole concentration in high- Tc cuprates

NASA Astrophysics Data System (ADS)

Honma, T.; Hor, P. H.; Hsieh, H. H.; Tanimoto, M.

2004-12-01

We have measured thermoelectric power (TEP) as a function of hole concentration per CuO2 layer Ppl in Y1-xCaxBa2Cu3O6 (Ppl=x/2) with no oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl , S290(Ppl) , of Y1-xCaxBa2Cu3O6 behaves identically to that of La2-zSrzCuO4 (Ppl=z) . We argue that S290(Ppl) represents a measure of the intrinsic equilibrium electronic states of doped holes and, therefore, can be used as a common scale for the carrier concentrations of layered cuprates. We shows that the Ppl determined by this new universal scale is consistent with both hole concentration microscopically determined by NQR and the hole concentration macroscopically determined by the formal valency of Cu . We find two characteristic scaling temperatures, TS* and TS2* , in the TEP versus temperature curves that change systematically with doping. Based on the universal scale, we uncover a universal phase diagram in which almost all the experimentally determined pseudogap temperatures as a function of Ppl fall on two common curves; lower pseudogap temperature defined by the TS* versus Ppl curve and upper pseudogap temperature defined by the TS2* versus Ppl curve. We find that while pseudogaps are intrinsic properties of doped holes of a single CuO2 layer for all high- Tc cuprates, Tc depends on the number of layers, therefore, the inter layer coupling, in each individual system.

Single-Band and Dual-Band Infrared Detectors

NASA Technical Reports Server (NTRS)

Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)

2015-01-01

Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.

Single-Band and Dual-Band Infrared Detectors

NASA Technical Reports Server (NTRS)

Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)

2017-01-01

Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.

On the Hole Injection for III-Nitride Based Deep Ultraviolet Light-Emitting Diodes.

PubMed

Li, Luping; Zhang, Yonghui; Xu, Shu; Bi, Wengang; Zhang, Zi-Hui; Kuo, Hao-Chung

2017-10-24

The hole injection is one of the bottlenecks that strongly hinder the quantum efficiency and the optical power for deep ultraviolet light-emitting diodes (DUV LEDs) with the emission wavelength smaller than 360 nm. The hole injection efficiency for DUV LEDs is co-affected by the p-type ohmic contact, the p-type hole injection layer, the p-type electron blocking layer and the multiple quantum wells. In this report, we review a large diversity of advances that are currently adopted to increase the hole injection efficiency for DUV LEDs. Moreover, by disclosing the underlying device physics, the design strategies that we can follow have also been suggested to improve the hole injection for DUV LEDs.

On the Hole Injection for III-Nitride Based Deep Ultraviolet Light-Emitting Diodes

PubMed Central

Li, Luping; Zhang, Yonghui; Kuo, Hao-Chung

2017-01-01

The hole injection is one of the bottlenecks that strongly hinder the quantum efficiency and the optical power for deep ultraviolet light-emitting diodes (DUV LEDs) with the emission wavelength smaller than 360 nm. The hole injection efficiency for DUV LEDs is co-affected by the p-type ohmic contact, the p-type hole injection layer, the p-type electron blocking layer and the multiple quantum wells. In this report, we review a large diversity of advances that are currently adopted to increase the hole injection efficiency for DUV LEDs. Moreover, by disclosing the underlying device physics, the design strategies that we can follow have also been suggested to improve the hole injection for DUV LEDs. PMID:29073738

Effects of bleed-hole geometry and plenum pressure on three-dimensional shock-wave/boundary-layer/bleed interactions

NASA Technical Reports Server (NTRS)

Chyu, Wei J.; Rimlinger, Mark J.; Shih, Tom I.-P.

1993-01-01

A numerical study was performed to investigate 3D shock-wave/boundary-layer interactions on a flat plate with bleed through one or more circular holes that vent into a plenum. This study was focused on how bleed-hole geometry and pressure ratio across bleed holes affect the bleed rate and the physics of the flow in the vicinity of the holes. The aspects of the bleed-hole geometry investigated include angle of bleed hole and the number of bleed holes. The plenum/freestream pressure ratios investigated range from 0.3 to 1.7. This study is based on the ensemble-averaged, 'full compressible' Navier-Stokes (N-S) equations closed by the Baldwin-Lomax algebraic turbulence model. Solutions to the ensemble-averaged N-S equations were obtained by an implicit finite-volume method using the partially-split, two-factored algorithm of Steger on an overlapping Chimera grid.

Ultrahigh mobility and efficient charge injection in monolayer organic thin-film transistors on boron nitride.

PubMed

He, Daowei; Qiao, Jingsi; Zhang, Linglong; Wang, Junya; Lan, Tu; Qian, Jun; Li, Yun; Shi, Yi; Chai, Yang; Lan, Wei; Ono, Luis K; Qi, Yabing; Xu, Jian-Bin; Ji, Wei; Wang, Xinran

2017-09-01

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2- b ][1]benzothiophene (C 8 -BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm 2 /Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C 8 -BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties.

Ultrahigh mobility and efficient charge injection in monolayer organic thin-film transistors on boron nitride

PubMed Central

He, Daowei; Qiao, Jingsi; Zhang, Linglong; Wang, Junya; Lan, Tu; Qian, Jun; Li, Yun; Shi, Yi; Chai, Yang; Lan, Wei; Ono, Luis K.; Qi, Yabing; Xu, Jian-Bin; Ji, Wei; Wang, Xinran

2017-01-01

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm2/Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C8-BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties. PMID:28913429

Interfacial Energy-Level Alignment for High-Performance All-Inorganic Perovskite CsPbBr3 Quantum Dot-Based Inverted Light-Emitting Diodes.

PubMed

Subramanian, Alagesan; Pan, Zhenghui; Zhang, Zhenbo; Ahmad, Imtiaz; Chen, Jing; Liu, Meinan; Cheng, Shuang; Xu, Yijun; Wu, Jun; Lei, Wei; Khan, Qasim; Zhang, Yuegang

2018-04-18

All-inorganic perovskite light-emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy-level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr 3 -based PeLED with an inverted architecture using lithium-doped TiO 2 nanoparticles as the electron transport layer (ETL). The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A -1 , a luminance efficiency of 2210 cd m -2 , and a low turn-on voltage of 2.3 V. The turn-on voltage is one of the lowest values among reported CsPbBr 3 -based PeLEDs. A 7-fold increase in device efficiencies has been obtained for lithium-doped TiO 2 compared to that for undoped TiO 2 -based devices.

Atomic layer-by-layer thermoelectric conversion in topological insulator bismuth/antimony tellurides.

PubMed

Sung, Ji Ho; Heo, Hoseok; Hwang, Inchan; Lim, Myungsoo; Lee, Donghun; Kang, Kibum; Choi, Hee Cheul; Park, Jae-Hoon; Jhi, Seung-Hoon; Jo, Moon-Ho

2014-07-09

Material design for direct heat-to-electricity conversion with substantial efficiency essentially requires cooperative control of electrical and thermal transport. Bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3), displaying the highest thermoelectric power at room temperature, are also known as topological insulators (TIs) whose electronic structures are modified by electronic confinements and strong spin-orbit interaction in a-few-monolayers thickness regime, thus possibly providing another degree of freedom for electron and phonon transport at surfaces. Here, we explore novel thermoelectric conversion in the atomic monolayer steps of a-few-layer topological insulating Bi2Te3 (n-type) and Sb2Te3 (p-type). Specifically, by scanning photoinduced thermoelectric current imaging at the monolayer steps, we show that efficient thermoelectric conversion is accomplished by optothermal motion of hot electrons (Bi2Te3) and holes (Sb2Te3) through 2D subbands and topologically protected surface states in a geometrically deterministic manner. Our discovery suggests that the thermoelectric conversion can be interiorly achieved at the atomic steps of a homogeneous medium by direct exploiting of quantum nature of TIs, thus providing a new design rule for the compact thermoelectric circuitry at the ultimate size limit.

Highly efficient and stable white organic light emitting diode base on double recombination zones of phosphorescent blue/orange emitters.

PubMed

Lee, Seok Jae; Koo, Ja Ryong; Lim, Dong Hwan; Park, Hye Rim; Kim, Young Kwan; Ha, Yunkyoung

2011-08-01

We demonstrated efficient and stable white phosphorescent organic light-emitting diodes (OLEDs) with double-emitting layers (D-EMLs), which were comprised of two emissive layers with a hole transport-type host of N,N'-dicarbazolyl-3,5-benzene (mCP) and a electron transport-type host of 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) with blue/orange emitters, respectively. We fabricated two type white devices with single emitting layer (S-EML) and D-EML of orange emitter, maintaining double recombination zone of blue emitter. In addition, the device architecture was developed to confine excitons inside the D-EMLs and to manage triplet excitons by controlling the charge injection. As a result, light-emitting performances of white OLED with D-EMLs were improved and showed the steady CIE coordinates compared to that with S-EML of orange emitter, which demonstrated the maximum luminous efficiency and external quantum efficiency were 21.38 cd/A and 11.09%. It also showed the stable white emission with CIE(x,y) coordinates from (x = 0.36, y = 0.37) at 6 V to (x = 0.33, y = 0.38) at 12 V.

Buffer transport mechanisms in intentionally carbon doped GaN heterojunction field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uren, Michael J.; Cäsar, Markus; Kuball, Martin

2014-06-30

Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer layers in a carbon doped GaN power heterojunction field effect transistor. Carbon doped GaN and multiple layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C doped layer is shown to occur by hole conduction in the valence band withmore » activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.« less

All-solution-processed, multilayered CuInS₂/ZnS colloidal quantum-dot-based electroluminescent device.

PubMed

Kim, Jong-Hoon; Yang, Heesun

2014-09-01

While significant progress of electroluminescent (EL) quantum dot light-emitting diodes (QD-LEDs) that rely exclusively on Cd-containing II-VI quantum dots (QDs) has been reported over the past two decades with respect to device processing and performance, devices based on non-Cd QDs as an active emissive layer (EML) remain at the early stage of development. In this work, utilizing highly luminescent colloidal CuInS2 (CIS)/ZnS QDs, all-solution-processed multilayered QD-LEDs are fabricated by sequentially spin depositing a hole transport layer of poly(9-vinlycarbazole), an EML of CIS/ZnS QDs, and an electron transport layer of ZnO nanoparticles. Our focus in device fabrication is to vary the thickness of the QD EML, which is one of the primary determinants in EL performance but has not been addressed in earlier reports. The device with an optimal EML thickness exhibits a peak luminance of 1564  cd/m2 and current efficiency of 2.52  cd/A. This record value in efficiency is higher by 3-4 times that of CIS QD-LEDs reported previously.

HOLEGAGE 1.0 - STRAIN GAGE HOLE DRILLING ANALYSIS PROGRAM

NASA Technical Reports Server (NTRS)

Hampton, R. W.

1994-01-01

There is no simple and perfect way to measure residual stresses in metal parts that have been welded or deformed to make complex structures such as pressure vessels and aircraft, yet these locked-in stresses can contribute to structural failure by fatigue and fracture. However, one proven and tested technique for determining the internal stress of a metal part is to drill a test hole while measuring the relieved strains around the hole, such as the hole-drilling strain gage method described in ASTM E 837. The program HOLEGAGE processes strain gage data and provides additional calculations of internal stress variations that are not obtained with standard E 837 analysis methods. The typical application of the technique uses a three gage rosette with a special hole-drilling fixture for drilling a hole through the center of the rosette to produce a hole with very small gage pattern eccentricity error. Another device is used to control the drilling and halt the drill at controlled depth steps. At each step, strains from all three strain gages are recorded. The influence coefficients used by HOLEGAGE to compute stresses from relieved hole strains were developed by published finite element method studies of thick plates for specific hole sizes and depths. The program uses a parabolic fit and an interpolating scheme to project the coefficients to other hole sizes and depths. Additionally, published experimental data are used to extend the coefficients to relatively thin plates. These influence coefficients are used to compute the stresses in the original part from the strain data. HOLEGAGE will compute interior planar stresses using strain data from each drilled hole depth layer. Planar stresses may be computed in three ways including: a least squares fit for a linear variation with depth, an integral method to give incremental stress data for each layer, or by a linear fit to the integral data (with some surface data points omitted) to predict surface stresses before strain gage sanding preparations introduced additional residual stresses. Options are included for estimating the effect of hole eccentricity on calculations, smoothing noise from the strain data, and inputting the program data either interactively or from a data file. HOLEGAGE was written in FORTRAN 77 for DEC VAX computers under VMS, and is transportable except for system-unique TIME and DATE system calls. The program requires 54K of main memory and was developed in 1990. The program is available on a 9-track 1600 BPI VAX BACKUP format magnetic tape (standard media) or a TK50 tape cartridge. The documentation is included on the tape. DEC VAX and VMS are trademarks of Digital Equipment Corporation.

Spatially resolved, substrate-induced rectification in C 60 bilayers on copper

DOE PAGES

Smerdon, J. A.; Darancet, P.; Guest, J. R.

2017-02-22

Here, we demonstrate rectification ratios ( RR) of ≳1000 at biases of 1.3 V in bilayers of C 60 deposited on copper. Using scanning tunneling spectroscopy and first-principles calculations, we show that the strong coupling between C 60 and the Cu(111) surface leads to the metallization of the bottom C 60 layer, while the molecular orbitals of the top C60 are essentially unaffected. Due to this substrate-induced symmetry breaking and to a tunneling transport mechanism, the system behaves as a hole-blocking layer, with a spatial dependence of the onset voltage on intra-layer coordination. Together with previous observations of strong electron-blockingmore » character of pentacene/C 60 bilayers on Cu(111), this work further demonstrates the potential of strongly hybridized, C 60-coated electrodes to harness the electrical functionality of molecular components.« less