Silicon nanowire array architecture for heterojunction electronics

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

Solovan, M. M., E-mail: m.solovan@chnu.edu.ua; Brus, V. V.; Mostovyi, A. I.

2017-04-15

Photosensitive nanostructured heterojunctions n-TiN/p-Si were fabricated by means of titanium nitride thin films deposition (n-type conductivity) by the DC reactive magnetron sputtering onto nano structured single crystal substrates of p-type Si (100). The temperature dependencies of the height of the potential barrier and series resistance of the n-TiN/p-Si heterojunctions were investigated. The dominant current transport mechanisms through the heterojunctions under investigation were determined at forward and reverse bias. The heterojunctions under investigation generate open-circuit voltage V{sub oc} = 0.8 V, short-circuit current I{sub sc} = 3.72 mA/cm{sup 2} and fill factor FF = 0.5 under illumination of 100 mW/cm{sup 2}.

Ultraviolet random lasing action from highly disordered n-AlN/p-GaN heterojunction.

PubMed

Yang, H Y; Yu, S F; Wong, J I; Cen, Z H; Liang, H K; Chen, T P

2011-05-01

Room-temperature random lasing is achieved from an n-AlN/p-GaN heterojunction. The highly disordered n-AlN layer, which was deposited on p-GaN:Mg layer via radio frequency magnetron sputtering, acts as a scattering medium to sustain coherent optical feedback. The p-GaN:Mg layer grown on sapphire provides optical amplification to the scattered light propagating along the heterojunction. Hence, lasing peaks of line width less than 0.4 nm are emerged from the emission spectra at round 370 nm for the heterojunction under forward bias larger than 5.1 V. Lasing characteristics of the heterojunction are in agreement with the behavior of random lasers.

Development of a Planar Heterojunction Bipolar Transistor for Very High Speed Logic.

DTIC Science & Technology

1983-12-01

AD- R136 341 DEVELOPMENT OF A PLANAR HETEROJUNCTION BIPOLAR i/i TRANSISTOR FOR VERV HIGH S..(U) CALIFORNIA UNIV SANTA BARBARA DEPT OF ELECTRICAL AND...GaAs material systems . Emphasis has been placed on growth and char- acterization of the above heterojunctions by Holecular Beam Epitaxy and on the...GaAs material system is used to fabricate discrete single heterojunction bipolar transistor structures. Conventional mesa-etch tech- niques will be used

A boron and gallium co-doped ZnO intermediate layer for ZnO/Si heterojunction diodes

NASA Astrophysics Data System (ADS)

Lu, Yuanxi; Huang, Jian; Li, Bing; Tang, Ke; Ma, Yuncheng; Cao, Meng; Wang, Lin; Wang, Linjun

2018-01-01

ZnO (Zinc oxide)/Si (Silicon) heterojunctions were prepared by depositing n-type ZnO films on p-type single crystal Si substrates using magnetron sputtering. A boron and gallium co-doped ZnO (BGZO) high conductivity intermediate layer was deposited between aurum (Au) electrodes and ZnO films. The influence of the BGZO layer on the properties of Au/ZnO contacts and the performance of ZnO/Si heterojunctions was investigated. The results show an improvement in contact resistance by introducing the BGZO layer. Compared with the ZnO/Si heterojunction, the BGZO/ZnO/Si heterojunction exhibits a larger forward current, a smaller turn-on voltage and higher ratio of ultraviolet (UV) photo current/dark current.

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

DOE PAGES

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; ...

2015-07-22

The formation of semiconductor heterojunctions and their high density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional (2D) crystalline semiconductors as building blocks in next generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate a process strategy for the formation of lithographically-patterned lateral semiconducting heterojunctions within a single 2D crystal. E-beam lithography is used to pattern MoSe 2 monolayer crystals with SiO 2, and the exposed locations are selectively and totally converted to MoS 2 using pulsed laser deposition (PLD) of sulfur in order to form MoSe 2/MoS 2 heterojunctions in predefinedmore » patterns. The junctions and conversion process are characterized by atomically resolved scanning transmission electron microscopy, photoluminescence, and Raman spectroscopy. This demonstration of lateral semiconductor heterojunction arrays within a single 2D crystal is an essential step for the lateral integration of 2D semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin circuitry.« less

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

PubMed Central

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; Lupini, Andrew R.; Lee, Jaekwang; Basile, Leonardo; Boulesbaa, Abdelaziz; Rouleau, Christopher M.; Puretzky, Alexander A.; Ivanov, Ilia N.; Xiao, Kai; Yoon, Mina; Geohegan, David B.

2015-01-01

The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices. PMID:26198727

Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy

DOE PAGES

Amrillah, Tahta; Bitla, Yugandhar; Shin, Kwangwoo; ...

2017-05-22

Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric–ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this paper, we investigated the magnetoelectric coupling in a self-assembled BiFeO 3 (BFO)–CoFe 2O 4 (CFO) bulk heterojunction epitaxially grownmore » on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO–CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Finally and therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.« less

Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy

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

Amrillah, Tahta; Bitla, Yugandhar; Shin, Kwangwoo

Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric–ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this paper, we investigated the magnetoelectric coupling in a self-assembled BiFeO 3 (BFO)–CoFe 2O 4 (CFO) bulk heterojunction epitaxially grownmore » on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO–CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Finally and therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.« less

Efficiency of bulk-heterojunction organic solar cells

PubMed Central

Scharber, M.C.; Sariciftci, N.S.

2013-01-01

During the last years the performance of bulk heterojunction solar cells has been improved significantly. For a large-scale application of this technology further improvements are required. This article reviews the basic working principles and the state of the art device design of bulk heterojunction solar cells. The importance of high power conversion efficiencies for the commercial exploitation is outlined and different efficiency models for bulk heterojunction solar cells are discussed. Assuming state of the art materials and device architectures several models predict power conversion efficiencies in the range of 10–15%. A more general approach assuming device operation close to the Shockley–Queisser-limit leads to even higher efficiencies. Bulk heterojunction devices exhibiting only radiative recombination of charge carriers could be as efficient as ideal inorganic photovoltaic devices. PMID:24302787

Fabrication and characterization of anisotype heterojunctions n-TiN/p-CdTe

NASA Astrophysics Data System (ADS)

Solovan, M. M.; Brus, V. V.; Maryanchuk, P. D.; Ilashchuk, M. I.; Rappich, J.; Nickel, N.; Abashin, S. L.

2014-01-01

Photosensitive heterojunctions n-TiN/p-CdTe were fabricated for the first time by means of titanium nitride thin film deposition (n-type conductivity) by the reactive magnetron sputtering onto freshly etched single crystal substrates CdTe (1 1 0) of p-type conductivity. The temperature dependences of the height of the potential barrier and series resistance of the n-TiN/p-CdTe heterojunction were investigated. The dominating current transport mechanisms through the heterojunctions under investigation were determined at forward and reverse bias. The heterojunctions under investigation generate open-circuit voltage Voc = 0.35 V, short-circuit current Isc = 1.88 mA см-2 and fill factor FF = 0.51 under illumination 80 mW сm-2.

Near room temperature and large-area synthesis of ZnO/Cu2O heterojunction for photocatalytic properties

NASA Astrophysics Data System (ADS)

Gao, Shiyong; Zhang, Jiejing; Li, Wenqiang; Jiao, Shujie; Nie, Yanguang; Fan, Huaiyun; Zeng, Zhi; Yu, Qingjiang; Wang, Jinzhong; Zhang, Xitian

2018-01-01

Large-area ZnO/Cu2O heterojunction have been successfully synthesized on Cu foil through a simple two-step solution method at near room temperature. The field emission scanning electron microscopy characterization indicates that the morphology of as-prepared Cu2O film grown on Cu foil is octahedral structure with diameter of ∼450 nm and ZnO is nanorod arrays structure with diameter of ∼150 nm. The current-voltage measurement of ZnO/Cu2O heterojunction shows a typical rectifying characteristics. Moreover, the photocatalytic test indicates that ZnO/Cu2O heterojunction exhibits high photocatalytic efficient for degradation of congo red dyes. The possible photocatalytic mechanism of ZnO/Cu2O heterojunction is also presented.

Enhanced photoelectrochemical response of plasmonic Au embedded BiVO4/Fe2O3 heterojunction.

PubMed

Verma, Anuradha; Srivastav, Anupam; Khan, Saif A; Rani Satsangi, Vibha; Shrivastav, Rohit; Kumar Avasthi, Devesh; Dass, Sahab

2017-06-14

The effect of embedding Au nanoparticles (NPs) in a BiVO 4 /Fe 2 O 3 heterojunction for photoelectrochemical water splitting is studied here for the first time. The present nanostructured heterojunction offers three major advantages over pristine BiVO 4 and Fe 2 O 3 : (i) the formation of a heterojunction between BiVO 4 and Fe 2 O 3 enhances the charge carrier separation and transfer, (ii) the layer of Fe 2 O 3 provides protection to BiVO 4 from photocorrosion and, (iii) the Au NPs possessing surface plasmon resonance (SPR) enhance the photoelectrochemical response by transferring energy to metal oxides by hot electron transfer (HET) and plasmon resonant energy transfer (PRET). The present study reveals that the heterojunction ITO/BiVO 4 /Fe 2 O 3 (with 32% v/v Au solution in both layers) gives the best performance and mitigates the limitations of both pristine Fe 2 O 3 and BiVO 4 . A thirteen-fold increment in applied bias photon-to-current conversion efficiency (ABPE) was observed at 1.24 V vs. RHE under the condition of 1 Sun illumination. Monochromatic incident photon-to-current conversion efficiency (IPCE) measurements indicated that an Au embedded heterojunction is more effective in harvesting visible light in comparison to a heterojunction without Au NPs.

High Detectivity Graphene-Silicon Heterojunction Photodetector.

PubMed

Li, Xinming; Zhu, Miao; Du, Mingde; Lv, Zheng; Zhang, Li; Li, Yuanchang; Yang, Yao; Yang, Tingting; Li, Xiao; Wang, Kunlin; Zhu, Hongwei; Fang, Ying

2016-02-03

A graphene/n-type silicon (n-Si) heterojunction has been demonstrated to exhibit strong rectifying behavior and high photoresponsivity, which can be utilized for the development of high-performance photodetectors. However, graphene/n-Si heterojunction photodetectors reported previously suffer from relatively low specific detectivity due to large dark current. Here, by introducing a thin interfacial oxide layer, the dark current of graphene/n-Si heterojunction has been reduced by two orders of magnitude at zero bias. At room temperature, the graphene/n-Si photodetector with interfacial oxide exhibits a specific detectivity up to 5.77 × 10(13) cm Hz(1/2) W(-1) at the peak wavelength of 890 nm in vacuum, which is highest reported detectivity at room temperature for planar graphene/Si heterojunction photodetectors. In addition, the improved graphene/n-Si heterojunction photodetectors possess high responsivity of 0.73 A W(-1) and high photo-to-dark current ratio of ≈10(7) . The current noise spectral density of the graphene/n-Si photodetector has been characterized under ambient and vacuum conditions, which shows that the dark current can be further suppressed in vacuum. These results demonstrate that graphene/Si heterojunction with interfacial oxide is promising for the development of high detectivity photodetectors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly Enhanced H2 Sensing Performance of Few-Layer MoS2/SiO2/Si Heterojunctions by Surface Decoration of Pd Nanoparticles.

PubMed

Hao, Lanzhong; Liu, Yunjie; Du, Yongjun; Chen, Zhaoyang; Han, Zhide; Xu, Zhijie; Zhu, Jun

2017-10-17

A novel few-layer MoS 2 /SiO 2 /Si heterojunction is fabricated via DC magnetron sputtering technique, and Pd nanoparticles are further synthesized on the device surface. The results demonstrate that the fabricated sensor exhibits highly enhanced responses to H 2 at room temperature due to the decoration of Pd nanoparticles. For example, the Pd-decorated MoS 2 /SiO 2 /Si heterojunction shows an excellent response of 9.2 × 10 3 % to H 2 , which is much higher than the values for the Pd/SiO 2 /Si and MoS 2 /SiO 2 /Si heterojunctions. In addition, the H 2 sensing properties of the fabricated heterojunction are dependent largely on the thickness of the Pd-nanoparticle layer and there is an optimized Pd thickness for the device to achieve the best sensing characteristics. Based on the microstructure characterization and electrical measurements, the sensing mechanisms of the Pd-decorated MoS 2 /SiO 2 /Si heterojunction are proposed. These results indicate that the Pd decoration of few-layer MoS 2 /SiO 2 /Si heterojunctions presents an effective strategy for the scalable fabrication of high-performance H 2 sensors.

Effects of Different Materials Used for Internal Floating Electrode on the Photovoltaic Properties of Tandem Type Organic Solar Cell

NASA Astrophysics Data System (ADS)

Triyana, Kuwat; Yasuda, Takeshi; Fujita, Katsuhiko; Tsutsui, Tetsuo

2004-04-01

Three thin heterojunctions sandwiched between indium tin oxide (ITO) and the top electrode as triple-heterojunction organic solar cells have been fabricated. Each heterojunction cell consists of CuPc as a donor layer and perilene tetracrboxylic-bis-benzimidazole (PTCBI) as an acceptor layer. Ultra thin (1 nm average thickness) layers of Ag or Au have been inserted between two heterojunctions as an internal electrode. Ag and Au were chosen as materials both for internal floating and top electrodes. Influences of different deposition sequences of the organic layer in each heterojunction cell and different electrode materials were also investigated. The optimum devices were obtained when the same material was used both as an internal electrode and a top electrode. When the deposition sequence of the heterojunction is PTCBI/CuPc, the most suitable electrode is Au and the ITO is negative relative to the top electrode. Meanwhile, Ag is suitable for an electrode when the deposition sequence is CuPc/PTCBI. In this second deposition sequence, the ITO is positive relative to the top electrode. The open circuit voltage (Voc) of both optimum devices is on the order of 1.35-1.5 V. These values are approximately three times higher than that in single-heterojunction organic solar cells.

Strain tunable light emitting diodes with germanium P-I-N heterojunctions

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

Lagally, Max G; Sanchez Perez, Jose Roberto

Tunable p-i-n diodes comprising Ge heterojunction structures are provided. Also provided are methods for making and using the tunable p-i-n diodes. Tunability is provided by adjusting the tensile strain in the p-i-n heterojunction structure, which enables the diodes to emit radiation over a range of wavelengths.

Toward designing semiconductor-semiconductor heterojunctions for photocatalytic applications

NASA Astrophysics Data System (ADS)

Zhang, Liping; Jaroniec, Mietek

2018-02-01

Semiconductor photocatalysts show a great potential for environmental and energy-related applications, however one of the major disadvantages is their relatively low photocatalytic performance due to the recombination of electron-hole pairs. Therefore, intensive research is being conducted toward design of heterojunctions, which have been shown to be effective for improving the charge-transfer properties and efficiency of photocatalysts. According to the type of band alignment and direction of internal electric field, heterojunctions are categorized into five different types, each of which is associated with its own charge transfer characteristics. Since the design of heterojunctions requires the knowledge of band edge positions of component semiconductors, the commonly used techniques for the assessment of band edge positions are reviewed. Among them the electronegativity-based calculation method is applied for a large number of popular visible-light-active semiconductors, including some widely investigated bismuth-containing semiconductors. On basis of the calculated band edge positions and the type of component semiconductors reported, heterojunctions composed of the selected bismuth-containing semiconductors are proposed. Finally, the most popular synthetic techniques for the fabrication of heterojunctions are briefly discussed.

Polarization-induced interfacial coupling modulations in BaTiO3/GaN heterojunction devices

NASA Astrophysics Data System (ADS)

Bhat, Thirumaleshwara N.; Pandey, B. K.; Krupanidhi, S. B.

2017-07-01

We report on the ferroelectric polarization-induced switchable interfacial coupling modulations in BaTiO3/GaN heterojunction transport behaviour. The ferroelectric barium titanate, BaTiO3 (BTO) was integrated with polar semiconductor gallium nitride (GaN). BTO with a tetragonal structure was deposited on a wurtzite (0 0 0 1) epitaxial GaN/c-Al2O3 substrate by pulsed laser deposition, which was further confirmed by x-ray diffraction and Raman spectroscopy. BTO/GaN heterojunctions with resistive switching behaviour exhibited modulations in transport characteristics due to the interfacial coupling. The ferroelectric nature and interfacial coupling effect of this heterojunction was confirmed with the help of piezo-response force microscopy. A valence band offset of 0.82 eV and conduction band offset of 0.62 eV were obtained for BTO/GaN heterojunctions by x-ray photo-electron spectroscopy. This interfacial coupling phenomenon was analysed and its effect on the carrier conduction in the heterojunction was investigated by band alignment studies.

Enhanced photocatalytic activity of graphitic carbon nitride/carbon nanotube/Bi2WO6 ternary Z-scheme heterojunction with carbon nanotube as efficient electron mediator.

PubMed

Jiang, Deli; Ma, Wanxia; Xiao, Peng; Shao, Leqiang; Li, Di; Chen, Min

2018-02-15

All-solid-state Z-scheme heterojunction has attracted much attention in photocatalytic field because of its strong ability in charge separation and transfer. In the present study, all-solid-state ternary Z-scheme heterojunction constructed by graphitic carbon nitride (CN) nanosheet, carbon nanotube (CNT), and Bi 2 WO 6 (BWO) nanosheet, in which CNT was employed as the electron mediator. The CN/CNT/BWO ternary Z-scheme heterojunction shows the enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride (TC) as compared to the pristine g-C 3 N 4 , Bi 2 WO 6 , CNT/BWO, CNT/CN, and CN/BWO. The significantly improved photocatalytic activity can be mainly ascribed to the formed CNT-mediated Z-scheme heterojunction, which facilitates the separation and transfer of photogenerated electron-hole pairs. Our work provides a rational design of all-solid-state Z-scheme heterojunction with CNT as the electron mediator for highly efficient photocatalysis. Copyright © 2017 Elsevier Inc. All rights reserved.

Ultraviolet photodetector with high internal gain enhanced by TiO₂/SrTiO₃ heterojunction.

PubMed

Zhang, Min; Zhang, Haifeng; Lv, Kaibo; Chen, Weiyou; Zhou, Jingran; Shen, Liang; Ruan, Shengping

2012-03-12

In this letter, TiO₂ nanocrystalline film was prepared on SrTiO₃ (001) substrate to form an n-n heterojunction active layer. Interdigitated Au electrodes were deposited on the top of TiO₂ film to fabricate modified HMSM (heterojunction metal-semiconductor-metal) ultraviolet photodetector. At 10 V bias, the dark current of the detector was only 0.2 nA and the responsivity was 46.1 A/W at 260 nm. The rise and fall times of the device were 3.5 ms and 1.4 s, respectively. The TiO₂/SrTiO₃ heterojunction contributed a lot to the high responsivity and reduced the fall time, which improved the device performance effectively. These results demonstrate the excellent application of TiO₂/SrTiO₃ heterojunction in fabricating high performance UV photodetectors.

Valence band offsets of Sc x Ga1-x N/AlN and Sc x Ga1-x N/GaN heterojunctions

NASA Astrophysics Data System (ADS)

Tsui, H. C. L.; Goff, L. E.; Palgrave, R. G.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.

2016-07-01

The valence band offsets of Sc x Ga1-x N/AlN heterojunctions were measured by x-ray photoelectron spectroscopy (XPS) and were found to increase from 0.42 eV to 0.95 eV as the Sc content x increased from 0 to 0.15. The increase in valence band offset with increasing x is attributed to the corresponding increase in spontaneous polarization of the wurtzite structure. The Sc x Ga1-x N/AlN heterojunction is type I, similar to other III-nitride-based heterojunctions. The data also indicate that a type II staggered heterojunction, which can enhance spatial charge separation, could be formed if Sc x Ga1-x N is grown on GaN.

Enhanced planar perovskite solar cell efficiency and stability using a perovskite/PCBM heterojunction formed in one step.

PubMed

Zhou, Long; Chang, Jingjing; Liu, Ziye; Sun, Xu; Lin, Zhenhua; Chen, Dazheng; Zhang, Chunfu; Zhang, Jincheng; Hao, Yue

2018-02-08

Perovskite/PCBM heterojunctions are efficient for fabricating perovskite solar cells with high performance and long-term stability. In this study, an efficient perovskite/PCBM heterojunction was formed via conventional sequential deposition and one-step formation processes. Compared with conventional deposition, the one-step process was more facile, and produced a perovskite thin film of substantially improved quality due to fullerene passivation. Moreover, the resulting perovskite/PCBM heterojunction exhibited more efficient carrier transfer and extraction, and reduced carrier recombination. The perovskite solar cell device based on one-step perovskite/PCBM heterojunction formation exhibited a higher maximum PCE of 17.8% compared with that from the conventional method (13.7%). The device also showed exceptional stability, retaining 83% of initial PCE after 60 days of storage under ambient conditions.

Near-infrared photodetectors utilizing MoS{sub 2}-based heterojunctions

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

Park, Min Ji; Min, Jung Ki; Yi, Sum-Gyun

2015-07-28

Near-infrared photodetectors are developed using graphene/MoS{sub 2} and WSe{sub 2}/MoS{sub 2} vertical heterojunctions. These heterojunctions exhibit diode-rectifying behavior in the dark and enhanced photocurrent upon near-infrared irradiation. The photocurrent increases with increasing near-infrared power, leading to the photoresponsibility of 0.14 and 0.3 A W{sup −1} for the graphene/MoS{sub 2} and WSe{sub 2}/MoS{sub 2} heterojunctions, respectively, which are much higher than the photoresponsibility reported for a multilayer MoS{sub 2} phototransistor.

The photoirradiation induced p-n junction in naphthylamine-based organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Bai, Linyi; Gao, Qiang; Xia, Youyi; Ang, Chung Yen; Bose, Purnandhu; Tan, Si Yu; Zhao, Yanli

2015-08-01

The bulk heterojunction (BHJ) plays an indispensable role in organic photovoltaics, and thus has been investigated extensively in recent years. While a p-n heterojunction is usually fabricated using two different donor and acceptor materials such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), it is really rare that such a BHJ is constructed by a single entity. Here, we presented a photoirradiation-induced p-n heterojunction in naphthylamine-based organic photovoltaic cells, where naphthylamine as a typical p-type semiconductor could be oxidized under photoirradiation and transformed into a new semiconductor with the n-type character. The p-n heterojunction was realized using both the remaining naphthylamine and its oxidative product, giving rise to the performance improvement in organic photovoltaic devices. The experimental results show that the power conversion efficiency (PCE) of the devices could be achieved up to 1.79% and 0.43% in solution and thin film processes, respectively. Importantly, this technology using naphthylamine does not require classic P3HT and PCBM to realize the p-n heterojunction, thereby simplifying the device fabrication process. The present approach opens up a promising route for the development of novel materials applicable to the p-n heterojunction.The bulk heterojunction (BHJ) plays an indispensable role in organic photovoltaics, and thus has been investigated extensively in recent years. While a p-n heterojunction is usually fabricated using two different donor and acceptor materials such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), it is really rare that such a BHJ is constructed by a single entity. Here, we presented a photoirradiation-induced p-n heterojunction in naphthylamine-based organic photovoltaic cells, where naphthylamine as a typical p-type semiconductor could be oxidized under photoirradiation and transformed into a new semiconductor with the n-type character. The p-n heterojunction was realized using both the remaining naphthylamine and its oxidative product, giving rise to the performance improvement in organic photovoltaic devices. The experimental results show that the power conversion efficiency (PCE) of the devices could be achieved up to 1.79% and 0.43% in solution and thin film processes, respectively. Importantly, this technology using naphthylamine does not require classic P3HT and PCBM to realize the p-n heterojunction, thereby simplifying the device fabrication process. The present approach opens up a promising route for the development of novel materials applicable to the p-n heterojunction. Electronic supplementary information (ESI) available: Additional synthesis and characterization details. See DOI: 10.1039/c5nr04471e

Design of BAs-AlN monolayered honeycomb heterojunction structures: A first-principles study

NASA Astrophysics Data System (ADS)

Camacho-Mojica, Dulce C.; López-Urías, Florentino

2016-04-01

BAs and AlN are semiconductor materials with an indirect and direct gap respectively in the bulk phase. Recently, electronic calculations have demonstrated that a single-layer or few layers of BAs and AlN exhibit a graphite-like structure with interesting electronic properties. In this work, infinite sheets single-layer heterojunction structures based on alternated strips with honeycomb BAs and AlN layers are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different strip widths joined along zigzag and armchair edges. Results in optimized heterojunction geometries revealed that BAs narrow strips exhibit a corrugation effect due to a lattice mismatch. It was found that zigzag heterojunctions are more energetically favored than armchair heterojunctions. Furthermore, the formation energy presents a maximum at the point where the heterojunction becomes a planar structure. Electronic charge density results yielded a more ionic behavior in Alsbnd N bonds than the Bsbnd As bonds in accordance with monolayer results. It was observed that the conduction band minimum for both heterojunctions exhibit confined states located mainly at the entire AlN strips whereas the valence band maximum exhibits confined states located mainly at BAs strips. We expect that the present investigation will motivate more experimental and theoretical studies on new layered materials made of III-V semiconductors.

Current Status and Future Prospects of Copper Oxide Heterojunction Solar Cells.

PubMed

Wong, Terence K S; Zhuk, Siarhei; Masudy-Panah, Saeid; Dalapati, Goutam K

2016-04-07

The current state of thin film heterojunction solar cells based on cuprous oxide (Cu₂O), cupric oxide (CuO) and copper (III) oxide (Cu₄O₃) is reviewed. These p-type semiconducting oxides prepared by Cu oxidation, sputtering or electrochemical deposition are non-toxic, sustainable photovoltaic materials with application potential for solar electricity. However, defects at the copper oxide heterojunction and film quality are still major constraining factors for achieving high power conversion efficiency, η. Amongst the Cu₂O heterojunction devices, a maximum η of 6.1% has been obtained by using pulsed laser deposition (PLD) of Al x Ga 1- x O onto thermal Cu₂O doped with Na. The performance of CuO/n-Si heterojunction solar cells formed by magnetron sputtering of CuO is presently limited by both native oxide and Cu rich copper oxide layers at the heterointerface. These interfacial layers can be reduced by using a two-step sputtering process. A high η of 2.88% for CuO heterojunction solar cells has been achieved by incorporation of mixed phase CuO/Cu₂O nanopowder. CuO/Cu₂O heterojunction solar cells fabricated by electrodeposition and electrochemical doping has a maximum efficiency of 0.64% after surface defect passivation and annealing. Finally, early stage study of Cu₄O₃/GaN deposited on sapphire substrate has shown a photovoltaic effect and an η of ~10 -2 %.

Energy level alignment at planar organic heterojunctions: influence of contact doping and molecular orientation.

PubMed

Opitz, Andreas

2017-04-05

Planar organic heterojunctions are widely used in photovoltaic cells, light-emitting diodes, and bilayer field-effect transistors. The energy level alignment in the devices plays an important role in obtaining the aspired gap arrangement. Additionally, the π-orbital overlap between the involved molecules defines e.g. the charge-separation efficiency in solar cells due to charge-transfer effects. To account for both aspects, direct/inverse photoemission spectroscopy and near edge x-ray absorption fine structure spectroscopy were used to determine the energy level landscape and the molecular orientation at prototypical planar organic heterojunctions. The combined experimental approach results in a comprehensive model for the electronic and morphological characteristics of the interface between the two investigated molecular semiconductors. Following an introduction on heterojunctions used in devices and on energy levels of organic materials, the energy level alignment of planar organic heterojunctions will be discussed. The observed energy landscape is always determined by the individual arrangement between the energy levels of the molecules and the work function of the electrode. This might result in contact doping due to Fermi level pinning at the electrode for donor/acceptor heterojunctions, which also improves the solar cell efficiency. This pinning behaviour can be observed across an unpinned interlayer and results in charge accumulation at the donor/acceptor interface, depending on the transport levels of the respective organic semiconductors. Moreover, molecular orientation will affect the energy levels because of the anisotropy in ionisation energy and electron affinity and is influenced by the structural compatibility of the involved molecules at the heterojunction. High structural compatibility leads to π-orbital stacking between different molecules at a heterojunction, which is of additional interest for photovoltaic active interfaces and for ground-state charge-transfer.

Interface-state density estimation of n-type nanocrystalline FeSi2/p-type Si heterojunctions fabricated by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Nopparuchikun, Adison; Promros, Nathaporn; Sittimart, Phongsaphak; Onsee, Peeradon; Duangrawa, Asanlaya; Teakchaicum, Sakmongkon; Nogami, Tomohiro; Yoshitake, Tsuyoshi

2017-09-01

By utilizing pulsed laser deposition (PLD), heterojunctions comprised of n-type nanocrystalline (NC) FeSi2 thin films and p-type Si substrates were fabricated at room temperature in this study. Both dark and illuminated current density-voltage (J-V) curves for the heterojunctions were measured and analyzed at room temperature. The heterojunctions demonstrated a large reverse leakage current as well as a weak near-infrared light response. Based on the analysis of the dark forward J-V curves, at the V value  ⩽  0.2 V, we show that a carrier recombination process was governed at the heterojunction interface. When the V value was  >  0.2 V, the probable mechanism of carrier transportation was a space-charge limited-current process. Both the measurement and analysis for capacitance-voltage-frequency (C-V-f ) and conductance-voltage-frequency (G-V-f ) curves were performed in the applied frequency (f ) range of 50 kHz-2 MHz at room temperature. From the C-V-f and G-V-f curves, the density of interface states (N ss) for the heterojunctions was computed by using the Hill-Coleman method. The N ss values were 9.19  ×  1012 eV-1 cm-2 at 2 MHz and 3.15  ×  1014 eV-1 cm-2 at 50 kHz, which proved the existence of interface states at the heterojunction interface. These interface states are the probable cause of the degraded electrical performance in the heterojunctions. Invited talk at 5th Thailand International Nanotechnology Conference (Nano Thailand-2016), 27-29 November 2016, Nakhon Ratchasima, Thailand.

Control of ZnO Nanorod Defects to Enhance Carrier Transportation in p-Cu₂O/i-ZnO Nanorods/n-IGZO Heterojunction.

PubMed

Ke, Nguyen Huu; Trinh, Le Thi Tuyet; Mung, Nguyen Thi; Loan, Phan Thi Kieu; Tuan, Dao Anh; Truong, Nguyen Huu; Tran, Cao Vinh; Hung, Le Vu Tuan

2017-01-01

The p-Cu₂O/i-ZnO nanorods/n-IGZO heterojunctions were fabricated by electrochemical and sputtering method. ZnO nanorods were grown on conductive indium gallium zinc oxide (IGZO) thin film and then p-Cu₂O layer was deposited on ZnO nanorods to form the heterojunction. ZnO nanorods play an important role in carrier transport mechanisms and performance of the junction. The changing of defects in ZnO nanorods by annealing samples in air and vacuum have studied. The XRD, photoluminescence (PL) spectroscopy, and FTIR were used to study about structure, and defects in ZnO nanorods. The SEM, i–V characteristics methods were also used to define structure, electrical properties of the heterojunctions layers. The results show that the defects in ZnO nanorods affected remarkably on performance of heterojunctions of solar cells.

Fabricate heterojunction diode by using the modified spray pyrolysis method to deposit nickel-lithium oxide on indium tin oxide substrate.

PubMed

Wu, Chia-Ching; Yang, Cheng-Fu

2013-06-12

P-type lithium-doped nickel oxide (p-LNiO) thin films were deposited on an n-type indium tin oxide (ITO) glass substrate using the modified spray pyrolysis method (SPM), to fabricate a transparent p-n heterojunction diode. The structural, optical, and electrical properties of the p-LNiO and ITO thin films and the p-LNiO/n-ITO heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), UV-visible spectroscopy, Hall effect measurement, and current-voltage (I-V) measurements. The nonlinear and rectifying I-V properties confirmed that a heterojunction diode characteristic was successfully formed in the p-LNiO/n-ITO (p-n) structure. The I-V characteristic was dominated by space-charge-limited current (SCLC), and the Anderson model demonstrated that band alignment existed in the p-LNiO/n-ITO heterojunction diode.

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor

NASA Astrophysics Data System (ADS)

Wu, Di; Lou, Zhenhua; Wang, Yuange; Xu, Tingting; Shi, Zhifeng; Xu, Junmin; Tian, Yongtao; Li, Xinjian

2017-10-01

Few-layer MoS2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS2/Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS2/SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS2-based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ˜50% RH), with good repeatability and selectivity of the MoS2/SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS2/SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

Band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterostructures measured by X-ray photoemission spectroscopy.

PubMed

Sang, Ling; Zhu, Qin Sheng; Yang, Shao Yan; Liu, Gui Peng; Li, Hui Jie; Wei, Hong Yuan; Jiao, Chun Mei; Liu, Shu Man; Wang, Zhan Guo; Zhou, Xiao Wei; Mao, Wei; Hao, Yue; Shen, Bo

2014-01-01

The band offsets of non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are measured by X-ray photoemission spectroscopy. A large forward-backward asymmetry is observed in the non-polar GaN/AlN and AlN/GaN heterojunctions. The valence-band offsets in the non-polar A-plane GaN/AlN and AlN/GaN heterojunctions are determined to be 1.33 ± 0.16 and 0.73 ± 0.16 eV, respectively. The large valence-band offset difference of 0.6 eV between the non-polar GaN/AlN and AlN/GaN heterojunctions is considered to be due to piezoelectric strain effect in the non-polar heterojunction overlayers.

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor.

PubMed

Wu, Di; Lou, Zhenhua; Wang, Yuange; Xu, Tingting; Shi, Zhifeng; Xu, Junmin; Tian, Yongtao; Li, Xinjian

2017-10-27

Few-layer MoS 2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS 2 /Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS 2 /SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS 2 -based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ∼50% RH), with good repeatability and selectivity of the MoS 2 /SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS 2 /SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

Optical and photoelectrochemical performance study based on n-ZnO nanorod arrays/p-CuAlO2 laminar films/Ni heterojunction

NASA Astrophysics Data System (ADS)

Ding, Juan; Yang, Haibin; Deng, Weiwen

2014-06-01

A novel ZnO nanorod arrays (NRs)/CuAlO2 laminar films heterojunction nanostructure was grown on the substrate of Ni plates using sol-gel synthesis for laminar films and subsequent hydrothermal reaction for nanorod arrays. The surface morphology, structure, optical and photoelectrochemical behaviors of this heterojunction were considered. Two significant absorption peaks of UV-vis spectra and a favorable forward current to reverse current ratio at applied voltage of -0.7 V to +2 V were observed in this heterojunction. Furthermore, the photoelectrochemical property was indicated that the highest photocurrent of 0.67 mA/cm2 was obtained under AM 1.5 illumination (vs Ag/AgCl). This heterojunction will play an important role in the optoelectronic fields and can be extended to other binary or ternary oxide compositions for optoelectronic applications.

Color tunable electroluminescence and resistance switching from a ZnO-nanorod-TaOx-p-GaN heterojunction.

PubMed

Zhao, J L; Teo, K L; Zheng, K; Sun, X W

2016-03-18

Well-aligned ZnO nanorods have been prepared on p-GaN-sapphire using a vapor phase transport (VPT) technique. A thin sputtered layer of TaOx is employed as the intermediate layer and an n-ZnO-TaOx-p-GaN heterojunction device has been achieved. The current transport of the heterojunction exhibited a typical resistance switching behavior, which originated from the filament forming and breaking in the TaOx layer. Color controllable electroluminescence (EL) was observed from the biased heterojunction at room temperature. Bluish-white wide band emission is achieved from the forward biased device in both the high resistance and low resistance states, while red emission can only be observed for the reverse biased device in the low resistance state. The correlation between the EL and resistance switching has been analyzed in-depth based on the interface band diagram of the heterojunction.

Nanostructured TaON/Ta3N5 as a highly efficient type-II heterojunction photoanode for photoelectrochemical water splitting.

PubMed

Pei, Lang; Wang, Hongxu; Wang, Xiaohui; Xu, Zhe; Yan, Shicheng; Zou, Zhigang

2018-06-20

Enhancing the charge separation by a semiconductor heterojunction is greatly promising and challenging for photoelectrochemical (PEC) water splitting. Here, we report for the first time the design and fabrication of a TaON/Ta3N5 heterojunction photoanode, in which the electrode Ta3N5 is the primary light absorber and TaON acts as an electron conductor. By combining the merits of the substantial light harvesting of Ta3N5 with the excellent charge transport capability of TaON, the TaON/Ta3N5 heterojunction photoanode, without any co-catalysts, shows a 350 mV negative shift of photocurrent onset potential to 0.65 V versus the reversible hydrogen electrode (RHE) compared to that of the Ta3N5 photoanode. The design and fabrication scheme can be readily extended to other (oxy)nitride semiconductors for heterojunction construction.

Transport properties of CNT/oligosilane/CNT heterojunctions

NASA Astrophysics Data System (ADS)

Yu, J.; Zhang, G. L.; Shang, Y.; Wang, K. D.; Zhang, H.; Sun, M.; Liu, B.; Zeng, T.

2013-02-01

Combining the non-equilibrium Green's function formalism with density functional theory, the transport properties of nine CNT/oligosilane/CNT heterojunctions were systematically studied. We have found that the incorporation of oligosilane linkage to the carbon nanotube mouth could significantly tune the transport properties compared with the pure oligosilane and pure CNT. The P- and B-dopings upon the oligosilane moiety could not only enhance the conductivity but also give rise to multiple negative differential resistance behavior for the CNT/oligosilane/CNT heterojunctions. The concentration of heteroatom plays an important role in the transport properties of the CNT/oligosilane/CNT heterojunctions, while the number of the oligosilane linkage exerts little effect on the conductivity. The B-doped CNT/oligosilane/CNT heterojunctions show higher conductivity than those of the P-doped ones. The p-n junction caused by B- and P-codopings exhibits a rectifying effect and the rectification ratio is up to 7.19.

Enhanced bulk heterojunction devices prepared by thermal and solvent vapor annealing processes

DOEpatents

Forrest, Stephen R.; Thompson, Mark E.; Wei, Guodan; Wang, Siyi

2017-09-19

A method of preparing a bulk heterojunction organic photovoltaic cell through combinations of thermal and solvent vapor annealing are described. Bulk heterojunction films may prepared by known methods such as spin coating, and then exposed to one or more vaporized solvents and thermally annealed in an effort to enhance the crystalline nature of the photoactive materials.

Synthesis and characterization of axial heterojunction inorganic-organic semiconductor nanowire arrays.

PubMed

Chen, Nan; Qian, Xuemin; Lin, Haowei; Liu, Huibiao; Li, Yongjun; Li, Yuliang

2011-11-07

The end-to-end P-N heterojunction nanowire arrays combined organic (poly[1,4-bis(pyrrol-2-yl)benzene], BPB) and inorganic (CdS) molecules have been successfully designed and fabricated. The electrical properties of P-N heterojunctions of organic-inorganic nanowire arrays were investigated. The diode nature and rectifying feature of P-N heterojunction nanowire arrays were observed. The rectification ratio of the diode increased from 29.9 to 129.7 as the illumination intensity increased. The material exhibits a new property, which is an improvement in the integration of the physical and chemical properties of the two independent components.

Precise, Self-Limited Epitaxy of Ultrathin Organic Semiconductors and Heterojunctions Tailored by van der Waals Interactions.

PubMed

Wu, Bing; Zhao, Yinghe; Nan, Haiyan; Yang, Ziyi; Zhang, Yuhan; Zhao, Huijuan; He, Daowei; Jiang, Zonglin; Liu, Xiaolong; Li, Yun; Shi, Yi; Ni, Zhenhua; Wang, Jinlan; Xu, Jian-Bin; Wang, Xinran

2016-06-08

Precise assembly of semiconductor heterojunctions is the key to realize many optoelectronic devices. By exploiting the strong and tunable van der Waals (vdW) forces between graphene and organic small molecules, we demonstrate layer-by-layer epitaxy of ultrathin organic semiconductors and heterostructures with unprecedented precision with well-defined number of layers and self-limited characteristics. We further demonstrate organic p-n heterojunctions with molecularly flat interface, which exhibit excellent rectifying behavior and photovoltaic responses. The self-limited organic molecular beam epitaxy (SLOMBE) is generically applicable for many layered small-molecule semiconductors and may lead to advanced organic optoelectronic devices beyond bulk heterojunctions.

Developing high-transmittance heterojunction diodes based on NiO/TZO bilayer thin films

PubMed Central

2013-01-01

In this study, radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and titanium-doped zinc oxide thin films (TZO, varying deposition powers) on glass substrates to form p(NiO)-n(TZO) heterojunction diodes with high transmittance. The structural, optical, and electrical properties of the TZO and NiO thin films and NiO/TZO heterojunction devices were investigated with scanning electron microscopy, X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall effect analysis, and current-voltage (I-V) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of TZO were observable in the NiO/TZO heterojunction devices, indicating that the TZO thin films showed a good c-axis orientation perpendicular to the glass substrates. When the sputtering deposition power for the TZO thin films was 100, 125, and 150 W, the I-V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/TZO heterojunction devices. We show that the NiO/TZO heterojunction diode was dominated by the space-charge limited current theory. PMID:23634999

Synthesis and Characterization of ZnO/polymer planar heterojunction solar cells

NASA Astrophysics Data System (ADS)

Gutierrez, Leandro; Manners, William; Nabizadeh, Arya; Albers, Patrick; Duran, Jesus; Scudieri, Anthony; Isah, Anne; McDougall, Michael; Sahiner, Mehmet; Wang, Weining

2014-03-01

ZnO/polymer heterojunction has been studied by many groups for its potential application in solar cell, LED, UV photodetection and other applications. However, there are few studies on ZnO/polymer heterojunction by synthesizing ZnO using pulsed laser deposition (PLD). Comparing with other methods, PLD has the advantage of congruent evaporation, and being able to grow high quality thin films at relatively low temperature. In our previous work in pulsed-laser-deposited (PLD) ZnO/PEDOT:PSS heterojunction, correlations between the annealing conditions of pulsed laser deposition and the electrical performance of solar cells have been observed. In this work, we report two new studies: 1) Studies on how the performance of the PLD-ZnO /PEDOT:PSS heterojunction depends on polymer conductivity; 2) Comparison studies on PLD-ZnO/PEDOT:PSS and PLD-ZnO/P3HT heterojunction. We studied how the performance of ZnO/polymer solar cells depend on the polymer work function and conductivities and deposition condition of ZnO. X-ray diffraction (XRD) and scanning electron microscopy were used to characterize the PLD-ZnO film. The correlation between the solar cell electrical performance and the polymer conductivity and pulsed laser deposition conditions will be discussed.

A facile one-pot preparation of Co3O4/g-C3N4 heterojunctions with excellent electrocatalytic activity for the detection of environmental phenolic hormones

NASA Astrophysics Data System (ADS)

Sun, Yanjuan; Jiang, Jizhou; Liu, Yi; Wu, Shengli; Zou, Jing

2018-02-01

The Co3O4/g-C3N4 heterojunctions were prepared by a facile one-pot thermal decomposition technique. Compared with g-C3N4, it was found that Co3O4/g-C3N4 heterojunctions possessed a higher Brunner-Emmet-Teller (BET) surface area, which was beneficial to the diffusion of aim molecules on the electrode surfaces. And the optimal Co3O4/g-C3N4 heterojunctions exhibited a narrower band gap and a higher donor density, resulting in an excellent electrocatalytic activity for environmental phenolic hormones. Moreover, the Co3O4/g-C3N4 heterojunctions were used for the electrochemical sensing of environmental phenolic hormones such as bisphenol A, pentachlorophenol, p-nitrophenol and octylphenol. All detection ranges reached three orders of magnitude, showing a lower limit of detection of 10-9 mol L-1. So, sensitivity and accurate determination of environmental phenolic hormones in real water samples may use this Co3O4/g-C3N4 heterojunctions modified electrode.

Strong room temperature electroluminescence from lateral p-SiGe/i-Ge/n-SiGe heterojunction diodes on silicon-on-insulator substrate

NASA Astrophysics Data System (ADS)

Lin, Guangyang; Yi, Xiaohui; Li, Cheng; Chen, Ningli; Zhang, Lu; Chen, Songyan; Huang, Wei; Wang, Jianyuan; Xiong, Xihuan; Sun, Jiaming

2016-10-01

A lateral p-Si0.05Ge0.95/i-Ge/n-Si0.05Ge0.95 heterojunction light emitting diode on a silicon-on-insulator (SOI) substrate was proposed, which is profitable to achieve higher luminous extraction compared to vertical junctions. Due to the high carrier injection ratio of heterostructures and optical reflection at the SiO2/Si interface of the SOI, strong room temperature electroluminescence (EL) at around 1600 nm from the direct bandgap of i-Ge with 0.30% tensile strain was observed. The EL peak intensity of the lateral heterojunction is enhanced by ˜4 folds with a larger peak energy than that of the vertical Ge p-i-n homojunction, suggesting that the light emitting efficiency of the lateral heterojunction is effectively improved. The EL peak intensity of the lateral heterojunction, which increases quadratically with injection current density, becomes stronger for diodes with a wider i-Ge region. The CMOS compatible fabrication process of the lateral heterojunctions paves the way for the integration of the light source with the Ge metal-oxide-semiconductor field-effect-transistor.

Defect States in InP/InGaAs/InP Heterostructures by Current-Voltage Characteristics and Deep Level Transient Spectroscopy.

PubMed

Vu, Thi Kim Oanh; Lee, Kyoung Su; Lee, Sang Jun; Kim, Eun Kyu

2018-09-01

We studied defect states in In0.53Ga0.47As/InP heterojunctions with interface control by group V atoms during metalorganic chemical vapor (MOCVD) deposition. From deep level transient spectroscopy (DLTS) measurements, two defects with activation energies of 0.28 eV (E1) and 0.15 eV (E2) below the conduction band edge, were observed. The defect density of E1 for In0.53Ga0.47As/InP heterojunctions with an addition of As and P atoms was about 1.5 times higher than that of the heterojunction added P atom only. From the temperature dependence of current- voltage characteristics, the thermal activation energies of In0.53Ga0.47As/InP of heterojunctions were estimated to be 0.27 and 0.25 eV, respectively. It appeared that the reverse light current for In0.53Ga0.47As/InP heterojunction added P atom increased only by illumination of a 940 nm-LED light source. These results imply that only the P addition at the interface can enhance the quality of InGaAs/InP heterojunction.

Enhanced photocatalytic activity of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalyst under simulated solar light

NASA Astrophysics Data System (ADS)

Wang, Chunlei; Hu, Liming; Chai, Bo; Yan, Juntao; Li, Jianfen

2018-02-01

Electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content have been synthesized via a facile electrospinning and subsequent in situ evaporation and calcination process for the first time, which are examined in terms of morphology, component content, optical properties, PL spectra, photocurrent response, EIS measurement, photocatalytic activity and mechanism. SEM images exhibit TiO2/g-C3N4-4 heterojunction photocatalyst possesses the excellent 1D structure. HRTEM and element mapping images confirm the formation of heterojunction structure. DRS tests identify that TiO2/g-C3N4-4 heterojunction exhibits the intensitive absorption in both UV and visible light region. The photoelectrochemical tests prove that the recombination between electrons and holes are effectively inhibited. Based on TG analysis and photodegradation experiments, TiO2/g-C3N4-4 heterojunction photocatalyst with TiO2 content of 29.30 wt% possesses the best photocatalytic degradation efficiency for the RhB among the g-C3N4, TiO2 and their mixture under simulated sunlight irradiation. Moreover, 1D morphology of TiO2/g-C3N4-4 heterojunction photocatalyst is in favor of separating from solution for reuse and transferring the electrons, and maintains a very high photocatalytic degradation efficiency of 96% even after four recycles experiments, which is beneficial for practical application.

Designing novel thin film polycrystalline solar cells for high efficiency: sandwich CIGS and heterojunction perovskite

NASA Astrophysics Data System (ADS)

Wang, Tianyue; Chen, Jiewei; Wu, Gaoxiang; Song, Dandan; Li, Meicheng

2017-01-01

Heterojunction and sandwich architectures are two new-type structures with great potential for solar cells. Specifically, the heterojunction structure possesses the advantages of efficient charge separation but suffers from band offset and large interface recombination; the sandwich configuration is favorable for transferring carriers but requires complex fabrication process. Here, we have designed two thin-film polycrystalline solar cells with novel structures: sandwich CIGS and heterojunction perovskite, referring to the advantages of the architectures of sandwich perovskite (standard) and heterojunction CIGS (standard) solar cells, respectively. A reliable simulation software wxAMPS is used to investigate their inherent characteristics with variation of the thickness and doping density of absorber layer. The results reveal that sandwich CIGS solar cell is able to exhibit an optimized efficiency of 20.7%, which is much higher than the standard heterojunction CIGS structure (18.48%). The heterojunction perovskite solar cell can be more efficient employing thick and doped perovskite films (16.9%) than these typically utilizing thin and weak-doping/intrinsic perovskite films (9.6%). This concept of structure modulation proves to be useful and can be applicable for other solar cells. Project supported by the National High-Tech R&D Program of China (No. 2015AA034601), the National Natural Science Foundation of China (Nos. 91333122, 61204064, 51202067, 51372082, 51402106, 11504107), the Ph.D. Programs Foundation of Ministry of Education of China (Nos. 20120036120006, 20130036110012), the Par-Eu Scholars Program, and the Fundamental Research Funds for the Central Universities.

p-n Heterojunction of doped graphene films obtained by pyrolysis of biomass precursors.

PubMed

Latorre-Sánchez, Marcos; Primo, Ana; Atienzar, Pedro; Forneli, Amparo; García, Hermenegildo

2015-02-25

Nitrogen-doped graphene [(N)G] obtained by pyrolysis at 900 °C of nanometric chitosan films exhibits a Hall effect characteristic of n-type semiconductors. In contrast, boron-doped graphene [(B)G] obtained by pyrolysis of borate ester of alginate behaves as a p-type semiconductor based also on the Hall effect. A p-n heterojunction of (B)G-(N)G films is built by stepwise coating of a quartz plate using a mask. The heterojunction is created by the partial overlapping of the (B)G-(N)G films. Upon irradiation with a xenon lamp of aqueous solutions of H(2) PtCl(6) and MnCl(2) in contact with the heterojunction, preferential electron migration from (B)G to (N)G with preferential location of positive holes on (B)G is established by observation in scanning electron microscopy of the formation of Pt nanoparticles (NP) on (N)G and MnO(2) NP on (B)G. The benefits of the heterojunction with respect to the devices having one individual component as a consequence of the electron migration through the p-n heterojunction are illustrated by measuring the photocurrent in the (B)G-(N)G heterojunction (180% current enhancement with respect to the dark current) and compared it to the photocurrent of the individual (B)G (15% enhancement) and (N)G (55% enhancement) components. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Construction of fiber-shaped silver oxide/tantalum nitride p-n heterojunctions as highly efficient visible-light-driven photocatalysts.

PubMed

Li, Shijie; Hu, Shiwei; Xu, Kaibing; Jiang, Wei; Liu, Yu; Leng, Zhe; Liu, Jianshe

2017-10-15

Constructing novel and efficient p-n heterojunction photocatalysts has stimulated great interest. Herein, we report the design and synthesis of fiber-shaped Ag 2 O/Ta 3 N 5 p-n heterojunctions as a kind of efficient photocatalysts. Ta 3 N 5 nanofibers were prepared by an electrospinning-calcination-nitridation method, and then the in-situ anchoring of Ag 2 O on their surfaces was realized by a facile deposition method. The resulting Ag 2 O/Ta 3 N 5 heterojunctions were comprised of porous Ta 3 N 5 nanofibers (diameter: ∼150nm) and Ag 2 O nanoparticles (size: ∼12nm). The photocatalytic activity of these heterojunctions were studied by decomposing rhodamine B (RhB) dye and tetracycline (TC) antibiotic under visible light (λ>400nm). In all the samples, the heterojunction with Ag 2 O/Ta 3 N 5 molar ratio of 0.2/1 displays the best activity. It is found that a synergistic effect contributes to the effective suppression of charges recombination between Ta 3 N 5 and Ag 2 O, leading to an enhanced photocatalytic activity with good stability. The photogenerated holes (h + ) and superoxide radicals (O 2 - ) play dominant roles in the photocatalytic process. These p-n heterojunctions will have great potential for environmental remediation because of the facile preparation process and exceptional photocatalytic activity. Copyright © 2017 Elsevier Inc. All rights reserved.

Current Status and Future Prospects of Copper Oxide Heterojunction Solar Cells

PubMed Central

Wong, Terence K. S.; Zhuk, Siarhei; Masudy-Panah, Saeid; Dalapati, Goutam K.

2016-01-01

The current state of thin film heterojunction solar cells based on cuprous oxide (Cu2O), cupric oxide (CuO) and copper (III) oxide (Cu4O3) is reviewed. These p-type semiconducting oxides prepared by Cu oxidation, sputtering or electrochemical deposition are non-toxic, sustainable photovoltaic materials with application potential for solar electricity. However, defects at the copper oxide heterojunction and film quality are still major constraining factors for achieving high power conversion efficiency, η. Amongst the Cu2O heterojunction devices, a maximum η of 6.1% has been obtained by using pulsed laser deposition (PLD) of AlxGa1−xO onto thermal Cu2O doped with Na. The performance of CuO/n-Si heterojunction solar cells formed by magnetron sputtering of CuO is presently limited by both native oxide and Cu rich copper oxide layers at the heterointerface. These interfacial layers can be reduced by using a two-step sputtering process. A high η of 2.88% for CuO heterojunction solar cells has been achieved by incorporation of mixed phase CuO/Cu2O nanopowder. CuO/Cu2O heterojunction solar cells fabricated by electrodeposition and electrochemical doping has a maximum efficiency of 0.64% after surface defect passivation and annealing. Finally, early stage study of Cu4O3/GaN deposited on sapphire substrate has shown a photovoltaic effect and an η of ~10−2%. PMID:28773398

p-i-n heterojunctions with BiFeO3 perovskite nanoparticles and p- and n-type oxides: photovoltaic properties.

PubMed

Chatterjee, Soumyo; Bera, Abhijit; Pal, Amlan J

2014-11-26

We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials.

Rational Design and Development of Reactive Multifunctional Micellar Composite Nano-particles for Destruction of Bio-agents

DTIC Science & Technology

2015-02-01

nanoparticles, , multifunction porous metal oxide -silica composites, porous silicon - Titania and PSi-silver heterojunctions ) have been successfully...nanoparticles, multifunctional porous metal oxide -silica composites, porous silicon -Titania and PSi-silver heterojunctions ) have been successfully...generated charge separation and enhance the photocatalytic oxidation . In the PSi-Ag heterojunctions , Ag can not only act as time-honored antibacterial

Heterojunction solar cell

DOEpatents

Olson, Jerry M.

1994-01-01

A high-efficiency single heterojunction solar cell wherein a thin emitter layer (preferably Ga.sub.0.52 In.sub.0.48 P) forms a heterojunction with a GaAs absorber layer. The conversion effiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the emitter layer.

In-Situ-Reduced Synthesis of Ti 3+ Self-Doped TiO 2 /g-C 3 N 4 Heterojunctions with High Photocatalytic Performance under LED Light Irradiation

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

Li, Kai; Gao, Shanmin; Wang, Qingyao

2015-04-27

A simple one-step calcination route was used to prepare Ti3+ self-doped TiO2/g-C3N4 heterojunctions by mixture of H2Ti3O7 and melamine. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) spectroscopy, and UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) technologies were used to characterize the structure, crystallinity, morphology, and chemical state of the as-prepared samples. The absorption of the prepared Ti3+ self-doped TiO2/g-C3N4 heterojunctions shifted to a longer wavelength region in comparison with pristine TiO2 and g-C3N4. The photocatalytic activities of the heterojunctions were studied by degrading methylene blue under a 30more » W visible-light-emitting diode irradiation source. The visible-light photocatalytic activities enhanced by the prepared Ti3+ self-doped TiO2/g-C3N4 heterojunctions were observed and proved to be better than that of pure TiO2 and g-C3N4. The photocatalysis mechanism was investigated and discussed. The intensive separation efficiency of photogenerated electron-hole in the prepared heterojunction was confirmed by photoluminescence (PL) spectra. The removal rate constant reached 0.038 min(-1) for the 22.3 wt % Ti3+ self-doped TiO2/g-C3N4 heterojunction, which was 26.76 and 7.6 times higher than that of pure TiO2 and g-C3N4, respectively. The established heterojunction between the interfaces of TiO2 nanoparticles and g-C3N4 nanosheets as well as introduced Ti3+ led to the rapid electron transfer rate and improved photoinduced electron-hole pair's separation efficiency, resulting in the improved photocatalytic performance of the Ti3+ self-doped TiO2/g-C3N4 heterojunctions.« less

Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

NASA Astrophysics Data System (ADS)

Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

2016-10-01

Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment Dipika Sharmaa, Vibha R. Satsangib, Rohit Shrivastava, Umesh V. Waghmarec, Sahab Dassa aDepartment of Chemistry, Dayalbagh Educational Institute, Agra-282 110 (India) bDepartment of Physics and Computer Sciences, Dayalbagh Educational Institute, Agra-282 110 (India) cTheoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560 064 (India) * Phone: +91-9219695960. Fax: +91-562-2801226. E-mail: drsahabdas@gmail.com. Study on photoelectrochemical activity of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction has been carried out using DFT based band offsets and charge carriers effective mass calculations and their experimental verification. The results of DFT calculations show that BaTiO3 and Cu2O have staggered type band alignment after the heterojunction formation and high mobility of electrons in Cu2O as compared to the electrons in BaTiO3. Staggered type band edges alignment and high mobility of electrons and holes improved the separation of photo-generated charge carriers in BaTiO3/Cu2O heterojunction. To validate the theoretical results experiments were carried out on pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction with varying thickness of Cu2O. All samples were characterized by X- Ray Diffractometer, SEM and UV-Vis spectrometry. Nanostructured thin films of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction were used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.44 mA/cm2 at 0.90 V/SCE was exhibited by 442 nm thick BaTiO3/Cu2O heterojunction photoelectrode Increased photocurrent density and enhanced photoconversion efficiency, exhibited by the heterojunction may be attributed to improved conductivity and enhanced separation of the photogenerated carriers at the BaTiO3/Cu2O interface. The experimental results and first-principles calculations compare well, thus suggesting that such calculations have the potential to be used in screening various metal oxide heterojunction before performing the experiments thereby saving precious chemicals, time and energy. Keywords: Photoelectrochemical, Water splitting, heterojunction, Cu2O, BaTiO3 References: [1] Surbhi Choudhary, et al. Nanostructured bilayered thin films in photoelectrochemical water splitting - A review: International Journal of Hydrogen Energy, (2012). [2] Dipika Sharma, Anuradha Verma, V.R. Satsangi, Rohit shrivastav, Sahab Dass Nanostructured SrTiO3 thin films sensitized by Cu2O for Photoelectrochemical Hydrogen Generation. International journal of Hydrogen Energy;42:,4230-4241, 2014.

Multi-channel unidirectional transmission of phononic crystal heterojunctions

NASA Astrophysics Data System (ADS)

Xu, Zhenlong; Tong, Jie; Wu, Fugen

2018-02-01

Two square steel columns are arranged in air to form two-dimensional square lattice phononic crystals (PNCs). Two PNCs can be combined into a non-orthogonal 45∘ heterojunction when the difference in the directional band gaps of the two PNC types is utilized. The finite element method is used to calculate the acoustic band structure, the heterogeneous junction transmission characteristics, acoustic field distribution, and many others. Results show that a non-orthogonal PNC heterojunction can produce a multi-channel unidirectional transmission of acoustic waves. With the square scatterer rotated, the heterojunction can select a frequency band for unidirectional transmission performance. This capability is particularly useful for constructing acoustic diodes with wide-bands and high-efficiency unidirectional transmission characteristics.

Current transport and capacitance-voltage characteristics of an n-PbTe/p-GaP heterojunction prepared using the electron beam deposition technique

NASA Astrophysics Data System (ADS)

Nasr, Mahmoud; El Radaf, I. M.; Mansour, A. M.

2018-04-01

In this study, a crystalline n-PbTe/p-GaP heterojunction was fabricated using the electron beam deposition technique. The structural properties of the prepared heterojunction were examined by X-ray diffraction and scanning electron microscopy. The dark current-voltage characteristics of the heterojunction were investigated at different temperatures ranging from 298 to 398 K. The rectification factor, series resistance, shunt resistance, diode ideality factor, and effective barrier height (ϕb) were determined. The photovoltaic parameters were identified based on the current density-voltage characteristics under illumination. The capacitance-voltage characteristics showed that the junction was abrupt in nature.

Design of a highly sensitive ethanol sensor using a nano-coaxial p-Co3O4/n-TiO2 heterojunction synthesized at low temperature.

PubMed

Liang, Y Q; Cui, Z D; Zhu, S L; Li, Z Y; Yang, X J; Chen, Y J; Ma, J M

2013-11-21

In this paper, we describe the design, fabrication and gas-sensing tests of nano-coaxial p-Co3O4/n-TiO2 heterojunction. Specifically, uniform TiO2 nanotubular arrays have been assembled by anodization and used as templates for generation of the Co3O4 one-dimensional nanorods. The structure morphology and composition of as-prepared products have been characterized by SEM, XRD, TEM, and XPS. A possible growth mechanism governing the formation of such nano-coaxial heterojunctions is proposed. The TiO2 nanotube sensor shows a normal n-type response to reducing ethanol gas, whereas TiO2-Co3O4 exhibits p-type response with excellent sensing performances. This conversion of sensing behavior can be explained by the formation of p-n heterojunction structures. A possible sensing mechanism is also illustrated, which can provide theoretical guidance for the further development of advanced gas-sensitive materials with p-n heterojunction.

Improved ultraviolet emission performance from polarization-engineered n-ZnO/p-GaN heterojunction diode

NASA Astrophysics Data System (ADS)

Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Shi, Zhifeng; Yan, Long; Li, Pengchong; Zhang, Baolin; Du, Guotong

2016-02-01

O-polar ZnO films were grown on N-polar p-GaN/sapphire substrates by photo-assisted metal-organic chemical vapor deposition, and further heterojunction light-emitting diodes based O-polar n-ZnO/N-polar p-GaN were proposed and fabricated. It is experimentally demonstrated that the interface polarization of O-polar n-ZnO/N-polar p-GaN heterojunction can shift the location of the depletion region from the interface deep into the ZnO side. When a forward bias is applied to the proposed diode, a strong and high-purity ultraviolet emission located at 385 nm can be observed. Compared with conventional Zn-polar n-ZnO/Ga-polar p-GaN heterostructure diode, the ultraviolet emission intensity of the proposed heterojunction diode is greatly enhanced due to the presence of polarization-induced inversion layer at the ZnO side of the heterojunction interface. This work provides an innovative path for the design and development of ZnO-based ultraviolet diode.

Changing the thickness of two layers: i-ZnO nanorods, p-Cu2O and its influence on the carriers transport mechanism of the p-Cu2O/i-ZnO nanorods/n-IGZO heterojunction.

PubMed

Ke, Nguyen Huu; Trinh, Le Thi Tuyet; Phung, Pham Kim; Loan, Phan Thi Kieu; Tuan, Dao Anh; Truong, Nguyen Huu; Tran, Cao Vinh; Hung, Le Vu Tuan

2016-01-01

In this study, two layers: i-ZnO nanorods and p-Cu2O were fabricated by electrochemical deposition. The fabricating process was the initial formation of ZnO nanorods layer on the n-IGZO thin film which was prepared by sputtering method, then a p-Cu2O layer was deposited on top of rods to form the p-Cu2O/i-ZnO nanorods/n-ZnO heterojunction. The XRD, SEM, UV-VIS, I-V characteristics methods were used to define structure, optical and electrical properties of these heterojunction layers. The fabricating conditions and thickness of the Cu2O layers significantly affected to the formation, microstructure, electrical and optical properties of the junction. The length of i-ZnO nanorods layer in the structure of the heterojunction has strongly affected to the carriers transport mechanism and performance of this heterojunction.

Transparent CH{sub 3}NH{sub 3}SnCl{sub 3}/Al-ZnO p-n heterojunction diode

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

Kumar, Sunil, E-mail: skbgudha@gmail.com; Ansari, Mohd Zubair; Khare, Neeraj

2016-05-23

A p-type Organic inorganic tin chloride (CH{sub 3}NH{sub 3}SnCl{sub 3}) perovskite thin film has been synthesized by solution method. An n-type 1% Al doped ZnO (AZO) film has been deposited on FTO substrate by ultrasonic assisted chemical vapor deposition technique. A transparent CH{sub 3}NH{sub 3}SnCl{sub 3}/AZO p-n heterojunction diode has been fabricated by spin coating technique. CH{sub 3}NH{sub 3}SnCl{sub 3}/AZO p-n heterojunction shows 75% transparency in the visible region. I-V characteristic of CH{sub 3}NH{sub 3}SnCl{sub 3}/AZO p-n heterojunction shows rectifying behavior of the diode. The diode parameters calculated as ideality factor η=2.754 and barrier height Φ= 0.76 eV. The resultmore » demonstrates the potentiality of CH{sub 3}NH{sub 3}SnCl{sub 3}/AZO p-n heterojunction for transparent electronics.« less

An efficient p-n heterojunction photocatalyst constructed from a coordination polymer nanoplate and a partically reduced graphene oxide for visible-light hydrogen production.

PubMed

Xu, Xinxin; Lu, Tingting; Liu, Xiaoxia; Wang, Xiuli

2015-10-05

A new p-n heterojunction photocatalyst has been synthesized successfully through chemical-bond-mediated combination of coordination polymer nanoplates (CPNPs) and partially reduced graphene oxide (PRGO) with a simple colloidal blending process. Photocatalytic H2 production by the p-n heterojunction photocatalyst PRGO/CPNP was investigated under visible-light irradiation, which illustrates that PRGO/CPNP exhibits a much higher photocatalytic H2 production rate than neat the CPNPs. The improvement of this photocatalytic property can be attributed to the inner electrical field formed in the p-n heterojunction, which impedes recombination of photogenerated electrons and holes. In PRGO/CPNP, the existence of the p-n heterojunction has been confirmed by electrochemical methods clearly. For PRGO/CPNP, the reductive degree of the PRGO has a great influence on the H2 production rate and an ideal condition to get a PRGO/CPNP photocatalyst with higher performance has been obtained. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transparent Cu4O3/ZnO heterojunction photoelectric devices

NASA Astrophysics Data System (ADS)

Kim, Hong-Sik; Yadav, Pankaj; Patel, Malkeshkumar; Kim, Joondong; Pandey, Kavita; Lim, Donggun; Jeong, Chaehwan

2017-12-01

The present article reports the development of flexible, self-biased, broadband, high speed and transparent heterojunction photodiode, which is essentially important for the next generation electronic devices. We grow semitransparent p-type Cu4O3 using the reactive sputtering method at room temperature. The structural and optical properties of the Cu4O3 film were investigated by using the X-ray diffraction and UV-visible spectroscopy, respectively. The p-Cu4O3/n-ZnO heterojunction diode under dark condition yields rectification behavior with an extremely low saturation current value of 1.8 × 10-10 A and a zero bias photocurrent under illumination condition. The transparent p-Cu4O3/n-ZnO heterojunction photodetector can be operated without an external bias, due to the light-induced voltage production. The metal oxide heterojunction based on Cu4O3/ZnO would provide a route for the transparent and flexible photoelectric devices, including photodetectors and photovoltaics.

Modulation of electrical potential and conductivity in an atomic-layer semiconductor heterojunction

PubMed Central

Kobayashi, Yu; Yoshida, Shoji; Sakurada, Ryuji; Takashima, Kengo; Yamamoto, Takahiro; Saito, Tetsuki; Konabe, Satoru; Taniguchi, Takashi; Watanabe, Kenji; Maniwa, Yutaka; Takeuchi, Osamu; Shigekawa, Hidemi; Miyata, Yasumitsu

2016-01-01

Semiconductor heterojunction interfaces have been an important topic, both in modern solid state physics and in electronics and optoelectronics applications. Recently, the heterojunctions of atomically-thin transition metal dichalcogenides (TMDCs) are expected to realize one-dimensional (1D) electronic systems at their heterointerfaces due to their tunable electronic properties. Herein, we report unique conductivity enhancement and electrical potential modulation of heterojunction interfaces based on TMDC bilayers consisted of MoS2 and WS2. Scanning tunneling microscopy/spectroscopy analyses showed the formation of 1D confining potential (potential barrier) in the valence (conduction) band, as well as bandgap narrowing around the heterointerface. The modulation of electronic properties were also probed as the increase of current in conducting atomic force microscopy. Notably, the observed band bending can be explained by the presence of 1D fixed charges around the heterointerface. The present findings indicate that the atomic layer heterojunctions provide a novel approach to realizing tunable 1D electrical potential for embedded quantum wires and ultrashort barriers of electrical transport. PMID:27515115

Strain distributions and their influence on electronic structures of WSe2-MoS2 laterally strained heterojunctions

NASA Astrophysics Data System (ADS)

Zhang, Chendong; Li, Ming-Yang; Tersoff, Jerry; Han, Yimo; Su, Yushan; Li, Lain-Jong; Muller, David A.; Shih, Chih-Kang

2018-02-01

Monolayer transition metal dichalcogenide heterojunctions, including vertical and lateral p-n junctions, have attracted considerable attention due to their potential applications in electronics and optoelectronics. Lattice-misfit strain in atomically abrupt lateral heterojunctions, such as WSe2-MoS2, offers a new band-engineering strategy for tailoring their electronic properties. However, this approach requires an understanding of the strain distribution and its effect on band alignment. Here, we study a WSe2-MoS2 lateral heterojunction using scanning tunnelling microscopy and image its moiré pattern to map the full two-dimensional strain tensor with high spatial resolution. Using scanning tunnelling spectroscopy, we measure both the strain and the band alignment of the WSe2-MoS2 lateral heterojunction. We find that the misfit strain induces type II to type I band alignment transformation. Scanning transmission electron microscopy reveals the dislocations at the interface that partially relieve the strain. Finally, we observe a distinctive electronic structure at the interface due to hetero-bonding.

Enhanced photoactivity of BiPO4/(001) facet-dominated square BiOBr flakes by combining heterojunctions with facet engineering effects

NASA Astrophysics Data System (ADS)

Shi, Jingzhi; Meng, Xiangying; Hao, Mengjian; Cao, Zhenzhu; He, Weiyan; Gao, Yanfang; Liu, Jinrong

2018-02-01

In this study, BiPO4/highly (001) facet exposed square BiOBr flake heterojunction photocatalysts with different molar ratios were fabricated via a two-step method. The synergetic effect of the heterojunction and facet engineering was systematically investigated. The physicochemical properties of the BiPO4/square BiOBr flake composites were characterized based on X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller method, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectra, photoluminescence, electrochemical impedance spectroscopy, and the photocurrent response. The BiPO4/square BiOBr flake heterojunction photocatalyst exhibited much higher photocatalytic performance compared with the individual BiPO4 and BiOBr. In particular, the BiPO4/BiOBr composite where P/Br = 1/3 exhibited the highest photocatalytic activity. The intensified separation of photoinduced charges at the p-n heterojunction between the BiPO4 nanoparticle and (001) facet of BiOBr was mainly responsible for the enhanced photoactivity.

Systematic Investigation of Organic Photovoltaic Cell Charge Injection/Performance Modulation by Dipolar Organosilane Interfacial Layers

DTIC Science & Technology

2013-08-13

performance in bulk- heterojunction (BHJ) organic photovoltaic (OPV) cells, the glass/tin-doped indium oxide (ITO) anodes are modified with a series of...anode in bulk- heterojunction (BHJ) organic photovoltaic cells (OPVs) plays a vital role in enhancing device performance. Appropriately tailored IFLs...unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT With the goal of investigating and enhancing anode performance in bulk- heterojunction (BHJ) organic

Heterojunction solar cell

DOEpatents

Olson, J.M.

1994-08-30

A high-efficiency single heterojunction solar cell is described wherein a thin emitter layer (preferably Ga[sub 0.52]In[sub 0.48]P) forms a heterojunction with a GaAs absorber layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the emitter layer. 1 fig.

Trap assisted space charge conduction in p-NiO/n-ZnO heterojunction diode

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

Tyagi, Manisha; Tomar, Monika; Gupta, Vinay, E-mail: drguptavinay@gmail.com

2015-06-15

Highlights: • p-NiO/n-ZnO heterojunction diode with enhanced junction parameters has been prepared. • Temperature dependent I–V throw insight into the involved conduction mechanism. • SCLC with exponential trap distribution was found to be the dominant mechanism. • C–V measurement at different frequencies support the presence of traps. - Abstract: The development of short-wavelength p–n junction is essentially important for the realization of transparent electronics for next-generation optoelectronic devices. In the present work, a p–n heterojunction diode based on p-NiO/n-ZnO has been prepared under the optimised growth conditions exhibiting improved electrical and junction parameters. The fabricated heterojunction gives typical current–voltage (I–V)more » characteristics with good rectifying behaviour (rectification ratio ≈ 10{sup 4} at 2 V). The temperature dependent current–voltage characteristics of heterojunction diode have been studied and origin of conduction mechanism is identified. The space-charge limited conduction with exponential trap distribution having deep level trap is found to be the dominant conduction mechanism in the fabricated p–n heterojunction diode. The conduction and valence band discontinuities for NiO/ZnO heterostructure have been determined from the capacitance–voltage (C–V) measurements.« less

Buried MoO x/Ag Electrode Enables High-Efficiency Organic/Silicon Heterojunction Solar Cells with a High Fill Factor.

PubMed

Xia, Zhouhui; Gao, Peng; Sun, Teng; Wu, Haihua; Tan, Yeshu; Song, Tao; Lee, Shuit-Tong; Sun, Baoquan

2018-04-25

Silicon (Si)/organic heterojunction solar cells based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n-type Si have attracted wide interests because they promise cost-effectiveness and high-efficiency. However, the limited conductivity of PEDOT:PSS leads to an inefficient hole transport efficiency for the heterojunction device. Therefore, a high dense top-contact metal grid electrode is required to assure the efficient charge collection efficiency. Unfortunately, the large metal grid coverage ratio electrode would lead to undesirable optical loss. Here, we develop a strategy to balance PEDOT:PSS conductivity and grid optical transmittance via a buried molybdenum oxide/silver grid electrode. In addition, the grid electrode coverage ratio is optimized to reduce its light shading effect. The buried electrode dramatically reduces the device series resistance, which leads to a higher fill factor (FF). With the optimized buried electrode, a record FF of 80% is achieved for flat Si/PEDOT:PSS heterojunction devices. With further enhancement adhesion between the PEDOT:PSS film and Si substrate by a chemical cross-linkable silance, a power conversion efficiency of 16.3% for organic/textured Si heterojunction devices is achieved. Our results provide a path to overcome the inferior organic semiconductor property to enhance the organic/Si heterojunction solar cell.

Ultrahigh broadband photoresponse of SnO2 nanoparticle thin film/SiO2/p-Si heterojunction.

PubMed

Ling, Cuicui; Guo, Tianchao; Lu, Wenbo; Xiong, Ya; Zhu, Lei; Xue, Qingzhong

2017-06-29

The SnO 2 /Si heterojunction possesses a large band offset and it is easy to control the transportation of carriers in the SnO 2 /Si heterojunction to realize high-response broadband detection. Therefore, we investigated the potential of the SnO 2 nanoparticle thin film/SiO 2 /p-Si heterojunction for photodetectors. It is demonstrated that this heterojunction shows a stable, repeatable and broadband photoresponse from 365 nm to 980 nm. Meanwhile, the responsivity of the device approaches a high value in the range of 0.285-0.355 A W -1 with the outstanding detectivity of ∼2.66 × 10 12 cm H 1/2 W -1 and excellent sensitivity of ∼1.8 × 10 6 cm 2 W -1 , and its response and recovery times are extremely short (<0.1 s). This performance makes the device stand out among previously reported oxide or oxide/Si based photodetectors. In fact, the photosensitivity and detectivity of this heterojunction are an order of magnitude higher than that of 2D material based heterojunctions such as (Bi 2 Te 3 )/Si and MoS 2 /graphene (photosensitivity of 7.5 × 10 5 cm 2 W -1 and detectivity of ∼2.5 × 10 11 cm H 1/2 W -1 ). The excellent device performance is attributed to the large Fermi energy difference between the SnO 2 nanoparticle thin film and Si, SnO 2 nanostructure, oxygen vacancy defects and thin SiO 2 layer. Consequently, practical highly-responsive broadband PDs may be actualized in the future.

Crystalline silicon photovoltaics via low-temperature TiO 2/Si and PEDOT/Si heterojunctions

NASA Astrophysics Data System (ADS)

Nagamatsu, Ken Alfred

The most important goals in developing solar cell technology are to achieve high power conversion efficiencies and lower costs of manufacturing. Solar cells based on crystalline silicon currently dominate the market because they can achieve high efficiency. However, conventional p-n junction solar cells require high-temperature diffusions of dopants, and conventional heterojunction cells based on amorphous silicon require plasma-enhanced deposition, both of which can add manufacturing costs. This dissertation investigates an alternative approach, which is to form crystalline-silicon-based solar cells using heterojunctions with materials that are easily deposited at low temperatures and without plasma enhancement, such as organic semiconductors and metal oxides. We demonstrate a heterojunction between the organic polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT), and crystalline silicon, which acts as a hole-selective contact and an alternative to a diffused p-n junction. We also present the use of a heterojunction between titanium dioxide and crystalline silicon as a passivating electron-selective contact. The Si/TiO2 heterojunction is demonstrated for the first time as a back-surface field in a crystalline silicon solar cell, and is incorporated into a PEDOT/Si device. The resulting PEDOT/Si/TiO2 solar cell represents an alternative to conventional silicon solar cells that rely on thermally-diffused junctions or plasma-deposited heterojunctions. Finally, we investigate the merits of using conductive networks of silver nanowires to enhance the photovoltaic performance of PEDOT/Si solar cells. The investigation of these materials and devices contributes to the growing body of work regarding crystalline silicon solar cells made with selective contacts.

Growth dynamics of SiGe nanowires by the vapour-liquid-solid method and its impact on SiGe/Si axial heterojunction abruptness.

PubMed

Pura, J L; Periwal, P; Baron, T; Jiménez, J

2018-08-31

The vapour-liquid-solid (VLS) method is by far the most extended procedure for bottom-up nanowire growth. This method also allows for the manufacture of nanowire axial heterojunctions in a straightforward way. To do this, during the growth process, precursor gases are switched on/off to obtain the desired change in the nanowire composition. Using this technique, axially heterostructured nanowires can be grown, which are crucial for the fabrication of electronic and optoelectronic devices. SiGe/Si nanowires are compatible with complementary metal oxide semiconductor (CMOS) technology, which improves their versatility and the possibility of integration with current electronic technologies. Abrupt heterointerfaces are fundamental for the development and correct operation of electronic and optoelectronic devices. Unfortunately, the VLS growth of SiGe/Si heterojunctions does not provide abrupt transitions because of the high solubility of group IV semiconductors in Au, with the corresponding reservoir effect that precludes the growth of sharp interfaces. In this work, we studied the growth dynamics of SiGe/Si heterojunctions based on already developed models for VLS growth. A composition map of the Si-Ge-Au liquid alloy is proposed to better understand the impact of the growing conditions on the nanowire growth process and the heterojunction formation. The solution of our model provides heterojunction profiles that are in good agreement with the experimental measurements. Finally, an in-depth study of the composition map provides a practical approach to the drastic reduction of heterojunction abruptness by reducing the Si and Ge concentrations in the catalyst droplet. This converges with previous approaches, which use catalysts aiming to reduce the solubility of the atomic species. This analysis opens new paths to the reduction of heterojunction abruptness using Au catalysts, but the model can be naturally extended to other catalysts and semiconductors.

Physical Modeling and Reliability Mechanisms in High Voltage AIGaN/GaN HFETs

DTIC Science & Technology

2013-02-01

heterojunction field effect transistor speed and stability has been established. The observed dependence of the LO phonon lifetime on the bulk carrier...aggregate, the cumulative data clearly point to the benefits of operation at or near resonance of LO phonon frequency and Plasmon frequency. Heterojunction ...of the structure such as quantum wells as in the case of light emitting diodes and lasers, heterojunction bipolar transistors. The FET case is

Low-Resistivity Zinc Selenide for Heterojunctions

NASA Technical Reports Server (NTRS)

Stirn, R. J.

1986-01-01

Magnetron reactive sputtering enables doping of this semiconductor. Proposed method of reactive sputtering combined with doping shows potential for yielding low-resistivity zinc selenide films. Zinc selenide attractive material for forming heterojunctions with other semiconductor compounds as zinc phosphide, cadmium telluride, and gallium arsenide. Semiconductor junctions promising for future optoelectronic devices, including solar cells and electroluminescent displays. Resistivities of zinc selenide layers deposited by evaporation or chemical vapor deposition too high to form practical heterojunctions.

MoS2 Heterojunctions by Thickness Modulation

PubMed Central

Tosun, Mahmut; Fu, Deyi; Desai, Sujay B.; Ko, Changhyun; Seuk Kang, Jeong; Lien, Der-Hsien; Najmzadeh, Mohammad; Tongay, Sefaattin; Wu, Junqiao; Javey, Ali

2015-01-01

In this work, we report lateral heterojunction formation in as-exfoliated MoS2 flakes by thickness modulation. Kelvin probe force microscopy is used to map the surface potential at the monolayer-multilayer heterojunction, and consequently the conduction band offset is extracted. Scanning photocurrent microscopy is performed to investigate the spatial photocurrent response along the length of the device including the source and the drain contacts as well as the monolayer-multilayer junction. The peak photocurrent is measured at the monolayer-multilayer interface, which is attributed to the formation of a type-I heterojunction. The work presents experimental and theoretical understanding of the band alignment and photoresponse of thickness modulated MoS2 junctions with important implications for exploring novel optoelectronic devices. PMID:26121940

Influence of external mechanical stress on electrical properties of single-crystal n-3C-SiC/p-Si heterojunction diode

NASA Astrophysics Data System (ADS)

Qamar, Afzaal; Veit Dao, Dzung; Tanner, Philip; Phan, Hoang-Phuong; Dinh, Toan; Dimitrijev, Sima

2015-06-01

This article reports for the first time the electrical properties of fabricated n-3C-SiC/p-Si heterojunction diodes under external mechanical stress in the [110] direction. An anisotype heterojunction diode of n-3C-SiC/p-Si was fabricated by depositing 3C-SiC onto the Si substrate by low-pressure chemical vapor deposition. The mechanical stress significantly affected the scaling current density of the heterojunction. The scaling current density increases with stress and is explained in terms of a band offset reduction at the SiC/Si interface under applied stress. A reduction in the barrier height across the junction owing to applied stress is also explained quantitatively.

MoS 2 Heterojunctions by Thickness Modulation

DOE PAGES

Tosun, Mahmut; Fu, Deyi; Desai, Sujay B.; ...

2015-06-30

In this work, we report lateral heterojunction formation in as-exfoliated MoS 2 flakes by thickness modulation. Kelvin probe force microscopy is used to map the surface potential at the monolayer-multilayer heterojunction, and consequently the conduction band offset is extracted. Scanning photocurrent microscopy is performed to investigate the spatial photocurrent response along the length of the device including the source and the drain contacts as well as the monolayer-multilayer junction. The peak photocurrent is measured at the monolayer-multilayer interface, which is attributed to the formation of a type-I heterojunction. Finally, the work presents experimental and theoretical understanding of the band alignmentmore » and photoresponse of thickness modulated MoS 2 junctions with important implications for exploring novel optoelectronic devices.« less

A small-signal generator based on a multi-layer graphene/molybdenum disulfide heterojunction

NASA Astrophysics Data System (ADS)

Tan, Zhen; Tian, He; Feng, Tingting; Zhao, Lianfeng; Xie, Dan; Yang, Yi; Xiao, Lei; Wang, Jing; Ren, Tian-Ling; Xu, Jun

2013-12-01

In this work, we fabricate a heterojunction small-signal generator (HSSG) based on a graphene-molybdenum disulfide (MoS2) heterojunction. The HSSG is fundamentally different from any analog device developed previously. The HSSG is composed of two quasi-2D heterojunctions and has three terminals named injector (I), recombinator (R), and generator (G). MoS2 serves as I and G, and graphene works as R in the HSSG. The scale coefficient (β = IG/IR) of the HSSG is 1.14 × 10-4 (VIG, IR = 0.2 V) to 1.95 × 10-4 (VIG, IR = 1 V). The current generated from G could be as low as pA scale, which reveals the good performance of the HSSG.

Epitaxial Growth of an Organic p-n Heterojunction: C60 on Single-Crystal Pentacene.

PubMed

Nakayama, Yasuo; Mizuno, Yuta; Hosokai, Takuya; Koganezawa, Tomoyuki; Tsuruta, Ryohei; Hinderhofer, Alexander; Gerlach, Alexander; Broch, Katharina; Belova, Valentina; Frank, Heiko; Yamamoto, Masayuki; Niederhausen, Jens; Glowatzki, Hendrik; Rabe, Jürgen P; Koch, Norbert; Ishii, Hisao; Schreiber, Frank; Ueno, Nobuo

2016-06-01

Designing molecular p-n heterojunction structures, i.e., electron donor-acceptor contacts, is one of the central challenges for further development of organic electronic devices. In the present study, a well-defined p-n heterojunction of two representative molecular semiconductors, pentacene and C60, formed on the single-crystal surface of pentacene is precisely investigated in terms of its growth behavior and crystallographic structure. C60 assembles into a (111)-oriented face-centered-cubic crystal structure with a specific epitaxial orientation on the (001) surface of the pentacene single crystal. The present experimental findings provide molecular scale insights into the formation mechanisms of the organic p-n heterojunction through an accurate structural analysis of the single-crystalline molecular contact.

Z-Scheme NiTiO 3 /g-C 3 N 4 Heterojunctions with Enhanced Photoelectrochemical and Photocatalytic Performances under Visible LED Light Irradiation

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

Huang, Zhenyu; Zeng, Xiaoqiao; Li, Kai

Direct Z-scheme NiTiO3/g-C3N4 heterojunctions were successfully assembled by using simple calcination method and the photoelectrochemical and photocatalytic performance were investigated by light emitting diode (LED). The photoanode composed by the heterojunction with about 50 wt% NiTiO3 content exhibits the best photoelectrochemical activity with photoconversion efficiency up to 0.066%, which is 4.4 and 3.13 times larger than NiTiO3 or g-C3N4. The remarkably enhanced photoelectrochemical and photocatalytic activity of the heterojunction can be due to the efficiently photogenerated electron-hole separation by a Z-scheme mechanism.

Interfacial coupling induced direct Z scheme water splitting in metal-free photocatalyst: C3N/g-C3N4 heterojunctions.

PubMed

Wang, Jiajun; Li, Xiaoting; You, Ya; Xintong, Yang; Wang, Ying; Li, Qunxiang

2018-06-21

Mimicking the natural photosynthesis in green plants, artificial Z-scheme photocatalysis enables more efficient utilization of solar energy for photocatalytic water splitting. Most currently designed g-C3N4-based Z-scheme heterojunctions are usually based on metal-containing semiconductor photocatalysts, thus exploiting metal-free photocatalysts for Z-scheme water splitting is of huge interest. Herein, we propose two metal-free C3N/g-C3N4 heterojunctions with the C3N monolayer covering g-C3N4 sheet (monolayer or bilayer) and systematically explore their electronic structures, charge distributions and photocatalytic properties by performing extensive hybrid density functional calculations. We clearly reveal that the relative strong built-in electric fields around their respective interface regions, caused by the charge transfer from C3N monolayer to g-C3N4 monolayer or bilayer, result in the bands bending, renders the transfer of photogenerated carriers in these two heterojunctions following the Z-scheme instead of the type-II pathway. Moreover, the photogenerated electrons and holes in these two C3N/g-C3N4 heterojunctions not only can be efficiently separated, but also have strong redox abilities for water oxidation and reduction. Compared with the isolated g-C3N4 sheets, the light absorption in visible to near-infrared region are significantly enhanced in these proposed heterojunctions. These theoretical findings suggest that these proposed metal-free C3N/g-C3N4 heterojunctions are promising direct Z-scheme photocatalysts for solar water splitting. © 2018 IOP Publishing Ltd.

The photovoltaic properties of an Al In As/InP heterojunctions grown by LPE method

NASA Technical Reports Server (NTRS)

Wang, Edward Y.

1989-01-01

Work is presented on heterojunction solar cells which were studied under the NASA/Arizona State University intern program. The heterojunction solar cells were fabricated by the liquid phase epitaxy method. The basic conversion efficiency was measured at 5 percent. It was determined that a thicker epilayer is needed, and that the density of recombination center should be reduced to give a smaller saturation current and hence a larger open-circuit voltage.

Heterojunction-Internal-Photoemission Infrared Detectors

NASA Technical Reports Server (NTRS)

Maserjian, Joseph

1991-01-01

New type of photodetector adds options for design of imaging devices. Heterojunction-internal-photoemission (HIP) infrared photodetectors proposed for incorporation into planar arrays in imaging devices required to function well at wavelengths from 8 to 17 micrometers and at temperatures above 65 K. Photoexcited electrons cross energy barrier at heterojunction and swept toward collection layer. Array of such detectors made by etching mesa structures. HIP layers stacked to increase quantum efficiency. Also built into integrated circuits including silicon multiplexer/readout circuits.

Band gap engineering in finite elongated graphene nanoribbon heterojunctions: Tight-binding model

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

Tayo, Benjamin O.

2015-08-15

A simple model based on the divide and conquer rule and tight-binding (TB) approximation is employed for studying the role of finite size effect on the electronic properties of elongated graphene nanoribbon (GNR) heterojunctions. In our model, the GNR heterojunction is divided into three parts: a left (L) part, middle (M) part, and right (R) part. The left part is a GNR of width W{sub L}, the middle part is a GNR of width W{sub M}, and the right part is a GNR of width W{sub R}. We assume that the left and right parts of the GNR heterojunction interactmore » with the middle part only. Under this approximation, the Hamiltonian of the system can be expressed as a block tridiagonal matrix. The matrix elements of the tridiagonal matrix are computed using real space nearest neighbor orthogonal TB approximation. The electronic structure of the GNR heterojunction is analyzed by computing the density of states. We demonstrate that for heterojunctions for which W{sub L} = W{sub R}, the band gap of the system can be tuned continuously by varying the length of the middle part, thus providing a new approach to band gap engineering in GNRs. Our TB results were compared with calculations employing divide and conquer rule in combination with density functional theory (DFT) and were found to agree nicely.« less

Atomic structure, electronic properties, and band offsets of SrRuO3/TiO2 heterojunctions

NASA Astrophysics Data System (ADS)

Ferdous, Naheed; Ertekin, Elif

2015-03-01

Photocatalytic water splitting by sunlight can in principle be an environmentally green approach to hydrogen fuel production, but at present photocatalytic conversion efficiencies remain too small. In titanium dioxide (TiO2) , the most commonly used photocatalyst, the biggest limitation arises from poor absorption of visible light. One way to increase the visible light absorption is to create a composite heterojunction by integrating TiO2 with a strongly light absorbing material. Inspired by experimental results demonstrating good light absorption in the correlated metal oxide Strontium Ruthenate (SrRuO3) , as well as enhanced photocatalytic activity of SrRuO3/TiO2 heterojunctions, we have carried out electronic structure calculations based on density functional theory to explain and improve on the observed properties of such heterojunctions. Our calculations present that this heterojunction exhibits type-II band alignment which is necessary to transport optically excited electrons from the SrRuO3 to the TiO2, with calculated work functions in good agreement with experimental measurements. Also, DFT calculations help to explain the origin of large light absorption in the correlated metal oxide, which arises from electronic excitations from O 2p levels into the Ru d-orbital quasiparticle states in the material. The use of correlated metal oxide/ TiO2 heterojunctions is a potentially interesting approach to improved photocatalytic activity.

Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode.

PubMed

Jariwala, Deep; Sangwan, Vinod K; Wu, Chung-Chiang; Prabhumirashi, Pradyumna L; Geier, Michael L; Marks, Tobin J; Lauhon, Lincoln J; Hersam, Mark C

2013-11-05

The p-n junction diode and field-effect transistor are the two most ubiquitous building blocks of modern electronics and optoelectronics. In recent years, the emergence of reduced dimensionality materials has suggested that these components can be scaled down to atomic thicknesses. Although high-performance field-effect devices have been achieved from monolayered materials and their heterostructures, a p-n heterojunction diode derived from ultrathin materials is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits. Here we demonstrate a gate-tunable p-n heterojunction diode using semiconducting single-walled carbon nanotubes (SWCNTs) and single-layer molybdenum disulfide as p-type and n-type semiconductors, respectively. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias to achieve a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 10(4). This heterojunction diode also responds strongly to optical irradiation with an external quantum efficiency of 25% and fast photoresponse <15 μs. Because SWCNTs have a diverse range of electrical properties as a function of chirality and an increasing number of atomically thin 2D nanomaterials are being isolated, the gate-tunable p-n heterojunction concept presented here should be widely generalizable to realize diverse ultrathin, high-performance electronics and optoelectronics.

Fabrication and Enhanced Photoelectrochemical Performance of MoS₂/S-Doped g-C₃N₄ Heterojunction Film.

PubMed

Ye, Lijuan; Wang, Dan; Chen, Shijian

2016-03-02

We report on a novel MoS2/S-doped g-C3N4 heterojunction film with high visible-light photoelectrochemical (PEC) performance. The heterojunction films are prepared by CVD growth of S-doped g-C3N4 film on indium-tin oxide (ITO) glass substrates, with subsequent deposition of a low bandgap, 1.69 eV, visible-light response MoS2 layer by hydrothermal synthesis. Adding thiourea into melamine as the coprecursor not only facilitates the growth of g-C3N4 films but also introduces S dopants into the films, which significantly improves the PEC performance. The fabricated MoS2/S-doped g-C3N4 heterojunction film offers an enhanced anodic photocurrent of as high as ∼1.2 × 10(-4) A/cm(2) at an applied potential of +0.5 V vs Ag/AgCl under the visible light irradiation. The enhanced PEC performance of MoS2/S-doped g-C3N4 film is believed due to the improved light absorption and the efficient charge separation of the photogenerated charge at the MoS2/S-doped g-C3N4 interface. The convenient preparation of carbon nitride based heterojunction films in this work can be widely used to design new heterojunction photoelectrodes or photocatalysts with high performance for H2 evolution.

p-p Heterojunction of Nickel Oxide-Decorated Cobalt Oxide Nanorods for Enhanced Sensitivity and Selectivity toward Volatile Organic Compounds.

PubMed

Suh, Jun Min; Sohn, Woonbae; Shim, Young-Seok; Choi, Jang-Sik; Song, Young Geun; Kim, Taemin L; Jeon, Jong-Myeong; Kwon, Ki Chang; Choi, Kyung Soon; Kang, Chong-Yun; Byun, Hyung-Gi; Jang, Ho Won

2018-01-10

The utilization of p-p isotype heterojunctions is an effective strategy to enhance the gas sensing properties of metal-oxide semiconductors, but most previous studies focused on p-n heterojunctions owing to their simple mechanism of formation of depletion layers. However, a proper choice of isotype semiconductors with appropriate energy bands can also contribute to the enhancement of the gas sensing performance. Herein, we report nickel oxide (NiO)-decorated cobalt oxide (Co 3 O 4 ) nanorods (NRs) fabricated using the multiple-step glancing angle deposition method. The effective decoration of NiO on the entire surface of Co 3 O 4 NRs enabled the formation of numerous p-p heterojunctions, and they exhibited a 16.78 times higher gas response to 50 ppm of C 6 H 6 at 350 °C compared to that of bare Co 3 O 4 NRs with the calculated detection limit of approximately 13.91 ppb. Apart from the p-p heterojunctions, increased active sites owing to the changes in the orientation of the exposed lattice surface and the catalytic effects of NiO also contributed to the enhanced gas sensing properties. The advantages of p-p heterojunctions for gas sensing applications demonstrated in this work will provide a new perspective of heterostructured metal-oxide nanostructures for sensitive and selective gas sensing.

Semiconducting Organic-Inorganic Nanodots Heterojunctions: Platforms for General Photoelectrochemical Bioanalysis Application.

PubMed

Wang, Qian; Ruan, Yi-Fan; Zhao, Wei-Wei; Lin, Peng; Xu, Jing-Juan; Chen, Hong-Yuan

2018-03-20

In this study, semiconducting organic polymer dots (Pdots) and inorganic quantum dots (Qdots) were first utilized to construct the organic-inorganic nanodots heterojunction for the photoelectrochemical (PEC) bioanalysis application. Specifically, n-type CdS Qdots, p-type CdTe Qdots, and tetraphenylporphyrin (TPP)-doped poly[(9,9-dioctylfluorenyl-2,7-diyl)- co-(1,4-benzo-{2,1',3}-thiadazole)] (PFBT) Pdots were fabricated, and their energy levels, that is, their valence band (VB)/conduction band (CB) or lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) values, were also determined. Then, these nanodots were integrated to construct four types of p-n and p-p organic-inorganic nanodots heterojunctions, that is, CdS Qdots/TPP-doped PFBT Pdots, TPP-doped PFBT Pdots/CdS Qdots, CdTe Qdots/TPP-doped PFBT Pdots, and TPP-doped PFBT Pdots/CdTe Qdots, on the transparent glass electrode. Upon light irradiation, four heterojunctions exhibited different PEC behaviors with some having prominent photocurrent enhancement. With the model molecule l-cysteine (l-cys) as target, the proposed PEC sensor exhibited good performances. In brief, this work presents the first semiconducting organic-inorganic nanodots heterojunction for PEC bioanalysis application, which could be easily used as a general platform for future PEC bioanalysis building. Besides, it is expected to inspire more interest in the design, development, and implementation of various organic-inorganic heterojunctions for advanced PEC bioanalysis in the future.

Gate-tunable carbon nanotube–MoS2 heterojunction p-n diode

PubMed Central

Jariwala, Deep; Sangwan, Vinod K.; Wu, Chung-Chiang; Prabhumirashi, Pradyumna L.; Geier, Michael L.; Marks, Tobin J.; Lauhon, Lincoln J.; Hersam, Mark C.

2013-01-01

The p-n junction diode and field-effect transistor are the two most ubiquitous building blocks of modern electronics and optoelectronics. In recent years, the emergence of reduced dimensionality materials has suggested that these components can be scaled down to atomic thicknesses. Although high-performance field-effect devices have been achieved from monolayered materials and their heterostructures, a p-n heterojunction diode derived from ultrathin materials is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits. Here we demonstrate a gate-tunable p-n heterojunction diode using semiconducting single-walled carbon nanotubes (SWCNTs) and single-layer molybdenum disulfide as p-type and n-type semiconductors, respectively. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias to achieve a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104. This heterojunction diode also responds strongly to optical irradiation with an external quantum efficiency of 25% and fast photoresponse <15 μs. Because SWCNTs have a diverse range of electrical properties as a function of chirality and an increasing number of atomically thin 2D nanomaterials are being isolated, the gate-tunable p-n heterojunction concept presented here should be widely generalizable to realize diverse ultrathin, high-performance electronics and optoelectronics. PMID:24145425

Mechanistic insights into the photoinduced charge carrier dynamics of BiOBr/CdS nanosheet heterojunctions for photovoltaic application.

PubMed

Jia, Huimin; Zhang, Beibei; He, Weiwei; Xiang, Yong; Zheng, Zhi

2017-03-02

The rational design of high performance hetero-structure photovoltaic devices requires a full understanding of the photoinduced charge transfer mechanism and kinetics at the interface of heterojunctions. In this paper, we intelligently fabricated p-BiOBr/n-CdS heterojunctions with perfect nanosheet arrays by using a facile successive ionic layer adsorption and reaction and chemical bath deposition methods at low temperature. A BiOBr/CdS heterojunction based solar cell has been fabricated which exhibited enhanced photovoltaic responses. Assisted by the surface photovoltage (SPV), transient photovoltage (TPV) and Kelvin probe technique, the photoinduced charge transfer dynamics on the BiOBr nanosheet and p-BiOBr/n-CdS interface were systematically investigated. It was found that the BiOBr/CdS nanosheet array heterojunctions were more efficient in facilitating charge carrier separation than both bare BiOBr and CdS films. The mechanism underlying the photoinduced charge carrier transfer behaviour was unravelled by allying the energy band of BiOBr/CdS p-n junctions from both the interfacial electric field and surface electric field. In addition, the CdS loading thickness in the p-BiOBr/n-CdS heterojunction and the incident wavelength affected greatly the transfer behavior of photoinduced charges, which was of great value for design of photovoltaic devices.

Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene-MoS2 van der Waals Heterojunction.

PubMed

Bettis Homan, Stephanie; Sangwan, Vinod K; Balla, Itamar; Bergeron, Hadallia; Weiss, Emily A; Hersam, Mark C

2017-01-11

van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS 2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS 2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS 2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS 2 decay processes, the hole transfer yield from MoS 2 to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS 2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.

Core-shell heterojunction of silicon nanowire arrays and carbon quantum dots for photovoltaic devices and self-driven photodetectors.

PubMed

Xie, Chao; Nie, Biao; Zeng, Longhui; Liang, Feng-Xia; Wang, Ming-Zheng; Luo, Linbao; Feng, Mei; Yu, Yongqiang; Wu, Chun-Yan; Wu, Yucheng; Yu, Shu-Hong

2014-04-22

Silicon nanostructure-based solar cells have lately intrigued intensive interest because of their promising potential in next-generation solar energy conversion devices. Herein, we report a silicon nanowire (SiNW) array/carbon quantum dot (CQD) core-shell heterojunction photovoltaic device by directly coating Ag-assisted chemical-etched SiNW arrays with CQDs. The heterojunction with a barrier height of 0.75 eV exhibited excellent rectifying behavior with a rectification ratio of 10(3) at ±0.8 V in the dark and power conversion efficiency (PCE) as high as 9.10% under AM 1.5G irradiation. It is believed that such a high PCE comes from the improved optical absorption as well as the optimized carrier transfer and collection capability. Furthermore, the heterojunction could function as a high-performance self-driven visible light photodetector operating in a wide switching wavelength with good stability, high sensitivity, and fast response speed. It is expected that the present SiNW array/CQD core-shell heterojunction device could find potential applications in future high-performance optoelectronic devices.

Embedded vertically aligned cadmium telluride nanorod arrays grown by one-step electrodeposition for enhanced energy conversion efficiency in three-dimensional nanostructured solar cells.

PubMed

Wang, Jun; Liu, Shurong; Mu, Yannan; Liu, Li; A, Runa; Yang, Jiandong; Zhu, Guijie; Meng, Xianwei; Fu, Wuyou; Yang, Haibin

2017-11-01

Vertically aligned CdTe nanorods (NRs) arrays are successfully grown by a simple one-step and template-free electrodeposition method, and then embedded in the CdS window layer to form a novel three-dimensional (3D) heterostructure on flexible substrates. The parameters of electrodeposition such as deposition potential and pH of the solution are varied to analyze their important role in the formation of high quality CdTe NRs arrays. The photovoltaic conversion efficiency of the solar cell based on the 3D heterojunction structure is studied in detail. In comparison with the standard planar heterojunction solar cell, the 3D heterojunction solar cell exhibits better photovoltaic performance, which can be attributed to its enhanced optical absorption ability, increased heterojunction area and improved charge carrier transport. The better photoelectric property of the 3D heterojunction solar cell suggests great application potential in thin film solar cells, and the simple electrodeposition process represents a promising technique for large-scale fabrication of other nanostructured solar energy conversion devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Phase transformation synthesis of TiO2/CdS heterojunction film with high visible-light photoelectrochemical activity

NASA Astrophysics Data System (ADS)

Liu, Canjun; Yang, Yahui; Li, Jie; Chen, Shu

2018-06-01

CdS/TiO2 heterojunction film used as a photoanode has attracted much attention in the past few years due to its good visible light photocatalytic activity. However, CdS/TiO2 films prepared by conventional methods (successive ionic layer adsorption and reaction, chemical bath deposition and electrodeposition) show numerous grain boundaries in the CdS layer and an imperfect contact at the heterojunction interface. In this study, we designed a phase transformation method to fabricate CdS/TiO2 nanorod heterojunction films. The characterization results showed that the CdS layer with fewer grain boundaries was conformally coated on the TiO2 nanorod surface and the formation mechanism has been explained in this manuscript. Moreover, the prepared CdS/TiO2 films show a high photocatalytic activity and the photocurrent density is as high as 9.65 mA cm‑2 at 0.80 V versus RHE. It may be attributed to fewer grain boundaries and a compact heterojunction contact, which can effectively improve charge separation and transportation.

Exciton-dissociation and charge-recombination processes in pentacene/C60 solar cells: theoretical insight into the impact of interface geometry.

PubMed

Yi, Yuanping; Coropceanu, Veaceslav; Brédas, Jean-Luc

2009-11-04

The exciton-dissociation and charge-recombination processes in organic solar cells based on pentacene/C(60) heterojunctions are investigated by means of quantum-mechanical calculations. The electronic couplings and the rates of exciton dissociation and charge recombination have been evaluated for several geometrical configurations of the pentacene/C(60) complex, which are relevant to bilayer and bulk heterojunctions. The results suggest that, irrespective of the actual pentacene-fullerene orientation, both pentacene-based and C(60)-based excitons are able to dissociate efficiently. Also, in the case of parallel configurations of the molecules at the pentacene/C(60) interface, the decay of the lowest charge-transfer state to the ground state is calculated to be very fast; as a result, it can compete with the dissociation process into mobile charge carriers. Since parallel configurations are expected to be found more frequently in bulk heterojunctions than in bilayer heterojunctions, the performance of pentacene/C(60) bulk-heterojunction solar cells is likely to be more affected by charge recombination than that of bilayer devices.

Rationally designed n-n heterojunction with highly efficient solar hydrogen evolution.

PubMed

Xu, Miao; Ye, Tiannan; Dai, Fang; Yang, Jindi; Shen, Jingmei; He, Qingquan; Chen, Wenlong; Liang, Na; Zai, Jiantao; Qian, Xuefeng

2015-04-13

In most of the reported n-n heterojunction photocatalysts, both the conduction and valence bands of one semiconductor are more negative than those of the other semiconductor. In this work, we designed and synthesized a novel n-n heterojunction photocatalyst, namely CdS-ZnWO4 heterojunctions, in which ZnWO4 has more negative conduction band and more positive valence band than those of CdS. The hydrogen evolution rate of CdS-30 mol %-ZnWO4 reaches 31.46 mmol h(-1)  g(-1) under visible light, which is approximately 8 and 755 times higher than that of pure CdS and ZnWO4 under similar conditions, respectively. The location of the surface active sites is researched and a plausible mechanism of performance enhancement by the tuning of the structure is proposed based on the photoelectrochemical characterization. The results illustrate that this kind of nonconventional n-n heterojunctions is also suitable and highly efficient for solar hydrogen evolution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters

PubMed Central

2013-01-01

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell. PMID:24188725

Efficient cascade multiple heterojunction organic solar cells with inverted structure

NASA Astrophysics Data System (ADS)

Guo, Tingting; Li, Mingtao; Qiao, Zhenfang; Yu, Leiming; Zhao, Jianhong; Feng, Nianjun; Shi, Peiguang; Wang, Xiaoyan; Pu, Xiaoyun; Wang, Hai

2018-05-01

In this work, we demonstrate an efficient cascade multiple heterojunction organic solar cell with inverted structure. By using two donor materials, poly(3-hexylthiosphene) (P3HT) and titanyl phthalocyanine (TiOPc), as well as two acceptor materials, [6,6]-phenyl C61 butyric acid methyl ester (PCBM) and C60, the cascade multiple heterojunctions of P3HT:PCBM/TiOPc:C60/C60 have been constructed. Applying the optimized inverted configuration of FTO/Zinc Tin Oxide (ZTO)/C60 (30 nm)/TiOPc:C60 (1:1.5, 25 nm)/P3HT:PCBM (1:0.8, 100 nm)/MoO3 (4 nm)/Ag, the considerably enhanced open circuit voltage (VOC) and short circuit current (JSC) can be harvested together, and the power conversion efficiency (PCE) is three times higher than that of the control cell with conventional structure. The significant improvements of the inverted cell are mostly due to the broadened spectral absorption and high efficient multi-interface exciton dissociation in the cascade multiple heterojunctions, indicating that the optimized cascade heterojunctions match the inverted structure well.

Solution processable inverted structure ZnO-organic hybrid heterojuction white LEDs

NASA Astrophysics Data System (ADS)

Bano, N.; Hussain, I.; Soomro, M. Y.; EL-Naggar, A. M.; Albassam, A. A.

2018-05-01

Improving luminance efficiency and colour purity are the most important challenges for zinc oxide (ZnO)-organic hybrid heterojunction light emitting diodes (LEDs), affecting their large area applications. If ZnO-organic hybrid heterojunction white LEDs are fabricated by a hydrothermal method, it is difficult to obtain pure and stable blue emission from PFO due to the presence of an undesirable green emission. In this paper, we present an inverted-structure ZnO-organic hybrid heterojunction LED to avoid green emission from PFO, which mainly originates during device processing. With this configuration, each ZnO nanorod (NR) forms a discrete p-n junction; therefore, large-area white LEDs can be designed without compromising the junction area. The configuration used for this novel structure is glass/ZnO NRs/PFO/PEDOT:PSS/L-ITO, which enables the development of efficient, large-area and low-cost hybrid heterojunction LEDs. Inverted-structure ZnO-organic hybrid heterojunction white LEDs offer several improvements in terms of brightness, size, colour, external quantum efficiency and a wider applicability as compared to normal architecture LEDs.

Structural and optical properties of the ZnS/GaSe heterojunctions

NASA Astrophysics Data System (ADS)

Alharbi, S. R.; Abdallaha, Maisam M. A.; Qasrawi, A. F.

2017-11-01

In the current work, the ZnS/GaSe thin film heterojunction interfaces are experimentally designed and characterized by means of x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy and optical spectroscopy techniques. The heterojunction is observed to exhibit physical nature of formation with an induced crystallization of GaSe by the ZnS substrate. For this heterojunction, the hot probe technique suggested the formation of a p-ZnS/n-GaSe interface. In addition, the designed energy band diagram of the heterojunction which was actualized with the help of the optical spectrophotometric data analysis revealed a respective conduction and valence band offsets of 0.67 and 0.73 eV. On the other hand, the dielectric dispersion analysis and modeling which was studied in the frequency range of 270-1000 THz, have shown that the interfacing of the ZnS with GaSe strongly affects the properties of ZnS as it reduces the number of free carriers, shifts down the plasmon frequency, increases the charge carrier scattering time and results in higher values of drift mobility at Terahertz frequencies.

Band alignment in atomically precise graphene nanoribbon junctions

NASA Astrophysics Data System (ADS)

Ma, Chuanxu; Liang, Liangbo; Hong, Kunlun; Li, An-Ping; Xiao, Zhongcan; Lu, Wenchang; Bernholc, Jerry

Building atomically precise graphene nanoribbon (GNR) heterojunctions down to molecular level opens a new realm to functional graphene-based devices. By employing a surface-assisted self-assembly process, we have synthesized heterojunctions of armchair GNRs (aGNR) with widths of seven, fourteen and twenty-one carbon atoms, denoted 7, 14 and 21-aGNR respectively. A combined study with scanning tunneling microscopy (STM) and density functional theory (DFT) allows the visualization of electronic band structures and energy level alignments at the heterojunctions with varying widths. A wide bandgap ( 2.6 eV) has been identified on semiconducting 7-aGNR, while the 14-aGNR appears nearly metallic and the 21-aGNR possesses a narrow bandgap. The spatially modulations of the energy bands are strongly confined at the heterojunctions within a width of about 2 nm. Clear band bending of about 0.4 eV and 0.1 eV are observed at the 7-14 and 14-21 aGNR heterojunctions, respectively. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Interplay of Nanoscale, Hybrid P3HT/ZTO Interface on Optoelectronics and Photovoltaic Cells.

PubMed

Lai, Jian-Jhong; Li, Yu-Hsun; Feng, Bo-Rui; Tang, Shiow-Jing; Jian, Wen-Bin; Fu, Chuan-Min; Chen, Jiun-Tai; Wang, Xu; Lee, Pooi See

2017-09-27

Photovoltaic effects in poly(3-hexylthiophene-2,5-diyl) (P3HT) have attracted much attention recently. Here, natively p-type doped P3HT nanofibers and n-type doped zinc tin oxide (ZTO) nanowires are used for making not only field-effect transistors (FETs) but also p-n nanoscale diodes. The hybrid P3HT/ZTO p-n heterojunction shows applications in many directions, and it also facilitates the investigation of photoelectrons and photovoltaic effects on the nanoscale. As for applications, the heterojunction device shows a simultaneously high on/off ratio of n- and p-type FETs, gatable p-n junction diodes, tristate buffer devices, gatable photodetectors, and gatable solar cells. On the other hand, P3HT nanofibers are taken as a photoactive layer and the role played by the p-n heterojunction in the photoelectric and photovoltaic effects is investigated. It is found that the hybrid P3HT/ZTO p-n heterojunction assists in increasing photocurrents and enhancing photovoltaic effects. Through the controllable gating of the heterojunction, we can discuss the background mechanisms of photocurrent generation and photovoltaic energy harvesting.

InGaAsN/GaAs heterojunction for multi-junction solar cells

DOEpatents

Kurtz, Steven R.; Allerman, Andrew A.; Klem, John F.; Jones, Eric D.

2001-01-01

An InGaAsN/GaAs semiconductor p-n heterojunction is disclosed for use in forming a 0.95-1.2 eV bandgap photodetector with application for use in high-efficiency multi-junction solar cells. The InGaAsN/GaAs p-n heterojunction is formed by epitaxially growing on a gallium arsenide (GaAs) or germanium (Ge) substrate an n-type indium gallium arsenide nitride (InGaAsN) layer having a semiconductor alloy composition In.sub.x Ga.sub.1-x As.sub.1-y N.sub.y with 070%.

Transport Properties of a MoS2/WSe2 Heterojunction Transistor and Its Potential for Application.

PubMed

Nourbakhsh, Amirhasan; Zubair, Ahmad; Dresselhaus, Mildred S; Palacios, Tomás

2016-02-10

This paper studies band-to-band tunneling in the transverse and lateral directions of van der Waals MoS2/WSe2 heterojunctions. We observe room-temperature negative differential resistance (NDR) in a heterojunction diode comprised of few-layer WSe2 stacked on multilayer MoS2. The presence of NDR is attributed to the lateral band-to-band tunneling at the edge of the MoS2/WSe2 heterojunction. The backward tunneling diode shows an average conductance slope of 75 mV/dec with a high curvature coefficient of 62 V(-1). Associated with the tunnel-diode characteristics, a positive-to-negative transconductance in the MoS2/WSe2 heterojunction transistors is observed. The transition is induced by strong interlayer coupling between the films, which results in charge density and energy-band modulation. The sign change in transconductance is particularly useful for multivalued logic (MVL) circuits, and we therefore propose and demonstrate for the first time an MVL-inverter that shows three levels of logic using one pair of p-type transistors.

Electro-optical modeling of bulk heterojunction solar cells

NASA Astrophysics Data System (ADS)

Kirchartz, Thomas; Pieters, Bart E.; Taretto, Kurt; Rau, Uwe

2008-11-01

We introduce a model for charge separation in bulk heterojunction solar cells that combines exciton transport to the interface between donor and acceptor phases with the dissociation of the bound electron/hole pair. We implement this model into a standard semiconductor device simulator, thereby creating a convenient method to simulate the optical and electrical characteristics of a bulk heterojunction solar cell with a commercially available program. By taking into account different collection probabilities for the excitons in the polymer and the fullerene, we are able to reproduce absorptance, internal and external quantum efficiency, as well as current/voltage curves of bulk heterojunction solar cells. We further investigate the influence of mobilities of the free excitons as well as the mobilities of the free charge carriers on the performance of bulk heterojunction solar cells. We find that, in general, the highest efficiencies are achieved with the highest mobilities. However, an optimum finite mobility of free charge carriers can result from a large recombination velocity at the contacts. In contrast, Langevin-type of recombination cannot lead to finite optimum mobilities even though this mechanism has a strong dependence on the free carrier mobilities.

Coherent Electron Transfer at the Ag / Graphite Heterojunction Interface

NASA Astrophysics Data System (ADS)

Tan, Shijing; Dai, Yanan; Zhang, Shengmin; Liu, Liming; Zhao, Jin; Petek, Hrvoje

2018-03-01

Charge transfer in transduction of light to electrical or chemical energy at heterojunctions of metals with semiconductors or semimetals is believed to occur by photogenerated hot electrons in metal undergoing incoherent internal photoemission through the heterojunction interface. Charge transfer, however, can also occur coherently by dipole coupling of electronic bands at the heterojunction interface. Microscopic physical insights into how transfer occurs can be elucidated by following the coherent polarization of the donor and acceptor states on the time scale of electronic dephasing. By time-resolved multiphoton photoemission spectroscopy (MPP), we investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Multidimensional MPP spectroscopy reveals a resonant two-photon transition, which dephases within 10 fs completing the coherent transfer.

Fabrication and investigation of photosensitive MoOx/n-CdTe heterojunctions

NASA Astrophysics Data System (ADS)

Solovan, M. M.; Gavaleshko, N. M.; Brus, V. V.; Mostovyi, A. I.; Maryanchuk, P. D.; Tresso, E.

2016-10-01

MoOx/n-CdTe photosensitive heterostructures were prepared by the deposition of molybdenum oxide thin films onto n-type single-crystal CdTe substrates by DC reactive magnetron sputtering. The obtained heterojunctions possessed sharply defined rectifying properties with the rectification ration RR ˜ 106. The temperature dependences of the height of the potential barrier and series resistance of the MoOx/CdTe heterojunctions were investigated. The dominating current transport mechanisms through the heterojunctions were determined at forward and reverse biases. The analysis of capacitance-voltage (C-V) characteristics, measured at different frequencies of the small amplitude AC signal and corrected by the effect of the series resistance, provided evidence of the presence of electrically charged interface states, which significantly affect the measured capacitance.

The recombination velocity at III-V compound heterojunctions with applications to Al (x) Ga(1-x)As-GaAs(1-y)Sb(y)

NASA Technical Reports Server (NTRS)

Kim, J. S.

1978-01-01

Interface recombination velocity in AlxGa1-xAs-GaAs and A10.85 Ga0.15As-GaAs1-ySby heterojunction systems was studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAsSb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates.

Crystallinity of the epitaxial heterojunction of C60 on single crystal pentacene

NASA Astrophysics Data System (ADS)

Tsuruta, Ryohei; Mizuno, Yuta; Hosokai, Takuya; Koganezawa, Tomoyuki; Ishii, Hisao; Nakayama, Yasuo

2017-06-01

The structure of pn heterojunctions is an important subject in the field of organic semiconductor devices. In this work, the crystallinity of an epitaxial pn heterojunction of C60 on single crystal pentacene is investigated by non-contact mode atomic force microscopy and high-resolution grazing incidence x-ray diffraction. Analysis shows that the C60 molecules assemble into grains consisting of single crystallites on the pentacene single crystal surface. The in-plane mean crystallite size exceeds 0.1 μm, which is at least five time larger than the size of crystallites deposited onto polycrystalline pentacene thin films grown on SiO2. The results indicate that improvement in the crystal quality of the underlying molecular substrate leads to drastic promotion of the crystallinity at the organic semiconductor heterojunction.

Ferromagnetic resonance of Ni wires fabricated on ferroelectric LiNbO3 substrate for studying magnetic anisotropy induced by the heterojunction

NASA Astrophysics Data System (ADS)

Yamaguchi, Akinobu; Nakao, Akiko; Ohkochi, Takuo; Yasui, Akira; Kinoshita, Toyohiko; Utsumi, Yuichi; Saiki, Tsunemasa; Yamada, Keisuke

2018-05-01

The electrical ferromagnetic resonance of micro-scale Ni wires with magnetic anisotropy induced by the heterojunction between the Ni layer and ferroelectric single crystalline LiNbO3 substrate was demonstrated by using rectifying effect. The two resonance modes were observed in the Ni wire aligned parallel to the applied magnetic field in plane. The lower resonance frequency mode is considered to correspond to the normal resonance mode with domain resonance, while the higher resonance mode is attributed to the mode which is contributed by the heterojunction between the Ni layer and LiNbO3 substrate. Our results manifest that the rectifying electrical detections are very useful for understating and evaluating the magnetic properties induced by the heterojunction.

Effect of random inhomogeneities in the spatial distribution of radiation-induced defect clusters on carrier transport through the thin base of a heterojunction bipolar transistor upon neutron irradiation

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

Puzanov, A. S.; Obolenskiy, S. V., E-mail: obolensk@rf.unn.ru; Kozlov, V. A.

We analyze the electron transport through the thin base of a GaAs heterojunction bipolar transistor with regard to fluctuations in the spatial distribution of defect clusters induced by irradiation with a fissionspectrum fast neutron flux. We theoretically demonstrate that the homogeneous filling of the working region with radiation-induced defect clusters causes minimum degradation of the dc gain of the heterojunction bipolar transistor.

Interfacial Characteristics of Efficient Bulk Heterojunction Solar Cells Fabricated on MoOx Anode Interlayers.

PubMed

Jasieniak, Jacek J; Treat, Neil D; McNeill, Christopher R; de Villers, Bertrand J Tremolet; Della Gaspera, Enrico; Chabinyc, Michael L

2016-05-01

The role of the interface between an MoOx anode interlayer and a polymer:fullerene bulk heterojunction is investigated. Processing differences in the MoOx induce large variations in the vertical stratification of the bulk heterojunction films. These variations are found to be inconsistent in predicting device performance, with a much better gauge being the quantity of polymer chemisorbed to the anode interlayer. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heterojunction solar cell with passivated emitter surface

DOEpatents

Olson, Jerry M.; Kurtz, Sarah R.

1994-01-01

A high-efficiency heterojunction solar cell wherein a thin emitter layer (preferably Ga.sub.0.52 In.sub.0.48 P) forms a heterojunction with a GaAs absorber layer. A passivating window layer of defined composition is disposed over the emitter layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the window layer.

Heterojunction solar cell with passivated emitter surface

DOEpatents

Olson, J.M.; Kurtz, S.R.

1994-05-31

A high-efficiency heterojunction solar cell is described wherein a thin emitter layer (preferably Ga[sub 0.52]In[sub 0.48]P) forms a heterojunction with a GaAs absorber layer. A passivating window layer of defined composition is disposed over the emitter layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the window layer. 1 fig.

The photovoltaic properties of an Al In As/InP heterojunctions grown by LPE method. Final technical report

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

Wang, E.Y.

1989-10-01

Work is presented on heterojunction solar cells which were studied under the NASA/Arizona State University intern program. The heterojunction solar cells were fabricated by the liquid phase epitaxy method. The basic conversion efficiency was measured at 5 percent. It was determined that a thicker epilayer is needed, and that the density of recombination center should be reduced to give a smaller saturation current and hence a larger open-circuit voltage.

Vertically aligned p-type single-crystalline GaN nanorod arrays on n-type Si for heterojunction photovoltaic cells.

PubMed

Tang, Y B; Chen, Z H; Song, H S; Lee, C S; Cong, H T; Cheng, H M; Zhang, W J; Bello, I; Lee, S T

2008-12-01

Vertically aligned Mg-doped GaN nanorods have been epitaxially grown on n-type Si substrate to form a heterostructure for fabricating p-n heterojunction photovoltaic cells. The p-type GaN nanorod/n-Si heterojunction cell shows a well-defined rectifying behavior with a rectification ratio larger than 10(4) in dark. The cell has a high short-circuit photocurrent density of 7.6 mAlcm2 and energy conversion efficiency of 2.73% under AM 1.5G illumination at 100 mW/cm2. Moreover, the nanorod array may be used as an antireflection coating for solar cell applications to effectively reduce light loss due to reflection. This study provides an experimental demonstration for integrating one-dimensional nanostructure arrays with the substrate to directly fabricate heterojunction photovoltaic cells.

An ion exchange strategy to BiOI/CH3COO(BiO) heterojunction with enhanced visible-light photocatalytic activity

NASA Astrophysics Data System (ADS)

Han, Qiaofeng; Yang, Zhen; Wang, Li; Shen, Zichen; Wang, Xin; Zhu, Junwu; Jiang, Xiaohong

2017-05-01

It is very significant to develop CH3COO(BiO) (denoted as BiOAc) based photocatalysts for the removal of pollutants due to its non-toxicity and availability. We previously reported that BiOAc exhibited excellent photocatalytic activity for rhodamine B (RhB) degradation under UV light irradiation. Herein, by an ion exchange approach, BiOI/BiOAc heterojunction could be easily obtained. The as-prepared heterojunction possessed enhanced photodegradation activity for multiple dyes including RhB and methyl orange (MO) under visible light illumination in comparison with individual materials. Good visible-light photocatalytic activity of the heterojunction could be attributed to the increased visible light response, effective charge transfer from the modified band position and close interfacial contact due to partial ion exchange method.

Two dimensional Z-scheme AgCl/Ag/CaTiO3 nano-heterojunctions for photocatalytic hydrogen production enhancement

NASA Astrophysics Data System (ADS)

Jiang, Ziyuan; Pan, Jiaqi; Wang, Beibei; Li, Chaorong

2018-04-01

The two dimensional(2D) Z-scheme AgCl/Ag/Ca/TiO3 nano-heterojunction is synthesized via simple preparation of hydrothermal-chemical co-deposition method. The results of SEM, EDS, elemental mapping, XRD, TEM, XPS and Raman shift imply that the AgCl/Ag nanoparticles have deposited on the surfaces of CaTiO3 nanosheets successfully. Compared with the unmodified samples, the photocatalytic activity of the as-prepared 2D AgCl/Ag/CaTiO3 nano-heterojunction exhibits a remarkable enhancement by the hydrogen production. Further, the photocatalytic process has been studied and the mechanism of the photocatalytic hydrogen production enhancement has been provided, which could be ascribed to the Z-scheme heterojunction and 2D lamellar structure of the CaTiO3.

The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode.

PubMed

Chang, Wen-Chung; Su, Sheng-Chien; Wu, Chia-Ching

2016-06-30

Vertically aligned p-type silicon nanowire (SiNW) arrays were fabricated through metal-assisted chemical etching (MACE) of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW) heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and current-voltage (I-V) measurements. Nonlinear and rectifying I-V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions.

Band-offset-induced lateral shift of valley electrons in ferromagnetic MoS2/WS2 planar heterojunctions

NASA Astrophysics Data System (ADS)

Ghadiri, Hassan; Saffarzadeh, Alireza

2018-03-01

Low-energy coherent transport and a Goos-Hänchen (GH) lateral shift of valley electrons in planar heterojunctions composed of normal MoS2 and ferromagnetic WS2 monolayers are theoretically investigated. Two types of heterojunctions in the forms of WS2/MoS2/WS2 (type-A) and MoS2/WS2/MoS2 (type-B) with incident electrons in the MoS2 region are considered in which the lateral shift of electrons is induced by band alignments of the two constituent semiconductors. It is shown that the type-A heterojunction can act as an electron waveguide due to electron confinement between the two WS2/MoS2 interfaces which cause the incident electrons with an appropriate incidence angle to propagate along the interfaces. In this case, the spin- and valley-dependent GH shifts of totally reflected electrons from the interface lead to separated electrons with distinct spin-valley indexes after traveling a sufficiently long distance. In the type-B heterojunction, however, transmission resonances occur for incident electron beams passing through the structure, and large spin- and valley-dependent lateral shift values in propagating states can be achieved. Consequently, the transmitted electrons are spatially well-separated into electrons with distinct spin-valley indexes. Our findings reveal that the planar heterojunctions of transition metal dichalcogenides can be utilized as spin-valley beam filters and/or splitters without external gating.

InN/InGaN complementary heterojunction-enhanced tunneling field-effect transistor with enhanced subthreshold swing and tunneling current

NASA Astrophysics Data System (ADS)

Peng, Yue; Han, Genquan; Wang, Hongjuan; Zhang, Chunfu; Liu, Yan; Wang, Yibo; Zhao, Shenglei; Zhang, Jincheng; Hao, Yue

2016-05-01

InN/In0.75Ga0.25N complementary heterojunction-enhanced tunneling field-effect transistors (HE-TFETs) were characterized using the numerical simulation. InN/In0.75Ga0.25N HE-TFET has an InN/In0.75Ga0.25N heterojunction located in the channel region with a distance of LT-H from the source/channel tunneling junction. We demonstrate that, for both n- and p-channel devices, HE-TFETs have a delay of onset voltage VONSET, a steeper subthreshold swing (SS), and an enhanced on-state current ION in comparison with the homo-TFETs. InN/In0.75Ga0.25N n- and p-channel HE-TFETs with a gate length LG of 25 nm and a LT-H of 5 nm achieve a 7 and 9 times ION improvement in comparison with the homo devices, respectively, at a supply voltage of 0.3 V. The performance enhancement in HE-TFETs is attributed to the modulating effect of heterojunction on band-to-band tunneling (BTBT). Because InN/In0.75Ga0.25N heterointerface shows the similar band offsets at conduction and valence bands, the InN/In0.75Ga0.25N heterojunction exhibits the improved effect on BTBT for both n- and p-channel devices. This makes InN/In0.75Ga0.25N heterojunction a promising structure for high performance complementary TFETs.

Probing interfacial electronic properties of graphene/CH3NH3PbI3 heterojunctions: A theoretical study

NASA Astrophysics Data System (ADS)

Hu, Jisong; Ji, Gepeng; Ma, Xinguo; He, Hua; Huang, Chuyun

2018-05-01

Interfacial interactions and electronic properties of graphene/CH3NH3PbI3 heterojunctions were investigated by first-principles calculations incorporating semiempirical dispersion-correction scheme to describe van der Waals interactions. Two lattice match configurations between graphene and CH3NH3PbI3(0 0 1) slab were constructed in parallel contact and both of them were verified to form remarkable van der Waals heterojunctions with similar work functions. Our calculated energy band structures show that the Dirac-cone of graphene and the direct band gap of CH3NH3PbI3 are still preserved in the heterojunctions, thus graphene can be a promising candidate either as a capping or supporting layer for encapsulating CH3NH3PbI3 layer. It is identified that the Schottky barrier of graphene/CH3NH3PbI3 heterojunctions can be controlled by the interlayer distance and affected by the stacking pattern of graphene and CH3NH3PbI3. The 3D charge density differences present the build-in internal electric field from graphene to CH3NH3PbI3 after interface equilibrium and thus, a low n-type Schottky barrier is needed for high efficient charge transferring in the interface. The possible mechanism of the band edge modulations in the heterojunctions and corresponding photoinduced charge transfer processes are also described.

Resistance change effect in SrTiO3/Si (001) isotype heterojunction

NASA Astrophysics Data System (ADS)

Huang, Xiushi; Gao, Zhaomeng; Li, Pei; Wang, Longfei; Liu, Xiansheng; Zhang, Weifeng; Guo, Haizhong

2018-02-01

Resistance switching has been observed in double and multi-layer structures of ferroelectric films. The higher switching ratio opens up a vast path for emerging ferroelectric semiconductor devices. An n-n+ isotype heterojunction has been fabricated by depositing an oxide SrTiO3 layer on a conventional n-type Si (001) substrate (SrTiO3/Si) by pulsed laser disposition. Rectification and resistive switching behaviors in the n-n+ SrTiO3/Si heterojunction were observed by a conductive atomic force microscopy, and the n-n+ SrTiO3/Si heterojunction exhibits excellent endurance and retention characteristics. The possible mechanism was proposed based on the band structure of the n-n+ SrTiO3/Si heterojunction, and the observed electrical behaviors could be attributed to the modulation effect of the electric field reversal on the width of accumulation and the depletion region, as well as the height of potential of the n-n+ junction formed at the STO/Si interface. Moreover, oxygen vacancies are also indicated to play a crucial role in causing insulator to semiconductor transition. These results open the way to potential application in future microelectronic devices based on perovskite oxide layers on conventional semiconductors.

Performance improvement in novel germanium-tin/germanium heterojunction-enhanced p-channel tunneling field-effect transistor

NASA Astrophysics Data System (ADS)

Wang, Hongjuan; Liu, Yan; Liu, Mingshan; Zhang, Qingfang; Zhang, Chunfu; Ma, Xiaohua; Zhang, Jincheng; Hao, Yue; Han, Genquan

2015-07-01

We design a novel GeSn-based heterojunction-enhanced p-channel tunneling field-effect transistor (HE-PTFET) with a Ge0.92Sn0.08/Ge heterojunction located in channel region, at a distance of LT-H from the Ge0.92Sn0.08 source-channel tunneling junction (TJ). HE-PTFETs demonstrate the negative shift of onset voltage VONSET, the steeper subthreshold swing S, and the improved on-state current ION compared to Ge0.92Sn0.08 homo-PTFET. At low VGS, the suppression of BTBT due to the widening of the tunneling barrier caused by the heterojunction leads to a negative shift of VONSET in HE-PTFETs. At high VGS, ION enhancement in HE-PTFETs is achieved over the homo device, which is attributed to the confinement of BTBT in Ge0.92Sn0.08 source-channel TJ region by the heterojunction, where the short tunneling paths lead to a high tunneling probability. Due to the steeper average S, HE-PTFET with a 6 nm LT-H achieves a 4 times higher ION compared to homo device at a VDD of -0.3 V.

Enhanced visible light photocatalytic water reduction from a g-C 3N 4/SrTa 2O 6 heterojunction

DOE PAGES

Adhikari, Shiba P.; Hood, Zachary D.; Wang, Hui; ...

2017-06-02

In this paper, a new g-C 3N 4/SrTa 2O 6 heterojunction photocatalyst was designed and prepared by chimie douce (soft chemistry) method where carbon nitride (g-C 3N 4) was deposited over the metastable perovskite phase of SrTa 2O 6. The morphological study of the heterojunction using SEM and STEM revealed that g-C 3N 4 nanofibers are dispersed uniformly on the surface of SrTa 2O 6 plates leading to the intimate contact between them. The heterojunction could achieve a high and stable visible light photocatalytic H 2 generation of 137 mmol/h/mole of g-C 3N 4, which is much larger than themore » amount of hydrogen generated by one mole of pristine g-C 3N 4. Finally, a plausible mechanism for the observed enhanced photocatalytic activity for the heterojunction is proposed on the basis of effective charge separation of photogenerated electron-hole pairs, supported by band position calculations and photo-physical properties of g-C 3N 4 and SrTa 2O 6.« less

Enhanced visible light photocatalytic water reduction from a g-C 3N 4/SrTa 2O 6 heterojunction

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

Adhikari, Shiba P.; Hood, Zachary D.; Wang, Hui

In this paper, a new g-C 3N 4/SrTa 2O 6 heterojunction photocatalyst was designed and prepared by chimie douce (soft chemistry) method where carbon nitride (g-C 3N 4) was deposited over the metastable perovskite phase of SrTa 2O 6. The morphological study of the heterojunction using SEM and STEM revealed that g-C 3N 4 nanofibers are dispersed uniformly on the surface of SrTa 2O 6 plates leading to the intimate contact between them. The heterojunction could achieve a high and stable visible light photocatalytic H 2 generation of 137 mmol/h/mole of g-C 3N 4, which is much larger than themore » amount of hydrogen generated by one mole of pristine g-C 3N 4. Finally, a plausible mechanism for the observed enhanced photocatalytic activity for the heterojunction is proposed on the basis of effective charge separation of photogenerated electron-hole pairs, supported by band position calculations and photo-physical properties of g-C 3N 4 and SrTa 2O 6.« less

Extraction of Photogenerated Electrons and Holes from a Covalent Organic Framework Integrated Heterojunction

PubMed Central

2014-01-01

Covalent organic frameworks (COFs) offer a strategy to position molecular semiconductors within a rigid network in a highly controlled and predictable manner. The π-stacked columns of layered two-dimensional COFs enable electronic interactions between the COF sheets, thereby providing a path for exciton and charge carrier migration. Frameworks comprising two electronically separated subunits can form highly defined interdigitated donor–acceptor heterojunctions, which can drive the photogeneration of free charge carriers. Here we report the first example of a photovoltaic device that utilizes exclusively a crystalline organic framework with an inherent type II heterojunction as the active layer. The newly developed triphenylene–porphyrin COF was grown as an oriented thin film with the donor and acceptor units forming one-dimensional stacks that extend along the substrate normal, thus providing an optimal geometry for charge carrier transport. As a result of the degree of morphological precision that can be achieved with COFs and the enormous diversity of functional molecular building blocks that can be used to construct the frameworks, these materials show great potential as model systems for organic heterojunctions and might ultimately provide an alternative to the current disordered bulk heterojunctions. PMID:25412210

Enhanced photocatalytic activity of graphitic carbon nitride/cadmium sulfide heterojunctions by protonating treatment

NASA Astrophysics Data System (ADS)

Yan, Mengdie; Ma, Yushuang; Zhang, Huanhuan; Ye, Boyong; Dong, Xiaoping

2018-05-01

Highly efficient visible-light-driven protonated g-C3N4 (pg-C3N4)/CdS heterojunctions with different weight ratios of CdS were prepared by treating g-C3N4 with hydrochloric acid and using an in-situ precipitation method. The structure and morphology of heterojunctions were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption technology. The as-prepared pg-C3N4/CdS heterojunction with 50 wt% of g-C3N4 exhibited much higher photocatalytic activity for photodegradation of methyl orange (MO) than pg-C3N4, CdS and g-C3N4/CdS without protonation as well, which could be contributed to the activation of hydrochloric acid treatment and the improved electron-hole separation due to their overlapping band structure of CdS and pg-C3N4. A possible photocatalytic mechanism of the pg-C3N4/CdS heterojunctions with superoxide radical species as the main active species in photocatalysis was proposed on the basis of experimental results.

Physical properties of the heterojunction MoOx/n-CdTe as a function of the parameters of CdTe crystals

NASA Astrophysics Data System (ADS)

Mostovyi, Andrii I.; Solovan, Mykhailo M.; Brus, Viktor V.; Pullerits, Toǧnu; Maryanchuk, Pavlo D.

2018-01-01

MoOx/n-CdTe photosensitive heterostructures were prepared by the deposition of molybdenum oxide thin films onto three different n-type CdTe substrates (ρ1=0.4 Ωṡcm, ρ2=10 Ωṡcm, ρ3=40 Ωṡcm) by DC reactive magnetron sputtering. The height of the potential barrier and series resistance of the MoOx/CdTe heterojunctions were investigated. The dominating current transport mechanisms through the heterojunctions were determined at forward and reverse biases.

Tunneling-assisted transport of carriers through heterojunctions.

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

Wampler, William R.; Myers, Samuel M.; Modine, Normand A.

The formulation of carrier transport through heterojunctions by tunneling and thermionic emission is derived from first principles. The treatment of tunneling is discussed at three levels of approximation: numerical solution of the one-band envelope equation for an arbitrarily specified potential profile; the WKB approximation for an arbitrary potential; and, an analytic formulation assuming constant internal field. The effects of spatially varying carrier chemical potentials over tunneling distances are included. Illustrative computational results are presented. The described approach is used in exploratory physics models of irradiated heterojunction bipolar transistors within Sandia's QASPR program.

Photoeletrocatalytic activity of an n-ZnO/p-Cu2O/n-TNA ternary heterojunction electrode for tetracycline degradation.

PubMed

Li, Jinhua; Lv, Shubin; Liu, Yanbiao; Bai, Jing; Zhou, Baoxue; Hu, Xiaofang

2013-11-15

In this study, a novel ternary heterojunction n-ZnO/p-Cu2O/n-TiO2 nanotube arrays (n-ZnO/p-Cu2O/n-TNA) nanophotocatalyst with a sandwich-like nanostructure was constructed and applied for the photoelectrocatalytic (PEC) degradation of typical PPCPs, tetracycline (TC). The ternary heterojunction n-ZnO/p-Cu2O/n-TNA was obtained by depositing Cu2O on the surface of TNA via sonoelectrochemical deposition (SED) and subsequently building a layer of ZnO onto the p-Cu2O/n-TNA surface through hydrothermal synthesis. After being deposited by the Cu2O, the absorption-band edge of the p-Cu2O/n-TNA was obviously red-shifted to the visible region (to 505 nm), and the band gap was reduced from its original 3.20 eV to 2.46 eV. The band gap absorption edge of the ternary n-ZnO/p-Cu2O/n-TNA is similar to that of p-Cu2O/n-TN and extends the visible spectrum absorption to 510 nm, corresponding to an Eg value of about 2.43 eV. Under illumination of visible light, the photocurrent density of the ternary heterojunction n-ZnO/p-Cu2O/n-TNA electrode at 0.5 V (vs. Ag/AgCl) was more than 106 times as high as that of the pure TNAs electrode, 3.6 times as high as that of the binary heterojunction p-Cu2O/n-TNA electrode. The degradation of TC indicated that the ternary heterojunction n-ZnO/p-Cu2O/n-TNA electrode maintained a very high photoelectrocatalytic activity and excellent stability and reliability. Such kind of ternary heterojunction electrode material has a broad application prospect not only in pollution control but also in many other fields. Copyright © 2013 Elsevier B.V. All rights reserved.

An InP/Si heterojunction photodiode fabricated by self-aligned corrugated epitaxial lateral overgrowth

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

Sun, Y. T., E-mail: yasun@kth.se; Omanakuttan, G.; Lourdudoss, S.

2015-05-25

An n-InP/p-Si heterojunction photodiode fabricated by corrugated epitaxial lateral overgrowth (CELOG) method is presented. N-InP/p-Si heterojunction has been achieved from a suitable pattern containing circular shaped openings in a triangular lattice on the InP seed layer on p-Si substrate and subsequent CELOG of completely coalesced n-InP. To avoid current path through the seed layer in the final photodiode, semi-insulating InP:Fe was grown with adequate thickness prior to n-InP growth in a low pressure hydride vapor phase epitaxy reactor. The n-InP/p-Si heterointerface was analyzed by scanning electron microscopy and Raman spectroscopy. Room temperature cross-sectional photoluminescence (PL) mapping illustrates the defect reductionmore » effect in InP grown on Si by CELOG method. The InP PL intensity measured above the InP/Si heterojunction is comparable to that of InP grown on a native planar substrate indicating low interface defect density of CELOG InP despite of 8% lattice mismatch with Si. The processed n-InP/p-Si heterojunction photodiodes show diode characteristics from the current-voltage (I-V) measurements with a dark current density of 0.324 mA/cm{sup 2} at a reverse voltage of −1 V. Under the illumination of AM1.5 conditions, the InP/Si heterojunction photodiode exhibited photovoltaic effect with an open circuit voltage of 180 mV, a short circuit current density of 1.89 mA/cm{sup 2}, an external quantum efficiency of 4.3%, and an internal quantum efficiency of 6.4%. This demonstration of epitaxially grown InP/Si heterojunction photodiode will open the door for low cost and high efficiency solar cells and photonic integration of III-Vs on silicon.« less

Photoelectric characteristics of CH3NH3PbI3/p-Si heterojunction

NASA Astrophysics Data System (ADS)

Yamei, Wu; Ruixia, Yang; Hanmin, Tian; Shuai, Chen

2016-05-01

Organic-inorganic hybrid perovskite CH3NH3PbI3 film is prepared on p-type silicon substrate using the one-step solution method to form a CH3NH3PbI3/p-Si heterojunction. The film morphology and structure are characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The photoelectric properties of the CH3NH3PbI3/p-Si heterojunction are studied by testing the current-voltage (I-V) with and without illumination and capacitance-voltage (C-V) characteristics. It turns out from the I-V curve without illumination that the CH3NH3PbI3/p-Si heterojunction has a rectifier feature with the rectification ratio over 70 at the bias of ±5 V. Also, there appears a photoelectric conversion phenomenon on this heterojunction with a short circuit current (Isc) of 0.16 μA and an open circuit voltage (Voc) of about 10 mV The high frequency C-V characteristic of the Ag/CH3NH3PbI3/p-Si heterojunction turns out to be similar to that of the metal-insulator-semiconductor (MIS) structure, and a parallel translation of the C-V curve along the forward voltage axis is found. This parallel translation means the existence of defects at the CH3NH3PbI3/p-Si interface and positive fixed charges in the CH3NH3PbI3 layer. The defects at the interface of the CH3NH3PbI3/p-Si heterojunction result in the dramatic decline of the Voc. Besides, the C-V test of CH3NH3PbI3 film shows a non-linear dielectric property and the dielectric value is about 4.64 as calculated. Project supported by the Hebei Province Natural Science Foundation of China (No. F2014202184) and the Tianjin Natural Science Foundation of China (No. 15JCZDJC37800).

Controlling astigmatism and polarization in a stripe heterojunction laser

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

Boroshnev, A.V.; Gorshkova, O.A.; Kobyakova, M.S.

1985-02-01

It is shown that it is possible to change the waveguide properties of a heterojunction laser and to control its optical characteristics in a single heterostructure fabricated on a substrate with a terraced profile. (AIP)

Indium oxide/n-silicon heterojunction solar cells

DOEpatents

Feng, Tom; Ghosh, Amal K.

1982-12-28

A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.

Nanocrystalline heterojunction materials

DOEpatents

Elder, Scott H.; Su, Yali; Gao, Yufei; Heald, Steve M.

2003-07-15

Mesoporous nanocrystalline titanium dioxide heterojunction materials are disclosed. In one disclosed embodiment, materials comprising a core of titanium dioxide and a shell of a molybdenum oxide exhibit a decrease in their photoadsorption energy as the size of the titanium dioxide core decreases.

Low Temperature Noise and Electrical Characterization of the Company Heterojunction Field-Effect Transistor

NASA Technical Reports Server (NTRS)

Cunningham, Thomas J.; Gee, Russell C.; Fossum, Eric R.; Baier, Steven M.

1993-01-01

This paper discusses the electrical properties of the complementary heterojunction field-effect transistor (CHFET) at 4K, including the gate leakage current, the subthreshold transconductance, and the input-referred noise voltage.

The effect of confinement on the crystalline microstructure of polymer: fullerene bulk heterojunctions

DOE PAGES

Ashraf, A.; Dissanayake, D. M. N. M.; Eisaman, M. D.

2015-07-01

We investigate the effect of confinement on the coherence length and the crystalline microstructure of the polymer component of polymer: fullerene bulk heterojunction thin films using grazing incidence wide angle x-ray scattering. We find that the polymer crystallite size decreases and the alignment of the molecules along the surface normal increases, as the thin-film thickness is reduced from 920nm to < 20nm and approaches the thin-film confinement regime. Furthermore, we find that the polymer crystallite size near the surface (air interface) is lower than the crystallite size in the bulk or the bottom (substrate interface) of bulk heterojunction films thickermore » than the confinement regime. Variation in polymer crystallite size can cause changes in charge carrier mobility and recombination rates, which in turn affect the performance of bulk heterojunction thin film devices such as photovoltaics and photodetectors« less

Gate-Controlled BP-WSe2 Heterojunction Diode for Logic Rectifiers and Logic Optoelectronics.

PubMed

Li, Dong; Wang, Biao; Chen, Mingyuan; Zhou, Jun; Zhang, Zengxing

2017-06-01

p-n junctions play an important role in modern semiconductor electronics and optoelectronics, and field-effect transistors are often used for logic circuits. Here, gate-controlled logic rectifiers and logic optoelectronic devices based on stacked black phosphorus (BP) and tungsten diselenide (WSe 2 ) heterojunctions are reported. The gate-tunable ambipolar charge carriers in BP and WSe 2 enable a flexible, dynamic, and wide modulation on the heterojunctions as isotype (p-p and n-n) and anisotype (p-n) diodes, which exhibit disparate rectifying and photovoltaic properties. Based on such characteristics, it is demonstrated that BP-WSe 2 heterojunction diodes can be developed for high-performance logic rectifiers and logic optoelectronic devices. Logic optoelectronic devices can convert a light signal to an electric one by applied gate voltages. This work should be helpful to expand the applications of 2D crystals. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-dimensional heterostructure materials

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

Geohegan, David B.; Rouleau, Christopher M.; Wang, Kai

Methods, articles of manufacture and systems for creating new nanoscale two dimensional materials comprising designed arrays of lateral or vertical heterojunctions may be fabricated by first lithographically masking a 2D material. Exposed, or unmasked, regions of the 2D material may be converted to a different composition of matter to form lateral or vertical heterojunctions according to the patterned mask. PLD and high kinetic energy impingement of atoms may replace or add atoms in the exposed regions, and a plurality of the exposed regions may be converted concurrently. The process may be repeated one or more times on either side ofmore » the same 2D material to form any suitable combination of lateral heterojunctions and/or vertical heterojunctions, comprising semiconductors, metals or insulators or any suitable combination thereof. Furthermore, the resulting 2D material may comprise p-n, n-n, p-p, n-p-n and p-n-p junctions, or any suitable combination thereof.« less

Visible light active 2D C3N4-CdS hetero-junction photocatalyst for effective removal of azo dye by photodegradation

NASA Astrophysics Data System (ADS)

Ghosh Chaudhuri, Rajib; Chaturvedi, Ashwin; Iype, Eldhose

2018-03-01

A hetero-junction two dimensional photocatalyst that consists of organic semiconductor carbon nitride (C3N4) and inorganic semiconductor CdS, which acts as the light harvesting units and heterogeneous catalyst, was developed for the degradation of azo dye methyl orange (MO). Both materials are visible light active semiconductor. So the effective band gap of this heterojunction materials does not significantly change the visible light activity, but the injection of electrons from excited C3N4 to CdS increases the stability of hole-electron pair and that ultimately enhances the photocatalytic activity. This heterojunction catalyst finally can remove 97% of dyes and that is comparatively higher than individual pure materials. Finally, by using DFT analysis the band structure and the level diagrams of this photocatalyst are also analyzed.

Low-Temperature Electrical Characteristics of Si-Based Device with New Tetrakis NiPc-SNS Active Layer

NASA Astrophysics Data System (ADS)

Yavuz, Arzu Büyükyağci; Carbas, Buket Bezgın; Sönmezoğlu, Savaş; Soylu, Murat

2016-01-01

A new tetrakis 4-(2,5-di-2-thiophen-2-yl-pyrrol-1-yl)-substituted nickel phthalocyanine (NiPc-SNS) has been synthesized. This synthesized NiPc-SNS thin film was deposited on p-type Si substrate using the spin coating method (SCM) to fabricate a NiPc-SNS/ p-Si heterojunction diode. The temperature-dependent electrical characteristics of the NiPc-SNS/ p-Si heterojunction with good rectifying behavior were investigated by current-voltage ( I- V) measurements between 50 K and 300 K. The results indicate that the ideality factor decreases while the barrier height increases with increasing temperature. The barrier inhomogeneity across the NiPc-SNS/ p-Si heterojunction reveals a Gaussian distribution at low temperatures. These results provide further evidence of the more complicated mechanisms occurring in this heterojunction. Based on these findings, NiPc-SNS/ p-Si junction diodes are feasible for use in low-temperature applications.

The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode

PubMed Central

Chang, Wen-Chung; Su, Sheng-Chien; Wu, Chia-Ching

2016-01-01

Vertically aligned p-type silicon nanowire (SiNW) arrays were fabricated through metal-assisted chemical etching (MACE) of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW) heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and current−voltage (I−V) measurements. Nonlinear and rectifying I−V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions. PMID:28773656

Bulk heterojunction perovskite solar cells based on room temperature deposited hole-blocking layer: Suppressed hysteresis and flexible photovoltaic application

NASA Astrophysics Data System (ADS)

Chen, Zhiliang; Yang, Guang; Zheng, Xiaolu; Lei, Hongwei; Chen, Cong; Ma, Junjie; Wang, Hao; Fang, Guojia

2017-05-01

Perovskite solar cells have developed rapidly in recent years as the third generation solar cells. In spite of the great improvement achieved, there still exist some issues such as undesired hysteresis and indispensable high temperature process. In this work, bulk heterojunction perovskite-phenyl-C61-butyric acid methyl ester solar cells have been prepared to diminish hysteresis using a facile two step spin-coating method. Furthermore, high quality tin oxide films are fabricated using pulse laser deposition technique at room temperature without any annealing procedure. The as fabricated tin oxide film is successfully applied in bulk heterojunction perovskite solar cells as a hole blocking layer. Bulk heterojunction devices based on room temperature tin oxide exhibit almost hysteresis-free characteristics with power conversion efficiency of 17.29% and 14.0% on rigid and flexible substrates, respectively.

Highly Tunable Heterojunctions from Multimetallic Sulfide Nanoparticles and Silver Nanowires.

PubMed

Liu, Dongliang; Liu, Yong; Huang, Peng; Zhu, Cheng; Kang, Zhenhui; Shu, Jie; Chen, Muzi; Zhu, Xing; Guo, Jun; Zhuge, Lanjian; Bu, Xianhui; Feng, Pingyun; Wu, Tao

2018-05-04

A facile and general strategy is presented to create well-defined heterojunctions with ultra-small multimetallic sulfide nanoparticles (MMSNPs) uniformly coated on sliver nanowires. A unique aspect of this method is the atomic-level pre-integration of multimetallic components by exploiting recently developed supertetrahedral metal sulfide nanoclusters. The use of such nanoclusters also enables the convenient formation of the ultrathin interfacial Ag 2 S layer via etching. The heterojunctions (denoted as MMSNPs/Ag 2 S/Ag-NWs) benefit from adjustable multimetallic components and display tunable visible-light-driven photocatalytic performance owing to the synergistic effect of multimetallic components from MMSNPs and the high carrier mobility of Ag-NWs. The synthetic strategy opens new routes to designing and fabricating various heterojunctions with multimetallic components, which could further expand their applications in catalysis, electronics, and photonics. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Facile Synthesis of γ-In2 Se3 Nanoflowers toward High Performance Self-Powered Broadband γ-In2 Se3 /Si Heterojunction Photodiode.

PubMed

Chen, Shuo; Liu, Xuemei; Qiao, Xvsheng; Wan, Xia; Shehzad, Khurram; Zhang, Xianghua; Xu, Yang; Fan, Xianping

2017-05-01

An effective colloidal process involving the hot-injection method is developed to synthesize uniform nanoflowers consisting of 2D γ-In 2 Se 3 nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In 2 Se 3 , a high-quality γ-In 2 Se 3 /Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long-term durability. In addition, the γ-In 2 Se 3 /Si heterojunction photodiode is self-powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ-In 2 Se 3 /Si heterojunction very interesting as highly efficient photodetectors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transition-metal impurities in semiconductors and heterojunction band lineups

NASA Astrophysics Data System (ADS)

Langer, Jerzy M.; Delerue, C.; Lannoo, M.; Heinrich, Helmut

1988-10-01

The validity of a recent proposal that transition-metal impurity levels in semiconductors may serve as a reference in band alignment in semiconductor heterojunctions is positively verified by using the most recent data on band offsets in the following lattice-matched heterojunctions: Ga1-xAlxAs/GaAs, In1-xGaxAsyP1-y/InP, In1-xGaxP/GaAs, and Cd1-xHgxTe/CdTe. The alignment procedure is justified theoretically by showing that transition-metal energy levels are effectively pinned to the average dangling-bond energy level, which serves as the reference level for the heterojunction band alignment. Experimental and theoretical arguments showing that an increasingly popular notion on transition-metal energy-level pinning to the vacuum level is unjustified and must be abandoned in favor of the internal-reference rule proposed recently [J. M. Langer and H. Heinrich, Phys. Rev. Lett. 55, 1414 (1985)] are presented.

High Performance Molybdenum Disulfide Amorphous Silicon Heterojunction Photodetector

PubMed Central

Esmaeili-Rad, Mohammad R.; Salahuddin, Sayeef

2013-01-01

One important use of layered semiconductors such as molybdenum disulfide (MoS2) could be in making novel heterojunction devices leading to functionalities unachievable using conventional semiconductors. Here we demonstrate a metal-semiconductor-metal heterojunction photodetector, made of MoS2 and amorphous silicon (a-Si), with rise and fall times of about 0.3 ms. The transient response does not show persistent (residual) photoconductivity, unlike conventional a-Si devices where it may last 3–5 ms, thus making this heterojunction roughly 10X faster. A photoresponsivity of 210 mA/W is measured at green light, the wavelength used in commercial imaging systems, which is 2−4X larger than that of a-Si and best reported MoS2 devices. The device could find applications in large area electronics, such as biomedical imaging, where a fast response is critical. PMID:23907598

Spatially resolved multicolor CsPbX 3 nanowire heterojunctions via anion exchange

DOE PAGES

Dou, Letian; Lai, Minliang; Kley, Christopher S.; ...

2017-06-26

Halide perovskites are promising semiconductor materials for solution-processed optoelectronic devices. Their strong ionic bonding nature results in highly dynamic crystal lattices, inherently allowing rapid ion exchange at the solid–vapor and solid–liquid interface. In this paper, we show that the anion-exchange chemistry can be precisely controlled in single-crystalline halide perovskite nanomaterials when combined with nanofabrication techniques. We demonstrate spatially resolved multicolor CsPbX 3 (X = Cl, Br, I, or alloy of two halides) nanowire heterojunctions with a pixel size down to 500 nm with the photoluminescence tunable over the entire visible spectrum. In addition, the heterojunctions show distinct electronic states acrossmore » the interface, as revealed by Kelvin probe force microscopy. Finally, these perovskite heterojunctions represent key building blocks for high-resolution multicolor displays beyond current state-of-the-art technology as well as high-density diode/transistor arrays.« less

Room temperature electroluminescence from the n-ZnO/p-GaN heterojunction device grown by MOCVD

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

Yang, T.P.; Zhu, H.C.; Bian, J.M.

2008-12-01

The heterojunction light-emitting diode with n-ZnO/p-GaN structure was grown on (0 0 0 1) sapphire substrate by metalorganic chemical vapor deposition (MOCVD) technique. The heterojunction structure was consisted of an Mg-doped p-type GaN layer with a hole concentration of {approx}10{sup 17} cm{sup -3} and a unintentionally doped n-type ZnO layer with an electron concentration of {approx}10{sup 18} cm{sup -3}. A distinct blue-violet electroluminescence with a dominant emission peak centered at {approx}415 nm was observed at room temperature from the heterojunction structure under forward bias conditions. The origins of the electroluminescence (EL) emissions are discussed in comparison with the photoluminescence spectra,more » and it was supposed to be attributed to a radiative recombination in both n-ZnO and p-GaN sides.« less

Tunneling-injection in vertical quasi-2D heterojunctions enabled efficient and adjustable optoelectronic conversion

PubMed Central

Tan, Wei-Chun; Chiang, Chia-Wei; Hofmann, Mario; Chen, Yang-Fang

2016-01-01

The advent of 2D materials integration has enabled novel heterojunctions where carrier transport proceeds thrsough different ultrathin layers. We here demonstrate the potential of such heterojunctions on a graphene/dielectric/semiconductor vertical stack that combines several enabling features for optoelectronic devices. Efficient and stable light emission was achieved through carrier tunneling from the graphene injector into prominent states of a luminescent material. Graphene’s unique properties enable fine control of the band alignment in the heterojunction. This advantage was used to produce vertical tunneling-injection light-emitting transistors (VtiLET) where gating allows adjustment of the light emission intensity independent of applied bias. This device was shown to simultaneously act as a light detecting transistor with a linear and gate tunable sensitivity. The presented development of an electronically controllable multifunctional light emitter, light detector and transistor open up a new route for future optoelectronics. PMID:27507171

Tunneling-injection in vertical quasi-2D heterojunctions enabled efficient and adjustable optoelectronic conversion

NASA Astrophysics Data System (ADS)

Tan, Wei-Chun; Chiang, Chia-Wei; Hofmann, Mario; Chen, Yang-Fang

2016-08-01

The advent of 2D materials integration has enabled novel heterojunctions where carrier transport proceeds thrsough different ultrathin layers. We here demonstrate the potential of such heterojunctions on a graphene/dielectric/semiconductor vertical stack that combines several enabling features for optoelectronic devices. Efficient and stable light emission was achieved through carrier tunneling from the graphene injector into prominent states of a luminescent material. Graphene’s unique properties enable fine control of the band alignment in the heterojunction. This advantage was used to produce vertical tunneling-injection light-emitting transistors (VtiLET) where gating allows adjustment of the light emission intensity independent of applied bias. This device was shown to simultaneously act as a light detecting transistor with a linear and gate tunable sensitivity. The presented development of an electronically controllable multifunctional light emitter, light detector and transistor open up a new route for future optoelectronics.

Direct Determination of Field Emission across the Heterojunctions in a ZnO/Graphene Thin-Film Barristor.

PubMed

Mills, Edmund M; Min, Bok Ki; Kim, Seong K; Kim, Seong Jun; Kang, Min-A; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok; Jung, Jongwan; Kim, Sangtae

2015-08-26

Graphene barristors are a novel type of electronic switching device with excellent performance, which surpass the low on-off ratios that limit the operation of conventional graphene transistors. In barristors, a gate bias is used to vary graphene's Fermi level, which in turn controls the height and resistance of a Schottky barrier at a graphene/semiconductor heterojunction. Here we demonstrate that the switching characteristic of a thin-film ZnO/graphene device with simple geometry results from tunneling current across the Schottky barriers formed at the ZnO/graphene heterojunctions. Direct characterization of the current-voltage-temperature relationship of the heterojunctions by ac-impedance spectroscopy reveals that this relationship is controlled predominantly by field emission, unlike most graphene barristors in which thermionic emission is observed. This governing mechanism makes the device unique among graphene barristors, while also having the advantages of simple fabrication and outstanding performance.

Theoretical evaluation of two dimensional electron gas characteristics of quaternary AlxInyGa1-x-yN/GaN hetero-junctions

NASA Astrophysics Data System (ADS)

Rahbardar Mojaver, Hassan; Manouchehri, Farzin; Valizadeh, Pouya

2016-04-01

The two dimensional electron gas (2DEG) characteristics of gated metal-face wurtzite AlInGaN/GaN hetero-junctions including positions of subband energy levels, fermi energy level, and the 2DEG concentration as functions of physical and compositional properties of the hetero-junction (i.e., barrier thickness and metal mole-fractions) are theoretically evaluated using the variational method. The calculated values of the 2DEG concentration are in good agreement with the sparsely available experimental data reported in the literature. According to our simulation results, a considerable shift in the positive direction of threshold voltage of AlInGaN/GaN hetero-junction field-effect transistors can be achieved by engineering both the spontaneous and the piezoelectric polarizations using a quaternary AlInGaN barrier-layer of appropriate mole-fractions.

Fabrication of Heterojunction Diode Based on n-ZnO Nanowires/p-Si Substrate: Temperature Dependent Transport Characteristics.

PubMed

Badran, R I; Umar, Ahmad

2017-01-01

Herein, we report the growth and characterizations of well-crystalline n-ZnO nanowires assembled in micro flower-shaped morphologies. The nanowires are grown on p-Silicon substrate and characterized in terms of their structural, morphological and electrical properties. Temperature dependent transport characteristics of the fabricated n-ZnO/p-Si heterojunction diode were examined. The morphological studies revealed that the nanowires are grown in high-density and arrange in special micro flower shaped morphology. The structural characterizations confirmed that the nanowires are well-crystalline and possessing wurtzite hexagonal phase. The electrical properties were evaluated by examining the I–V characteristics of the fabricated n-ZnO/p-Si heterojunction diode. The I–V characteristics were studied at temperature <300 K and ≥300 K in the forward and reverse bias conditions. The detailed temperature dependent electrical properties revealed that the fabricated heterojunction assembly shows a diode-like behavior with a turn-on voltage of 5 V at almost all temperatures and the delivered current changes between ˜1 to ˜5 μA when temperature changes from 77 K to 425 K. The rectifying behavior of the fabricated heterojunction diode, at 5 V, was demonstrated by rectifying ratio of ˜4 at 77 K which decreases to ˜1.5 at 425 K. This analysis also showed that the mean potential barrier of the fabricated heterojunction (˜1.2 eV) is larger than the energy difference (0.72 eV) of the work functions between Si and ZnO.

Perovskite-structured CaTiO3 coupled with g-C3N4 as a heterojunction photocatalyst for organic pollutant degradation

PubMed Central

Kumar, Ashish; Schuerings, Christian; Kumar, Suneel; Kumar, Ajay

2018-01-01

A novel graphitic carbon nitride (g-C3N4)–CaTiO3 (CTCN) organic–inorganic heterojunction photocatalyst was synthesized by a facile mixing method, resulting in the deposition of CaTiO3 (CT) nanoflakes onto the surface of g-C3N4 nanosheets. The photocatalytic activity of the as-synthesized heterojunction (along with the controls) was evaluated by studying the degradation of an aqueous solution of rhodamine B (RhB) under UV, visible and natural sunlight irradiation. The CTCN heterojunction with 1:1 ratio of g-C3N4/CT showed the highest photocatalytic activity under sunlight irradiation and was also demonstrated to be effective for the degradation of a colorless, non-photosensitizing pollutant, bisphenol A (BPA). The superior photocatalytic performance of the CTCN heterojunction could be attributed to the appropriate band positions, close interfacial contact between the constituents and extended light absorption (both UV and visible region), all of which greatly facilitate the transfer of photogenerated charges across the heterojunction and inhibit their fast recombination. In addition, the two-dimensional (2D) morphology of g-C3N4nanosheets and CT nanoflakes provides enough reaction sites due to their larger surface area and enhances the overall photocatalytic activity. Furthermore, the active species trapping experiments validate the major role played by superoxide radicals (O2 −•) in the degradation of pollutants. Based on scavenger studies and theoretically calculated band positions, a plausible mechanism for the photocatalytic degradation of pollutants has been proposed and discussed. PMID:29527441

Insight into synergistically enhanced adsorption and visible light photocatalytic performance of Z-scheme heterojunction of SrTiO3(La,Cr)-decorated WO3 nanosheets

NASA Astrophysics Data System (ADS)

Liu, Xin; Jiang, Junzhe; Jia, Yushuai; Qiu, Jinmin; Xia, Tonglin; Zhang, Yuhong; Li, Yuqin; Chen, Xiangshu

2017-08-01

The efficient treatment of dye wastewater has been a hot topic of environment field. The integration of adsorption and photocatalytic degradation via fabrication of bi-component heterojunction photocatalyst is considered as a facile and effective strategy to enhance the dye elimination efficiency. In this report, a Z-scheme heterojunction material, SrTiO3(La,Cr)/WO3 with bifunction of adsorption and photocatalysis was successfully synthesized for efficient removal of methylene blue (MB) under visible light irradiation. The morphology and microstructure characterization demonstrates that the SrTiO3(La,Cr) nanoparticles are uniformly decorated on the WO3 nanosheets, forming an intimate heterojunction interface. MB degradation results indicate that the removal efficiency by the synergistic adsorption-photocatalysis process is greatly improved compared to pure WO3 and SrTiO3(La,Cr) with the adsorption and photocatalytic activity closely related to the composition of the material. The possible mechanism for the enhanced photocatalytic activity could be ascribed to the formation of a Z-scheme heterojunction system based on active species trapping experiments. Furthermore, the investigations of adsorption kinetics and isotherm show that the adsorption process follows pseudo-second-order kinetic model and Langmuir isotherm, respectively. Due to the synergistic advantages of negative zeta potential, large surface area and accelerated separation of photogenerated carriers driven by Z-scheme heterojunction, SrTiO3(La,Cr)/WO3 exhibits excellent adsorption-photocatalytic performance and stability on MB removal, which could be potentially used for practical wastewater treatment.

Method for forming indium oxide/n-silicon heterojunction solar cells

DOEpatents

Feng, Tom; Ghosh, Amal K.

1984-03-13

A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.

Copper oxide/N-silicon heterojunction photovoltaic device

DOEpatents

Feng, Tom; Ghosh, Amal K.

1982-01-01

A photovoltaic device having characteristics of a high efficiency solar cell comprising a Cu.sub.x O/n-Si heterojunction. The Cu.sub.x O layer is formed by heating a deposited copper layer in an oxygen containing ambient.

Carrier tunneling in models of irradiated heterojunction bipolar transistors

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

Wampler, William R.; Myers, Samuel Maxwell

2014-08-01

As part of Sandia's program to simulate the effect of displacement damage on operation of heterojunction bipolar transistors (HBTs), we are examining the formulation in 1-D of band-to-band (bb) and band-to-trap (b-t) carrier tunneling.

Double-heterojunction nanorod light-responsive LEDs for display applications.

PubMed

Oh, Nuri; Kim, Bong Hoon; Cho, Seong-Yong; Nam, Sooji; Rogers, Steven P; Jiang, Yiran; Flanagan, Joseph C; Zhai, You; Kim, Jae-Hwan; Lee, Jungyup; Yu, Yongjoon; Cho, Youn Kyoung; Hur, Gyum; Zhang, Jieqian; Trefonas, Peter; Rogers, John A; Shim, Moonsub

2017-02-10

Dual-functioning displays, which can simultaneously transmit and receive information and energy through visible light, would enable enhanced user interfaces and device-to-device interactivity. We demonstrate that double heterojunctions designed into colloidal semiconductor nanorods allow both efficient photocurrent generation through a photovoltaic response and electroluminescence within a single device. These dual-functioning, all-solution-processed double-heterojunction nanorod light-responsive light-emitting diodes open feasible routes to a variety of advanced applications, from touchless interactive screens to energy harvesting and scavenging displays and massively parallel display-to-display data communication. Copyright © 2017, American Association for the Advancement of Science.

Electrical circuit model of ITO/AZO/Ge photodetector.

PubMed

Patel, Malkeshkumar; Kim, Joondong

2017-10-01

In this data article, ITO/AZO/Ge photodetector was investigated for electrical circuit model. Due to the double (ITO and AZO) transparent metal-oxide films (DOI:10.1016/j.mssp.2016.03.007) (Yun et al., 2016) [1], the Ge heterojunction device has a better interface quality due to the AZO layer with a low electrical resistance due to the ITO layer (Yun et al., 2015) [2]. The electrical and interfacial benefitted ITO/AZO/Ge heterojunction shows the quality Schottky junction. In order to investigate the device, the ITO/AZO/Ge heterojunction was analyzed by R-C circuit model using the impedance spectroscopy.

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction.

PubMed

Ji, Liang-Wen; Hsiao, Yu-Jen; Tang, I-Tseng; Meen, Teen-Hang; Liu, Chien-Hung; Tsai, Jenn-Kai; Wu, Tien-Chuan; Wu, Yue-Sian

2013-11-09

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%.

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction

PubMed Central

2013-01-01

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%. PMID:24206942

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction

NASA Astrophysics Data System (ADS)

Ji, Liang-Wen; Hsiao, Yu-Jen; Tang, I.-Tseng; Meen, Teen-Hang; Liu, Chien-Hung; Tsai, Jenn-Kai; Wu, Tien-Chuan; Wu, Yue-Sian

2013-11-01

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%.

Fabrication and Characteristics of an nc-Si/c-Si Heterojunction MOSFETs Pressure Sensor

PubMed Central

Zhao, Xiaofeng; Wen, Dianzhong; Li, Gang

2012-01-01

A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W) ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor. PMID:22778646

Self-Aligned van der Waals Heterojunction Diodes and Transistors.

PubMed

Sangwan, Vinod K; Beck, Megan E; Henning, Alex; Luo, Jiajia; Bergeron, Hadallia; Kang, Junmo; Balla, Itamar; Inbar, Hadass; Lauhon, Lincoln J; Hersam, Mark C

2018-02-14

A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS 2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of antiambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated antiambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. For example, the versatility of this scheme is demonstrated via contact-doped MoS 2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with subdiffraction channel lengths in the range of 150-800 nm using photolithography on large-area MoS 2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step toward the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems.

Monolithic Inorganic ZnO/GaN Semiconductors Heterojunction White Light-Emitting Diodes.

PubMed

Jeong, Seonghoon; Oh, Seung Kyu; Ryou, Jae-Hyun; Ahn, Kwang-Soon; Song, Keun Man; Kim, Hyunsoo

2018-01-31

Monolithic light-emitting diodes (LEDs) that can generate white color at the one-chip level without the wavelength conversion through packaged phosphors or chip integration for photon recycling are of particular importance to produce compact, cost-competitive, and smart lighting sources. In this study, monolithic white LEDs were developed based on ZnO/GaN semiconductor heterojunctions. The electroluminescence (EL) wavelength of the ZnO/GaN heterojunction could be tuned by a post-thermal annealing process, causing the generation of an interfacial Ga 2 O 3 layer. Ultraviolet, violet-bluish, and greenish-yellow broad bands were observed from n-ZnO/p-GaN without an interfacial layer, whereas a strong greenish-yellow band emission was the only one observed from that with an interfacial layer. By controlled integration of ZnO/GaN heterojunctions with different postannealing conditions, monolithic white LED was demonstrated with color coordinates in the range (0.3534, 0.3710)-(0.4197, 0.4080) and color temperatures of 4778-3349 K in the Commission Internationale de l'Eclairage 1931 chromaticity diagram. Furthermore, the monolithic white LED produced approximately 2.1 times higher optical output power than a conventional ZnO/GaN heterojunction due to the carrier confinement effect at the Ga 2 O 3 /n-ZnO interface.

Determination of band alignment at two-dimensional MoS2/Si van der Waals heterojunction

NASA Astrophysics Data System (ADS)

Goel, Neeraj; Kumar, Rahul; Mishra, Monu; Gupta, Govind; Kumar, Mahesh

2018-06-01

To understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.66 ± 0.17 eV and a conduction band offset of 0.42 ± 0.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon.

Mutual Photoluminescence Quenching and Photovoltaic Effect in Large-Area Single-Layer MoS2-Polymer Heterojunctions.

PubMed

Shastry, Tejas A; Balla, Itamar; Bergeron, Hadallia; Amsterdam, Samuel H; Marks, Tobin J; Hersam, Mark C

2016-11-22

Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted attention due to their superlative optical and electronic properties. In particular, their extraordinary optical absorption and semiconducting band gap have enabled demonstrations of photovoltaic response from heterostructures composed of TMDCs and other organic or inorganic materials. However, these early studies were limited to devices at the micrometer scale and/or failed to exploit the unique optical absorption properties of single-layer TMDCs. Here we present an experimental realization of a large-area type-II photovoltaic heterojunction using single-layer molybdenum disulfide (MoS 2 ) as the primary absorber, by coupling it to the organic π-donor polymer PTB7. This TMDC-polymer heterojunction exhibits photoluminescence intensity that is tunable as a function of the thickness of the polymer layer, ultimately enabling complete quenching of the TMDC photoluminescence. The strong optical absorption in the TMDC-polymer heterojunction produces an internal quantum efficiency exceeding 40% for an overall cell thickness of less than 20 nm, resulting in exceptional current density per absorbing thickness in comparison to other organic and inorganic solar cells. Furthermore, this work provides insight into the recombination processes in type-II TMDC-polymer heterojunctions and thus provides quantitative guidance to ongoing efforts to realize efficient TMDC-based solar cells.

Modulating the Surface State of SiC to Control Carrier Transport in Graphene/SiC.

PubMed

Jia, Yuping; Sun, Xiaojuan; Shi, Zhiming; Jiang, Ke; Liu, Henan; Ben, Jianwei; Li, Dabing

2018-05-28

Silicon carbide (SiC) with epitaxial graphene (EG/SiC) shows a great potential in the applications of electronic and photoelectric devices. The performance of devices is primarily dependent on the interfacial heterojunction between graphene and SiC. Here, the band structure of the EG/SiC heterojunction is experimentally investigated by Kelvin probe force microscopy. The dependence of the barrier height at the EG/SiC heterojunction to the initial surface state of SiC is revealed. Both the barrier height and band bending tendency of the heterojunction can be modulated by controlling the surface state of SiC, leading to the tuned carrier transport behavior at the EG/SiC interface. The barrier height at the EG/SiC(000-1) interface is almost ten times that of the EG/SiC(0001) interface. As a result, the amount of carrier transport at the EG/SiC(000-1) interface is about ten times that of the EG/SiC(0001) interface. These results offer insights into the carrier transport behavior at the EG/SiC heterojunction by controlling the initial surface state of SiC, and this strategy can be extended in all devices with graphene as the top layer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanocrystalline Heterojunction Materials

DOEpatents

Elder, Scott H.; Su, Yali; Gao, Yufei; Heald, Steve M.

2004-02-03

Mesoporous nanocrystalline titanium dioxide heterojunction materials and methods of making the same are disclosed. In one disclosed embodiment, materials comprising a core of titanium dioxide and a shell of a molybdenum oxide exhibit a decrease in their photoadsorption energy as the size of the titanium dioxide core decreases.

Electrical property heterogeneity at transparent conductive oxide/organic semiconductor interfaces: mapping contact ohmicity using conducting-tip atomic force microscopy.

PubMed

MacDonald, Gordon A; Veneman, P Alexander; Placencia, Diogenes; Armstrong, Neal R

2012-11-27

We demonstrate mapping of electrical properties of heterojunctions of a molecular semiconductor (copper phthalocyanine, CuPc) and a transparent conducting oxide (indium-tin oxide, ITO), on 20-500 nm length scales, using a conductive-probe atomic force microscopy technique, scanning current spectroscopy (SCS). SCS maps are generated for CuPc/ITO heterojunctions as a function of ITO activation procedures and modification with variable chain length alkyl-phosphonic acids (PAs). We correlate differences in small length scale electrical properties with the performance of organic photovoltaic cells (OPVs) based on CuPc/C(60) heterojunctions, built on these same ITO substrates. SCS maps the "ohmicity" of ITO/CuPc heterojunctions, creating arrays of spatially resolved current-voltage (J-V) curves. Each J-V curve is fit with modified Mott-Gurney expressions, mapping a fitted exponent (γ), where deviations from γ = 2.0 suggest nonohmic behavior. ITO/CuPc/C(60)/BCP/Al OPVs built on nonactivated ITO show mainly nonohmic SCS maps and dark J-V curves with increased series resistance (R(S)), lowered fill-factors (FF), and diminished device performance, especially near the open-circuit voltage. Nearly optimal behavior is seen for OPVs built on oxygen-plasma-treated ITO contacts, which showed SCS maps comparable to heterojunctions of CuPc on clean Au. For ITO electrodes modified with PAs there is a strong correlation between PA chain length and the degree of ohmicity and uniformity of electrical response in ITO/CuPc heterojunctions. ITO electrodes modified with 6-8 carbon alkyl-PAs show uniform and nearly ohmic SCS maps, coupled with acceptable CuPc/C(60)OPV performance. ITO modified with C14 and C18 alkyl-PAs shows dramatic decreases in FF, increases in R(S), and greatly enhanced recombination losses.

Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

NASA Astrophysics Data System (ADS)

Sun, Haiding; Torres Castanedo, C. G.; Liu, Kaikai; Li, Kuang-Hui; Guo, Wenzhe; Lin, Ronghui; Liu, Xinwei; Li, Jingtao; Li, Xiaohang

2017-10-01

Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5-4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (-201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be -0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of -1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

Band Offset Measurements in Atomic-Layer-Deposited Al2O3/Zn0.8Al0.2O Heterojunction Studied by X-ray Photoelectron Spectroscopy.

PubMed

Yan, Baojun; Liu, Shulin; Heng, Yuekun; Yang, Yuzhen; Yu, Yang; Wen, Kaile

2017-12-01

Pure aluminum oxide (Al 2 O 3 ) and zinc aluminum oxide (Zn x Al 1-x O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (E g ) of the Zn x Al 1-x O (0.2 ≤ x ≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction were investigated in detail using charge-corrected X-ray photoelectron spectroscopy. In this work, different methodologies were adopted to recover the actual position of the core levels in insulator materials which were easily affected by differential charging phenomena. Valence band offset (ΔE V ) and conduction band offset (ΔE C ) for the interface of the Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction have been constructed. An accurate value of ΔE V  = 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied Al 2 O 3 thickness. Given the experimental E g of 6.8 eV for Al 2 O 3 and 5.29 eV for Zn 0.8 Al 0.2 O, a type-I heterojunction with a ΔE C of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of Al 2 O 3 /Zn 0.8 Al 0.2 O heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.

A theoretical study of heterojunction and graded band gap type solar cells

NASA Technical Reports Server (NTRS)

Chiang, J. P. C.; Hauser, J. R.

1979-01-01

The work performed concentrated on including multisun effects, high temperature effects, and electron irradiation effects into the computer analysis program for heterojunction and graded bandgap solar cells. These objectives were accomplished and the program is now available for such calculations.

Inverted organic photosensitive devices

DOEpatents

Forrest, Stephen R.; Bailey-Salzman, Rhonda F.

2016-12-06

The present disclosure relates to organic photosensitive optoelectronic devices grown in an inverted manner. An inverted organic photosensitive optoelectronic device of the present disclosure comprises a reflective electrode, an organic donor-acceptor heterojunction over the reflective electrode, and a transparent electrode on top of the donor-acceptor heterojunction.

Phthalocyanine Blends Improve Bulk Heterojunction Solar Cells

PubMed Central

Varotto, Alessandro; Nam, Chang-Yong; Radivojevic, Ivana; Tomé, Joao; Cavaleiro, José A.S.; Black, Charles T.; Drain, Charles Michael

2010-01-01

A core phthalocyanine platform allows engineering the solubility properties the band gap; shifting the maximum absorption toward the red. A simple method to increase the efficiency of heterojunction solar cells uses a self-organized blend of the phthalocyanine chromophores fabricated by solution processing. PMID:20136126

Organic-inorganic hybrid inverted photodiode with planar heterojunction for achieving low dark current and high detectivity

NASA Astrophysics Data System (ADS)

Ha, JaeUn; Yoon, Seongwon; Lee, Jong-Soo; Chung, Dae Sung

2016-03-01

In this study, the strategy of using an organic-inorganic hybrid planar heterojunction consisting of polymeric semiconductors and inorganic nanocrystals is introduced to realize a high-performance hybrid photodiode (HPD) with low dark current and high detectivity. To prevent undesired charge injection under the reverse bias condition, which is the major dark current source of the photodiode, a well-defined planar heterojunction is strategically constructed via smart solution process techniques. The optimized HPD renders a low dark current of ˜10-5 mA cm-2 at -5 V and ˜10-6 mA cm-2 at -1 V, as well as a high detectivity ˜1012 Jones across the entire visible wavelength range. Furthermore, excellent photocurrent stability is demonstrated under continuous light exposure. We believe that the solution-processed planar heterojunction with inverted structure can be an attractive alternative diode structure for fabricating high-performance HPDs, which usually suffer from high dark current issues.

Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

DOE PAGES

Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; ...

2015-09-18

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealedmore » both electron and hole transfer processes at the donor–acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.« less

Two-dimensional n -InSe/p -GeSe(SnS) van der Waals heterojunctions: High carrier mobility and broadband performance

NASA Astrophysics Data System (ADS)

Xia, Cong-xin; Du, Juan; Huang, Xiao-wei; Xiao, Wen-bo; Xiong, Wen-qi; Wang, Tian-xing; Wei, Zhong-ming; Jia, Yu; Shi, Jun-jie; Li, Jing-bo

2018-03-01

Recently, constructing van der Waals (vdW) heterojunctions by stacking different two-dimensional (2D) materials has been considered to be effective strategy to obtain the desired properties. Here, through first-principles calculations, we find theoretically that the 2D n -InSe/p -GeSe(SnS) vdW heterojunctions are the direct-band-gap semiconductor with typical type-II band alignment, facilitating the effective separation of photogenerated electron and hole pairs. Moreover, they possess the high optical absorption strength (˜105 ), broad spectrum width, and excellent carrier mobility (˜103c m2V-1s-1 ). Interestingly, under the influences of the interlayer coupling and external electric field, the characteristics of type-II band alignment is robust, while the band-gap values and band offset are tunable. These results indicate that 2D n -InSe/p -GeSe(SnS) heterojunctions possess excellent optoelectronic and transport properties, and thus can become good candidates for next-generation optoelectronic nanodevices.

Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells.

PubMed

Zhong, Yu; Trinh, M Tuan; Chen, Rongsheng; Purdum, Geoffrey E; Khlyabich, Petr P; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y; Black, Charles T; Steigerwald, Michael L; Loo, Yueh-Lin; Ng, Fay; Zhu, X-Y; Nuckolls, Colin

2015-09-18

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

Gate-tunable diode-like current rectification and ambipolar transport in multilayer van der Waals ReSe2/WS2 p-n heterojunctions.

PubMed

Wang, Cong; Yang, Shengxue; Xiong, Wenqi; Xia, Congxin; Cai, Hui; Chen, Bin; Wang, Xiaoting; Zhang, Xinzheng; Wei, Zhongming; Tongay, Sefaattin; Li, Jingbo; Liu, Qian

2016-10-12

Vertically stacked van der Waals (vdW) heterojunctions of two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted a great deal of attention due to their fascinating properties. In this work, we report two important gate-tunable phenomena in new artificial vdW p-n heterojunctions created by vertically stacking p-type multilayer ReSe 2 and n-type multilayer WS 2 : (1) well-defined strong gate-tunable diode-like current rectification across the p-n interface is observed, and the tunability of the electronic processes is attributed to the tunneling-assisted interlayer recombination induced by majority carriers across the vdW interface; (2) the distinct ambipolar behavior under gate voltage modulation both at forward and reverse bias voltages is found in the vdW ReSe 2 /WS 2 heterojunction transistors and a corresponding transport model is proposed for the tunable polarity behaviors. The findings may provide some new opportunities for building nanoscale electronic and optoelectronic devices.

Ultrasensitive NO2 gas sensors using hybrid heterojunctions of multi-walled carbon nanotubes and on-chip grown SnO2 nanowires

NASA Astrophysics Data System (ADS)

Nguyet, Quan Thi Minh; Van Duy, Nguyen; Manh Hung, Chu; Hoa, Nguyen Duc; Van Hieu, Nguyen

2018-04-01

Hybrid heterojunction devices are designed for ultrahigh response to NO2 toxic gas. The devices were constructed by assembling multi-walled carbon nanotubes (MWCNTs) on a microelectrode chip bridged bare Pt-electrode and a Pt-electrode with pre-grown SnO2 nanowires (NWs). All heterojunction devices were realized using different types of MWCNTs, which exhibit ultrahigh response to sub-ppm NO2 gas at 50 °C operated in the reverse bias mode. The response to 1 ppm NO2 gas reaches 11300, which is about 100 times higher than that of a back-to-back heterojunction device fabricated from SnO2 NWs and MWCNTs. In addition, the present device exhibits an ultralow detection limit of about 0.68 ppt. The modulation of trap-assisted tunneling current under reverse bias is the main gas-sensing mechanism. This principle device presents a concept for developing gas sensors made of a hybrid between semiconductor metal oxide NWs and CNTs.

Facial development of high performance room temperature NO2 gas sensors based on ZnO nanowalls decorated rGO nanosheets

NASA Astrophysics Data System (ADS)

Liu, Zongyuan; Yu, Lingmin; Guo, Fen; Liu, Sheng; Qi, Lijun; Shan, Minyu; Fan, Xinhui

2017-11-01

A highly sensitive NO2 gas sensor based on ZnO nanowalls decorated rGO nanosheets was fabricated using a thermal reduction and soft solution process. The highly developed interconnected microporous networks of ZnO nanowalls were anchored homogeneously on the surface of reduced graphene oxide (rGO). Sensors fabricated with heterojunction structures achieved a higher response (S = 9.61) and shorter response-recovery (25 s, 15 s) behavior at room temperature to 50 ppm level NO2 effectively in contrast to those sensors based on net ZnO nanowalls or rGO layers. The stability and selectivity of ZnO/rGO heterojunction were carried out. Meanwhile, the effects of humidity on ZnO/rGO heterojunction gas sensor were investigated. The more preferable sensing performance of ZnO/rGO heterojunction to NO2 was discussed. It can be surmised that this NO2 gas sensor has potential for use as a portable room temperature gas sensor.

Synthesis and characterization of metal oxide semiconductors by a facile co-electroplating-annealing method and formation of ZnO/CuO pn heterojunctions with rectifying behavior

NASA Astrophysics Data System (ADS)

Turkdogan, Sunay; Kilic, Bayram

2018-01-01

We have developed a unique growth method and demonstrated the growth of CuO and ZnO semiconductor materials and the fabrication of their pn heterojunctions in ambient atmosphere. The pn heterojunctions were constructed using inherently p-type CuO and inherently n-type ZnO materials. Both p- and n-type semiconductors and pn heterojunctions were prepared using a simple but versatile growth method that relies on the transformation of electroplated Cu and Zn metals into CuO and ZnO semiconductors, respectively and is capable of a large-scale production desired in most of the applications. The structural, chemical, optical and electrical properties of the materials and junctions were investigated using various characterization methods and the results show that our growth method, materials and devices are quite promising to be utilized for various applications including but not limited to solar cells, gas/humidity sensors and photodetectors.

ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector

PubMed Central

2013-01-01

ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode. PMID:24103153

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

NASA Astrophysics Data System (ADS)

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-09-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+-[WO4]2--[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Efficiency enhancement using a Zn1- x Ge x -O thin film as an n-type window layer in Cu2O-based heterojunction solar cells

NASA Astrophysics Data System (ADS)

Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

2016-05-01

Efficiency enhancement was achieved in Cu2O-based heterojunction solar cells fabricated with a zinc-germanium-oxide (Zn1- x Ge x -O) thin film as the n-type window layer and a p-type Na-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing Cu sheets. The Ge content (x) dependence of the obtained photovoltaic properties of the heterojunction solar cells is mainly explained by the conduction band discontinuity that results from the electron affinity difference between Zn1- x Ge x -O and Cu2O:Na. The optimal value of x in Zn1- x Ge x -O thin films prepared by pulsed laser deposition was observed to be 0.62. An efficiency of 8.1% was obtained in a MgF2/Al-doped ZnO/Zn0.38Ge0.62-O/Cu2O:Na heterojunction solar cell.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

PubMed Central

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-01-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface. PMID:26359212

Enhanced Photoelectrochemical Activity by Autologous Cd/CdO/CdS Heterojunction Photoanodes with High Conductivity and Separation Efficiency.

PubMed

Xie, Shilei; Zhang, Peng; Zhang, Min; Liu, Peng; Li, Wei; Lu, Xihong; Cheng, Faliang; Tong, Yexiang

2017-07-18

The development for hydrogen from solar energy has attracted great attention due to the global demand for clean, environmentally friendly energy. Herein, autologous Cd/CdO/CdS heterojunctions were prepared in a carefully controlled process with metallic Cd as the inner layer and CdO as the interlayer. Further research revealed that the transportation and separation of photogenerated pairs were enhanced due to low resistance of the Cd inner layer and the type II CdO/CdS heterojunction. As a result, the optimized Cd/CdO/CdS heterojunction photoanode showed outstanding and long-term photoelectrochemical activity for water splitting, with a current density of 3.52 mA cm -2 , or a benchmark specific hydrogen production rate of 1.65 μmol cm -2  min -1 at -0.3 V versus Ag/AgCl, by using the environmental pollutants of sulfide and sulfite as sacrificial agents. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Fabrication of Bulk Heterojunction P3HT: PCBM Organic Photovoltaics

NASA Astrophysics Data System (ADS)

Darwis, D.; Sesa, E.; Farhamza, D.; Iqbal

2018-05-01

Bulk heterojunction Organic photovoltaic (OPV) devices are gaining a lot of interest due to their potential for ease of processing and lower manufacturing cost sustainable energy generation. In consequence, the number of studies into the properties and characteristics of organic solar cell devices has been increased to improving their power conversion. A further advancement over past decade has shown that improved efficiency could be obtained by mixed of poly(3 - hexylthiophene) (P3HT) and [1] – phenyl - C61-butyric acid methyl ester (PCBM) as an active layer. A series of optimizations of this P3HT: PCBM blends, such as the mixture ratio variation, the annealing treatments, and solvent treatment, have been emerged to improve the efficiency of the OPV. As a result, significant improvements were achieved. Here, we report the fabrication heterojunction devices of 2.9 % efficiency. This result has been achieved using the configuration of a typical heterojunction solar cell modules consists of layered glass/ITO/PEDOT: PSS/active layer/cathode interlayer

Fabrication of Si/ZnS radial nanowire heterojunction arrays for white light emitting devices on Si substrates.

PubMed

Katiyar, Ajit K; Sinha, Arun Kumar; Manna, Santanu; Ray, Samit K

2014-09-10

Well-separated Si/ZnS radial nanowire heterojunction-based light-emitting devices have been fabricated on large-area substrates by depositing n-ZnS film on p-type nanoporous Si nanowire templates. Vertically oriented porous Si nanowires on p-Si substrates have been grown by metal-assisted chemical etching catalyzed using Au nanoparticles. Isolated Si nanowires with needle-shaped arrays have been made by KOH treatment before ZnS deposition. Electrically driven efficient white light emission from radial heterojunction arrays has been achieved under a low forward bias condition. The observed white light emission is attributed to blue and green emission from the defect-related radiative transition of ZnS and Si/ZnS interface, respectively, while the red arises from the porous surface of the Si nanowire core. The observed white light emission from the Si/ZnS nanowire heterojunction could open up the new possibility to integrate Si-based optical sources on a large scale.

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Le, H. Q.; Lim, S. K.; Goh, G. K. L.; Chua, S. J.; Ang, N. S. S.; Liu, W.

2010-09-01

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl2O4 spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×1020 cm-3 (and carrier mobility of 28 cm2/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

PubMed Central

Ambrosio, Antonio; Boscardin, Maurizio; Castrucci, Paola; Crivellari, Michele; Cilmo, Marco; De Crescenzi, Maurizio; De Nicola, Francesco; Fiandrini, Emanuele; Grossi, Valentina; Maddalena, Pasqualino; Passacantando, Maurizio; Santucci, Sandro; Scarselli, Manuela; Valentini, Antonio

2015-01-01

Summary A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube–silicon (CNT–Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise. PMID:25821710

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube-silicon heterojunction.

PubMed

Aramo, Carla; Ambrosio, Antonio; Ambrosio, Michelangelo; Boscardin, Maurizio; Castrucci, Paola; Crivellari, Michele; Cilmo, Marco; De Crescenzi, Maurizio; De Nicola, Francesco; Fiandrini, Emanuele; Grossi, Valentina; Maddalena, Pasqualino; Passacantando, Maurizio; Santucci, Sandro; Scarselli, Manuela; Valentini, Antonio

2015-01-01

A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube-silicon (CNT-Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise.

Atomic-Monolayer Two-Dimensional Lateral Quasi-Heterojunction Bipolar Transistors with Resonant Tunneling Phenomenon.

PubMed

Lin, Che-Yu; Zhu, Xiaodan; Tsai, Shin-Hung; Tsai, Shiao-Po; Lei, Sidong; Shi, Yumeng; Li, Lain-Jong; Huang, Shyh-Jer; Wu, Wen-Fa; Yeh, Wen-Kuan; Su, Yan-Kuin; Wang, Kang L; Lan, Yann-Wen

2017-11-28

High-frequency operation with ultrathin, lightweight, and extremely flexible semiconducting electronics is highly desirable for the development of mobile devices, wearable electronic systems, and defense technologies. In this work, the experimental observation of quasi-heterojunction bipolar transistors utilizing a monolayer of the lateral WSe 2 -MoS 2 junctions as the conducting p-n channel is demonstrated. Both lateral n-p-n and p-n-p heterojunction bipolar transistors are fabricated to exhibit the output characteristics and current gain. A maximum common-emitter current gain of around 3 is obtained in our prototype two-dimensional quasi-heterojunction bipolar transistors. Interestingly, we also observe the negative differential resistance in the electrical characteristics. A potential mechanism is that the negative differential resistance is induced by resonant tunneling phenomenon due to the formation of quantum well under applying high bias voltages. Our results open the door to two-dimensional materials for high-frequency, high-speed, high-density, and flexible electronics.

Fabrication of n-ZnO:Al/p-Si(100) heterojunction diode and its characterization

NASA Astrophysics Data System (ADS)

Parvathy Venu, M.; Dharmaprakash, S. M.; Byrappa, K.

2018-04-01

Aluminum doped ZnO (n-ZnO:Al) nanostructured thin films were grown on ZnO seed layer coated p-Si(100) substrate employing hydrothermal technique. X-ray diffraction pattern revealed that the ZnO:Al film possess hexagonal wurtzite structure with preferential orientation along (002) direction. Photoluminescence of the sample displayed near band edge emission peak in the ultra-violet region and defect level emission peak in the visible region. The as grown thin film was used in the fabrication of n-ZnO:Al/p-Si heterojunction diode and the room temperature current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied. The heterojunction exhibited fairly good rectification with an ideality of 2.49 and reverse saturation current of 2 nA. The barrier height was found to be 0.668 eV from the I-V measurements. The C-V measurements showed a decrease in the capacitance of the heterojunction with an increase in the reverse bias voltage.

High-performance zero-bias ultraviolet photodetector based on p-GaN/n-ZnO heterojunction

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

Su, Longxing; Zhang, Quanlin; Chen, Mingming

2014-08-18

Lattice-match p-GaN and n-ZnO bilayers were heteroepitaxially grown on the c-sapphire substrate by metal organic chemical vapor deposition and molecular beam epitaxy technique, respectively. X-ray diffraction and photoluminescence investigations revealed the high crystal quality of the bilayer films. Subsequently, a p-GaN/n-ZnO heterojunction photodetector was fabricated. The p-n junction exhibited a clear rectifying I-V characteristic with a turn-on voltage of 3.7 V. At zero-bias voltage, the peak responsivity was 0.68 mA/W at 358 nm, which is one of the best performances reported for p-GaN/n-ZnO heterojunction detectors due to the excellent crystal quality of the bilayer films. These show that the high-performance p-GaN/n-ZnO heterojunction diodemore » is potential for applications of portable UV detectors without driving power.« less

Direct Observation of 2D Electrostatics and Ohmic Contacts in Template-Grown Graphene/WS2 Heterostructures.

PubMed

Zheng, Changxi; Zhang, Qianhui; Weber, Bent; Ilatikhameneh, Hesameddin; Chen, Fan; Sahasrabudhe, Harshad; Rahman, Rajib; Li, Shiqiang; Chen, Zhen; Hellerstedt, Jack; Zhang, Yupeng; Duan, Wen Hui; Bao, Qiaoliang; Fuhrer, Michael S

2017-03-28

Large-area two-dimensional (2D) heterojunctions are promising building blocks of 2D circuits. Understanding their intriguing electrostatics is pivotal but largely hindered by the lack of direct observations. Here graphene-WS 2 heterojunctions are prepared over large areas using a seedless ambient-pressure chemical vapor deposition technique. Kelvin probe force microscopy, photoluminescence spectroscopy, and scanning tunneling microscopy characterize the doping in graphene-WS 2 heterojunctions as-grown on sapphire and transferred to SiO 2 with and without thermal annealing. Both p-n and n-n junctions are observed, and a flat-band condition (zero Schottky barrier height) is found for lightly n-doped WS 2 , promising low-resistance ohmic contacts. This indicates a more favorable band alignment for graphene-WS 2 than has been predicted, likely explaining the low barriers observed in transport experiments on similar heterojunctions. Electrostatic modeling demonstrates that the large depletion width of the graphene-WS 2 junction reflects the electrostatics of the one-dimensional junction between two-dimensional materials.

22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector

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

Geissbühler, Jonas, E-mail: jonas.geissbuehler@epfl.ch; Werner, Jérémie; Martin de Nicolas, Silvia

2015-08-24

Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.

Interface Structure, Band Alignment, and Built-In Potentials at LaFeO 3 / n - SrTiO 3 Heterojunctions

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

Comes, Ryan; Chambers, Scott

We demonstrate that LaFeO 3/n-SrTiO 3(001) heterojunctions engineered to have opposite interface polarities exhibit very similar band offsets and built-in potentials within the LaFeO 3 layer of the same sign. However, heterojunctions with the TiO20-LaO+ interface structure attract electronic charge from the n-STO substrate, whereas those with the SrO0-FeO2-1 interface structure do not. These results suggest that the latter would more effectively facilitate photogenerated electron-hole pair separation than the former, an important result for photoelectrochemical water splitting

Preparation and Optoelectrical Properties of p-CuO/n-Si Heterojunction by a Simple Sol-Gel Method

NASA Astrophysics Data System (ADS)

He, Bo; Xu, Jing; Ning, Huanpo; Zhao, Lei; Xing, Huaizhong; Chang, Chien-Cheng; Qin, Yuming; Zhang, Lei

The Cuprous oxide (CuO) thin film was prepared on texturized Si wafer by a simple sol-gel method to fabricate p-CuO/n-Si heterojunction photoelectric device. The novel sol-gel method is very cheap and convenient. The structural, optical and electrical properties of the CuO film were studied by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometer and Hall effect measurement. A good nonlinear rectifying behavior is obtained for the p-CuO/n-Si heterojunction. Under reverse bias, good photoelectric behavior is obtained.

Preparation of ZnS microdisks using chemical bath deposition and ZnS/p-Si heterojunction solar cells

NASA Astrophysics Data System (ADS)

Hsiao, Y. J.; Meen, T. H.; Ji, L. W.; Tsai, J. K.; Wu, Y. S.; Huang, C. J.

2013-10-01

The synthesis and heterojunction solar cell properties of ZnS microdisks prepared by the chemical bath deposition method were investigated. The ZnS deposited on the p-Si blanket substrate exhibits good coverage. The lower reflectance spectra were found as the thickness of the ZnS film increased. The optical absorption spectra of the 80 °C ZnS microdisk exhibited a band-gap energy of 3.4 eV and the power conversion efficiency (PCE) of the AZO/ZnS/p-Si heterojunction solar cell with a 300 nm thick ZnS film was η=2.72%.

On a direct connection of the transition metal impurity levels to the band edge discontinuities in semiconductor heterojunctions

NASA Astrophysics Data System (ADS)

Langer, Jerzy M.; Heinrich, Helmut

1985-11-01

Our recent proposal of using the transition metal impurity levels to predict the isovalent heterojunction (HJ) band-edge discontinuities is further discussed. It is shown that for Ga 1-xAl xAs/GaAs heterojunctions most of the recent discontinuity data follow within experimental error the prediction of the ΔE cb: ΔE vb= 0.64:0.36 discontinuity ratio derived from the Fe 2+ level position in Ga 1-xAl xAs compound. Predictions of valence-band discontinuities for the other III-V and II-VI HJ systems are also given.

Fabrication and characterization of n-ZnO nanonails array/p(+)-GaN heterojunction diode.

PubMed

Zhu, G Y; Chen, G F; Li, J T; Shi, Z L; Lin, Y; Ding, T; Xu, X Y; Dai, J; Xu, C X

2012-10-01

A novel heterojunctional structure of n-ZnO nanonails array/p(+)-GaN light-emitting diode was fabricated by Chemical Vapor Deposition method. A broad electroluminescence spectrum shows two peaks centered at 435 nm and 478 nm at room temperature, respectively. By comparing the photoluminescence and electroluminescence spectra, together with analyzing the energy band structure of heterojunction light emitting diode, it suggested that the electroluminescence peak located at 435 nm originates from Mg acceptor level of p(+)-GaN layer, whereas the electroluminescence peak located at 478 nm originates from the defects of n-ZnO nanonails array.

22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector

DOE PAGES

Geissbühler, Jonas; Werner, Jérémie; Nicolas, Silvia Martin de; ...

2015-08-24

Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. Furthermore, we circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.

Band alignment investigations of heterostructure NiO/TiO2 nanomaterials used as efficient heterojunction earth-abundant metal oxide photocatalysts for hydrogen production.

PubMed

Uddin, Md T; Nicolas, Y; Olivier, C; Jaegermann, W; Rockstroh, N; Junge, H; Toupance, T

2017-07-26

Earth-abundant NiO/anatase TiO 2 heteronanostructures were prepared by a straightforward one-pot sol-gel synthetic route followed by a suitable thermal post-treatment. The resulting 0.1-4 wt% NiO-decorated anatase TiO 2 nanoparticles were characterized by X-ray diffraction, electron microscopy, Raman and UV-visible spectroscopy and N 2 sorption analysis, and showed both nanocrystallinity and mesoporosity. The careful determination of the energy band alignment diagram by a suitable combination of XPS/UPS and absorption spectroscopy data revealed significant band bending at the interface of the p-n NiO/anatase TiO 2 heterojunction nanoparticles. Furthermore, these heterojunction photocatalysts exhibited an improved photocatalytic activity in H 2 production by methanol photoreforming compared to pure anatase TiO 2 and commercial P25. Thus, an average H 2 production rate of 2693 μmol h -1 g -1 was obtained for the heterojunction of a 1 wt% NiO/anatase photocatalyst, which is one of the most efficient NiO/anatase TiO 2 systems ever reported. An enhanced dissociation efficiency of the photogenerated electron-hole pairs resulting from an internal electric field developed at the interface of the NiO/anatase TiO 2 p-n heterojunctions is suggested to be the reason of this enhanced photocatalytic activity.

Non-covalent doping of graphitic carbon nitride with ultrathin graphene oxide and molybdenum disulfide nanosheets: an effective binary heterojunction photocatalyst under visible light irradiation.

PubMed

Hu, S W; Yang, L W; Tian, Y; Wei, X L; Ding, J W; Zhong, J X; Chu, Paul K

2014-10-01

A proof of concept integrating binary p-n heterojunctions into a semiconductor hybrid photocatalyst is demonstrated by non-covalent doping of graphite-like carbon nitride (g-C3N4) with ultrathin GO and MoS2 nanosheets using a facile sonochemical method. In this unique ternary hybrid, the layered MoS2 and GO nanosheets with a large surface area enhance light absorption to generate more photoelectrons. On account of the coupling between MoS2 and GO with g-C3N4, the ternary hybrid possesses binary p-n heterojunctions at the g-C3N4/MoS2 and g-C3N4/GO interfaces. The space charge layers created by the p-n heterojunctions not only enhance photogeneration, but also promote charge separation and transfer of electron-hole pairs. In addition, the ultrathin MoS2 and GO with high mobility act as electron mediators to facilitate separation of photogenerated electron-hole pairs at each p-n heterojunction. As a result, the ternary hybrid photocatalyst exhibits improved photoelectrochemical and photocatalytic activity under visible light irradiation compared to other reference materials. The results provide new insights into the large-scale production of semiconductor photocatalysts. Copyright © 2014 Elsevier Inc. All rights reserved.

Simulation of a high-efficiency silicon-based heterojunction solar cell

NASA Astrophysics Data System (ADS)

Jian, Liu; Shihua, Huang; Lü, He

2015-04-01

The basic parameters of a-Si:H/c-Si heterojunction solar cells, such as layer thickness, doping concentration, a-Si:H/c-Si interface defect density, and the work functions of the transparent conducting oxide (TCO) and back surface field (BSF) layer, are crucial factors that influence the carrier transport properties and the efficiency of the solar cells. The correlations between the carrier transport properties and these parameters and the performance of a-Si:H/c-Si heterojunction solar cells were investigated using the AFORS-HET program. Through the analysis and optimization of a TCO/n-a-Si:H/i-a-Si:H/p-c-Si/p+-a-Si:H/Ag solar cell, a photoelectric conversion efficiency of 27.07% (VOC) 749 mV, JSC: 42.86 mA/cm2, FF: 84.33%) was obtained through simulation. An in-depth understanding of the transport properties can help to improve the efficiency of a-Si:H/c-Si heterojunction solar cells, and provide useful guidance for actual heterojunction with intrinsic thin layer (HIT) solar cell manufacturing. Project supported by the National Natural Science Foundation of China (No. 61076055), the Open Project Program of Surface Physics Laboratory (National Key Laboratory) of Fudan University (No. FDS-KL2011-04), the Zhejiang Provincial Science and Technology Key Innovation Team (No. 2011R50012), and the Zhejiang Provincial Key Laboratory (No. 2013E10022).

Vertical nanowire heterojunction devices based on a clean Si/Ge interface.

PubMed

Chen, Lin; Fung, Wayne Y; Lu, Wei

2013-01-01

Different vertical nanowire heterojunction devices were fabricated and tested based on vertical Ge nanowires grown epitaxially at low temperatures on (111) Si substrates with a sharp and clean Si/Ge interface. The nearly ideal Si/Ge heterojuctions with controlled and abrupt doping profiles were verified through material analysis and electrical characterizations. In the nSi/pGe heterojunction diode, an ideality factor of 1.16, subpicoampere reverse saturation current, and rectifying ratio of 10(6) were obtained, while the n+Si/p+Ge structure leads to Esaki tunnel diodes with a high peak tunneling current of 4.57 kA/cm(2) and negative differential resistance at room temperature. The large valence band discontinuity between the Ge and Si in the nanowire heterojunctions was further verified in the p+Si/pGe structure, which shows a rectifying behavior instead of an Ohmic contact and raises an important issue in making Ohmic contacts to heterogeneously integrated materials. A raised Si/Ge structure was further developed using a self-aligned etch process, allowing greater freedom in device design for applications such as the tunneling field-effect transistor (TFET). All measurement data can be well-explained and fitted with theoretical models with known bulk properties, suggesting that the Si/Ge nanowire system offers a very clean heterojunction interface with low defect density, and holds great potential as a platform for future high-density and high-performance electronics.

Two-dimensional CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible photodetectors boosted by charge transfer

NASA Astrophysics Data System (ADS)

Shen, Yalong; Yu, Dejian; Wang, Xiong; Huo, Chengxue; Wu, Ye; Zhu, Zhengfeng; Zeng, Haibo

2018-02-01

Inorganic halide perovskites exhibited promising potentials for high-performance wide-band photodetectors (PDs) due to their high light absorption coefficients, long carrier diffusion length and wide light absorption ranges. Here, we report two-dimensional (2D) CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible PDs, whose performances can be greatly boosted by the charge transfer through the energy-aligned interface. The 2D CsPbBr3 nanosheets with high crystallinity were fabricated via a simple solution-process at room temperature, and then assembled into flexible heterojunctions films with polymerphenyl-C61-butyric acid methyl ester (PCBM). Significantly, the efficient and fast charge transfer at the heterojunctions interface was evidenced by the obvious photoluminescence quenching and variation of recombination dynamics. Subsequently, such heterojunctions PD exhibited an enhanced responsivity of 10.85 A W-1 and an ultrahigh detectivity of 3.06 × 1013 Jones. In addition, the PD shows a broad linear dynamic range of 73 dB, a fast response speed with rise time of 44 μs and decay time of 390 μs, respectively. Moreover, the PD lying on polyethylene terephthalate substrates exhibited an outstanding mechanical flexibility and a robust electrical stability. These results could provide a new avenue for integration of 2D perovskites and organic functional materials and for high-performance flexible PDs.

Crystallization-mediated amorphous CuxO (x = 1, 2)/crystalline CuI p-p type heterojunctions with visible light enhanced and ultraviolet light restrained photocatalytic dye degradation performance

NASA Astrophysics Data System (ADS)

Wang, Hongli; Cai, Yun; Zhou, Jian; Fang, Jun; Yang, Yang

2017-04-01

We report simple and cost-effective fabrication of amorphous CuxO (x = 1, 2)/crystalline CuI p-p type heterojunctions based on crystallization-mediated approaches including antisolvent crystallization and crystal reconstruction. Starting from CuI acetonitrile solution, large crystals in commercial CuI can be easily converted to aggregates consisting of small particles by the crystallization processes while the spontaneous oxidation of CuI by atmospheric/dissolved oxygen can induce the formation of trace CuxO on CuI surface. As a proof of concept, the as-fabricated CuxO/CuI heterojunctions exhibit effective photocatalytic activity towards the degradation of methyl blue and other organic pollutants under visible light irradiation, although the wide band-gap semiconductor CuI is insensible to visible light. Unexpectedly, the CuxO/CuI heterojunctions exhibit restrained photocatalytic activity when ultraviolet light is applied in addition to the visible. It is suggested that the CuxO/CuI interface can enhance the spatial separation of the electron-hole pairs with the excitation of CuxO under visible light and prolong the lifetime of photogenerated charges with high redox ability. The present work represents a critically important step in advancing the crystallization technique for potential mass production of semiconductor heterojunctions in a mild manner.

Structural and optical properties of axial silicon-germanium nanowire heterojunctions

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

Wang, X.; Tsybeskov, L., E-mail: tsybesko@njit.edu; Kamins, T. I.

2015-12-21

Detailed studies of the structural and optical properties of axial silicon-germanium nanowire heterojunctions show that despite the 4.2% lattice mismatch between Si and Ge they can be grown without a significant density of structural defects. The lattice mismatch induced strain is partially relieved due to spontaneous SiGe intermixing at the heterointerface during growth and lateral expansion of the Ge segment of the nanowire. The mismatch in Ge and Si coefficients of thermal expansion and low thermal conductivity of Si/Ge nanowire heterojunctions are proposed to be responsible for the thermally induced stress detected under intense laser radiation in photoluminescence and Ramanmore » scattering measurements.« less

Fabrication and characterization of Ga-doped ZnO / Si heterojunction nanodiodes

NASA Astrophysics Data System (ADS)

Akgul, Guvenc; Akgul, Funda Aksoy

2017-02-01

In this study, temperature-dependent electrical properties of n-type Ga-doped ZnO thin film / p-type Si nanowire heterojunction diodes were reported. Metal-assisted chemical etching (MACE) process was performed to fabricate Si nanowires. Ga-doped ZnO films were then deposited onto nanowires through chemical bath deposition (CBD) technique to build three-dimensional nanowire-based heterojunction diodes. Fabricated devices revealed significant diode characteristics in the temperature range of 220 - 360 K. Electrical measurements shown that diodes had a well-defined rectifying behavior with a good rectification ratio of 103 ±3 V at room temperature. Ideality factor (n) were changed from 2.2 to 1.2 with increasing temperature.

Hybrid nanostructure heterojunction solar cells fabricated using vertically aligned ZnO nanotubes grown on reduced graphene oxide.

PubMed

Yang, Kaikun; Xu, Congkang; Huang, Liwei; Zou, Lianfeng; Wang, Howard

2011-10-07

Using reduced graphene oxide (rGO) films as the transparent conductive coating, inorganic/organic hybrid nanostructure heterojunction photovoltaic devices have been fabricated through hydrothermal synthesis of vertically aligned ZnO nanorods (ZnO-NRs) and nanotubes (ZnO-NTs) on rGO films followed by the spin casting of a poly(3-hexylthiophene) (P3HT) film. The data show that larger interfacial area in ZnO-NT/P3HT composites improves the exciton dissociation and the higher electrode conductance of rGO films helps the power output. This study offers an alternative to manufacturing nanostructure heterojunction solar cells at low temperatures using potentially low cost materials.

Electro-magnetic transport and rectifying property of Fe{sub 2.5}Mn{sub 0.5}O{sub 4}/p-Si heterojunction

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

Aireddy, H.; Das, A. K., E-mail: amal@phy.iitkgp.ernet.in

2016-05-06

Fe{sub 2.5}Mn{sub 0.5}O{sub 4}/p-Si heterojunction was fabricated using a pulsed laser deposition technique and investigated it’s structural and electrical transport properties. The high-resolution transmission electron microscopy results reveal the formation of a polycrystalline film on silicon substrate. The heterojunction shows good rectifying property and giant negative junction magnetoresistance especially in reverse bias condition at room temperature. The origin of this giant negative junction magnetoresistance may be attributing to the injection of electrons to the majority spin-up band of the Fe{sub 2.5}Mn{sub 0.5}O{sub 4} film.

Hydrogen effects on the electroluminescence of n-ZnO nanorod/p-GaN film heterojunction light-emitting diodes.

PubMed

Fang, Fang; Zhao, Dongxu; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

2010-07-07

Through a facile low-temperature solution process, vertically n-type ZnO nanorod arrays were grown on a GaN film to form a n-ZnO nanorod/p-GaN film heterojunction. A study of the electroluminescence (EL) characteristics of the heterojunction in air and in air with 2000 ppm hydrogen revealed the sensitivity of such a device to the surrounding atmosphere. The additional hydrogen shallow donors increased the effective electron concentration in ZnO nanorods and the EL recombination zone changed from the ZnO nanorods to the GaN film, which can be identified visually from the color change.

Effect of germanium concentrations on tunnelling current calculation of Si/Si1-xGex/Si heterojunction bipolar transistor

NASA Astrophysics Data System (ADS)

Hasanah, L.; Suhendi, E.; Khairrurijal

2018-05-01

Tunelling current calculation on Si/Si1-xGex/Si heterojunction bipolar transistor was carried out by including the coupling between transversal and longitudinal components of electron motion. The calculation results indicated that the coupling between kinetic energy in parallel and perpendicular to S1-xGex barrier surface affected tunneling current significantly when electron velocity was faster than 1x105 m/s. This analytical tunneling current model was then used to study how the germanium concentration in base to Si/Si1-xGex/Si heterojunction bipolar transistor influenced the tunneling current. It is obtained that tunneling current increased as the germanium concentration given in base decreased.

Small molecule BODIPY dyes as non-fullerene acceptors in bulk heterojunction organic photovoltaics.

PubMed

Poe, Ambata M; Della Pelle, Andrea M; Subrahmanyam, Ayyagari V; White, William; Wantz, Guillaume; Thayumanavan, S

2014-03-18

A series of acceptor-donor-acceptor molecules containing terminal BODIPY moieties conjugated through the meso position were synthesized. Deep LUMO energy levels and good visible absorption led to their use as acceptors in bulk heterojunction solar cells. Inverted devices were fabricated, reaching efficiencies as high as 1.51%.

Topological Quantum Information Processing Mediated Via Hybrid Topological Insulator Structures

DTIC Science & Technology

2013-11-13

manipulation, entanglement and detection ofMajorana fermions in diamond-topological insulator - superconductor heterojunctions. Furthennore, we propose to...the formation, manipulation, entanglement and detection of Majorana fermions in diamond-topological insulator - superconductor heterojunctions...Interactions between Superconductors and Topological Insulators Recent advances have revealed a new type of information processing, topological quantum

An Evaluation of Structural, Topographic, Optical, and Temperature-Dependent Electrical Features of Sol-Gel Spin-Coated p-NiO/n-Si Heterojunction

NASA Astrophysics Data System (ADS)

Turgut, Güven; Duman, Songül; Özcelik, Fikriye Şeyma

2017-06-01

p-NiO/n-Si heterodiode was deposited with an easy and cheap sol-gel route using a spin coater. The XRD results revealed that NiO film had polycrystalline cubic bunsenite structure with (200) preferential direction. The AFM and SEM micrographs indicated that the film was composed of homogenously distributed nanoparticles on n-Si surface. The uniform scattering of Ni and O elements was also seen from EDX mapping pictures. The band gap value for NiO sample was found to be 3.74 eV. The current-voltage ( I- V) properties of Ag/p-NiO/n-Si heterojunction were inquired in the temperature range of 80 K to 300 K (-193 °C to 27 °C). The temperature coefficient of barrier height of the Ag/p-NiO/n-Si heterojunction was determined to be 2.6 meV/K. The I- V measurements showed that the barrier height of the heterojunction increased with an increment in the temperature.

Laterally inherently thin amorphous-crystalline silicon heterojunction photovoltaic cell

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

Chowdhury, Zahidur R., E-mail: zr.chowdhury@utoronto.ca; Kherani, Nazir P., E-mail: kherani@ecf.utoronto.ca

2014-12-29

This article reports on an amorphous-crystalline silicon heterojunction photovoltaic cell concept wherein the heterojunction regions are laterally narrow and distributed amidst a backdrop of well-passivated crystalline silicon surface. The localized amorphous-crystalline silicon heterojunctions consisting of the laterally thin emitter and back-surface field regions are precisely aligned under the metal grid-lines and bus-bars while the remaining crystalline silicon surface is passivated using the recently proposed facile grown native oxide–plasma enhanced chemical vapour deposited silicon nitride passivation scheme. The proposed cell concept mitigates parasitic optical absorption losses by relegating amorphous silicon to beneath the shadowed metallized regions and by using optically transparentmore » passivation layer. A photovoltaic conversion efficiency of 13.6% is obtained for an untextured proof-of-concept cell illuminated under AM 1.5 global spectrum; the specific cell performance parameters are V{sub OC} of 666 mV, J{sub SC} of 29.5 mA-cm{sup −2}, and fill-factor of 69.3%. Reduced parasitic absorption, predominantly in the shorter wavelength range, is confirmed with external quantum efficiency measurement.« less

Annealing dependence on flexible p-CuGaO2/n-ZnO heterojunction diode deposited by RF sputtering method

NASA Astrophysics Data System (ADS)

Li Lam, Mui; Hafiz Abu Bakar, Muhammad; Lam, Wai Yip; Alias, Afishah; Rahman, Abu Bakar Abd; Anuar Mohamad, Khairul; Uesugi, Katsuhiro

2017-11-01

In this work, p-CuGaO2/n-ZnO heterojunction diodes were deposited by RF powered sputtering method on polyethylene terephthalate (PETP, PET) substrates. Structural, morphology, optical and electrical properties of CuGaO2/ZnO heterojunction was investigated as a function of annealing duration. The structural properties show the ZnO films (002) peak were stronger at the range of 34° while CuGaO2 (015) peak is not visible at 44°. The surface morphology revealed that RMS roughness become smoother as the annealing duration increase to 30 minutes and become rougher as the annealing duration is increased to 60 minutes. The optical properties of CuGaO2/ZnO heterojunction diode at 30 minutes exhibit approximately 75% optical transmittance in the invisible region. The diodes exhibited a rectifying characteristic and the maximum forward current was observed for the diode annealed for 30 minutes. The diodes show an ideality factor range from 43.69 to 71.29 and turn on voltage between 0.75 V and 1.05 V.

Heterojunction solar cell with 6% efficiency based on an n-type aluminum-gallium-oxide thin film and p-type sodium-doped Cu2O sheet

NASA Astrophysics Data System (ADS)

Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

2015-02-01

In this paper, we describe efforts to enhance the efficiency of Cu2O-based heterojunction solar cells fabricated with an aluminum-gallium-oxide (Al-Ga-O) thin film as the n-type layer and a p-type sodium (Na)-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing copper sheets. The optimal Al content [X; Al/(Ga + Al) atomic ratio] of an AlX-Ga1-X-O thin-film n-type layer was found to be approximately 2.5 at. %. The optimized resistivity was approximately 15 Ω cm for n-type AlX-Ga1-X-O/p-type Cu2O:Na heterojunction solar cells. A MgF2/AZO/Al0.025-Ga0.975-O/Cu2O:Na heterojunction solar cell with 6.1% efficiency was fabricated using a 60-nm-thick n-type oxide thin-film layer and a 0.2-mm-thick Cu2O:Na sheet with the optimized resistivity.

Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells

PubMed Central

2014-01-01

A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells. PMID:25386107

Efficient Band-to-Trap Tunneling Model Including Heterojunction Band Offset

DOE PAGES

Gao, Xujiao; Huang, Andy; Kerr, Bert

2017-10-25

In this paper, we present an efficient band-to-trap tunneling model based on the Schenk approach, in which an analytic density-of-states (DOS) model is developed based on the open boundary scattering method. The new model explicitly includes the effect of heterojunction band offset, in addition to the well-known field effect. Its analytic form enables straightforward implementation into TCAD device simulators. It is applicable to all one-dimensional potentials, which can be approximated to a good degree such that the approximated potentials lead to piecewise analytic wave functions with open boundary conditions. The model allows for simulating both the electric-field-enhanced and band-offset-enhanced carriermore » recombination due to the band-to-trap tunneling near the heterojunction in a heterojunction bipolar transistor (HBT). Simulation results of an InGaP/GaAs/GaAs NPN HBT show that the proposed model predicts significantly increased base currents, due to the hole-to-trap tunneling enhanced by the emitter-base junction band offset. Finally, the results compare favorably with experimental observation.« less

Efficient Band-to-Trap Tunneling Model Including Heterojunction Band Offset

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

Gao, Xujiao; Huang, Andy; Kerr, Bert

In this paper, we present an efficient band-to-trap tunneling model based on the Schenk approach, in which an analytic density-of-states (DOS) model is developed based on the open boundary scattering method. The new model explicitly includes the effect of heterojunction band offset, in addition to the well-known field effect. Its analytic form enables straightforward implementation into TCAD device simulators. It is applicable to all one-dimensional potentials, which can be approximated to a good degree such that the approximated potentials lead to piecewise analytic wave functions with open boundary conditions. The model allows for simulating both the electric-field-enhanced and band-offset-enhanced carriermore » recombination due to the band-to-trap tunneling near the heterojunction in a heterojunction bipolar transistor (HBT). Simulation results of an InGaP/GaAs/GaAs NPN HBT show that the proposed model predicts significantly increased base currents, due to the hole-to-trap tunneling enhanced by the emitter-base junction band offset. Finally, the results compare favorably with experimental observation.« less

ZnO nanorod array/CuAlO2 nanofiber heterojunction on Ni substrate: synthesis and photoelectrochemical properties.

PubMed

Ding, Juan; Sui, Yongming; Fu, Wuyou; Yang, Haibin; Zhao, Bo; Li, Minghui

2011-07-22

A novel ZnO nanorod array (NR)/CuAlO(2) nanofiber (NF) heterojunction nanostructure was grown on a substrate of Ni plates using sol-gel synthesis for the NFs and hydrothermal reaction for the NRs. Compared with a traditional ZnO/CuAlO(2) laminar film nanostructure, the photocurrent of this fibrous network heterojunction is significantly increased. A significant blue-shift of the absorption edge and a favorable forward current to reverse current ratio at applied voltages of -2 to +2 V were observed in this heterojunction with the increase of Zn(2+) ion concentration in the hydrothermal reaction. Furthermore, the photoelectrochemical properties were investigated and the highest photocurrent of 3.1 mA cm(-2) was obtained under AM 1.5 illumination with 100 mW cm(-2) light intensity at 0.71 V (versus Ag/AgCl). This novel 3D fibrous network nanostructure plays an important role in the optoelectronic field and can be extended to other binary or ternary oxide compositions for various applications.

ZnO nanorod array/CuAlO2 nanofiber heterojunction on Ni substrate: synthesis and photoelectrochemical properties

NASA Astrophysics Data System (ADS)

Ding, Juan; Sui, Yongming; Fu, Wuyou; Yang, Haibin; Zhao, Bo; Li, Minghui

2011-07-01

A novel ZnO nanorod array (NR)/CuAlO2 nanofiber (NF) heterojunction nanostructure was grown on a substrate of Ni plates using sol-gel synthesis for the NFs and hydrothermal reaction for the NRs. Compared with a traditional ZnO/CuAlO2 laminar film nanostructure, the photocurrent of this fibrous network heterojunction is significantly increased. A significant blue-shift of the absorption edge and a favorable forward current to reverse current ratio at applied voltages of - 2 to + 2 V were observed in this heterojunction with the increase of Zn2 + ion concentration in the hydrothermal reaction. Furthermore, the photoelectrochemical properties were investigated and the highest photocurrent of 3.1 mA cm - 2 was obtained under AM 1.5 illumination with 100 mW cm - 2 light intensity at 0.71 V (versus Ag/AgCl). This novel 3D fibrous network nanostructure plays an important role in the optoelectronic field and can be extended to other binary or ternary oxide compositions for various applications.

Investigation of performance enhancement in InAs/InGaAs heterojunction-enhanced N-channel tunneling field-effect transistor

NASA Astrophysics Data System (ADS)

Han, Genquan; Zhao, Bin; Liu, Yan; Wang, Hongjuan; Liu, Mingshan; Zhang, Chunfu; Hu, Shengdong; Hao, Yue

2015-12-01

We design a heterojunction-enhanced n-channel tunneling field effect transistor (HE-TFET) with an InAs/In1-xGaxAs heterojunction located in channel region with a distance of LT-H from source/channel tunneling junction. The influence of LT-H on the performance of HE-TFETs is investigated by simulation. Compared with InAs homo-NTFET, the positive shift of onset voltage, the steeper subthreshold swing (SS), and the enhanced on-state current ION are achieved in HE-NTFETs, which is attributed to the modulation of the heterojunction on band-to-band tunneling. At a supply voltage of 0.3 V, ION of InAs/In0.9Ga0.1As HE-NTFET with a LT-H of 6 nm demonstrates an enhancement of 119.3% in comparison with the homo device. Furthermore, the impact of Ga composition on the performance of HE-NTFETs is studied. As the Ga composition increases, the average SS characteristics of HE-NTFETs are improved, while the drive current of devices is reduced due to the increasing of tunneling barrier.

Room temperature electroluminescence from n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction device grown by PLD

NASA Astrophysics Data System (ADS)

Zhang, Lichun; Li, Qingshan; Wang, Feifei; Qu, Chong; Zhao, Fengzhou

2014-05-01

The n-ZnO:Ga/ p-GaN:Mg and n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated by the pulsed laser deposition (PLD) technique. The blue electroluminescence (EL) of the n-ZnO:Ga/ p-GaN:Mg heterojunction LEDs is emitted mainly from the p-GaN layer instead of the n-ZnO:Ga layer, for the reason that the electron injection from n-ZnO:Ga prevailed over the hole injection from p-GaN:Mg due to the higher carrier concentration and carrier mobility in n-ZnO:Ga. On the other hand, the n-ZnO:Ga/ i-ZnO/ p-GaN:Mg heterojunction LEDs exhibited dominant ultraviolet-blue emission. The reason for this difference is attributed to the inserted undoped i-ZnO layer between n-ZnO:Ga and p-GaN:Mg, in which the holes from p-GaN:Mg and the electrons from n-ZnO:Ga are recombined.

Fabrication of p-Si/n-ZnO:Al heterojunction diode and determination of electrical parameters

NASA Astrophysics Data System (ADS)

Ilican, Saliha; Gorgun, Kamuran; Aksoy, Seval; Caglar, Yasemin; Caglar, Mujdat

2018-03-01

We present a fundamental experimental study of a microwave assisted chemical bath deposition (MW-CBD) method for Al doped ZnO films. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) spectroscopy were used to analyze the microstructures and crystalline structures of these films, respectively. The p-Si/n-ZnO:Al heterojunction diodes were fabricated. The current-voltage (I-V) characteristics of these diodes were measured at room temperature. The important electrical parameters such as series resistance, the ideality factor and the barrier height were determined by performing plots from the forward bias I-V characteristics using different methods. The obtained results indicate that Al doping improve the electrical properties of the p-Si/n-ZnO diode. The best rectification properties were observed in the p-Si/n-ZnO:5%Al heterojunction diode, so only capacitance-voltage (C-V) measurements of this diode were taken. Electrical parameter values such as series resistance, the built-in potential and the acceptor concentration calculated for this heterojunction diode.

Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells.

PubMed

Tan, Furui; Qu, Shengchun; Zhang, Weifeng; Wang, Zhanguo

2014-01-01

A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells.

InP and InAs nanowires hetero- and homojunctions: energetic stability and electronic properties.

PubMed

Dionízio Moreira, M; Venezuela, P; Miwa, R H

2010-07-16

We performed an ab initio total energy investigation, within the density functional theory, of the energetic stability and the electronic properties of hydrogenated InAs/InP nanowire (NW) heterojunctions, as well as InAs and InP homojunctions composed of different structural arrangements, zinc-blend (zb) and wurtzite (w). For InAs/InP NW heterojunctions our results indicate that w and zb NW heterojunctions are quite similar, energetically, for thin NWs. We also examined the robustness of the abrupt interface through an atomic <--> swap at the InAs/InP interface. Our results support the formation of abrupt (non-abrupt) interfaces in w (zb) InAs/InP heterojunctions. Concerning InAs/InP NW-SLs, our results indicate a type-I band alignment, with the energy barrier at the InP layers, in accordance with experimental works. For InAs or InP zb/w homojunctions, we also found a type-I band alignment for thin NWs, however, on increasing the NW diameter both InAs and InP homojunctions exhibit a type-II band alignment.

Annealing Time Effect on Nanostructured n-ZnO/p-Si Heterojunction Photodetector Performance

NASA Astrophysics Data System (ADS)

Habubi, Nadir. F.; Ismail, Raid. A.; Hamoudi, Walid K.; Abid, Hassam. R.

2015-02-01

In this work, n-ZnO/p-Si heterojunction photodetectors were prepared by drop casting of ZnO nanoparticles (NPs) on single crystal p-type silicon substrates, followed by (15-60) min; step-annealing at 600∘C. Structural, electrical, and optical properties of the ZnO NPs films deposited on quartz substrates were studied as a function of annealing time. X-ray diffraction studies showed a polycrystalline, hexagonal wurtizte nanostructured ZnO with preferential orientation along the (100) plane. Atomic force microscopy measurements showed an average ZnO grain size within the range of 75.9 nm-99.9 nm with a corresponding root mean square (RMS) surface roughness between 0.51 nm-2.16 nm. Dark and under illumination current-voltage (I-V) characteristics of the n-ZnO/p-Si heterojunction photodetectors showed an improving rectification ratio and a decreasing saturation current at longer annealing time with an ideality factor of 3 obtained at 60 min annealing time. Capacitance-voltage (C-V) characteristics of heterojunctions were investigated in order to estimate the built-in-voltage and junction type. The photodetectors, fabricated at optimum annealing time, exhibited good linearity characteristics. Maximum sensitivity was obtained when ZnO/Si heterojunctions were annealed at 60 min. Two peaks of response, located at 650 nm and 850 nm, were observed with sensitivities of 0.12-0.19 A/W and 0.18-0.39 A/W, respectively. Detectivity of the photodetectors as function of annealing time was estimated.

Synthesis and characterization of CdS/BiPO{sub 4} heterojunction photocatalyst

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

Chen, Daimei, E-mail: chendaimei@cugb.edu.cn; Kuang, Zheng; Zhu, Qian

2015-06-15

Highlights: • A CdS/BiPO{sub 4} heterojunction was prepared by the solvothermal method. • The CdS/BiPO{sub 4} composite has the higher photocatalytic activity than the individual ones. • The optimal mass ratio of CdS to BiPO{sub 4} was 0.5. • The heterojunction structure of CdS/BiPO{sub 4} induces an effective electron–hole separation. - Abstract: A series of CdS/BiPO{sub 4} heterojunction photocatalysts with the visible-light response were synthesized by the solvothermal method. The resulting products were characterized by X-ray diffraction, Transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflection spectroscopy. CdS nanoparticles with the size at range of 5–7 nm were immobilizedmore » on the surface of BiPO{sub 4} nanorods. The CdS/BiPO{sub 4} composite exhibited much higher photodegradation rate of methylene blue under visible light irradation compared to the pure CdS and BiPO{sub 4}. The optimal mass ratio of CdS to BiPO{sub 4} was 0.5, the photodegradation rate of which is 2.1 times higher than that of CdS. The enhancement of photocatalytic activity is attributed to the heterojunction structure of CdS/BiPO{sub 4} composite which induced the effective electron–hole separation between CdS and BiPO{sub 4}.« less

Holey Reduced Graphene Oxide Coupled with an Mo2 N-Mo2 C Heterojunction for Efficient Hydrogen Evolution.

PubMed

Yan, Haijing; Xie, Ying; Jiao, Yanqing; Wu, Aiping; Tian, Chungui; Zhang, Xiaomeng; Wang, Lei; Fu, Honggang

2018-01-01

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small-sized Mo 2 N-Mo 2 C heterojunction (Mo 2 N-Mo 2 C/HGr). The method includes the first immobilization of H 3 PMo 12 O 40 (PMo 12 ) clusters on graphite oxide (GO), followed by calcination in air and NH 3 to form Mo 2 N-Mo 2 C/HGr. PMo 12 not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH 3 simultaneously react with the Mo species to form an Mo 2 N-Mo 2 C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H 2 SO 4 ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm -2 ). The good activity of Mo 2 N-Mo 2 C/HGr is ascribed to its small size, the heterojunction of Mo 2 N-Mo 2 C, and the good charge/mass-transfer ability of HGr, as supported by a series of experiments and theoretical calculations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Interfacial electronic structure of a hybrid organic-inorganic optical upconverter device: The role of interface states

NASA Astrophysics Data System (ADS)

Tsai, K. Y. F.; Helander, M. G.; Lu, Z. H.

2009-04-01

Organic-inorganic hybrid heterojunctions are critical for the integration of organic electronics with traditional Si and III-V semiconductor microelectronics. The amorphous nature of organic semiconductors eliminates the stringent lattice-matching requirements in semiconductor monolithic growth. However, as of yet it is unclear what driving forces dictate the energy-level alignment at hybrid organic-inorganic heterojunctions. Using photoelectron spectroscopy we investigate the energy-level alignment at the hybrid organic-inorganic heterojunction formed between S-passivated InP(100) and several commonly used hole injection/transport molecules, namely, copper phthalocyanine (CuPc), N ,N'-diphenyl-N ,N'-bis-(1-naphthyl)-1-1'-biphenyl-4,4'-diamine (α-NPD), and fullerene (C60). The energy-level alignment at the hybrid organic-inorganic heterojunction is found to be consistent with traditional interface dipole theory, originally developed to describe Schottky contacts. Contrary to conventional wisdom, hole injection from S-passivated InP(100) into an organic semiconductor is found to originate from interface states at or near the Fermi level, rather than from the valance band maximum of the semiconductor. As a result the barrier height for hole injection is defined by the offset between the surface Fermi level of the S-passivated InP(100) and the highest occupied molecular orbital of the organic. This finding sheds new light on the unusual trend in device performance reported in literature for such hybrid organic-inorganic heterojunction devices.

Ultrafast Plasmon-Enhanced Hot Electron Generation at Ag Nanocluster/Graphite Heterojunctions.

PubMed

Tan, Shijing; Liu, Liming; Dai, Yanan; Ren, Jindong; Zhao, Jin; Petek, Hrvoje

2017-05-03

Hot electron processes at metallic heterojunctions are central to optical-to-chemical or electrical energy transduction. Ultrafast nonlinear photoexcitation of graphite (Gr) has been shown to create hot thermalized electrons at temperatures corresponding to the solar photosphere in less than 25 fs. Plasmonic resonances in metallic nanoparticles are also known to efficiently generate hot electrons. Here we deposit Ag nanoclusters (NC) on Gr to study the ultrafast hot electron generation and dynamics in their plasmonic heterojunctions by means of time-resolved two-photon photoemission (2PP) spectroscopy. By tuning the wavelength of p-polarized femtosecond excitation pulses, we find an enhancement of 2PP yields by 2 orders of magnitude, which we attribute to excitation of a surface-normal Mie plasmon mode of Ag/Gr heterojunctions at 3.6 eV. The 2PP spectra include contributions from (i) coherent two-photon absorption of an occupied interface state (IFS) 0.2 eV below the Fermi level, which electronic structure calculations assign to chemisorption-induced charge transfer, and (ii) hot electrons in the π*-band of Gr, which are excited through the coherent screening response of the substrate. Ultrafast pump-probe measurements show that the IFS photoemission occurs via virtual intermediate states, whereas the characteristic lifetimes attribute the hot electrons to population of the π*-band of Gr via the plasmon dephasing. Our study directly probes the mechanisms for enhanced hot electron generation and decay in a model plasmonic heterojunction.

Enhanced photocatalytic and photoelectrochemical activities of reduced TiO 2-x /BiOCl heterojunctions

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

Fu, Rongrong; Zeng, Xiaoqiao; Ma, Lu

2016-04-01

A key issue to design highly efficient photoelectrodes for hydrogen production is how to prohibit the rapid carrier recombination. In order to use the visible light and reduce the recombination of electrons and holes, reduced TiO 2-x/BiOCl heterojunctions are successfully synthesized and the photoelectrodes are assembled in this work. The effects of various Bi/Ti molar ratios on the structural, morphological, optical, photoelectrochemical and photocatalytic activities of the resultant samples are investigated systematically. The TiO 2-x nanoparticles contain Ti 3+, Ti 2+, and oxygen vacancies (Ov), while the BiOCl nanosheets exposed {001} facet. Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS) results indicatemore » that the existence of Ti 3+, Ti 2+ and Ov expand the light-response range. Linear scan voltammetry and electrochemical impedance spectroscopy results indicate that more efficient electron transportation is presented in the heterojunctions with the appropriate Bi/Ti molar ratio. Consequently, the reduced TiO 2-x/BiOCl heterojunction with the most appropriate Bi/Ti molar ratio exhibits a high photocurrent density of 0.755 mA cm -2 with photoconversion efficiency up to 0.634%, 10.5 and 22.6 times larger than that of pure TiO 2 and BiOCl. Furthermore, this heterojunction exhibit 48.38 and 12.54 times enhancement for the visible-light decomposition of rhodamine B compared with pure TiO 2 and BiOCl.« less

Strategies for increasing the efficiency of heterojunction organic solar cells: material selection and device architecture.

PubMed

Heremans, Paul; Cheyns, David; Rand, Barry P

2009-11-17

Thin-film blends or bilayers of donor- and acceptor-type organic semiconductors form the core of heterojunction organic photovoltaic cells. Researchers measure the quality of photovoltaic cells based on their power conversion efficiency, the ratio of the electrical power that can be generated versus the power of incident solar radiation. The efficiency of organic solar cells has increased steadily in the last decade, currently reaching up to 6%. Understanding and combating the various loss mechanisms that occur in processes from optical excitation to charge collection should lead to efficiencies on the order of 10% in the near future. In organic heterojunction solar cells, the generation of photocurrent is a cascade of four steps: generation of excitons (electrically neutral bound electron-hole pairs) by photon absorption, diffusion of excitons to the heterojunction, dissociation of the excitons into free charge carriers, and transport of these carriers to the contacts. In this Account, we review our recent contributions to the understanding of the mechanisms that govern these steps. Starting from archetype donor-acceptor systems of planar small-molecule heterojunctions and solution-processed bulk heterojunctions, we outline our search for alternative materials and device architectures. We show that non-planar phthalocynanines have appealing absorption characteristics but also have reduced charge carrier transport. As a result, the donor layer needs to be ultrathin, and all layers of the device have to be tuned to account for optical interference effects. Using these optimization techniques, we illustrate cells with 3.1% efficiency for the non-planar chloroboron subphthalocyanine donor. Molecules offering a better compromise between absorption and carrier mobility should allow for further improvements. We also propose a method for increasing the exciton diffusion length by converting singlet excitons into long-lived triplets. By doping a polymer with a phosphorescent molecule, we demonstrate an increase in the exciton diffusion length of a polymer from 4 to 9 nm. If researchers can identify suitable phosphorescent dopants, this method could be employed with other materials. The carrier transport from the junction to the contacts is markedly different for a bulk heterojunction cell than for planar junction cells. Unlike for bulk heterojunction cells, the open-circuit voltage of planar-junction cells is independent of the contact work functions, as a consequence of the balance of drift and diffusion currents in these systems. This understanding helps to guide the development of new materials (particularly donor materials) that can further boost the efficiency of single-junction cells to 10%. With multijunction architectures, we expect that efficiencies of 12-16% could be attained, at which point organic photovoltaic cells could become an important renewable energy source.

Internal stress and degradation in short-wavelength AlGaAs double-heterojunction devices

NASA Technical Reports Server (NTRS)

Ladany, I.; Furman, T. R.; Marinelli, D. P.

1979-01-01

Aging tests of incoherently operated zinc-doped double-heterojunction (DH) lasers designed for short-wavelength (0.71-0.72 micron) operation show that the introduction of buffer layers between the substrate and the DH structure leads to a drastic reduction in gradual degradation. This is attributed to a decrease in lattice mismatch stress.

Temperature dependences of the time of electron-electron interactions in two-dimensional heterojunction

NASA Astrophysics Data System (ADS)

Bukhenskyy, K. V.; Dubois, A. B.; Kucheryavyy, S. I.; Mashnina, S. N.; Safoshkin, A. S.; Baukov, A. A.; Shchigorev, E. Yu

2017-12-01

The article discusses the joint solution of the Schrödinger and Poisson equations for two-dimensional semiconductor heterojunction. The application of a triangular potential of well approximation for the calculation of the electron-electron interaction is offered in the paper. The influence of the parameters of the selected approximation was analyzed.

The porous TiO2 nanotubes/Ag3PO4 heterojunction for enhancing sunlight photocatalytic activity

NASA Astrophysics Data System (ADS)

Chi, Chunyan; Pan, Jiaqi; You, Mingzhu; Dong, Zongjun; Zhao, Weijie; Song, Changsheng; Zheng, Yingying; Li, Chaorong

2018-03-01

The porous TiO2 nanotubes/Ag3PO4 heterojunction are synthesized via simple electrospining and chemical co-deposition method. The results of SEM, XRD, TEM and XPS imply that the Ag3PO4 nanoparticles have been introduced on to the surface of TiO2 nanotubes successfully. Compared with the unmodified samples, the photocatalytic activity of the as-prepared porous TiO2 nanotubes/Ag3PO4 heterojunction exhibit a remarkable enhancement by the degradation of methylene blue (MB) under the sunlight. Further, the Z-Scheme structure of the samples and the porous-tubular structure of the TiO2 are considered as the main reasons for the enhancement.

Epitaxial growth and electronic properties of well ordered phthalocyanine heterojunctions MnPc/F{sub 16}CoPc

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

Lindner, Susi; Mahns, Benjamin; Treske, Uwe

2014-09-07

We have prepared phthalocyanine heterojunctions out of MnPc and F{sub 16}CoPc, which were studied by means of X-ray absorption spectroscopy. This heterojunction is characterized by a charge transfer at the interface, resulting in charged MnPc{sup δ} {sup +} and F{sub 16}CoPc{sup δ} {sup −} species. Our data reveal that the molecules are well ordered and oriented parallel to the substrate surface. Furthermore, we demonstrate the filling of the Co 3d{sub z{sup 2}} orbital due to the charge transfer, which supports the explanation of the density functional theory, that the charge transfer is local and affects the metal centers only.

III-N light emitting diodes fabricated using RF nitrogen gas source MBE

NASA Astrophysics Data System (ADS)

Van Hove, J. M.; Carpenter, G.; Nelson, E.; Wowchak, A.; Chow, P. P.

1996-07-01

Homo- and heterojunction III-N light emitting diodes using RF atomic nitrogen plasma molecular beam epitaxy have been grown. GaN films deposited on sapphire using this growth technique exhibited an extremely sharp X-ray diffraction with a full width half maximum of 112 arc sec. p-type doping of the nitride films was done with elemental Mg and resulted in as-grown p-type material with resistivities as low as 2 Ω · cm. Both homo- and heterojunction LEDs showed clear rectification. Emission from the GaN homojunction deposited on n-type SiC was peaked at 410 nm while the AlGaNGaN(Zn)AlGaN double heterojunction LEDs emission was centered about 520 nm.

Structural, electrical and photovoltaic properties of CoS/Si heterojunction prepared by spray pyrolysis

NASA Astrophysics Data System (ADS)

El Radaf, I. M.; Nasr, Mahmoud; Mansour, A. M.

2018-01-01

Au/p-CoS/n-Si/Al heterojunction device was fabricated by spray pyrolysis technique. The structural and morphological features were examined by x-ray diffraction, scanning electron microscope and energy dispersive x-ray analysis. The capacitance-voltage characteristics of the prepared heterojunction were analyzed at room temperature in the dark. The current-voltage characteristics were examined under dark and different incident light intensities 20-100 mW cm-2. The rectification ratio, series resistance, shunt resistance, diode ideality factor and the effective barrier height were determined at dark and illumination conditions. The photovoltaic parameters such as short circuit current density, open circuit voltage, fill factor and power conversion efficiency were calculated at different incident light intensities.

Construction of High Activity Titanium Dioxide Crystal Surface Heterostructures and Characterization of Its Basic Properties

NASA Astrophysics Data System (ADS)

Wang, Chunxiao; Li, DanQi; Shen, Tingting; Lu, Cheng; Sun, Jing; Wang, Xikui

2018-01-01

Heterogeneous photocatalytic materials, which combine the advantages of photocatalytic materials and heterojunction, have been developed rapidly in the field of environmental pollution control. In this paper, TiO2 surface heterojunction catalysts with different catalytic activity were prepared by controlling the amount of HF, and their XRD characterization was also carried out. In addition, the optimum amount of HF was determined by photocatalytic degradation of simulated dye wastewater by methylene blue solution. And the optimal amount of catalyst and the optimal pH reaction conditions for degradation experiments were used to screen the highly reactive titania surface heterojunction system and its optimum application conditions. It provides the possibility of application in the degradation of industrial wastewater and environmental treatment.

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

NASA Astrophysics Data System (ADS)

Morfa, Anthony J.; Rowlen, Kathy L.; Reilly, Thomas H.; Romero, Manuel J.; van de Lagemaat, Jao

2008-01-01

Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle layers were fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase in optical electrical field inside the photoactive layer, the inclusion of such particle films lead to increased optical absorption and consequently increased photoconversion at solar-conversion relevant wavelengths. The resulting solar energy conversion efficiency for a bulk heterojunction photovoltaic device of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester was found to increase from 1.3%±0.2% to 2.2%±0.1% for devices employing thin plasmon-active layers. Based on six measurements, the improvement factor of 1.7 was demonstrated to be statistically significant.

Silicon heterojunction solar cell with passivated hole selective MoOx contact

NASA Astrophysics Data System (ADS)

Battaglia, Corsin; de Nicolás, Silvia Martín; De Wolf, Stefaan; Yin, Xingtian; Zheng, Maxwell; Ballif, Christophe; Javey, Ali

2014-03-01

We explore substoichiometric molybdenum trioxide (MoOx, x < 3) as a dopant-free, hole-selective contact for silicon solar cells. Using an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the silicon absorber, we demonstrate a high open-circuit voltage of 711 mV and power conversion efficiency of 18.8%. Due to the wide band gap of MoOx, we observe a substantial gain in photocurrent of 1.9 mA/cm2 in the ultraviolet and visible part of the solar spectrum, when compared to a p-type amorphous silicon emitter of a traditional silicon heterojunction cell. Our results emphasize the strong potential for oxides as carrier selective heterojunction partners to inorganic semiconductors.

In situ one-pot fabrication of g-C3N4 nanosheets/NiS cocatalyst heterojunction with intimate interfaces for efficient visible light photocatalytic H2 generation

NASA Astrophysics Data System (ADS)

He, Kelin; Xie, Jun; Li, Mingli; Li, Xin

2018-02-01

Constructing high-quality earth-abundant semionconductor/cocatalyst heterojunction remains a grand challenge in the promising fields of photocatalytic solar fuel H2 production. Herein, an intimate g-C3N4 nanosheet/NiS cocatalyst heterojunction is fabricated by in situ one-step calcination of urea, thiourea and nickel acetate. Interestingly, thiourea could act as both the precursor of g-C3N4 and the sulfur source of NiS. The H2-evolution activity of as-obtained photocatalysts was tested in a triethanolamine (TEOA) scavenger solution under visible light irradiation. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) mapping analysis clearly demonstrated that the NiS catalyst nanoparticles could be in situ fabricated and homogeneously distributed on the surface of g-C3N4 nanosheets without an obvious aggregation. The maximum H2-production rate of 29.68 μmol h-1 could be achieved, which is nearly comparable to that of 0.5 wt% Pt loaded sample. It is believed that the intimate heterojunction interfaces between NiS nanoparticles and g-C3N4 nanosheets could be in situ constructed by high temperature calcination, which achieved the improved charge separation, the enhanced oxidation ability of TEOA and the accelerated the sluggish H2-evolution kinetics, thus resulting in the remarkably enhanced hydrogen evolution. Therefore, our study provides insights into constructing high-quality robust g-C3N4-based heterojunction material for photocatalytic applications by using a simple one-step in-situ calcination technique.

Size effect on the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2 nanoribbon

NASA Astrophysics Data System (ADS)

Wen, Yan-Ni; Xia, Ming-Gang; Zhang, Sheng-Li

2016-05-01

By using the VASP, we studied the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2-nanoribbons (WS2-MoS2-NRs). Our results show that the NRs' edge chirality and width affect significantly its magnetic and electronic properties. The monolayer lateral hetero-junction ZZ-WS2-MoS2-NRs(ZZ: zigzag) exhibitmetallic behavior and have considerable magnetic moment. Their magnetic moments decrease in the order of Nz = 2, 6 and 4 (the width of NRs). While, the magnetic moment decreases with the increased rz (the number of the Mo-S chains, rz ≠ 0 and rz ≠ Nz) at the same width Nz. The NA-AC-WS2-NR (AC: armchair) and NA-AC-WS2-MoS2-NR-1 (the number of the Mo-S chain is 1) show metallic behavior when NA = 3 (the width of NRs). The other monolayer lateral hetero-junction AC-WS2-MoS2-NRs remain the nonmagnetic and semiconductingbehavior as bulk. But they are indirect band-gap except for the NA = 3, rA = 2 (the number of the Mo-S chains) and NA = 7, rA = 0 when NA < 9. However they are direct band-gap when NA ≥ 9. Their lowest and highest band gaps are 0.150 eV and 0.581 eV, respectively. These unique magnetic and electronic properties will provide guidanceon the WS2-MoS2 hetero-junction application in nanodevice.

The synergistic effect of phase heterojunction and surface heterojunction to improve photocatalytic activity of VO •-TiO2: the co-catalytic effect of H3PW12O40

NASA Astrophysics Data System (ADS)

Li, Haiyan; Cai, Shengnan; Yang, Pengfei; Bai, Yan; Dang, Dongbin

2018-06-01

With nanotube titanic acid (abbreviated as NTA) and the 12-tungstophosphoric acid (H3PW12O40• xH2O, denoted as HPW) as start materials, respectively, according to a simple hydrothermal process in acid medium, we successfully prepared HPW modified VO •-TiO2 composite photocatalysts. During heat treatment companied by the transformation of NTA to TiO2, a kind of single-electron-trapped oxygen vacancy (VO •) could be formed contributing to the visible light absorption of catalysts. The morphology, phase and chemical structure, optical and electronic properties, and so on of the produced catalysts with various HPW loadings are characterized. The size range of synthesized photocatalyst nanoparticles are about 10 50 nm. Taking aqueous rhodamine B (RhB) dye as model pollutant, we carried out photocatalytic activity test of the achieved catalysts, revealing that the hybrid photocatalysts display significantly enhanced visible light-driven ( λ ≥ 420 nm) photocatalytic activity for degradation of RhB. Among various catalysts, HPWN-0.1-120 composite with nominal loading of 0.1 g HPW and heat treatment temperature of 120 °C possesses the highest photocatalytic performance in visible light, which is closely related to the co-effect of phase heterojunction of rutile/anatase, surface heterojunction of anatase/HPW, and oxygen vacancy (VO •). The two types of heterojunction promote greatly the separation efficiency of photoelectrons and photoholes and oxygen vacancy lures response of catalysts to visible light.

All-nanoparticle self-assembly ZnO/TiO₂ heterojunction thin films with remarkably enhanced photoelectrochemical activity.

PubMed

Yuan, Sujun; Mu, Jiuke; Mao, Ruiyi; Li, Yaogang; Zhang, Qinghong; Wang, Hongzhi

2014-04-23

The multilaminated ZnO/TiO2 heterojunction films were successfully deposited on conductive substrates including fluorine-doped tin oxide (FTO) glass and flexible indium tin oxide coated poly(ethylene terephthalate) via the layer-by-layer (LBL) self assembly method from the oxide colloids without using any polyelectrolytes. The positively charged ZnO nanoparticles and the negatively charged TiO2 nanoparticles were directly used as the components in the consecutive deposition process to prepare the heterojunction thin films by varying the thicknesses. Moreover, the crystal growth of both oxides could be efficiently inhibited by the good connection between ZnO and TiO2 nanoparticles even after calcination at 500 °C, especially for ZnO which was able to keep the crystallite size under 25 nm. The as-prepared films were used as the working electrodes in the three-electrode photoelectrochemical cells. Because the well-contacted nanoscale heterojunctions were formed during the LBL self-assembling process, the ZnO/TiO2 all-nanoparticle films deposited on both substrates showed remarkably enhanced photoelectrochemical properties compared to that of the well-established TiO2 LBL thin films with similar thicknesses. The photocurrent response collected from the ZnO/TiO2 electrode on the FTO glass substrate was about five times higher than that collected from the TiO2 electrode. Owing to the absence of the insulating layer of dried polyelectrolytes, the ZnO/TiO2 all-nanoparticle heterojunction films were expected to be used in the photoelectrochemical device before calcination.

Construction of 1D SnO2-coated ZnO nanowire heterojunction for their improved n-butylamine sensing performances

NASA Astrophysics Data System (ADS)

Wang, Liwei; Li, Jintao; Wang, Yinghui; Yu, Kefu; Tang, Xingying; Zhang, Yuanyuan; Wang, Shaopeng; Wei, Chaoshuai

2016-10-01

One-dimensional (1D) SnO2-coated ZnO nanowire (SnO2/ZnO NW) N-N heterojunctions were successfully constructed by an effective solvothermal treatment followed with calcination at 400 °C. The obtained samples were characterized by means of XRD, SEM, TEM, Scanning TEM coupled with EDS and XPS analysis, which confirmed that the outer layers of N-type SnO2 nanoparticles (avg. 4 nm) were uniformly distributed onto our pre-synthesized n-type ZnO nanowire supports (diameter 80~100 nm, length 12~16 μm). Comparisons of the gas sensing performances among pure SnO2, pure ZnO NW and the as-fabricated SnO2/ZnO NW heterojunctions revealed that after modification, SnO2/ZnO NW based sensor exhibited remarkably improved response, fast response and recovery speeds, good selectivity and excellent reproducibility to n-butylamine gas, indicating it can be used as promising candidates for high-performance organic amine sensors. The enhanced gas-sensing behavior should be attributed to the unique 1D wire-like morphology of ZnO support, the small size effect of SnO2 nanoparticles, and the semiconductor depletion layer model induced by the strong interfacial interaction between SnO2 and ZnO of the heterojunctions. The as-prepared SnO2/ZnO NW heterojunctions may also supply other novel applications in the fields like photocatalysis, lithium-ion batteries, waste water purification, and so on.

DFT investigation on two-dimensional GeS/WS2 van der Waals heterostructure for direct Z-scheme photocatalytic overall water splitting

NASA Astrophysics Data System (ADS)

Ju, Lin; Dai, Ying; Wei, Wei; Li, Mengmeng; Huang, Baibiao

2018-03-01

Recently, extensive attention has been paid to the direct Z-scheme systems for photocatalytic water splitting where carriers migrate directly between the two semiconductors without a redox mediator. In the present work, the electronic structure and related properties of two-dimensional (2D) van de Waals (vdW) GeS/WX2 (X = O, S, Se, Te) heterojunction are systematically investigated by first-principles calculations. Our results demonstrate that, the GeS/WS2 heterojunction could form a direct Z-scheme system for photocatalytic water splitting, whereas the GeS/WX2 (X = O, Se, Te) can't, because of their respective unsuitable electronic structures. For the GeS/WS2 heterojunction, the GeS and WS2 monolayers serve as photocatalysts for the hydrogen evolution reactionand oxygen evolution reaction, respectively. The internal electric field induced by the electron transfer at the interface can promote the separation of photo-generated charge carriers and formation of the interface Z-scheme electron transfer. Remarkably, the designed GeS/WS2 heterojunction not only enhances the hydrogen production activity of GeS and the oxygen production ability of WS2 but also improves the light absorption of the two monolayers by reducing the band gaps. Moreover, it is found that narrowing the interlayer distance could enhance the internal electric field, improving the photocatalytic ability of the vdW heterojunction. This work provides fundamental insights for further design and preparation of emergent metal dichalcogenide catalysts, beneficial for the development in clean energy.

Band Gap Engineering of Titania Film through Cobalt Regulation for Oxidative Damage of Bacterial Respiration and Viability.

PubMed

Li, Jinhua; Wang, Jiaxing; Wang, Donghui; Guo, Geyong; Yeung, Kelvin W K; Zhang, Xianlong; Liu, Xuanyong

2017-08-23

Biomaterial-related bacterial infections cause patient suffering, mortality, and extended periods of hospitalization and impose a substantial burden on medical systems. In this context, understanding the interactions between nanomaterials and bacteria is clinically significant. Herein, TiO 2 -based heterojunctions, including Co-TiO 2 , CoO-TiO 2 , and Co 3 O 4 -TiO 2 , were first designed by optimizing magnetron sputtering to establish a platform to explore the interactions between nanomaterials and bacteria. We found that the energy band bending and band gap narrowing were effectively promoted at the contact interface of the heterojunctions, which have the ability to induce abiotic reactive oxygen species formation. Using methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, in vitro studies showed that the heterojunctions of Co-TiO 2 , CoO-TiO 2 , and especially Co 3 O 4 -TiO 2 can effectively downregulate the expression levels of bacterial respiratory genes and cause oxidative damage to bacterial membrane respiration and viability. As a result, the surfaces of the heterojunctions possess a favorable antiadherent bacterial activity. Moreover, using an osteomyelitis model, the preclinical study on rats further confirmed the favorable anti-infection effect of the elaborately designed heterojunctions (especially Co 3 O 4 -TiO 2 ). We hope this study can provide new insights into the surface antibacterial design of biomaterials using energy band engineering for both basic research and clinical needs. Meanwhile, this attempt may also contribute to expanding the biomedical applications of cobalt-based nanoparticles for the treatment of antibiotic-resistant infections.

Vertical MoSe2-MoO x p-n heterojunction and its application in optoelectronics.

PubMed

Chen, Xiaoshuang; Liu, Guangbo; Hu, Yunxia; Cao, Wenwu; Hu, PingAn; Hu, Wenping

2018-01-26

The hybrid n-type 2D transition-metal dichalcogenide (TMD)/p-type oxide van der Waals (vdW) heterojunction nanosheets consist of 2D layered MoSe 2 (the n-type 2D material) and MoO x (the p-type oxide) which are grown on SiO 2 /Si substrates for the first time via chemical vapor deposition technique, displaying the regular hexagon structures with the average length dimension of sides of ∼8 μm. Vertical MoSe 2 -MoO x p-n heterojunctions demonstrate obviously current-rectifying characteristic, and it can be tuned via gate voltage. What is more, the photodetector based on vertical MoSe 2 -MoO x heterojunctions displays optimal photoresponse behavior, generating the responsivity, detectivity, and external quantum efficiency to 3.4 A W -1 , 0.85 × 10 8 Jones, and 1665.6%, respectively, at V ds  = 5 V with the light wavelength of 254 nm under 0.29 mW cm -2 . These results furnish a building block on investigating the flexible and transparent properties of vdW and further optimizing the structure of the devices for better optoelectronic and electronic performance.

Silicon homo-heterojunction solar cells: A promising candidate to realize high performance more stably

NASA Astrophysics Data System (ADS)

Tan, Miao; Zhong, Sihua; Wang, Wenjie; Shen, Wenzhong

2017-08-01

We have investigated the influences of diverse physical parameters on the performances of a silicon homo-heterojunction (H-H) solar cell, which encompasses both homojunction and heterojunction, together with their underlying mechanisms by the aid of AFORS-HET simulation. It is found that the performances of H-H solar cell are less sensitive to (i) the work function of the transparent conductive oxide layer, (ii) the interfacial density of states at the front hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) interface, (iii) the peak dangling bond defect densities within the p-type a-Si:H (p-a-Si:H) layer, and (iv) the doping concentration of the p-a-Si:H layer, when compared to that of the conventional heterojunction with intrinsic thin layer (HIT) counterparts. These advantages are due to the fact that the interfacial recombination and the recombination within the a-Si:H region are less affected by all the above parameters, which fundamentally benefit from the field-effect passivation of the homojunction. Therefore, the design of H-H structure can provide an opportunity to produce high-efficiency solar cells more stably.

Preparation and visible light photocatalytic activity of Bi2O3/Bi2WO6 heterojunction photocatalysts

NASA Astrophysics Data System (ADS)

Yan, C. Y.; Yi, W. T.; Xiong, J.; Ma, J.

2018-03-01

The Bi2O3 nanorods, flower-like Bi2WO6 and Bi2O3/Bi2WO6 heterojunction composites with the molar ratio of nBi:nW from 2:1, 2.5:1, to 3:1 have been synthesized via one-step hydrothermal method and two-step hydrothermal method, respectively. The products are characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV-vis DRS), and scanning electron microscopy (SEM). Photocatalytic experiments indicate that such Bi2O3/Bi2WO6 composite possesses higher photocatalytic activity for RhB degradation under visible-light irradiation in comparison with pure Bi2O3 and Bi2WO6. The enhancement of the photocatalytic activity of the Bi2O3/Bi2WO6 heterojunction catalysts can be ascribed to the reduced recombination of the photoexcited electrons and holes during the photocatalytic reaction. The effect of the molar ratio of nBi:nW on the catalytic performance of the heterojunction catalysts was also investigated. And the optimal molar ratio of nBi:nW is 2.5:1 which was synthesized by one-step hydrothermal method.

A solar light driven dual photoelectrode photocatalytic fuel cell (PFC) for simultaneous wastewater treatment and electricity generation.

PubMed

Bai, Jing; Wang, Rui; Li, Yunpo; Tang, Yuanyuan; Zeng, Qingyi; Xia, Ligang; Li, Xuejin; Li, Jinhua; Li, Caolong; Zhou, Baoxue

2016-07-05

In this paper, a novel dual heterojunction Photocatalytic Fuel Cell (PFC) system based on BiVO4/TiO2 nanotubes/FTO photoanode and ZnO/CuO nanowires/FTO photocathode has been designed. Compared with the electrodes in PFCs reported in earlier literatures, the proposed heterojunction not only enhances the visible light absorption but also offers a higher photoconversion efficiency. In addition, the nanostructured heterojunction owns a large surface area that ensures a large amount of active sites for organics degradation. The performance of the PFC base on the dual photoelectrodes was also studied herein. The results indicated that the PFC in ths paper exhibits a superior performance and its JV(max) reached 0.116 mw cm(-2), which is higher than that in most of reported PFCs with a Pt-free photocathode. When hazardous organic compounds such as methyl orange, Congo red and methylene blue were decomposed, the degradation rates obtained is to be 76%, 83%, and 90% respectively after 80 mins reaction. The proposed heterojunction photoelectrodes provided great potential for cost-effective and high-efficiency organic pollutants degradation and electricity generation in a PFC system. Copyright © 2016 Elsevier B.V. All rights reserved.

Growth and electrical characterization of two-dimensional layered MoS{sub 2}/SiC heterojunctions

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

Lee, Edwin W.; Nath, Digbijoy N.; Lee, Choong Hee

2014-11-17

The growth and electrical characterization of the heterojunction formed between two-dimensional (2D) layered p-molybdenum disulfide (MoS{sub 2}) and nitrogen-doped 4H silicon carbide (SiC) are reported. The integration of 2D semiconductors with the conventional three-dimensional (3D) substrates could enable semiconductor heterostructures with unprecedented properties. In this work, direct growth of p-type MoS{sub 2} films on SiC was demonstrated using chemical vapor deposition, and the MoS{sub 2} films were found to be high quality based on x-ray diffraction and Raman spectra. The resulting heterojunction was found to display rectification and current-voltage characteristics consistent with a diode for which forward conduction in themore » low-bias region is dominated by multi-step recombination tunneling. Capacitance-voltage measurements were used to determine the built-in voltage for the p-MoS{sub 2}/n-SiC heterojunction diode, and we propose an energy band line up for the heterostructure based on these observations. The demonstration of heterogeneous material integration between MoS{sub 2} and SiC enables a promising new class of 2D/3D heterostructures.« less

MoS2-InGaZnO Heterojunction Phototransistors with Broad Spectral Responsivity.

PubMed

Yang, Jaehyun; Kwak, Hyena; Lee, Youngbin; Kang, Yu-Seon; Cho, Mann-Ho; Cho, Jeong Ho; Kim, Yong-Hoon; Jeong, Seong-Jun; Park, Seongjun; Lee, Hoo-Jeong; Kim, Hyoungsub

2016-04-06

We introduce an amorphous indium-gallium-zinc-oxide (a-IGZO) heterostructure phototransistor consisting of solution-based synthetic molybdenum disulfide (few-layered MoS2, with a band gap of ∼1.7 eV) and sputter-deposited a-IGZO (with a band gap of ∼3.0 eV) films as a novel sensing element with a broad spectral responsivity. The MoS2 and a-IGZO films serve as a visible light-absorbing layer and a high mobility channel layer, respectively. Spectroscopic measurements reveal that appropriate band alignment at the heterojunction provides effective transfer of the visible light-induced electrons generated in the few-layered MoS2 film to the underlying a-IGZO channel layer with a high carrier mobility. The photoresponse characteristics of the a-IGZO transistor are extended to cover most of the visible range by forming a heterojunction phototransistor that harnesses a visible light responding MoS2 film with a small band gap prepared through a large-area synthetic route. The MoS2-IGZO heterojunction phototransistors exhibit a photoresponsivity of approximately 1.7 A/W at a wavelength of 520 nm (an optical power of 1 μW) with excellent time-dependent photoresponse dynamics.

Vertical MoSe2-MoO x p-n heterojunction and its application in optoelectronics

NASA Astrophysics Data System (ADS)

Chen, Xiaoshuang; Liu, Guangbo; Hu, Yunxia; Cao, Wenwu; Hu, PingAn; Hu, Wenping

2018-01-01

The hybrid n-type 2D transition-metal dichalcogenide (TMD)/p-type oxide van der Waals (vdW) heterojunction nanosheets consist of 2D layered MoSe2 (the n-type 2D material) and MoO x (the p-type oxide) which are grown on SiO2/Si substrates for the first time via chemical vapor deposition technique, displaying the regular hexagon structures with the average length dimension of sides of ˜8 μm. Vertical MoSe2-MoO x p-n heterojunctions demonstrate obviously current-rectifying characteristic, and it can be tuned via gate voltage. What is more, the photodetector based on vertical MoSe2-MoO x heterojunctions displays optimal photoresponse behavior, generating the responsivity, detectivity, and external quantum efficiency to 3.4 A W-1, 0.85 × 108 Jones, and 1665.6%, respectively, at V ds = 5 V with the light wavelength of 254 nm under 0.29 mW cm-2. These results furnish a building block on investigating the flexible and transparent properties of vdW and further optimizing the structure of the devices for better optoelectronic and electronic performance.

Photogenerated Hole-Induced Chemical Redox Cycling on Bi2S3/Bi2Sn2O7 Heterojunction: Toward General Amplified Split-Type Photoelectrochemical Immunoassay.

PubMed

Cao, Jun-Tao; Wang, Bing; Dong, Yu-Xiang; Wang, Qian; Ren, Shu-Wei; Liu, Yan-Ming; Zhao, Wei-Wei

2018-06-04

This work reports the elegant bridging of enzymatic generation of electron donor with photogenerated hole-induced chemical redox cycling amplification (RCA) for innovative photoelectrochemical (PEC) immunoassay, by the aid of a heterojunction photoelectrode with split-type strategy. Specifically, the system was exemplified by the alkaline phosphatase (ALP) catalytic generation of ascorbic acid (AA), the redox cycling of AA by tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of a novel Bi 2 S 3 /Bi 2 Sn 2 O 7 heterojunction and myoglobin (Myo) as the photoelectrode and the target, respectively. After the immunoreaction and ALP-induced production of AA, the subsequent oxidation of AA by the photogenerated holes of the Bi 2 S 3 /Bi 2 Sn 2 O 7 heterojunction could be cycled via the regeneration of AA by TCEP from the oxidized product of dehydroascorbic acid, leading to easy signal amplification for the sensitive immunoassay of Myo in real samples. It is believed that this work provided a basis for further design and development of general RCA-based PEC immunoassays.

A van der Waals pn heterojunction with organic/inorganic semiconductors

NASA Astrophysics Data System (ADS)

He, Daowei; Pan, Yiming; Nan, Haiyan; Gu, Shuai; Yang, Ziyi; Wu, Bing; Luo, Xiaoguang; Xu, Bingchen; Zhang, Yuhan; Li, Yun; Ni, Zhenhua; Wang, Baigeng; Zhu, Jia; Chai, Yang; Shi, Yi; Wang, Xinran

2015-11-01

van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials have attracted tremendous attention due to their excellent electrical/optical properties and device applications. However, current 2D heterojunctions are largely limited to atomic crystals, and hybrid organic/inorganic structures are rarely explored. Here, we fabricate the hybrid 2D heterostructures with p-type dioctylbenzothienobenzothiophene (C8-BTBT) and n-type MoS2. We find that few-layer C8-BTBT molecular crystals can be grown on monolayer MoS2 by vdW epitaxy, with pristine interface and controllable thickness down to monolayer. The operation of the C8-BTBT/MoS2 vertical heterojunction devices is highly tunable by bias and gate voltages between three different regimes: interfacial recombination, tunneling, and blocking. The pn junction shows diode-like behavior with rectifying ratio up to 105 at the room temperature. Our devices also exhibit photovoltaic responses with a power conversion efficiency of 0.31% and a photoresponsivity of 22 mA/W. With wide material combinations, such hybrid 2D structures will offer possibilities for opto-electronic devices that are not possible from individual constituents.

Fabrication and characterization study of ZnTe/n-Si heterojunction solar cell application

NASA Astrophysics Data System (ADS)

AlMaiyaly, BushraK H.; Hussein, Bushra H.; Shaban, Auday H.

2018-05-01

Different thicknesses (150 250 and 350) ±20 nm has been deposited on the glass substrate and nSi wafer to fabricate ZnTe/n-Si heterojunction solar cell by vacuum evaporation technique Structural optical electrical and photovoltaic properties are investigated for the samples. The structural characteristics studied via X ray analyses indicated that the films are polycrystalline besides having a cubic (zinc blende) structure also average diameter and surface roughness calculated from AFM images The optical measurements of the deposited films were performed in different thicknesses to determine the transmission spectrum as a function of incident wavelength in the range of wavelength (4001000) nm and the optical energy gap calculated from the optical absorption spectra was found to reduse with thickness The IV characteristic at (dark and illuminated) and CV measurement for ZnTe/n-Si heterojunction shows the good rectifying behaviour under dark condition. The measurements of opencircuit voltage (VOC) short-circuit current density (JSC) fill factor (FF) and quantum fficiencies of the ZnTe/n-Si heterojunction are calculated for all samples The results of these studies are presented and discussed in this paper.

3D Band Diagram and Photoexcitation of 2D-3D Semiconductor Heterojunctions.

PubMed

Li, Bo; Shi, Gang; Lei, Sidong; He, Yongmin; Gao, Weilu; Gong, Yongji; Ye, Gonglan; Zhou, Wu; Keyshar, Kunttal; Hao, Ji; Dong, Pei; Ge, Liehui; Lou, Jun; Kono, Junichiro; Vajtai, Robert; Ajayan, Pulickel M

2015-09-09

The emergence of a rich variety of two-dimensional (2D) layered semiconductor materials has enabled the creation of atomically thin heterojunction devices. Junctions between atomically thin 2D layers and 3D bulk semiconductors can lead to junctions that are fundamentally electronically different from the covalently bonded conventional semiconductor junctions. Here we propose a new 3D band diagram for the heterojunction formed between n-type monolayer MoS2 and p-type Si, in which the conduction and valence band-edges of the MoS2 monolayer are drawn for both stacked and in-plane directions. This new band diagram helps visualize the flow of charge carriers inside the device in a 3D manner. Our detailed wavelength-dependent photocurrent measurements fully support the diagrams and unambiguously show that the band alignment is type I for this 2D-3D heterojunction. Photogenerated electron-hole pairs in the atomically thin monolayer are separated and driven by an external bias and control the "on/off" states of the junction photodetector device. Two photoresponse regimes with fast and slow relaxation are also revealed in time-resolved photocurrent measurements, suggesting the important role played by charge trap states.

Electrical and optical characteristics of heterojunction devices composed of silicon nanowires and mercury selenide nanoparticle films on flexible plastics.

PubMed

Yeo, Minje; Yun, Junggwon; Kim, Sangsig

2013-09-01

A pn heterojunction device based on p-type silicon (Si) nanowires (NWs) prepared by top-down method and n-type mercury selenide (HgSe) nanoparticles (NPs) synthesized by the colloidal method have been fabricated on a flexible plastic substrate. The synthesized HgSe NPs were analyzed through the effective mass approximation. The characteristics of the heterojunction device were examined and studied with the energy band diagram. The device showed typical diode characteristics with a turn-on voltage of 1.5 V and exhibited a high rectification ratio of 10(3) under relatively low forward bias. Under illumination of 633-nm-wavelength light, the device presented photocurrent efficiency of 117.5 and 20.1 nA/W under forward bias and reverse bias conditions, respectively. Moreover, the photocurrent characteristics of the device have been determined by bending of the plastic substrate upward and downward with strain of 0.8%. Even though the photocurrent efficiency has fluctuations during the bending cycles, the values are roughly maintained for 10(4) bending cycles. This result indicates that the fabricated heterojunction device has the potential to be applied as fundamental elements of flexible nanoelectronics.

Tunable reverse-biased graphene/silicon heterojunction Schottky diode sensor.

PubMed

Singh, Amol; Uddin, Ahsan; Sudarshan, Tangali; Koley, Goutam

2014-04-24

A new chemical sensor based on reverse-biased graphene/Si heterojunction diode has been developed that exhibits extremely high bias-dependent molecular detection sensitivity and low operating power. The device takes advantage of graphene's atomically thin nature, which enables molecular adsorption on its surface to directly alter graphene/Si interface barrier height, thus affecting the junction current exponentially when operated in reverse bias and resulting in ultrahigh sensitivity. By operating the device in reverse bias, the work function of graphene, and hence the barrier height at the graphene/Si heterointerface, can be controlled by the bias magnitude, leading to a wide tunability of the molecular detection sensitivity. Such sensitivity control is also possible by carefully selecting the graphene/Si heterojunction Schottky barrier height. Compared to a conventional graphene amperometric sensor fabricated on the same chip, the proposed sensor demonstrated 13 times higher sensitivity for NO₂ and 3 times higher for NH₃ in ambient conditions, while consuming ∼500 times less power for same magnitude of applied voltage bias. The sensing mechanism based on heterojunction Schottky barrier height change has been confirmed using capacitance-voltage measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Threshold-voltage modulated phase change heterojunction for application of high density memory

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

Yan, Baihan; Tong, Hao, E-mail: tonghao@hust.edu.cn; Qian, Hang

2015-09-28

Phase change random access memory is one of the most important candidates for the next generation non-volatile memory technology. However, the ability to reduce its memory size is compromised by the fundamental limitations inherent in the CMOS technology. While 0T1R configuration without any additional access transistor shows great advantages in improving the storage density, the leakage current and small operation window limit its application in large-scale arrays. In this work, phase change heterojunction based on GeTe and n-Si is fabricated to address those problems. The relationship between threshold voltage and doping concentration is investigated, and energy band diagrams and X-raymore » photoelectron spectroscopy measurements are provided to explain the results. The threshold voltage is modulated to provide a large operational window based on this relationship. The switching performance of the heterojunction is also tested, showing a good reverse characteristic, which could effectively decrease the leakage current. Furthermore, a reliable read-write-erase function is achieved during the tests. Phase change heterojunction is proposed for high-density memory, showing some notable advantages, such as modulated threshold voltage, large operational window, and low leakage current.« less

Two-step electrodeposition to fabricate the p-n heterojunction of a Cu2O/BiVO4 photoanode for the enhancement of photoelectrochemical water splitting.

PubMed

Bai, Shouli; Liu, Jingchao; Cui, Meng; Luo, Ruixian; He, Jing; Chen, Aifan

2018-05-15

A Cu2O/BiVO4 p-n heterojunction based photoanode in photoelectrochemical (PEC) water splitting is fabricated by a two-step electrodeposition method on an FTO substrate followed by annealing treatment. The structures and properties of the samples are characterized by XRD, FESEM, HRTEM, XPS and UV-visible spectra. The photoelectrochemical activity of the photoanode in water oxidation has been investigated and measured in a three electrode quartz cell system; the obtained maximum photocurrent density of 1.72 mA cm-2 at 1.23 V vs. RHE is 4.5 times higher than that of pristine BiVO4 thin films (∼0.38 mA cm-2). The heterojunction based photoanode also exhibits a tremendous cathodic shift of the onset potential (∼420 mV) and enhancement in the IPCE value by more than 4-fold. The enhanced photoelectrochemical properties of the Cu2O/BiVO4 photoelectrode are attributed to the efficient separation of the photoexcited electron-hole pairs caused by the inner electronic field (IEF) of the p-n heterojunction.

Study of Cu2O\\ZnO nanowires heterojunction designed by combining electrodeposition and atomic layer deposition

NASA Astrophysics Data System (ADS)

Makhlouf, Houssin; Weber, Matthieu; Messaoudi, Olfa; Tingry, Sophie; Moret, Matthieu; Briot, Olivier; Chtoutou, Radhouane; Bechelany, Mikhael

2017-12-01

Cu2O/ZnO nanowires (NWs) heterojunctions were successfully prepared by combining Atomic layer Deposition (ALD) and Electrochemical Deposition (ECD) processes. The crystallinity, morphology and photoconductivity properties of the Cu2O/ZnO nanostructures have been investigated. The properties of the Cu2O absorber layer and the nanostructured heterojunction were studied in order to understand the mechanisms lying behind the low photoconductivity measured. It has been found that the interface state defects and the high resistivity of Cu2O film were limiting the photovoltaic properties of the prepared devices. The understanding presented in this work is expected to enable the optimization of solar cell devices based on Cu2O/ZnO nanomaterials and improve their overall performance.

Transparent electrodes in silicon heterojunction solar cells: Influence on contact passivation

DOE PAGES

Tomasi, Andrea; Sahli, Florent; Seif, Johannes Peter; ...

2015-10-26

Charge carrier collection in silicon heterojunction solar cells occurs via intrinsic/doped hydrogenated amorphous silicon layer stacks deposited on the crystalline silicon wafer surfaces. Usually, both the electron and hole collecting stacks are externally capped by an n-type transparent conductive oxide, which is primarily needed for carrier extraction. Earlier, it has been demonstrated that the mere presence of such oxides can affect the carrier recombination in the crystalline silicon absorber. Here, we present a detailed investigation of the impact of this phenomenon on both the electron and hole collecting sides, including its consequences for the operating voltages of silicon heterojunction solarmore » cells. As a result, we define guiding principles for improved passivating contact design for high-efficiency silicon solar cells.« less

Electrically Active Defects In Solar Cells Based On Amorphous Silicon/Crystalline Silicon Heterojunction After Irradiation By Heavy Xe Ions

NASA Astrophysics Data System (ADS)

Harmatha, Ladislav; Mikolášek, Miroslav; Stuchlíková, L'ubica; Kósa, Arpád; Žiška, Milan; Hrubčín, Ladislav; Skuratov, Vladimir A.

2015-11-01

The contribution is focused on the diagnostics of structures with a heterojunction between amorphous and crystalline silicon prepared by HIT (Heterojunction with an Intrinsic Thin layer) technology. The samples were irradiated by Xe ions with energy 167 MeV and doses from 5 × 108 cm-2 to 5 × 1010 cm-2. Radiation defects induced in the bulk of Si and at the hydrogenated amorphous silicon and crystalline silicon (a-Si:H/c-Si) interface were identified by Deep Level Transient Spectroscopy (DLTS). Radiation induced A-centre traps, boron vacancy traps and different types of divacancies with a high value of activation energy were observed. With an increased fluence of heavy ions the nature and density of the radiation induced defects was changed.

On the theory of Carriers's Electrostatic Interaction near an Interface

NASA Astrophysics Data System (ADS)

Waters, Michael; Hashemi, Hossein; Kieffer, John

2015-03-01

Heterojunction interfaces are common in non-traditional photovoltaic device designs, such as those based small molecules, polymers, and perovskites. We have examined a number of the effects of the heterojunction interface region on carrier/exciton energetics using a mixture of both semi-classical and quantum electrostatic methods, ab initio methods, and statistical mechanics. Our theoretical analysis has yielded several useful relationships and numerical recipes that should be considered in device design regardless of the particular materials system. As a demonstration, we highlight these formalisms as applied to carriers and polaron pairs near a C60/subphthalocyanine interface. On the regularly ordered areas of the heterojunction, the effect of the interface is a significant set of corrections to the carrier energies, which in turn directly affects device performance.

Transparent electrodes in silicon heterojunction solar cells: Influence on contact passivation

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

Tomasi, Andrea; Sahli, Florent; Seif, Johannes Peter

Charge carrier collection in silicon heterojunction solar cells occurs via intrinsic/doped hydrogenated amorphous silicon layer stacks deposited on the crystalline silicon wafer surfaces. Usually, both the electron and hole collecting stacks are externally capped by an n-type transparent conductive oxide, which is primarily needed for carrier extraction. Earlier, it has been demonstrated that the mere presence of such oxides can affect the carrier recombination in the crystalline silicon absorber. Here, we present a detailed investigation of the impact of this phenomenon on both the electron and hole collecting sides, including its consequences for the operating voltages of silicon heterojunction solarmore » cells. As a result, we define guiding principles for improved passivating contact design for high-efficiency silicon solar cells.« less

Silicon heterojunction solar cell with passivated hole selective MoO{sub x} contact

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

Battaglia, Corsin; Yin, Xingtian; Zheng, Maxwell

2014-03-17

We explore substoichiometric molybdenum trioxide (MoO{sub x}, x < 3) as a dopant-free, hole-selective contact for silicon solar cells. Using an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the silicon absorber, we demonstrate a high open-circuit voltage of 711 mV and power conversion efficiency of 18.8%. Due to the wide band gap of MoO{sub x}, we observe a substantial gain in photocurrent of 1.9 mA/cm{sup 2} in the ultraviolet and visible part of the solar spectrum, when compared to a p-type amorphous silicon emitter of a traditional silicon heterojunction cell. Our results emphasize the strong potential for oxides as carrier selectivemore » heterojunction partners to inorganic semiconductors.« less

Edge-emitting ultraviolet n-ZnO:Al/i-ZnO/p-GaN heterojunction light-emitting diode with a rib waveguide.

PubMed

Liang, H K; Yu, S F; Yang, H Y

2010-02-15

An edge-emitting ultraviolet n-ZnO:Al/i-ZnO/p-GaN heterojunction light-emitting diode with a rib waveguide is fabricated by filtered cathodic vacuum arc technique at low deposition temperature (approximately 150 degrees C). Electroluminescence with emission peak at 387 nm is observed. Good correlation between electro- and photo- luminescence spectra suggests that the i-ZnO layer of the heterojunction supports radiative excitonic recombination. Furthermore, it is found that the emission intensity can be enhanced by approximately 5 times due to the presence of the rib waveguide. Only fundamental TE and TM polarizations are supported inside the rib waveguide and the intensity of TE polarization is approximately 2.2 time larger than that of TM polarization.

High Photoelectric Conversion Efficiency of Metal Phthalocyanine/Fullerene Heterojunction Photovoltaic Device

PubMed Central

Lin, Chi-Feng; Zhang, Mi; Liu, Shun-Wei; Chiu, Tien-Lung; Lee, Jiun-Haw

2011-01-01

This paper introduces the fundamental physical characteristics of organic photovoltaic (OPV) devices. Photoelectric conversion efficiency is crucial to the evaluation of quality in OPV devices, and enhancing efficiency has been spurring on researchers to seek alternatives to this problem. In this paper, we focus on organic photovoltaic (OPV) devices and review several approaches to enhance the energy conversion efficiency of small molecular heterojunction OPV devices based on an optimal metal-phthalocyanine/fullerene (C60) planar heterojunction thin film structure. For the sake of discussion, these mechanisms have been divided into electrical and optical sections: (1) Electrical: Modification on electrodes or active regions to benefit carrier injection, charge transport and exciton dissociation; (2) Optical: Optional architectures or infilling to promote photon confinement and enhance absorption. PMID:21339999

Analysis of improved dc and ac performances of an InGaP/GaAs heterojunction bipolar transistor with a graded Al xGa 1- xAs layer at emitter/base heterojunction

NASA Astrophysics Data System (ADS)

Cheng, Shiou-Ying

2004-07-01

An InGaP/GaAs heterojunction bipolar transistor (HBT) with a continuous conduction-band structure is demonstrated and theoretically investigated. This device exhibited good performance including lower turn-on voltage, lower offset voltage and smaller collector current saturation voltage. The novel aspect of device structure design is the adoption of the compositionally linear-graded AlGaAs layer between the InGaP-emitter and GaAs-base layers. Therefore, the device studied shows better dc and ac performances than a conventional device. Consequently, this causes the substantial benefit for practical analog and digital applications especially for lower operation voltage, lower power consumption commercial and military products.

Differential conductance (dI/dV) imaging of a heterojunction-nanorod

NASA Astrophysics Data System (ADS)

Kundu, Biswajit; Bera, Abhijit; Pal, Amlan J.

2017-03-01

Through scanning tunneling spectroscopy, we envisage imaging a heterostructure, namely a junction formed in a single nanorod. While the differential conductance spectrum provides location of conduction and valence band edges, dI/dV images record energy levels of materials. Such dI/dV images at different voltages allowed us to view p- and n-sections of heterojunction nanorods and more importantly the depletion region in such a junction that has a type-II band alignment. Viewing of selective sections in a heterojunction occurred due to band-bending in the junction and is correlated to the density of states spectrum of the individual semiconductors. The dI/dV images recorded at different voltages could be used to generate a band diagram of a pn junction.

Exciton transport, charge extraction, and loss mechanisms in organic photovoltaics

NASA Astrophysics Data System (ADS)

Scully, Shawn Ryan

Organic photovoltaics have attracted significant interest over the last decade due to their promise as clean low-cost alternatives to large-scale electric power generation such as coal-fired power, natural gas, and nuclear power. Many believe power conversion efficiency targets of 10-15% must be reached before commercialization is possible. Consequently, understanding the loss mechanisms which currently limit efficiencies to 4-5% is crucial to identify paths to reach higher efficiencies. In this work, we investigate the dominant loss mechanisms in some of the leading organic photovoltaic architectures. In the first class of architectures, which include planar heterojunctions and bulk heterojunctions with large domains, efficiencies are primarily limited by the distance photogenerated excitations (excitons) can be transported (termed the exciton diffusion length) to a heterojunction where the excitons may dissociate. We will discuss how to properly measure the exciton diffusion length focusing on the effects of optical interference and of energy transfer when using fullerenes as quenching layers and show how this explains the variety of diffusion lengths reported for the same material. After understanding that disorder and defects limit exciton diffusion lengths, we suggest some approaches to overcome this. We then extensively investigate the use of long-range resonant energy transfer to increase exciton harvesting. Using simulations and experiments as support, we discuss how energy transfer can be engineered into architectures to increase the distance excitons can be harvested. In an experimental model system, DOW Red/PTPTB, we will show how the distance excitons are harvested can be increased by almost an order of magnitude up to 27 nm from a heterojunction and give design rules and extensions of this concept for future architectures. After understanding exciton harvesting limitations we will look at other losses that are present in planar heterojunctions. One of the primary losses that puts stringent requirements on the charge carrier mobilities in these cells is the recombination losses due to space charge build up at the heterojunction. Because electrons are confined to the acceptor and holes to the donor, net charge density always exists even when mobilities are matched, in contrast to bulk heterojunctions wherein matched mobilities lead to zero net charge. This net charge creates an electric field which opposes the built-in field and limits the current that can be carried away from this heterojunction. Using simulations we show that for relevant current densities charge carrier mobilities must be higher than 10-4 cm2/V.s to avoid significant losses due to space charge formation. In the last part of this work, we will focus on the second class of architectures in which exciton harvesting is efficient. We will present a systematic analysis of one of the leading polymer:fullerene bulk heterojunction cells to show that losses in this architecture are due to charge recombination. Using optical measurements and simulations, exciton harvesting measurements, and device characteristics we will show that the dominant loss is likely due to field-dependent geminate recombination of the electron and hole pair created immediately following exciton dissociation. No losses in this system are seen due to bimolecular recombination or space charge which provides information on charge-carrier mobility targets necessary for the future design of high efficiency organic photovoltaics.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Line width of a single longitudinal mode emitted by an AlGaAs heterojunction laser

NASA Astrophysics Data System (ADS)

Bogatov, Alexandr P.; Eliseev, P. G.; Luk'yanov, S. A.; Pak, G. T.; Petrakova, T. V.

1988-11-01

A nonmonotonic dependence of the emission line width on the power was observed for a single longitudinal mode of an AlGaAs heterojunction laser. This behavior could be due to the dependence of the waveguide coefficient of the amplitude-phase coupling on the nature of operation of the laser.

A photovoltaic self-powered gas sensor based on a single-walled carbon nanotube/Si heterojunction.

PubMed

Liu, L; Li, G H; Wang, Y; Wang, Y Y; Li, T; Zhang, T; Qin, S J

2017-12-07

We present a novel photovoltaic self-powered gas sensor based on a p-type single-walled carbon nanotube (SWNT) and n-type silicon (n-Si) heterojunction. The energy from visible light suffices to drive the device owing to a built-in electric field (BEF) induced by the differences between the Fermi levels of SWNTs and n-Si.

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

Rational Design of Zinc Phosphide Heterojunction Photovoltaics

NASA Astrophysics Data System (ADS)

Bosco, Jeffrey Paul

The prospect of terawatt-scale electricity generation using a photovoltaic (PV) device places strict requirements on the active semiconductor optoelectronic properties and elemental abundance. After reviewing the constraints placed on an ``earth-abundant'' solar absorber, we find zinc phosphide (α-Zn 3P2) to be an ideal candidate. In addition to its near-optimal direct band gap of 1.5 eV, high visible-light absorption coefficient (>10. 4cm-1), and long minority-carrier diffusion length (>5 μm), Zn3P 2 is composed of abundant Zn and P elements and has excellent physical properties for scalable thin-film deposition. However, to date, a Zn 3P2 device of sufficient efficiency for commercial applications has not been demonstrated. Record efficiencies of 6.0% for multicrystalline and 4.3% for thin-film cells have been reported, respectively. Performance has been limited by the intrinsic p-type conductivity of Zn3P 2 which restricts us to Schottky and heterojunction device designs. Due to our poor understanding of Zn3P2 interfaces, an ideal heterojunction partner has not yet been found. The goal of this thesis is to explore the upper limit of solar conversion efficiency achievable with a Zn3P2 absorber through the design of an optimal heterojunction PV device. To do so, we investigate three key aspects of material growth, interface energetics, and device design. First, the growth of Zn3P2 on GaAs(001) is studied using compound-source molecular-beam epitaxy (MBE). We successfully demonstrate the pseudomorphic growth of Zn3P2 epilayers of controlled orientation and optoelectronic properties. Next, the energy-band alignments of epitaxial Zn3P2 and II-VI and III-V semiconductor interfaces are measured via high-resolution x-ray photoelectron spectroscopy in order to determine the most appropriate heterojunction partner. From this work, we identify ZnSe as a nearly ideal n-type emitter for a Zn3P 2 PV device. Finally, various II-VI/Zn3P2 heterojunction solar cells designs are fabricated, including substrate and superstrate architectures, and evaluated based on their solar conversion efficiency.

Visible light degradation of Orange II using xCuyOz/TiO2 heterojunctions.

PubMed

Helaïli, N; Bessekhouad, Y; Bouguelia, A; Trari, M

2009-08-30

Cu(2)O/TiO(2), Cu/Cu(2)O/TiO(2) and Cu/Cu(2)O/CuO/TiO(2) heterojunctions were prepared and studied for their potential application as photocatalysts able to induce high performance under visible light. Orange II was used as a representative dye molecule. The effect of the amount and composition of the photosensitizers toward the activation of TiO(2) was studied. In each case, the global mechanism of Inter Particle Electrons Injection (IPEI) was discussed. The highest photocatalytic activity was observed for the system Cu/Cu(2)O/CuO (MB2 catalyst) under visible light (t(1/2)=24 min, k=159.7 x 10(-3)min(-1)) and for the heterojunction cascade Cu/Cu(2)O/CuO/TiO(2) (MB2 (50%)/TiO(2)) under UV-vis light (t(1/2)=4 min, k=1342 x 10(-3)min(-1)). In the last case, the high performance was attributed firstly to the electromotive forces developed under this configuration in which CuO energy bands mediate the electrons transfer from Cu(2)O to TiO(2). The formation of monobloc sensitizers also accounts for the decrease of the probability of the charges lost. It was demonstrated that "Cu(2)O/CuO" governs the capability of the heterojunction cascade and Cu does not play a significant role regardless of the heterojunction cascade efficiency. The electrical energy consumption per order of magnitude for photocatalytic degradation of Orange II was investigated for some representative catalytic systems. Visible/MB2 and UV/vis MB2 (50%)/TiO(2) exhibited respectively 0.340 and 0.05 kW hm(-3) demonstrating the high efficiency of the systems.

BiVO4/WO3/SnO2 Double-Heterojunction Photoanode with Enhanced Charge Separation and Visible-Transparency for Bias-Free Solar Water-Splitting with a Perovskite Solar Cell.

PubMed

Baek, Ji Hyun; Kim, Byeong Jo; Han, Gill Sang; Hwang, Sung Won; Kim, Dong Rip; Cho, In Sun; Jung, Hyun Suk

2017-01-18

Coupling dissimilar oxides in heterostructures allows the engineering of interfacial, optical, charge separation/transport and transfer properties of photoanodes for photoelectrochemical (PEC) water splitting. Here, we demonstrate a double-heterojunction concept based on a BiVO 4 /WO 3 /SnO 2 triple-layer planar heterojunction (TPH) photoanode, which shows simultaneous improvements in the charge transport (∼93% at 1.23 V vs RHE) and transmittance at longer wavelengths (>500 nm). The TPH photoanode was prepared by a facile solution method: a porous SnO 2 film was first deposited on a fluorine-doped tin oxide (FTO)/glass substrate followed by WO 3 deposition, leading to the formation of a double layer of dense WO 3 and a WO 3 /SnO 2 mixture at the bottom. Subsequently, a BiVO 4 nanoparticle film was deposited by spin coating. Importantly, the WO 3 /(WO 3 +SnO 2 ) composite bottom layer forms a disordered heterojunction, enabling intimate contact, lower interfacial resistance, and efficient charge transport/transfer. In addition, the top BiVO 4 /WO 3 heterojunction layer improves light absorption and charge separation. The resultant TPH photoanode shows greatly improved internal quantum efficiency (∼80%) and PEC water oxidation performance (∼3.1 mA/cm 2 at 1.23 V vs RHE) compared to the previously reported BiVO 4 /WO 3 photoanodes. The PEC performance was further improved by a reactive-ion etching treatment and CoO x electrocatalyst deposition. Finally, we demonstrated a bias-free and stable solar water-splitting by constructing a tandem PEC device with a perovskite solar cell (STH ∼3.5%).

Substrate nitridation induced modulations in transport properties of wurtzite GaN/p-Si (100) heterojunctions grown by molecular beam epitaxy

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

Bhat, Thirumaleshwara N.; Rajpalke, Mohana K.; Krupanidhi, S. B.

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic ({beta}) and hexagonal ({alpha}) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 deg. C when compared to the samples grown in the absence of silicon nitridemore » buffer layer and with silicon nitride buffer layer grown at 600 deg. C. Core-level photoelectron spectroscopy of Si{sub x}N{sub y} layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors ({approx}1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively.« less

Toward Eco-Friendly and Highly Efficient Solar Water Splitting Using In2S3/Anatase/Rutile TiO2 Dual-Staggered-Heterojunction Nanodendrite Array Photoanode.

PubMed

Yang, Jih-Sheng; Wu, Jih-Jen

2018-01-31

The TiO 2 -based heterojunction nanodendrite (ND) array composed of anatase nanoparticles (ANPs) on the surface of the rutile ND (RND) array is selected as the model photoanode to demonstrate the strategies toward eco-friendly and efficient solar water splitting using neutral electrolyte and seawater. Compared with the performances in alkaline electrolyte, a non-negligible potential drop across the electrolyte as well as impeded charge injection and charge separation is monitored in the ANP/RND array photoanode with neutral electrolyte, which are, respectively, ascribed to the series resistance of neutral electrolyte, the fundamentally pH-dependent water oxidation mechanism on TiO 2 surface, as well as the less band bending at the interface of TiO 2 and neutral electrolyte. Accordingly, a TiO 2 -based dual-staggered heterojunction ND array photoanode is further designed in this work to overcome the issue of less band bending with the neutral electrolyte. The improvement of charge separation efficiency is realized by the deposition of a transparent In 2 S 3 layer on the ANP/RND array photoanode for constructing additional staggered heterojunction. Under illumination of AM 1.5G (100 mW cm -2 ), the improved photocurrent densities acquired both in neutral electrolyte and seawater at 1.23 V vs reversible hydrogen electrode (RHE), which approach the theoretical value for rutile TiO 2 , are demonstrated in the dual-staggered-heterojunction ND array photoanode. Faradaic efficiencies of ∼95 and ∼32% for solar water oxidation in neutral electrolyte and solar seawater oxidation for 2 h are acquired at 1.23 V vs RHE, respectively.

Phase control synthesis of α, β and α/β Bi2O3 hetero-junction with enhanced and synergistic photocatalytic activity on degradation of toxic dye, Rhodamine-B under natural sunlight.

PubMed

Bera, Kamal Kanti; Majumdar, Rituparna; Chakraborty, Malay; Bhattacharya, Swapan Kumar

2018-06-15

Nano particles of a few α/β Bi 2 O 3 hetero-junctions of various compositions synthesized by one- pot hydrothermal method, exhibit exceptional and synergistic photo-catalytic activity for the degradation of Rhodamine-B in aqueous solution under natural sunlight. Pure α and pure β Bi 2 O 3 are also synthesized by control post heating of synthesized hetero-junction. The nano-materials were characterized by diffraction (XRD), microscopic and spectroscopic techniques. The XRD reveals α-β phase hetero-junctions of Bi 2 O 3 are made of α-Bi 2 O 3 and β-Bi 2 O 3 with average dimensions within 13-113 and 5-71 nm respectively and having band gap range of 2.4- 2.9 eV. The spectrophotometrically determined % degradation of the dye and associated rate constant on the best hetero-junction are increased by 4.5(/2.1) and 3.3(/1.2) times than these on pure α (/β). The effects of operational parameters and trapping agents have been analyzed. The maximum removal of the dye was achieved up to 99.6% in 3 h using 0.5 g/L photo-catalyst at pH 3. The reusability test shows that the photo-catalytic activity is retained excellently due to change in chemical nature of the catalyst from α -Bi 2 O 3 to β-Bi 2 O 3, Bi 2 O 2 CO 3 and BiOCl. A suitable mechanism is proposed. Copyright © 2018 Elsevier B.V. All rights reserved.

TiO2 Nanorod Arrays Based Self-Powered UV Photodetector: Heterojunction with NiO Nanoflakes and Enhanced UV Photoresponse.

PubMed

Gao, Yanyan; Xu, Jianping; Shi, Shaobo; Dong, Hong; Cheng, Yahui; Wei, Chengtai; Zhang, Xiaosong; Yin, Shougen; Li, Lan

2018-04-04

The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO 2 nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiO x thin film can improve the morphological and carrier transport properties of TiO 2 NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO 2 nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 10 4 and 1.45 × 10 5 for NiO/TiO 2 NRs and NiO/TiO 2 NRs/TiO x , respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast response and recovery speeds without external applied bias under the weak light radiation. The devices demonstrate good stability and repeatability under UV light radiation. The self-powered performance could be attributed to the proper built-in electric field of the heterojunction. TiO 2 NRs and NiO nanoflakes construct the well-aligned energy-band structure. The enhanced responsivity and detectivity for the devices with TiO x thin films is related to the increased interfacial charge separation efficiency, reduced carrier recombination, and relatively good electron transport of TiO 2 NRs.

A Solar-Blind UV Detector Based on Graphene-Microcrystalline Diamond Heterojunctions.

PubMed

Wei, Minsong; Yao, Kaiyuan; Liu, Yumeng; Yang, Chen; Zang, Xining; Lin, Liwei

2017-09-01

An ultraviolet detector is demonstrated through a whole-wafer, thin diamond film transfer process to realize the heterojunction between graphene and microcrystalline diamond (MCD). Conventional direct transfer processes fail to deposit graphene onto the top surface of the MCD film. However, it is found that the 2 µm thick MCD diamond film can be easily peeled off from the growth silicon substrate to expose its smooth backside for the graphene transfer process for high-quality graphene/MCD heterojunctions. A vertical graphene/MCD/metal structure is constructed as the photodiode device using graphene as the transparent top electrode for solar-blind ultraviolet sensing with high responsivity and gain factor. As such, this material system and device architecture could serve as the platform for next-generation optoelectronic systems. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Virtually pure near-infrared electroluminescence from exciplexes at polyfluorene/hexaazatrinaphthylene interfaces

NASA Astrophysics Data System (ADS)

Tregnago, G.; Fléchon, C.; Choudhary, S.; Gozalvez, C.; Mateo-Alonso, A.; Cacialli, F.

2014-10-01

Electronic processes at the heterojunction between chemically different organic semiconductors are of special significance for devices such as light-emitting diodes (LEDs) and photovoltaic diodes. Here, we report the formation of an exciplex state at the heterojunction of an electron-transporting material, a functionalized hexaazatrinaphthylene, and a hole-transporting material, poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)diphenylamine) (TFB). The energetics of the exciplex state leads to a spectral shift of ˜1 eV between the exciton and the exciplex peak energies (at 2.58 eV and 1.58 eV, respectively). LEDs incorporating such bulk heterojunctions display complete quenching of the exciton luminescence, and a nearly pure near-infrared electroluminescence arising from the exciplex (at ˜1.52 eV) with >98% of the emission at wavelengths above 700 nm at any operational voltage.

Improving performance of Si/CdS micro-/nanoribbon p-n heterojunction light emitting diodes by trenched structure

NASA Astrophysics Data System (ADS)

Huang, Shiyuan; Wu, Yuanpeng; Ma, Xiangyang; Yang, Zongyin; Liu, Xu; Yang, Qing

2018-05-01

Realizing high performance silicon based light sources has been an unremitting pursuit for researchers. In this letter, we propose a simple structure to enhance electroluminescence emission and reduce the threshold of injected current of silicon/CdS micro-/nanoribbon p-n heterojunction visible light emitting diodes, by fabricating trenched structure on silicon substrate to mount CdS micro-/nanoribbon. A series of experiments and simulation analysis favors the rationality and validity of our mounting design. After mounting the CdS micro-/nanoribbon, the optical field confinement increases, and absorption and losses from high refractive silicon substrate are effectively reduced. Meanwhile the sharp change of silicon substrate near heterojunction also facilitates the balance between electron current and hole current, which substantially conduces to the stable amplification of electroluminescence emission in CdS micro-/nanoribbon.

Microwave assisted synthesis of porous ZnO/SnS heterojunction and its application in visible light degradation of ciprofloxacin

NASA Astrophysics Data System (ADS)

Makama, A. B.; Salmiaton, A.; Saion, E. B.; Choong, T. S. Y.; Abdullah, N.

2016-07-01

Porous ZnO/SnS heterojunctions were successfully synthesized via microwave-assisted heating of aqueous solutions containing different amounts of SnS precursors (SnCl2 and Na2S) in the presence of fixed amount of ZnCO3 nanoparticles. The experimental results revealed that the heterojunctions exhibited much higher visible light-driven photocatalytic activity for the degradation of the ciprofloxacin than pure SnS nanocrystals. The photocatalytic degradation efficiency (1-Ct/C0) of the pollutant for the most active heterogeneous nanostructure is about four times more efficient than pure SnS. The enhanced photocatalytic efficiency is ascribed to the synergic effect of high photon absorption and reduction in the recombination of electrons and holes because of efficient separation and electron transfer from the SnS to ZnO nanoparticles.

Structural, electrical, and photoelectric properties of p-NiO/n-CdTe heterojunctions

NASA Astrophysics Data System (ADS)

Parkhomenko, Hryhorii; Solovan, Mykhaylo; Brus, Viktor; Maystruk, Eduard; Maryanchuk, Pavlo

2018-01-01

p-NiO/n-CdTe-photosensitive heterojunctions were prepared by the deposition of nickel oxide thin films onto n-type single-crystal CdTe substrates by DC reactive magnetron sputtering. The analysis of capacitance-voltage (C-V) characteristics, measured at different frequencies of the small amplitude AC signal and corrected by the effect of the series resistance, provided evidence of the presence of electrically charged interface states, which significantly affect the measured capacitance. The dominant current transport mechanisms in the heterojunctions were determined at forward and reverse biases. Using "light" I-V characteristics, we determined the open-circuit voltage Voc=0.42 V, the short-circuit current Isc=57.5 μA/cm2, and the fill factor FF=0.24 under white light illumination with the intensity of 80 mW.

Preparation of TNAs/NiO p-n heterojunction and their applications in UV photosensor

NASA Astrophysics Data System (ADS)

Yusoff, M. M.; Mamat, M. H.; Malek, M. F.; Abdullah, M. A. R.; Ismail, A. S.; Saidi, S. A.; Mohamed, R.; Suriani, A. B.; Khusaimi, Z.; Rusop, M.

2018-05-01

A nanocomposite consisted of n-type titanium dioxide (TiO2) nanorod arrays (TNAs) and p-type nickel oxide (NiO) were deposited using a novel facile low-temperature aqueous chemical route (ACR) in a Schott bottle with cap clamps and sol-gel spin coating method, respectively on a transparent conductive oxide (TCO) glass substrate for the application of ultraviolet (UV) photosensor. The p-n heterojunction photosensor exhibited an increase in photocurrent under UV light (365 nm, 750 µW/cm2) at applied reverse bias. The measured UV response also revealed an increase in photocurrent, and dark current with increasing applied reverse bias on the p-n heterojunction. In this study, the fabricated TNAs/NiO composite nanostructures showed potential applications for photosensor based on the steady photocurrent results obtained under UV irradiation

Fabrication of Planar Heterojunction Perovskite Solar Cells by Controlled Low-Pressure Vapor Annealing.

PubMed

Li, Yanbo; Cooper, Jason K; Buonsanti, Raffaella; Giannini, Cinzia; Liu, Yi; Toma, Francesca M; Sharp, Ian D

2015-02-05

A new method for achieving high efficiency planar CH3NH3I3-xClx perovskite photovoltaics, based on a low pressure, reduced temperature vapor annealing is demonstrated. Heterojunction devices based on this hybrid halide perovskite exhibit a top PCE of 16.8%, reduced J-V hysteresis, and highly repeatable performance without need for a mesoporous or nanocrystalline metal oxide layer. Our findings demonstrate that large hysteresis is not an inherent feature of planar heterojunctions, and that efficient charge extraction can be achieved with uniform halide perovskite materials with desired composition. X-ray diffraction, valence band spectroscopy, and transient absorption measurements of these thin films reveal that structural modifications induced by chlorine clearly dominate over chemical and electronic doping effects, without affecting the Fermi level or photocarrier lifetime in the material.

High mobility and high concentration Type-III heterojunction FET

NASA Astrophysics Data System (ADS)

Tsu, R.; Fiddy, M. A.; Her, T.

2018-02-01

The PN junction was introduced in transistors by doping, resulting in high losses due to Coulomb scattering from the dopants. The MOSFET introduced carriers in the form of electrons and holes with an applied bias to the oxide barrier, resulting in carrier transfer without doping. This avoids high scattering losses and dominates the IC industries. With heterojunctions having valence-band maxima near and even above the conduction-band minimum in the formation of Type-III superlattices, very useful devices, introduced by Tsu, Sai-Halacz, and Esaki, soon followed. If the layer thicknesses are more than the carrier mean-free-path, incoherent scattering results in the formation of carrier transfer via diffusion instead of opening up new energy gaps. The exploitation of carriers without scattering represents a new and significant opportunity in what we call a Broken Gap Heterojunction FET.

Characteristics of zinc oxide nanorod array/titanium oxide film heterojunction prepared by aqueous solution deposition

NASA Astrophysics Data System (ADS)

Lee, Ming-Kwei; Hong, Min-Hsuan; Li, Bo-Wei

2016-07-01

The characteristics of a ZnO nanorod array/TiO2 film heterojunction were investigated. A TiO2 film was prepared on glass by aqueous solution deposition with precursors of ammonium hexafluorotitanate and boric acid at 40 °C. Then, a ZnO seed layer was prepared on a TiO2 film/glass substrate by RF sputtering. A vertically oriented ZnO nanorod array was grown on a ZnO seed layer/TiO2 film/glass substrate by aqueous solution deposition with precursors of zinc nitrate and hexamethylenetetramine (HMT) at 70 °C. After thermal annealing in N2O ambient at 300 °C, this heterojunction used as an oxygen gas sensor shows much better rise time, decay time, and on/off current ratio than as-grown and annealed ZnO nanorods.

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

Dou, Letian; Lai, Minliang; Kley, Christopher S.

Halide perovskites are promising semiconductor materials for solution-processed optoelectronic devices. Their strong ionic bonding nature results in highly dynamic crystal lattices, inherently allowing rapid ion exchange at the solid–vapor and solid–liquid interface. In this paper, we show that the anion-exchange chemistry can be precisely controlled in single-crystalline halide perovskite nanomaterials when combined with nanofabrication techniques. We demonstrate spatially resolved multicolor CsPbX 3 (X = Cl, Br, I, or alloy of two halides) nanowire heterojunctions with a pixel size down to 500 nm with the photoluminescence tunable over the entire visible spectrum. In addition, the heterojunctions show distinct electronic states acrossmore » the interface, as revealed by Kelvin probe force microscopy. Finally, these perovskite heterojunctions represent key building blocks for high-resolution multicolor displays beyond current state-of-the-art technology as well as high-density diode/transistor arrays.« less

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

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

Jeong, Junseok; Choi, Ji Eun; Hong, Young Joon, E-mail: yjhong@sejong.ac.kr

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p–n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunnelingmore » probability determined by wire/film junction geometry and size.« less

Ga2O3 Schottky barrier and heterojunction diodes for power electronics applications

NASA Astrophysics Data System (ADS)

Tadjer, Marko J.; Mahadik, Nadeemullah A.; Freitas, Jaime A.; Glaser, Evan R.; Koehler, Andrew D.; Luna, Lunet E.; Feigelson, Boris N.; Hobart, Karl D.; Kub, Fritz J.; Kuramata, A.

2018-02-01

We present novel approaches for the development of Ga2O3 Schottky barrier and heterojunction diodes. Samples of β- Ga2O3 were first annealed in N2 and O2 to demonstrate the effect of annealing on the carrier concentration. Cathodoluminescence and electron spin resonance measurements were also performed. Schottky barrier diodes on asgrown and O2-annealed epitaxial Ga2O3 films were fabricated and breakdown voltages were compared. Lower reverse current and a breakdown voltage of about 857 V were measured on the O2-annealed device. Finally, we report preliminary results from the development of anisotype heterojunctions between n-type Ga2O3 with a sputtered NiO layer. Rectifying current-voltage characteristics were obtained when the NiO was deposited both at room temperature and at 450 °C.

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Jeong, Junseok; Choi, Ji Eun; Kim, Yong-Jin; Hwang, Sunyong; Kim, Sung Kyu; Kim, Jong Kyu; Jeong, Hu Young; Hong, Young Joon

2016-09-01

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p-n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunneling probability determined by wire/film junction geometry and size.

Dithienogermole as a fused electron donor in bulk heterojunction solar cells.

PubMed

Amb, Chad M; Chen, Song; Graham, Kenneth R; Subbiah, Jegadesan; Small, Cephas E; So, Franky; Reynolds, John R

2011-07-06

We report the synthesis and bulk heterojunction photovoltaic performance of the first dithienogermole (DTG)-containing conjugated polymer. Stille polycondensation of a distannyl-DTG derivative with 1,3-dibromo-N-octyl-thienopyrrolodione (TPD) results in an alternating copolymer which displays light absorption extending to 735 nm, and a higher HOMO level than the analogous copolymer containing the commonly utilized dithienosilole (DTS) heterocycle. When polyDTG-TPD:PC(70)BM blends are utilized in inverted bulk heterojunction solar cells, the cells display average power conversion efficiencies of 7.3%, compared to 6.6% for the DTS-containing cells prepared in parallel under identical conditions. The performance enhancement is a result of a higher short-circuit current and fill factor in the DTG-containing cells, which comes at the cost of a slightly lower open circuit voltage than for the DTS-based cells.

Microcrystalline silicon growth for heterojunction solar cells

NASA Technical Reports Server (NTRS)

Iles, P. A.; Leung, D. C.; Fang, P. H.

1984-01-01

A single source of evaporation with B mixed with highly doped Si is used instead of the coevaporation of separate Si and B sources to reduce possible carbon contamination. The results of both the heterojunction or heteroface structures, however, are similar when evaporation is used. The best Voc of the heterojunction is about 460mV and no improvement in Voc in the heteroface structure is observed. Slight Voc degradation occurred. A study of the p m-Si/p c-Si structure showed a negative Voc in many cases. The interface properties between the two materials are such that instead of repelling minority carriers from the substrate carrier, collection actually occurred. Another study of cells made in the part of substrates not covered by n-Si results in performance lower than the controls. This indicates possible substrate degradation in the process.

Development of 1.0- to 1.4-Micrometer Heterojunction LEDs.

DTIC Science & Technology

1980-04-01

dispersion of silica fibers decreases with increasing wavelength (2]. This is due to the wavelength dependence of the refractive index , which predicts...shown here is sufficient to provide strong electron confine- ment in the low-energy material (InGaAs). A similar difference in refractive index for these...bandgap and refractive - index steps discussed above form the basis of fabricating heterojunction emitters (both edge-emitting LEDs and lasers

Fast-Response Photonic Device Based on Organic-Crystal Heterojunctions Assembled into a Vertical-Yet-Open Asymmetric Architecture.

PubMed

Zhang, Lei; Pavlica, Egon; Zhong, Xiaolan; Liscio, Fabiola; Li, Songlin; Bratina, Gvido; Orgiu, Emanuele; Samorì, Paolo

2017-03-01

Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis(triisopropylsilylethynyl) pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Titanium dioxide/silicon hole-blocking selective contact to enable double-heterojunction crystalline silicon-based solar cell

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

Nagamatsu, Ken A., E-mail: knagamat@princeton.edu; Man, Gabriel; Jhaveri, Janam

2015-03-23

In this work, we use an electron-selective titanium dioxide (TiO{sub 2}) heterojunction contact to silicon to block minority carrier holes in the silicon from recombining at the cathode contact of a silicon-based photovoltaic device. We present four pieces of evidence demonstrating the beneficial effect of adding the TiO{sub 2} hole-blocking layer: reduced dark current, increased open circuit voltage (V{sub OC}), increased quantum efficiency at longer wavelengths, and increased stored minority carrier charge under forward bias. The importance of a low rate of recombination of minority carriers at the Si/TiO{sub 2} interface for effective blocking of minority carriers is quantitatively described.more » The anode is made of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) heterojunction to silicon which forms a hole selective contact, so that the entire device is made at a maximum temperature of 100 °C, with no doping gradients or junctions in the silicon. A low rate of recombination of minority carriers at the Si/TiO{sub 2} interface is crucial for effective blocking of minority carriers. Such a pair of complementary carrier-selective heterojunctions offers a path towards high-efficiency silicon solar cells using relatively simple and near-room temperature fabrication techniques.« less

Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: multi-parameter measurement reliability and precision studies.

PubMed

Zhang, Y; Melnikov, A; Mandelis, A; Halliop, B; Kherani, N P; Zhu, R

2015-03-01

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results were studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.

Investigations on structural and electrical parameters of p-Si/ MgxZn1-xO thin film heterojunction diodes grown by RF magnetron sputtering technique

NASA Astrophysics Data System (ADS)

Singh, Satyendra Kumar; Hazra, Purnima

2018-05-01

This work reports fabrication and characterization of p-Si/ MgxZn1-xO thin film heterojunction diodes grown by RF magnetron sputtering technique. In this work, ZnO powder was mixed with MgO powder at per their weight percentage from 0 to 10% to prepare MgxZn1-xO target. The microstructural, surface morphological and optical properties of as-deposited p-Si/MgxZn1-xO heterostructure thin films have been studied using X-ray Diffraction, atomic force microscopy and variable angle ellipsometer. XRD spectra exhibit that undoped ZnO thin films has preferred crystal orientation in (002) plane. However, with increase in Mg-doping, ZnO (101) crystal plane is enhanced progressively due to phase segregation, even though preferred growth orientation of ZnO crystals is still towards (002) plane. The electrical characteristics of Si/ MgxZn1-xO heterojunction diodes with large area Al/Ti ohmic contacts are evaluated using semiconductor parameter analyzer. With rectification ratio of 27894, reverse saturation current of 20.5 nA and barrier height of 0.724 eV, Si/Mg0.5Zn0.95O thin film heterojunction diode is believed to have potential to be used in wider bandgap nanoelectronic device applications.

Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: Multi-parameter measurement reliability and precision studies

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

Zhang, Y.; Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094; Melnikov, A.

2015-03-15

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results weremore » studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.« less

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.

High-performance for hydrogen evolution and pollutant degradation of reduced graphene oxide/two-phase g-C3N4 heterojunction photocatalysts.

PubMed

Song, Chengjie; Fan, Mingshan; Shi, Weidong; Wang, Wei

2018-05-01

We have successfully synthesized the composites of two-phase g-C 3 N 4 heterojunction photocatalysts by one-step method. And the reduced graphene oxide/two-phase g-C 3 N 4 heterojunction photocatalyst was fabricated via a facile hydrothermal reduction method. The characterization results indicated that the two-phase g-C 3 N 4 was integrated closely, and the common phenomenon of agglomeration for g-C 3 N 4 was significantly reduced. Moreover, the oxidized graphene was reduced successfully in the composites and the graphene was overlaid on the surface or the interlayers of g-C 3 N 4 heterojunction composite uniformly. In addition, we have carried out the photocatalytic activity experiments by H 2 evolution and rhodamine B removal, tetracycline removal under the visible light irradiation. The results revealed that the composite has improved the separation efficiency a lot than the pure photocatalyst. The photocurrent test demonstrated that the recombination of electrons and holes were efficiently inhibited as well as enhanced the photocatalytic activity. The 0.4% rGO loaded samples, 0.4% rGOCN2, own the best performance. Its rate of H 2 evolution was 15 times as high as that of the pure g-C 3 N 4 .

Gate- and Light-Tunable pn Heterojunction Microwire Arrays Fabricated via Evaporative Assembly.

PubMed

Park, Jae Hoon; Kim, Jong Su; Choi, Young Jin; Lee, Wi Hyoung; Lee, Dong Yun; Cho, Jeong Ho

2017-02-01

One-dimensional (1D) nano/microwires have attracted considerable attention as versatile building blocks for use in diverse electronic, optoelectronic, and magnetic device applications. The large-area assembly of nano/microwires at desired positions presents a significant challenge for developing high-density electronic devices. Here, we demonstrated the fabrication of cross-stacked pn heterojunction diode arrays by integrating well-aligned inorganic and organic microwires fabricated via evaporative assembly. We utilized solution-processed n-type inorganic indium-gallium-zinc-oxide (IGZO) microwires and p-type organic 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) microwires. The formation of organic TIPS-PEN semiconductor microwire and their electrical properties were optimized by controlling both the amounts of added insulating polymer and the widths of the microwires. The resulting cross-stacked IGZO/TIPS-PEN microwire pn heterojunction devices exhibited rectifying behavior with a forward-to-reverse bias current ratio exceeding 10 2 . The ultrathin nature of the underlying n-type IGZO microwires yielded gate tunability in the charge transport behaviors, ranging from insulating to rectifying. The rectifying behaviors of the heterojunction devices could be modulated by controlling the optical power of the irradiated light. The fabrication of semiconducting microwires through evaporative assembly provides a facile and reliable approach to patterning or positioning 1D microwires for the fabrication of future flexible large-area electronics.

Interface energy band alignment at the all-transparent p-n heterojunction based on NiO and BaSnO3

NASA Astrophysics Data System (ADS)

Zhang, Jiaye; Han, Shaobo; Luo, Weihuang; Xiang, Shuhuai; Zou, Jianli; Oropeza, Freddy E.; Gu, Meng; Zhang, Kelvin H. L.

2018-04-01

Transparent oxide semiconductors hold great promise for many optoelectronic devices such as transparent electronics, UV-emitting devices, and photodetectors. A p-n heterojunction is the most ubiquitous building block to realize these devices. In this work, we report the fabrication and characterization of the interface properties of a transparent heterojunction consisting of p-type NiO and n-type perovskite BaSnO3. We show that high-quality NiO thin films can be epitaxially grown on BaSnO3 with sharp interfaces because of a small lattice mismatch (˜1.3%). The diode fabricated from this heterojunction exhibits rectifying behavior with a ratio of 500. X-ray photoelectron spectroscopy reveals a type II or "staggered" band alignment with valence and conduction band offsets of 1.44 eV and 1.86 eV, respectively. Moreover, a large upward band bending potential of 0.90 eV for BaSnO3 and a downward band bending potential of 0.15 eV for NiO were observed in the interface region. Such electronic properties have important implication for optoelectronic applications as the large built-in potential provides favorable energetics for photo-generated electron-hole separation/migration.

Electrostatically Gated Graphene-Zinc Oxide Nanowire Heterojunction.

PubMed

You, Xueqiu; Pak, James Jungho

2015-03-01

This paper presents an electrostatically gated graphene-ZnO nanowire (NW) heterojunction for the purpose of device applications for the first time. A sub-nanometer-thick energy barrier width was formed between a monatomic graphene layer and electrochemically grown ZnO NWs. Because of the narrow energy barrier, electrons can tunnel through the barrier when a voltage is applied across the junction. A near-ohmic current-voltage (I-V) curve was obtained from the graphene-electrochemically grown ZnO NW heterojunction. This near-ohmic contact changed to asymmetric I-V Schottky contact when the samples were exposed to an oxygen environment. It is believed that the adsorbed oxygen atoms or molecules on the ZnO NW surface capture free electrons of the ZnO NWs, thereby creating a depletion region in the ZnO NWs. Consequentially, the electron concentration in the ZnO NWs is dramatically reduced, and the energy barrier width of the graphene-ZnO NW heterojunction increases greatly. This increased energy barrier width reduces the electron tunneling probability, resulting in a typical Schottky contact. By adjusting the back-gate voltage to control the graphene-ZnO NW Schottky energy barrier height, a large modulation on the junction current (on/off ratio of 10(3)) was achieved.

Fast Response and High Sensitivity of ZnO Nanowires-Cobalt Phthalocyanine Heterojunction Based H2S Sensor.

PubMed

Kumar, Ashwini; Samanta, Soumen; Singh, Ajay; Roy, Mainak; Singh, Surendra; Basu, Saibal; Chehimi, Mohmad M; Roy, Kallol; Ramgir, Niranjan; Navaneethan, M; Hayakawa, Y; Debnath, Anil K; Aswal, Dinesh K; Gupta, Shiv K

2015-08-19

The room temperature chemiresistive response of n-type ZnO nanowire (ZnO NWs) films modified with different thicknesses of p-type cobalt phthalocyanine (CoPc) has been studied. With increasing thickness of CoPc (>15 nm), heterojunction films exhibit a transition from n- to p-type conduction due to uniform coating of CoPc on ZnO. The heterojunction films prepared with a 25 nm thick CoPc layer exhibit the highest response (268% at 10 ppm of H2S) and the fastest response (26 s) among all samples. The X-ray photoelectron spectroscopy and work function measurements reveal that electron transfer takes place from ZnO to CoPc, resulting in formation of a p-n junction with a barrier height of 0.4 eV and a depletion layer width of ∼8.9 nm. The detailed XPS analysis suggests that these heterojunction films with 25 nm thick CoPc exhibit the least content of chemisorbed oxygen, enabling the direct interaction of H2S with the CoPc molecule, and therefore exhibit the fastest response. The improved response is attributed to the high susceptibility of the p-n junctions to the H2S gas, which manipulates the depletion layer width and controls the charge transport.

Synergistic Effect of a Molecular Cocatalyst and a Heterojunction in a 1 D Semiconductor Photocatalyst for Robust and Highly Efficient Solar Hydrogen Production.

PubMed

Jiang, Daochuan; Irfan, Rana Muhammad; Sun, Zijun; Lu, Dapeng; Du, Pingwu

2016-11-09

Photocatalytic production of hydrogen by water splitting is a promising pathway for the conversion of solar energy into chemical energy. However, the photocatalytic conversion efficiency is often limited by the sluggish transfer of the photogenerated charge carriers, charge recombination, and subsequent slow catalytic reactions. Herein, we report a highly active noble-metal-free photocatalytic system for hydrogen production in water. The system contains a water-soluble nickel complex as a molecular cocatalyst and zinc sulfide on 1D cadmium sulfide as the heterojunction photocatalyst. The complex can efficiently transport photogenerated electrons and holes over a heterojunction photocatalyst to hamper charge recombination, leading to highly improved catalytic efficiency and durability of a heterojunction photocatalyst- molecular cocatalyst system. The results show that under optimal conditions, the average apparent quantum yield was approximately 58.3 % after 7 h of irradiation with monochromatic 420 nm light. In contrast, the value is only 16.8 % if the molecular cocatalyst is absent. Such a remarkable performance in a molecular cocatalyst-based photocatalytic system without any noble metal loading has, to the best of our knowledge, not been reported to date. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Integration of CdSe/CdSexTe1−x Type-II Heterojunction Nanorods into Hierarchically Porous TiO2 Electrode for Efficient Solar Energy Conversion

PubMed Central

Lee, Sangheon; Flanagan, Joseph C.; Kang, Joonhyeon; Kim, Jinhyun; Shim, Moonsub; Park, Byungwoo

2015-01-01

Semiconductor sensitized solar cells, a promising candidate for next-generation photovoltaics, have seen notable progress using 0-D quantum dots as light harvesting materials. Integration of higher-dimensional nanostructures and their multi-composition variants into sensitized solar cells is, however, still not fully investigated despite their unique features potentially beneficial for improving performance. Herein, CdSe/CdSexTe1−x type-II heterojunction nanorods are utilized as novel light harvesters for sensitized solar cells for the first time. The CdSe/CdSexTe1−x heterojunction-nanorod sensitized solar cell exhibits ~33% improvement in the power conversion efficiency compared to its single-component counterpart, resulting from superior optoelectronic properties of the type-II heterostructure and 1-octanethiol ligands aiding facile electron extraction at the heterojunction nanorod-TiO2 interface. Additional ~32% enhancement in power conversion efficiency is achieved by introducing percolation channels of large pores in the mesoporous TiO2 electrode, which allow 1-D sensitizers to infiltrate the entire depth of electrode. These strategies combined together lead to 3.02% power conversion efficiency, which is one of the highest values among sensitized solar cells utilizing 1-D nanostructures as sensitizer materials. PMID:26638994

Electronic Structure and Band Alignment at the NiO and SrTiO3 p-n Heterojunctions.

PubMed

Zhang, Kelvin H L; Wu, Rui; Tang, Fengzai; Li, Weiwei; Oropeza, Freddy E; Qiao, Liang; Lazarov, Vlado K; Du, Yingge; Payne, David J; MacManus-Driscoll, Judith L; Blamire, Mark G

2017-08-09

Understanding the energetics at the interface, including the alignment of valence and conduction bands, built-in potentials, and ionic and electronic reconstructions, is an important challenge in designing oxide interfaces that have controllable multifunctionalities for novel (opto-)electronic devices. In this work, we report detailed investigations on the heterointerface of wide-band-gap p-type NiO and n-type SrTiO 3 (STO). We show that despite a large lattice mismatch (∼7%) and dissimilar crystal structure, high-quality NiO and Li-doped NiO (LNO) thin films can be epitaxially grown on STO(001) substrates through a domain-matching epitaxy mechanism. X-ray photoelectron spectroscopy studies indicate that NiO/STO heterojunctions form a type II "staggered" band alignment. In addition, a large built-in potential of up to 0.97 eV was observed at the interface of LNO and Nb-doped STO (NbSTO). The LNO/NbSTO p-n heterojunctions exhibit not only a large rectification ratio of 2 × 10 3 but also a large ideality factor of 4.3. The NiO/STO p-n heterojunctions have important implications for applications in photocatalysis and photodetectors as the interface provides favorable energetics for facile separation and transport of photogenerated electrons and holes.

Fabrication of the heterojunction diode from Y-doped ZnO thin films on p-Si substrates by sol-gel method

NASA Astrophysics Data System (ADS)

Sharma, Sanjeev K.; Singh, Satendra Pal; Kim, Deuk Young

2018-02-01

The heterojunction diode of yttrium-doped ZnO (YZO) thin films was fabricated on p-Si(100) substrates by sol-gel method. The post-annealing process was performed at 600 °C in vacuum for a short time (3 min) to prevent inter-diffusion of Zn, Y, and Si atoms. X-ray diffraction (XRD) pattern of as-grown and annealed (600 °C in vacuum) films showed the preferred orientation along the c-axis (002) regardless of dopant concentrations. The uniform surface microstructure and the absence of other metal/oxide peaks in XRD pattern confirmed the excellence of films. The increasing bandgap and carrier concentration of YZO thin films were interpreted by the BM shift, that is, the Fermi level moves towards the conduction band edge. The current-voltage characteristics of the heterojunction diode, In/n-ZnO/p-Si/Al, showed a rectification behavior. The turn-on voltage and ideality factor of n-ZnO/p-Si and n-YZO/p-Si were observed to be 3.47 V, 2.61 V, and 1.97, 1.89, respectively. Y-dopant in ZnO thin films provided more donor electrons caused the shifting of Fermi-energy level towards the conduction band and strengthen the interest for heterojunction diodes.

Cd doping at PVD-CdS/CuInGaSe 2 heterojunctions

DOE PAGES

He, Xiaoqing; Paulauskas, Tadas; Ercius, Peter; ...

2017-02-20

In this paper, we report on direct evidence of Cd doping of the CuInGaSe 2 (CIGS) surface in physical vapor deposited (PVD) CdS/CIGS heterojunctions by scanning transmission electron microscopy (STEM) and related techniques. We find Cd doping of the CIGS near-surface region regardless of the presence or absence of Cu rich domains in the CdS for both zinc-blende (zb) and wurtzite (wz) CdS. However, we find that the Cd penetrates much farther into the CIGS when Cu-rich domains are present in the CdS. This suggests that Cu exchanges with Cd, increasing the concentration gradient for Cd in the CIGS andmore » thus driving Cd into the CIGS surface. The Cd doping is clearly resolved at atomic resolution in aberration-corrected STEM-high angle annular dark field images. In zb-CdS/CIGS heterojunctions, Cd is shown to substitute for both Cu and Ga atoms, while in wz-CdS/CIGS heterojunctions Cd seems to predominantly occupy Cu sites. Finally, Cd doping in the CIGS surface layer suggests the formation of a p-n homojunction in the CIGS, which may account for the high device efficiencies, comparable to CBD-CdS/CIGS processed structures.« less

Modulation-Doped In2 O3 /ZnO Heterojunction Transistors Processed from Solution.

PubMed

Khim, Dongyoon; Lin, Yen-Hung; Nam, Sungho; Faber, Hendrik; Tetzner, Kornelius; Li, Ruipeng; Zhang, Qiang; Li, Jun; Zhang, Xixiang; Anthopoulos, Thomas D

2017-05-01

This paper reports the controlled growth of atomically sharp In 2 O 3 /ZnO and In 2 O 3 /Li-doped ZnO (In 2 O 3 /Li-ZnO) heterojunctions via spin-coating at 200 °C and assesses their application in n-channel thin-film transistors (TFTs). It is shown that addition of Li in ZnO leads to n-type doping and allows for the accurate tuning of its Fermi energy. In the case of In 2 O 3 /ZnO heterojunctions, presence of the n-doped ZnO layer results in an increased amount of electrons being transferred from its conduction band minimum to that of In 2 O 3 over the interface, in a process similar to modulation doping. Electrical characterization reveals the profound impact of the presence of the n-doped ZnO layer on the charge transport properties of the isotype In 2 O 3 /Li-ZnO heterojunctions as well as on the operating characteristics of the resulting TFTs. By judicious optimization of the In 2 O 3 /Li-ZnO interface microstructure, and Li concentration, significant enhancement in both the electron mobility and TFT bias stability is demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Integration of CdSe/CdSexTe1-x Type-II Heterojunction Nanorods into Hierarchically Porous TiO2 Electrode for Efficient Solar Energy Conversion.

PubMed

Lee, Sangheon; Flanagan, Joseph C; Kang, Joonhyeon; Kim, Jinhyun; Shim, Moonsub; Park, Byungwoo

2015-12-07

Semiconductor sensitized solar cells, a promising candidate for next-generation photovoltaics, have seen notable progress using 0-D quantum dots as light harvesting materials. Integration of higher-dimensional nanostructures and their multi-composition variants into sensitized solar cells is, however, still not fully investigated despite their unique features potentially beneficial for improving performance. Herein, CdSe/CdSe(x)Te(1-x) type-II heterojunction nanorods are utilized as novel light harvesters for sensitized solar cells for the first time. The CdSe/CdSe(x)Te(1-x) heterojunction-nanorod sensitized solar cell exhibits ~33% improvement in the power conversion efficiency compared to its single-component counterpart, resulting from superior optoelectronic properties of the type-II heterostructure and 1-octanethiol ligands aiding facile electron extraction at the heterojunction nanorod-TiO(2) interface. Additional ~31% enhancement in power conversion efficiency is achieved by introducing percolation channels of large pores in the mesoporous TiO(2) electrode, which allow 1-D sensitizers to infiltrate the entire depth of electrode. These strategies combined together lead to 3.02% power conversion efficiency, which is one of the highest values among sensitized solar cells utilizing 1-D nanostructures as sensitizer materials.

3D Band Diagram and Photoexcitation of 2D–3D Semiconductor Heterojunctions

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

Li, Bo; Shi, Gang; Lei, Sidong

2015-08-17

The emergence of a rich variety of two-dimensional (2D) layered semiconductor materials has enabled the creation of atomically thin heterojunction devices. Junctions between atomically thin 2D layers and 3D bulk semiconductors can lead to junctions that are fundamentally electronically different from the covalently bonded conventional semiconductor junctions. In this paper, we propose a new 3D band diagram for the heterojunction formed between n-type monolayer MoS 2 and p-type Si, in which the conduction and valence band-edges of the MoS 2 monolayer are drawn for both stacked and in-plane directions. This new band diagram helps visualize the flow of charge carriersmore » inside the device in a 3D manner. Our detailed wavelength-dependent photocurrent measurements fully support the diagrams and unambiguously show that the band alignment is type I for this 2D-3D heterojunction. Photogenerated electron–hole pairs in the atomically thin monolayer are separated and driven by an external bias and control the “on/off” states of the junction photodetector device. Finally, two photoresponse regimes with fast and slow relaxation are also revealed in time-resolved photocurrent measurements, suggesting the important role played by charge trap states.« less

Degradation of microcystin-LR by highly efficient AgBr/Ag3PO4/TiO2 heterojunction photocatalyst under simulated solar light irradiation

NASA Astrophysics Data System (ADS)

Wang, Xin; Utsumi, Motoo; Yang, Yingnan; Li, Dawei; Zhao, Yingxin; Zhang, Zhenya; Feng, Chuanping; Sugiura, Norio; Cheng, Jay Jiayang

2015-01-01

A novel photocatalyst AgBr/Ag3PO4/TiO2 was developed by a simple facile in situ deposition method and used for degradation of mirocystin-LR. TiO2 (P25) as a cost effective chemical was used to improve the stability of AgBr/Ag3PO4 under simulated solar light irradiation. The photocatalytic activity tests for this heterojunction were conducted under simulated solar light irradiation using methyl orange as targeted pollutant. The results indicated that the optimal Ag to Ti molar ratio for the photocatalytic activity of the resulting heterojunction AgBr/Ag3PO4/TiO2 was 1.5 (named as 1.5 BrPTi), which possessed higher photocatalytic capacity than AgBr/Ag3PO4. The 1.5 BrPTi heterojunction was also more stable than AgBr/Ag3PO4 in photocatalysis. This highly efficient and relatively stable photocatalyst was further tested for degradation of the hepatotoxin microcystin-LR (MC-LR). The results suggested that MC-LR was much more easily degraded by 1.5 BrPTi than by AgBr/Ag3PO4. The quenching effects of different scavengers proved that reactive h+ and •OH played important roles for MC-LR degradation.

Room-temperature preparation of trisilver-copper-sulfide/polymer based heterojunction thin film for solar cell application

NASA Astrophysics Data System (ADS)

Lei, Yan; Yang, Xiaogang; Gu, Longyan; Jia, Huimin; Ge, Suxiang; Xiao, Pin; Fan, Xiaoli; Zheng, Zhi

2015-04-01

Solar cells devices based on inorganic/polymer heterojunction can be a possible solution to harvest solar energy and convert to electric energy with high efficiency through a cost-effective fabrication. The solution-process method can be easily used to produce large area devices. Moreover, due to the intrinsic different charge separation, diffusion or recombination in various semiconductors, the interfaces between each component may strongly influence the inorganic/polymer heterojunction performance. Here we prepared a n-type Ag3CuS2 (Eg = 1.25 eV) nanostructured film through a room-temperature element reaction process, which was confirmed as direct bandgap semiconductor through density function theory simulation. This Ag3CuS2 film was spin-coated with an organic semiconducting poly(3-hexythiophene) (P3HT) or polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) film, which formed an inorganic/polymer heterojunction. After constructing it to a solar cell device, the power conversion efficiencies of 0.79% and 0.31% were achieved with simulated solar illumination on Ag3CuS2/P3HT and Ag3CuS2/PTB7, respectively. A possible mechanism was discussed and we showed the charge separation at interface of inorganic and polymer semiconductors played an important role.

Charge carrier transport and injection across organic heterojunctions

NASA Astrophysics Data System (ADS)

Tsang, Sai Wing

The discovery of highly efficient organic light-emitting diodes (OLEDs) in the 1980s has stimulated extensive research on organic semiconductors and devices. Underlying this breakthrough is the realization of the organic heterojunction (OH). Besides OLEDs, the implementation of the OH also significantly improves the power conversion efficiency in organic photovoltaic cells (OPVs). The continued technological advancements in organic electronic devices depend on the accumulation of knowledge of the intrinsic properties of organic materials and related interfaces. Among them, charge-carrier transport and carrier injection are two key factors that govern the performance of a device. This thesis mainly focuses on the charge carrier injection and transport at organic heterojunctions. The carrier transport properties of different organic materials used in this study are characterized by time-of-flight (TOF) and admittance spectroscopy (AS). An injection model is formulated by considering the carrier distribution at both sides of the interface. Using a steady-state simulation approach, the effect of accumulated charges on energy level alignment at OH is revealed. Instead of a constant injection barrier, it is found that the barrier varies with applied voltage. Moreover, an escape probability function in the injection model is modified by taking into account the total hopping rate and available hopping sites at the interface. The model predicts that the injection current at low temperature can be dramatically modified by an extremely small density of deep trap states. More importantly, the temperature dependence of the injection current is found to decrease with increasing barrier height. This suggests that extracting the barrier height from the J vs 1/T plot, as commonly employed in the literature, is problematic. These theoretical predictions are confirmed by a series of experiments on heterojunction devices with various barrier heights. In addition, the presence of deep trap states is also consistent with carrier mobility measurements at low temperature. From the point of view of application, an interface chemical doping method is proposed to engineer the carrier injection at an organic heterojunction. It is found that the injection current can be effectively increased or suppressed by introducing a thin (2 nm) doped organic layer at the interface. This technique is further extended to study the impact of an injection barrier at the OH, in OLEDs, on device performance. It is shown that a 0.3 eV injection barrier at the OH, that is normally negligible at metal/organic interface, can reduce the device efficiency by 25%. This is explained by the carrier distribution in the density-of-states at the OH. Furthermore, the carrier transport properties in a bulk heterojunction system are investigated. The bulk heterojunction consists of an interpenetrating network of a polymeric electron donor and a molecular electron acceptor. This material system has been studied in the last few years as an attractive power conversion efficiency (5% under AM 1.5) of OPV cells has been demonstrated. It is found that the electron mobility is greatly dependent on the thermal treatment of the film. Interfacial dipole effect at the heterojunction between the donor and the acceptor is proposed to be the determining factor that alters the carrier mobility in different nanoscale structures.

Efficient planar heterojunction perovskite solar cells employing graphene oxide as hole conductor.

PubMed

Wu, Zhongwei; Bai, Sai; Xiang, Jian; Yuan, Zhongcheng; Yang, Yingguo; Cui, Wei; Gao, Xingyu; Liu, Zhuang; Jin, Yizheng; Sun, Baoquan

2014-09-21

Graphene oxide (GO) is employed as a hole conductor in inverted planar heterojunction perovskite solar cells, and the devices with CH₃NH₃PbI₃-xClx as absorber achieve an efficiency of over 12%. The perovskite film grown on GO exhibits enhanced crystallization, high surface coverage ratio as well as preferred in-plane orientation of the (110) plane. Efficient hole extraction from the perovskite to GO is demonstrated.

Current and lattice matched tandem solar cell

DOEpatents

Olson, Jerry M.

1987-01-01

A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga.sub.x In.sub.1-x P (0.505.ltoreq.X.ltoreq.0.515) top cell semiconductor lattice matched to a GaAs bottom cell semiconductor at a low-resistance heterojunction, preferably a p+/n+ heterojunction between the cells. The top and bottom cells are both lattice matched and current matched for high efficiency solar radiation conversion to electrical energy.

InP Heterojunction Bipolar Transistor Amplifiers to 255 GHz

NASA Technical Reports Server (NTRS)

Radisic, Vesna; Sawdai, Donald; Scott, Dennis; Deal, William; Dang, Linh; Li, Danny; Cavus, Abdullah; To, Richard; Lai, Richard

2009-01-01

Two single-stage InP heterojunction bipolar transistor (HBT) amplifiers operate at 184 and 255 GHz, using Northrop Grumman Corporation s InP HBT MMIC (monolithic microwave integrated circuit) technology. At the time of this reporting, these are reported to be the highest HBT amplifiers ever created. The purpose of the amplifier design is to evaluate the technology capability for high-frequency designs and verify the model for future development work.

Charge-Carrier Balance for Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells.

PubMed

Chen, Ke; Hu, Qin; Liu, Tanghao; Zhao, Lichen; Luo, Deying; Wu, Jiang; Zhang, Yifei; Zhang, Wei; Liu, Feng; Russell, Thomas P; Zhu, Rui; Gong, Qihuang

2016-12-01

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stimulated emission within the exciplex band by plasmonic-nanostructured polymeric heterojunctions.

PubMed

Zhang, Xinping; Li, Hongwei; Wang, Yimeng; Liu, Feifei

2015-03-19

Organic heterojunctions have been extensively employed in the design of light-emitting diodes, photovoltaic devices, and thin-film field-effect transistors, which can be achieved by constructing a bilayer or a multi-layered thin-film deposition, or by blending two or more organic semiconductors with different charge-transport performances. Charge transfer excited states or exciplex may form on the heterointerfaces. Efficient light-emitting diodes have been demonstrated using exciplex emission. However, lasing or stimulated emission processes have not been observed with exciplex formation at organic heterojunctions. In this work, we demonstrate strong coherent interaction between photons and exciplex formation in the blends of poly-9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine (PFB) and poly-9,9'-dioctylfluorene-co-benzothiadiazole (F8BT), leading to transient stimulated exciplex emission. The responsible mechanisms involve plasmonic local-field enhancement and plasmonic feedback in a three-dimensional gold-nanoparticle matrix.

Band-Gap Engineering at a Semiconductor-Crystalline Oxide Interface

DOE PAGES

Jahangir-Moghadam, Mohammadreza; Ahmadi-Majlan, Kamyar; Shen, Xuan; ...

2015-02-09

The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to integrating the functionalities of oxides onto semiconductors is controlling the band alignment at interfaces between the two materials. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally coherent interfaces between SrZr xTi 1-xO₃ and Ge, in which the band gap of the former is enhanced with Zr content x.more » We present structural and electrical characterization of SrZr xTi 1-xO₃-Ge heterojunctions and demonstrate a type-I band offset can be achieved. These results demonstrate that band gap engineering can be exploited to realize functional semiconductor crystalline oxide heterojunctions.« less

A High Sensitivity Isopropanol Vapor Sensor Based on Cr₂O₃-SnO₂ Heterojunction Nanocomposites via Chemical Precipitation Route.

PubMed

Jawaher, K Rackesh; Indirajith, R; Krishnan, S; Robert, R; Pasha, S K Khadheer; Deshmukh, Kalim; Sastikumar, D; Das, S Jerome

2018-08-01

Cr2O3-SnO2 heterojunction nanocomposites were prepared via chemical precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra and Field Emission Electron Microscopy (FESEM). The XRD spectrum confirms the presence of both tetragonal rutile SnO2 and rhombohedral corundum Cr2O3 structure. Further investigation into the gas sensing performances of the prepared Cr2O3-SnO2 nanocomposites exhibited an enhanced sensitivity towards VOPs such as isopropanol, acetone, ethanol and formaldehyde. Especially, isopropanol vapor sensor shows excellent sensitivity at an operating temperature of 100 °C. The highest sensitivity for Cr2O3-SnO2 heterojunction nanocomposites indicate that these materials can be a good candidate for the production of high-performance isopropanol sensors.

Enhanced Photocatalytic Activity of Two-Pot-Synthesized BiFeO3-ZnFe2O4 Heterojunction Nanocomposite

NASA Astrophysics Data System (ADS)

Ghasemi, A.; Hasheminiasari, M.; Masoudpanah, S. M.; Safizade, B.

2018-04-01

BiFeO3-ZnFe2O4 heterojunction nanocomposites have been produced by a chemical synthesis method using one- and two-pot approaches. X-ray diffraction patterns of as-calcined samples indicated formation of pure zinc ferrite (ZnFe2O4) and bismuth ferrite (BiFeO3) phases, each retaining its crystal structure. Diffuse reflectance spectrometry was applied to calculate the optical bandgap of the photocatalysts, revealing values in the range from 2.03 eV to 2.17 eV, respectively. The maximum photodegradation of methylene blue of about 97% was achieved using two-pot-synthesized photocatalyst after 120 min of visible-light irradiation due to the higher probability of charge separation of photogenerated electron-hole pairs in the heterojunction structure. Photoluminescence spectra showed lower emission intensity of two-pot-synthesized photocatalyst, due to its lower recombination rate originating from greater charge separation.

Maximizing ion current rectification in a bipolar conical nanopore fluidic diode using optimum junction location.

PubMed

Singh, Kunwar Pal

2016-10-12

The ion current rectification has been obtained as a function of the location of a heterojunction in a bipolar conical nanopore fluidic diode for different parameters to determine the junction location for maximum ion current rectification using numerical simulations. Forward current peaks for a specific location of the junction and reverse current decreases with the junction location due to a change in ion enrichment/depletion in the pore. The optimum location of the heterojunction shifts towards the tip with base/tip diameter and surface charge density, and towards the base with the electrolyte concentration. The optimum location of the heterojunction has been approximated by an equation as a function of pore length, base/tip diameter, surface charge density and electrolyte concentration. The study is useful to design a rectifier with maximum ion current rectification for practical purposes.

Demonstration of high-responsivity epitaxial β-Ga2O3/GaN metal–heterojunction-metal broadband UV-A/UV-C detector

NASA Astrophysics Data System (ADS)

Kalra, Anisha; Vura, Sandeep; Rathkanthiwar, Shashwat; Muralidharan, Rangarajan; Raghavan, Srinivasan; Nath, Digbijoy N.

2018-06-01

We demonstrate epitaxial β-Ga2O3/GaN-based vertical metal–heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >103, and a photo-to-dark current ratio of ∼100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga2O3 on metal organic chemical vapor deposition (MOCVD)-grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.

Charge Transfer and Collection in Dilute Organic Donor-Acceptor Heterojunction Blends.

PubMed

Ding, Kan; Liu, Xiao; Forrest, Stephen R

2018-05-09

Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor-acceptor (D-A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D-A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C 70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C 70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C 70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations.

Light Harvesting for Organic Photovoltaics

PubMed Central

2016-01-01

The field of organic photovoltaics has developed rapidly over the last 2 decades, and small solar cells with power conversion efficiencies of 13% have been demonstrated. Light absorbed in the organic layers forms tightly bound excitons that are split into free electrons and holes using heterojunctions of electron donor and acceptor materials, which are then extracted at electrodes to give useful electrical power. This review gives a concise description of the fundamental processes in photovoltaic devices, with the main emphasis on the characterization of energy transfer and its role in dictating device architecture, including multilayer planar heterojunctions, and on the factors that impact free carrier generation from dissociated excitons. We briefly discuss harvesting of triplet excitons, which now attracts substantial interest when used in conjunction with singlet fission. Finally, we introduce the techniques used by researchers for characterization and engineering of bulk heterojunctions to realize large photocurrents, and examine the formed morphology in three prototypical blends. PMID:27951633

Applied research on 2-6 compound materials for heterojunction solar cells

NASA Technical Reports Server (NTRS)

Bube, R. H.

1975-01-01

Several II-VI heterojunctions show promise for photovoltaic conversion of solar energy. The three of greatest interest are p-CdTe/n-CdS, p-CdTe/n-ZnSe, and p-ZnTe/n-CdSe. Several p-CdTe/n-CdS heterojunction cells have been prepared by close spaced transport deposition of p-CdTe on single crystal n-CdS, and by two source vacuum evaporation of n-CdS on single crystal p-CdTe. Both types of cells, in an experimental stage, are quite comparable, exhibiting values of quantum efficiency between 0.5 and 0.9, open circuit voltages between 0.50 and 0.66 V, fill factors between 0.4 and 0.6, and solar efficiencies up to 4 percent. Cells of p-ZnTe/n-CdSe have also been made by close spaced vapor transport deposition of n-CdSe on single crystal p-ZnTe.

Interaction at the silicon/transition metal oxide heterojunction interface and its effect on the photovoltaic performance.

PubMed

Liang, Zhimin; Su, Mingze; Zhou, Yangyang; Gong, Li; Zhao, Chuanxi; Chen, Keqiu; Xie, Fangyan; Zhang, Weihong; Chen, Jian; Liu, Pengyi; Xie, Weiguang

2015-11-07

The interfacial reaction and energy level alignment at the Si/transition metal oxide (TMO, including MoO3-x, V2O5-x, WO3-x) heterojunction are systematically investigated. We confirm that the interfacial reaction appears during the thermal deposition of TMO, with the reaction extent increasing from MoO3-x, to V2O5-x, and to WO3-x. The reaction causes the surface oxidation of silicon for faster electron/hole recombination, and the reduction of TMO for effective hole collection. The photovoltaic performance of the Si/TMO heterojunction devices is affected by the interface reaction. MoO3-x are the best hole selecting materials that induce least surface oxidation but strongest reduction. Compared with H-passivation, methyl group passivation is an effective way to reduce the interface reaction and improve the interfacial energy level alignment for better electron and hole collection.

Synthesis of p-type nickel oxide nanosheets on n-type titanium dioxide nanorod arrays for p-n heterojunction-based UV photosensor

NASA Astrophysics Data System (ADS)

Yusoff, M. M.; Mamat, M. H.; Malek, M. F.; Abdullah, M. A. R.; Ismail, A. S.; Saidi, S. A.; Mohamed, R.; Suriani, A. B.; Khusaimi, Z.; Rusop, M.

2018-05-01

Titanium dioxide (TiO2) nanorod arrays (TNAs) were synthesized and deposited on fluorine tin oxide (FTO)-coated glass substrate using a novel and facile immersion method in a glass container. The synthesis and deposition of p-type nickel oxide (NiO) nanosheets (NS) on the n-type TNAs was investigated in the p-n heterojunction photodiode (PD) for the application of ultraviolet (UV) photosensor. The fabricated TNAs/NiO NS based UV photosensor exhibited a highly increased photocurrent of 4.3 µA under UV radiation (365 nm, 750 µW/cm2) at 1.0 V reverse bias. In this study, the fabricated TNAs/NiO NS p-n heterojunction based photodiode showed potential applications for UV photosensor based on the stable photo-generated current attained under UV radiation.

Carbon Nanotube-Silicon Nanowire Heterojunction Solar Cells with Gas-Dependent Photovoltaic Performances and Their Application in Self-Powered NO2 Detecting.

PubMed

Jia, Yi; Zhang, Zexia; Xiao, Lin; Lv, Ruitao

2016-12-01

A multifunctional device combining photovoltaic conversion and toxic gas sensitivity is reported. In this device, carbon nanotube (CNT) membranes are used to cover onto silicon nanowire (SiNW) arrays to form heterojunction. The porous structure and large specific surface area in the heterojunction structure are both benefits for gas adsorption. In virtue of these merits, gas doping is a feasible method to improve cell's performance and the device can also work as a self-powered gas sensor beyond a solar cell. It shows a significant improvement in cell efficiency (more than 200 times) after NO2 molecules doping (device working as a solar cell) and a fast, reversible response property for NO2 detection (device working as a gas sensor). Such multifunctional CNT-SiNW structure can be expected to open a new avenue for developing self-powered, efficient toxic gas-sensing devices in the future.

Nanotetrapods: quantum dot hybrid for bulk heterojunction solar cells

PubMed Central

2013-01-01

Hybrid thin film solar cell based on all-inorganic nanoparticles is a new member in the family of photovoltaic devices. In this work, a novel and performance-efficient inorganic hybrid nanostructure with continuous charge transportation and collection channels is demonstrated by introducing CdTe nanotetropods (NTs) and CdSe quantum dots (QDs). Hybrid morphology is characterized, demonstrating an interpenetration and compacted contact of NTs and QDs. Electrical measurements show enhanced charge transfer at the hybrid bulk heterojunction interface of NTs and QDs after ligand exchange which accordingly improves the performance of solar cells. Photovoltaic and light response tests exhibit a combined optic-electric contribution from both CdTe NTs and CdSe QDs through a formation of interpercolation in morphology as well as a type II energy level distribution. The NT and QD hybrid bulk heterojunction is applicable and promising in other highly efficient photovoltaic materials such as PbS QDs. PMID:24139059

Method of fabricating an optoelectronic device having a bulk heterojunction

DOEpatents

Shtein, Max [Ann Arbor, MI; Yang, Fan [Princeton, NJ; Forrest, Stephen R [Princeton, NJ

2008-10-14

A method of fabricating an optoelectronic device comprises: depositing a first layer having protrusions over a first electrode, in which the first layer comprises a first organic small molecule material; depositing a second layer on the first layer such that the second layer is in physical contact with the first layer; in which the smallest lateral dimension of the protrusions are between 1 to 5 times the exciton diffusion length of the first organic small molecule material; and depositing a second electrode over the second layer to form the optoelectronic device. A method of fabricating an organic optoelectronic device having a bulk heterojunction is also provided and comprises: depositing a first layer with protrusions over an electrode by organic vapor phase deposition; depositing a second layer on the first layer where the interface of the first and second layers forms a bulk heterojunction; and depositing another electrode over the second layer.

Effects of Piezoelectric Potential of ZnO on Resistive Switching Characteristics of Flexible ZnO/TiO2 Heterojunction Cells

NASA Astrophysics Data System (ADS)

Li, Hongxia; Zhou, You; Du, Gang; Huang, Yanwei; Ji, Zhenguo

2018-03-01

Flexible resistance random access memory (ReRAM) devices with a heterojunction structure of PET/ITO/ZnO/TiO2/Au were fabricated on polyethylene terephthalate/indium tin oxide (PET/ITO) substrates by different physical and chemical preparation methods. X-ray diffraction, scanning electron microscopy and atomic force microscopy were carried out to investigate the crystal structure, surface topography and cross-sectional structure of the prepared films. X-ray photoelectron spectroscopy was also used to identify the chemical state of Ti, O and Zn elements. Theoretical and experimental analyses were conducted to identify the effect of piezoelectric potential of ZnO on resistive switching characteristics of flexible ZnO/TiO2 heterojunction cells. The results showed a pathway to enhance the performance of ReRAM devices by engineering the interface barrier, which is also feasible for other electronics, optoelectronics and photovoltaic devices.

Reinventing solid state electronics: Harnessing quantum confinement in bismuth thin films

NASA Astrophysics Data System (ADS)

Gity, Farzan; Ansari, Lida; Lanius, Martin; Schüffelgen, Peter; Mussler, Gregor; Grützmacher, Detlev; Greer, J. C.

2017-02-01

Solid state electronics relies on the intentional introduction of impurity atoms or dopants into a semiconductor crystal and/or the formation of junctions between different materials (heterojunctions) to create rectifiers, potential barriers, and conducting pathways. With these building blocks, switching and amplification of electrical currents and voltages are achieved. As miniaturisation continues to ultra-scaled transistors with critical dimensions on the order of ten atomic lengths, the concept of doping to form junctions fails and forming heterojunctions becomes extremely difficult. Here, it is shown that it is not needed to introduce dopant atoms nor is a heterojunction required to achieve the fundamental electronic function of current rectification. Ideal diode behavior or rectification is achieved solely by manipulation of quantum confinement using approximately 2 nm thick films consisting of a single atomic element, the semimetal bismuth. Crucially for nanoelectronics, this approach enables room temperature operation.

Electromagnetic Field Enhancement on Axially Heterostructured NWs: The Role of the Heterojunctions

NASA Astrophysics Data System (ADS)

Pura, J. L.; Souto, J.; Periwal, P.; Baron, T.; Jiménez, J.

2018-05-01

Semiconductor nanowires are the building blocks of future nanoelectronic devices. The study of the interaction between nanowires and visible light reveals resonances that promise light absorption/scattering engineering for photonic applications. We carried out experimental measurements through the micro-Raman spectroscopy of different group IV nanowires, both homogeneous Si nanowires and axially heterostructured SiGe/Si nanowires. These experimental measurements show an enhancement of the Raman signal in the vicinity of the heterojunction of SiGe/Si nanowires. The results are analysed in terms of the electromagnetic modelling of the light/nanowire interaction using finite element methods. The presence of axial heterostructures is shown to produce electromagnetic resonances, and the results are understood as a consequence of a finite change in the relative permittivity of the material at the SiGe/Si heterojunction. This effect opens a path to controlling interactions between light and matter at the nanoscale with direct applications in photonic nanodevices.

Photo-controllable memristive behavior of graphene/diamond heterojunctions

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

Ueda, K.; Aichi, S.; Asano, H.

2016-05-30

Graphene/diamond (carbon sp{sup 2}-sp{sup 3}) heterojunctions are demonstrated as photo-controllable memristors with photoswitchable multiple resistance states and nonvolatile memory functions. The ratio of conductivity change between the higher and lower resistance states of the junctions was ∼10{sup 3}. The junctions exhibit light wavelength selectivity, and the resistance states can be switched only by blue or violet light irradiation. The mechanism for the change in photoconductivity is considered to be caused by oxidation-reduction of the graphene and/or graphene-diamond (sp{sup 2}-sp{sup 3}) interfaces through the movement of oxygen ions by bias with photo-irradiation because they have wavelength selectivity and require air exposuremore » for several days to exhibit memristive behavior. These results indicate that graphene-diamond, carbon sp{sup 2}-sp{sup 3} heterojunctions can be used as photo-controllable devices with both photomemory and photoswitching functions.« less

Vertical phase separation in bulk heterojunction solar cells formed by in situ polymerization of fulleride

PubMed Central

Zhang, Lipei; Xing, Xing; Zheng, Lingling; Chen, Zhijian; Xiao, Lixin; Qu, Bo; Gong, Qihuang

2014-01-01

Vertical phase separation of the donor and the acceptor in organic bulk heterojunction solar cells is crucial to improve the exciton dissociation and charge transport efficiencies. This is because whilst the exciton diffusion length is limited, the organic film must be thick enough to absorb sufficient light. However, it is still a challenge to control the phase separation of a binary blend in a bulk heterojunction device architecture. Here we report the realization of vertical phase separation induced by in situ photo-polymerization of the acrylate-based fulleride. The power conversion efficiency of the devices with vertical phase separation increased by 20%. By optimising the device architecture, the power conversion efficiency of the single junction device reached 8.47%. We believe that in situ photo-polymerization of acrylate-based fulleride is a universal and controllable way to realise vertical phase separation in organic blends. PMID:24861168

Improvement of UV electroluminescence of n-ZnO/p-GaN heterojunction LED by ZnS interlayer.

PubMed

Zhang, Lichun; Li, Qingshan; Shang, Liang; Wang, Feifei; Qu, Chong; Zhao, Fengzhou

2013-07-15

n-ZnO/p-GaN heterojunction light emitting diodes with different interfacial layers were fabricated by pulsed laser deposition. The electroluminescence (EL) spectra of the n-ZnO/p-GaN diodes display a broad blue-violet emission centered at 430 nm, whereas the n-ZnO/ZnS/p-GaN and n-ZnO/AlN/p-GaN devices exhibit ultraviolet (UV) emission. Compared with the AlN interlayer, which is blocking both electron and hole at hetero-interface, the utilization of ZnS as intermediate layer can lower the barrier height for holes and keep an effective blocking for electron. Thus, an improved UV EL intensity and a low turn-on voltage (~5V) were obtained. The results were studied by peak-deconvolution with Gaussian functions and were discussed using the band diagram of heterojunctions.

Pure ultraviolet emission from ZnO quantum dots-based/GaN heterojunction diodes by MgO interlayer

NASA Astrophysics Data System (ADS)

Chen, Cheng; Liang, Renli; Chen, Jingwen; Zhang, Jun; Wang, Shuai; Zhao, Chong; Zhang, Wei; Dai, Jiangnan; Chen, Changqing

2017-07-01

We demonstrate the fabrication and characterization of ZnO/GaN-based heterojunction light-emitting diodes (LEDs) by using air-stable and solution-processable ZnO quantum dots (QDs) with a thin MgO interlayer acting as an electron blocking layer (EBL). The ZnO QDs/MgO/ p-GaN heterojunction can only display electroluminescence (EL) characteristic in reverse bias regime. Under sufficient reverse bias, a fairly pure ultraviolet EL emission located at 370 nm deriving from near band edge of ZnO with a full width at half maximum (FWHM) of 8.3 nm had been obtained, while the deep-level emission had been almost totally suppressed. The EL origination and corresponding carrier transport mechanisms were investigated qualitatively in terms of photoluminescence (PL) results and energy band diagram.[Figure not available: see fulltext.

Negative differential resistance in low Al-composition p-GaN/Mg-doped Al0.15Ga0.85N/n+-GaN hetero-junction grown by metal-organic chemical vapor deposition on sapphire substrate

NASA Astrophysics Data System (ADS)

Zhang, Kexiong; Liang, Hongwei; Shen, Rensheng; Wang, Dongsheng; Tao, Pengcheng; Liu, Yang; Xia, Xiaochuan; Luo, Yingmin; Du, Guotong

2014-02-01

Negative differential resistance (NDR) behavior was observed in low Al-composition p-GaN/Mg-doped-Al0.15Ga0.85N/n+-GaN hetero-junction grown by metal-organic chemical vapor deposition on sapphire substrate. The energy band and free carrier concentration of hetero-junction were studied by the model of the self-consistent solution of Schrödinger-Poisson equations combined with polarization engineering theory. At the forward bias of 0.95 V, the NDR effect has a high peak-to-valley current ratio of ˜9 with a peak current of 22.4 mA (˜current density of 11.4 A/cm2). An interesting phenomenon of NDR disappearance after consecutive scans and recurrence after electrical treatment was observed, which was associated with Poole-Frenkel effect.

Recombination in polymer-fullerene bulk heterojunction solar cells

NASA Astrophysics Data System (ADS)

Cowan, Sarah R.; Roy, Anshuman; Heeger, Alan J.

2010-12-01

Recombination of photogenerated charge carriers in polymer bulk heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and the fill factor (FF). Identifying the mechanism of recombination is, therefore, fundamentally important for increasing the power conversion efficiency. Light intensity and temperature-dependent current-voltage measurements on polymer BHJ cells made from a variety of different semiconducting polymers and fullerenes show that the recombination kinetics are voltage dependent and evolve from first-order recombination at short circuit to bimolecular recombination at open circuit as a result of increasing the voltage-dependent charge carrier density in the cell. The “missing 0.3 V” inferred from comparison of the band gaps of the bulk heterojunction materials and the measured open-circuit voltage at room-temperature results from the temperature dependence of the quasi-Fermi levels in the polymer and fullerene domains—a conclusion based on the fundamental statistics of fermions.

Shelf life and outdoor degradation studies of organic bulk heterojunction solar cells

NASA Astrophysics Data System (ADS)

Gergova, R.; Sendova-Vassileva, M.; Popkirov, G.; Gancheva, V.; Grancharov, G.

2018-03-01

We studied the degradation of different types of bulk heterojunction devices, in which the materials comprising the active layer and/or the materials used for the back electrode are varied. The devices are deposited on ITO covered glass and have the structure PEDOT:PSS/BHJ/Me, where PEDOT:PSS is the hole transport layer, BHJ (bulk heterojunction) is the active layer comprising a polymer donor (e.g. PTB7, PCDTBT) and a fullerene derivative acceptor (e.g. PC60BM, PC70BM) deposited by spin coating, Me is the metal back contact, which is either Ag or Al deposited by magnetron sputtering or thermal evaporation. The device performance was monitored after storage in the dark at ambient conditions by following the evolution of the J-V curve over time. Results of real conditions outdoor degradation studies are also presented. The stability of the different solar cell structures studied is compared.

Fabrication of InP-pentacene inorganic-organic hybrid heterojunction using MOCVD grown InP for photodetector application

NASA Astrophysics Data System (ADS)

Sarkar, Kalyan Jyoti; Pal, B.; Banerji, P.

2018-04-01

We fabricated inorganic-organic hybrid heterojunction between indium phosphide (InP) and pentacene for photodetector application. InP layer was grown on n-Si substrate by atmospheric pressure metal organic chemical vapour deposition (MOCVD) technique. Morphological properties of InP and pentacene thin film were characterized by atomic force microscopy (AFM). Current-voltage characteristics were investigated in dark and under illumination condition at room temperature. During illumination, different wavelengths of visible and infrared light source were employed to perform the electrical measurement. Enhancement of photocurrent was observed with decreasing in wavelength of incident photo radiation. Ideality factor was found to be 1.92. High rectification ratio of 225 was found at ± 3 V in presence of infrared light source. This study provides new insights of inorganic-organic hybrid heterojunction for broadband photoresponse in visible to near infrared (IR) region under low reverse bias condition.

Orientation independence of heterojunction-band offsets at GaAs-AlAs heterointerfaces characterized by x-ray photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Hirakawa, K.; Hashimoto, Y.; Ikoma, T.

1990-12-01

We systematically studied the orientation and the growth sequence dependence of the valence-band offset ΔEv at the lattice-matched common anion GaAs-AlAs interfaces. High quality GaAs-AlAs heterojunctions were carefully grown on GaAs substrates with three major orientations, namely, (100), (110), and (111)B. The core level energy distance ΔECL between Ga 3d and Al 2p levels was measured by in situ x-ray photoemission spectroscopy. ΔECL is found to be independent of the substrate orientation and the growth sequence, which clearly indicates the face independence of ΔEv. This result suggests that the band lineup at lattice-matched isovalent semiconductor heterojunctions is determined by the bulk properties of the constituent materials. ΔEv is determined to be 0.44 ± 0.05 eV.

Synthesis and interface structures of zinc sulfide sheathed zinc-cadmium nanowire heterojunctions.

PubMed

Shen, Guozhen; Bando, Yoshio; Gao, Yihua; Golberg, Dmitri

2006-07-27

Zinc sulfide (ZnS) sheathed zinc (Zn)-cadmium (Cd) nanowire heterojunctions have been prepared by thermal evaporating of ZnS and CdS powders in a vertical induction furnace at 1200 degrees C. Studies found that both the Zn and Cd subnanowires, within a single nanoheterojunction, are single-crystallines with the growth directions perpendicular to the [210] plane, whereas the sheathed ZnS is polycrystalline with a thickness of ca. 5 nm. The Zn/Cd interface structure in the ZnS sheathed Zn-Cd nanowire heterojunctions was thoroughly experimentally studied by high-resolution transmission electron microscopy and theoretically studied using a near-coincidence site lattice (NCSL) concept. The results show that the Cd and Zn have a crystalline orientation relationship as [0001]Zn//[0001]Cd, (10(-)10)Zn//(10(-)10)Cd, (01(-)10)Zn//(01(-)10)Cd, and ((-)1100)Zn//((-)1100)Cd.

Heterojunction CuO-TiO2 nanocomposite synthesis for significant photocatalytic hydrogen production

NASA Astrophysics Data System (ADS)

Manjunath, K.; Souza, V. S.; Ramakrishnappa, T.; Nagaraju, G.; Scholten, J. D.; Dupont, J.

2016-11-01

Effective and low-cost photocatalysts have been synthesized by a simple hydrothermal process. In this process, the two CuO and TiO2 bound one over the other and formed a heterojunction CuO-TiO2 nanocomposite. CuO serves as electron reservoir by receiving electrons from TiO2, which suppresses the recombination of e-/h+ and transfers the received electron to split water, which results in enhanced H2 production. Heterojunction CuO-TiO2 nanocomposite material recorded a maximum of 9284 μmolg-1 H2 production for 2.5 h. The recorded result is 15 times higher than bare TiO2 and 16 times higher than bare CuO. The synthesized materials were characterized and analyzed using various analytical techniques such as XRD, FTIR, UV-vis spectra and the morphology was studied using SEM, TEM, and HRTEM images.

NANOELECTRONICS. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface.

PubMed

Li, Ming-Yang; Shi, Yumeng; Cheng, Chia-Chin; Lu, Li-Syuan; Lin, Yung-Chang; Tang, Hao-Lin; Tsai, Meng-Lin; Chu, Chih-Wei; Wei, Kung-Hwa; He, Jr-Hau; Chang, Wen-Hao; Suenaga, Kazu; Li, Lain-Jong

2015-07-31

Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface. Copyright © 2015, American Association for the Advancement of Science.

Cu2O-based solar cells using oxide semiconductors

NASA Astrophysics Data System (ADS)

Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

2016-01-01

We describe significant improvements of the photovoltaic properties that were achieved in Al-doped ZnO (AZO)/n-type oxide semiconductor/p-type Cu2O heterojunction solar cells fabricated using p-type Cu2O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu2O sheets under various deposition conditions using a pulsed laser deposition method. In Cu2O-based heterojunction solar cells fabricated using various ternary compounds as the n-type oxide thin-film layer, the best photovoltaic performance was obtained with an n-ZnGa2O4 thin-film layer. In most of the Cu2O-based heterojunction solar cells using multicomponent oxides composed of combinations of various binary compounds, the obtained photovoltaic properties changed gradually as the chemical composition was varied. However, with the ZnO-MgO and Ga2O3-Al2O3 systems, higher conversion efficiencies (η) as well as a high open circuit voltage (Voc) were obtained by using a relatively small amount of MgO or Al2O3, e.g., (ZnO)0.91-(MgO)0.09 and (Ga2O3)0.975-(Al2O3)0.025, respectively. When Cu2O-based heterojunction solar cells were fabricated using Al2O3-Ga2O3-MgO-ZnO (AGMZO) multicomponent oxide thin films deposited with metal atomic ratios of 10, 60, 10 and 20 at.% for the Al, Ga, Mg and Zn, respectively, a high Voc of 0.98 V and an η of 4.82% were obtained. In addition, an enhanced η and an improved fill factor could be achieved in AZO/n-type multicomponent oxide/p-type Cu2O heterojunction solar cells fabricated using Na-doped Cu2O (Cu2O:Na) sheets that featured a resistivity controlled by optimizing the post-annealing temperature and duration. Consequently, an η of 6.25% and a Voc of 0.84 V were obtained in a MgF2/AZO/n-(Ga2O3-Al2O3)/p-Cu2O:Na heterojunction solar cell fabricated using a Cu2O:Na sheet with a resistivity of approximately 10 Ω·cm and a (Ga0.975Al0.025)2O3 thin film with a thickness of approximately 60 nm. In addition, a Voc of 0.96 V and an η of 5.4% were obtained in a MgF2/AZO/n-AGMZO/p-Cu2O:Na heterojunction solar cell.

Synthesis of g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction with enhanced photocatalytic performance

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

He, Peizhi; Song, Limin; Zhang, Shujuan, E-mail: songlmnk@sohu.com

2014-03-01

Graphical abstract: g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst with visible-light response was prepared by a facile coprecipitation method. The results show that g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} possesses a much higher activity for the decomposition of RhB than that of the pure Ag{sub 3}PO{sub 4} particles. The most mechanism is that g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst can efficiently separate the photogenerated electron–hole pairs, enhancing the photocatalytic activity of g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} composites. - Highlights: • g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction showed much higher activity than that of Ag{sub 3}PO{sub 4}. • The high activitymore » could be attributed to g-C{sub 3}N{sub 4} for modifying Ag{sub 3}PO{sub 4}. • More ·OH radicals may be significant reason to improve Ag{sub 3}PO{sub 4} activity. - Abstract: g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst with visible-light response was prepared by a facile coprecipitation method. The photocatalysts were characterized by X-ray powder diffraction, transmission electron microscopy, UV–vis absorption spectroscopy and Fourier transform infrared spectroscopy. The photocatalytic activities of the obtained samples were tested by using Rhodamine B (RhB) as the degradation target under visible light irradiation. g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} decomposed RhB more effectively than the pure Ag{sub 3}PO{sub 4} particles did, and 2 wt.% g-C{sub 3}N{sub 4} had the highest activity. Furthermore, 2 wt.% g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} degraded high-concentration RhB more potently than unmodified Ag{sub 3}PO{sub 4} did, probably because g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst enhanced the photocatalytic activity by efficiently separating the photogenerated electron–hole pairs.« less

Soluble P3HT-Grafted Graphene for Efficient Bilayer-Heterojunction Photovoltaic Devices

DTIC Science & Technology

2010-01-01

lem, particularly in the bulk heterojunction photovol- taic devices. As the building blocks for CNTs and other carbon nanomaterials , the two...known carbon nanomaterials .25 Compared with CNTs, the one-atom thickness and 2-D carbon net- work of graphene lead to a much higher specific sur- face...Nanotube Hybrid Films for Supercapacitors . J. Phys. Chem. Lett. 2010, 1, 467–470. 28. Liu, Y.; Yu, D.; Zeng, C.; Miao, Z.; Dai., L. Biocompatible Graphene

Enhanced photoelectrochemical activity in all-oxide heterojunction devices based on correlated "metallic" oxides.

PubMed

Apgar, Brent A; Lee, Sungki; Schroeder, Lauren E; Martin, Lane W

2013-11-20

n-n Schottky, n-n ohmic, and p-n Schottky heterojunctions based on TiO2 /correlated "metallic" oxide couples exhibit strong solar-light absorption driven by the unique electronic structure of the "metallic" oxides. Photovoltaic and photocatalytic responses are driven by hot electron injection from the "metallic" oxide into the TiO2 , enabling new modalities of operation for energy systems. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solar cells having integral collector grids

NASA Technical Reports Server (NTRS)

Evans, J. C., Jr. (Inventor)

1978-01-01

A heterojunction or Schottky barrier photovoltaic device is described, comprising a conductive base metal layer. A back surface field region was formed at the interface between the device and the base metal layer, a transparent, conductive mixed metal oxide layer in integral contact with the n-type layer of the heterojunction or Schottky barrier device. A metal alloy grid network was included. An insulating layer prevented electrical contact between the conductive metal base layer and the transparent, conductive metal oxide layer.

Low-threshold high-T/0/ constricted double heterojunction AlGaAs diode lasers

NASA Technical Reports Server (NTRS)

Botez, D.; Connolly, J. C.

1980-01-01

Constricted double heterojunction diode lasers of relatively low CW thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. These values are obtained while still using standard 10 microns wide oxide-defined stripe contacts. Over the 20-70 C temperature interval, threshold current temperature coefficients as high as 320 C and a virtually constant external differential quantum efficiency, are found.

Designing of spin-filtering devices in zigzag graphene nanoribbons heterojunctions by asymmetric hydrogenation and B-N doping

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

Zhang, Dan; Zhang, Xiaojiao; Ouyang, Fangping

2015-01-07

Using nonequilibrium Green's function in combination with the spin-polarized density functional theory, the spin-dependent transport properties of boron and nitrogen doped zigzag graphene nanoribbons (ZGNRs) heterojunctions with single or double edge-saturated hydrogen have been investigated. Our results show that the perfect spin-filtering effect (100%), rectifying behavior and negative differential resistance can be realized in the ZGNRs-based systems. And the corresponding physical analysis has been given.

Fabrication of heterojunction solar cells by improved tin oxide deposition on insulating layer

DOEpatents

Feng, Tom; Ghosh, Amal K.

1980-01-01

Highly efficient tin oxide-silicon heterojunction solar cells are prepared by heating a silicon substrate, having an insulating layer thereon, to provide a substrate temperature in the range of about 300.degree. C. to about 400.degree. C. and thereafter spraying the so-heated substrate with a solution of tin tetrachloride in a organic ester boiling below about 250.degree. C. Preferably the insulating layer is naturally grown silicon oxide layer.

Narrow Gap, High Mobility, and Stable Pi Conjugated Polymers

DTIC Science & Technology

2012-09-20

wide-angle X-ray scattering (2D-WAXS) of P5.1 (extruded at 210oC). This trend is reflected in conventional bulk- heterojunction OPV devices as shown...Additives in Molecular Bulk Heterojunction Solar Cells Using a bithiophene capped, isoindigo core, DAD molecule as the donor phase, and PCBM as the...PCE values of 3.7% as illustrated in Figure 11. Figure 11. Combining interface control using MoOx as an electron transport material and PDMS

Heterojunction bipolar transistor technology for data acquisition and communication

NASA Technical Reports Server (NTRS)

Wang, C.; Chang, M.; Beccue, S.; Nubling, R.; Zampardi, P.; Sheng, N.; Pierson, R.

1992-01-01

Heterojunction Bipolar Transistor (HBT) technology has emerged as one of the most promising technologies for ultrahigh-speed integrated circuits. HBT circuits for digital and analog applications, data conversion, and power amplification have been realized, with speed performance well above 20 GHz. At Rockwell, a baseline AlGaAs/GaAs HBT technology has been established in a manufacturing facility. This paper describes the HBT technology, transistor characteristics, and HBT circuits for data acquisition and communication.

Catalyst-free fabrication of novel ZnO/CuO core-Shell nanowires heterojunction: Controlled growth, structural and optoelectronic properties

NASA Astrophysics Data System (ADS)

Khan, Muhammad Arif; Wahab, Yussof; Muhammad, Rosnita; Tahir, Muhammad; Sakrani, Samsudi

2018-03-01

Development of controlled growth and vertically aligned ZnO/CuO core-shell heterojunction nanowires (NWs) with large area by a catalyst free vapor deposition and oxidation approach has been investigated. Structural characterization reveals successful fabrication of a core ZnO nanowire having single crystalline hexagonal wurtzite structure along [002] direction and CuO nanostructure shell with thickness (8-10 nm) having polycrystalline monoclinic structure. The optical property analysis suggests that the reflectance spectrum of ZnO/CuO heterostructure nanowires is decreased by 18% in the visible range, which correspondingly shows high absorption in this region as compared to pristine ZnO nanowires. The current-voltage (I-V) characteristics of core-shell heterojunction nanowires measured by conductive atomic force microscopy (C-AFM) shows excellent rectifying behavior, which indicates the characteristics of a good p-n junction. The high-resolution transmission electron microscopy (HRTEM) has confirmed the sharp junction interface between the core-shell heterojunction nanowire arrays. The valence band offset and conduction band offset at ZnO/CuO heterointerfaces are measured to be 2.4 ± 0.05 and 0.23 ± 0.005 eV respectively, using X-ray photoelectron spectroscopy (XPS) and a type-II band alignment structure is found. The results of this study contribute to the development of new advanced device heterostructures for solar energy conversion and optoelectronics applications.

Persistent photoconductivity in two-dimensional Mo 1-xW xSe 2–MoSe 2 van der Waals heterojunctions

DOE PAGES

Puretzky, Alexander A.; Basile, Leonardo; Idrobo, Juan Carlos; ...

2016-02-16

Van der Waals (vdW) heterojunctions consisting of vertically-stacked individual or multiple layers of two-dimensional (2D) layered semiconductors, especially the transition metal dichalcogenides (TMDs), are fascinating new artificial solids just nanometers-thin that promise novel optoelectronic functionalities due to the sensitivity of their electronic and optical properties to strong quantum confinement and interfacial interactions. Here, monolayers of n-type MoSe 2 and p-type Mo 1-xW xSe 2–MoSe 2 are grown by vapor transport methods, then transferred and stamped to form artificial vdW heterostructures with different interlayer orientations. Atomic-resolution Z-contrast electron microscopy and electron diffraction are used to characterize both the individual monolayers andmore » the atomic registry between layers in the bilayer vdW heterostructures. These measurements are compared with photoluminescence and low-frequency Raman spectroscopy, which indicates strong interlayer coupling in heterostructures. Remarkably, the heterojunctions exhibit an unprecedented photoconductivity effect that persists at room temperature for several days. This persistent photoconductivity is shown to be tunable by applying a gate bias that equilibrates the charge distribution. Furthermore, these measurements indicate that such ultrathin vdW heterojunctions can function as rewritable optoelectronic switches or memory elements under time-dependent photo-illumination, an effect which appears promising for new monolayer TMDs-based optoelectronic devices applications.« less

Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes

PubMed Central

2015-01-01

The p–n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. Here, we demonstrate that an atomically thin and sharp heterojunction p–n diode can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) and n-type few-layer molybdenum disulfide (MoS2). Electrical measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic investigation shows distinct layer-number dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron–orbital interaction in TMDs. We believe that these atomically thin heterojunction p–n diodes represent an interesting system for probing the fundamental electro-optical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers. PMID:25157588

Current Modulation of a Heterojunction Structure by an Ultra-Thin Graphene Base Electrode.

PubMed

Alvarado Chavarin, Carlos; Strobel, Carsten; Kitzmann, Julia; Di Bartolomeo, Antonio; Lukosius, Mindaugas; Albert, Matthias; Bartha, Johann Wolfgang; Wenger, Christian

2018-02-27

Graphene has been proposed as the current controlling element of vertical transport in heterojunction transistors, as it could potentially achieve high operation frequencies due to its metallic character and 2D nature. Simulations of graphene acting as a thermionic barrier between the transport of two semiconductor layers have shown cut-off frequencies larger than 1 THz. Furthermore, the use of n-doped amorphous silicon, (n)-a-Si:H, as the semiconductor for this approach could enable flexible electronics with high cutoff frequencies. In this work, we fabricated a vertical structure on a rigid substrate where graphene is embedded between two differently doped (n)-a-Si:H layers deposited by very high frequency (140 MHz) plasma-enhanced chemical vapor deposition. The operation of this heterojunction structure is investigated by the two diode-like interfaces by means of temperature dependent current-voltage characterization, followed by the electrical characterization in a three-terminal configuration. We demonstrate that the vertical current between the (n)-a-Si:H layers is successfully controlled by the ultra-thin graphene base voltage. While current saturation is yet to be achieved, a transconductance of ~230 μ S was obtained, demonstrating a moderate modulation of the collector-emitter current by the ultra-thin graphene base voltage. These results show promising progress towards the application of graphene base heterojunction transistors.

Self-Powered, High-Speed and Visible-Near Infrared Response of MoO(3-x)/n-Si Heterojunction Photodetector with Enhanced Performance by Interfacial Engineering.

PubMed

Zhao, Chuanxi; Liang, Zhimin; Su, Mingze; Liu, Pengyi; Mai, Wenjie; Xie, Weiguang

2015-11-25

Photodetectors with a wide spectrum response are important components for sensing, imaging, and other optoelectronic applications. A molybdenum oxide (MoO(3-x))/Si heterojunction has been applied as solar cells with great success, but its potential in photodetectors has not been explored yet. Herein, a self-powered, high-speed heterojunction photodetector fabricated by coating an n-type Si hierarchical structure with an ultrathin hole-selective layer of molybdenum oxide (MoO(3-x)) is first investigated. Excellent and stable photoresponse performance is obtained by using a methyl group passivated interface. The heterojunction photodetector demonstrated high sensitivity to a wide spectrum from 300 to 1100 nm. The self-powered photodetector shows a high detectivity of (∼6.29 × 10(12) cmHz(1/2) W(-1)) and fast response time (1.0 μs). The excellent photodetecting performance is attributed to the enhanced interfacial barrier height and three-dimensional geometry of Si nanostructures, which is beneficial for efficient photocarrier collection and transportation. Finally, our devices show excellent long-term stability in air for 6 months with negligible performance degradation. The thermal evaporation method for large-scale fabrication of MoO(3-x)/n-Si photodetectors makes it suitable for self-powered, multispectral, and high-speed response photodetecting applications.

Catalyst- and template-free low-temperature in situ growth of n-type CdS nanowire on p-type CdTe film and p-n heterojunction properties

PubMed Central

Ma, Ligang; Liu, Wenchao; Cai, Hongling; Zhang, Fengming; Wu, Xiaoshan

2016-01-01

CdS is an important semiconductor used in optoelectronic devices. Simple techniques for growing CdS nanostructures are thus essential at a low cost. This study presents a novel method for growing single-crystal n-type CdS nanowires on p-type CdTe films by thermal annealing in an H2S/N2 mixed gas flow, which does not require the help of a catalyst or template. The formation process and growth mechanism of the nanowires are investigated. Well-dispersed whiskerlike CdS nanostructures are obtained at an appropriate annealing temperature and duration. We suggest that the stress-driving mechanism of nanowire formation may contribute to the growth of CdS nanowires, and that the evaporation of Te through the boundaries of the CdS grain seeds plays an important role in the sustainable growth of nanowire. In addition, CdS/CdTe heterojunction device is fabricated on Mo glass. The I-V characteristic of the heterojunction in dark shows typical rectifying diode behavior. The turn-on voltage can be regulated by annealing conditions. Meanwhile, the obvious photovoltaic effect is obtained on the in situ growth heterojunction prepared at low annealing temperature. Hence, this is a new fabricated method for CdTe-based materials in the field of energy conversion. PMID:27958306

High-Speed Scalable Silicon-MoS2 P-N Heterojunction Photodetectors

PubMed Central

Dhyani, Veerendra; Das, Samaresh

2017-01-01

Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetector owing to its favourable band gap and high absorption coefficient. However, their commercial applications are limited by the lack of high quality p-n junction and large wafer scale fabrication process. A high speed Si/MoS2 p-n heterojunction photodetector with simple and CMOS compatible approach has been reported here. The large area MoS2 thin film on silicon platform has been synthesized by sulfurization of RF-sputtered MoO3 films. The fabricated molecular layers of MoS2 on silicon offers high responsivity up to 8.75 A/W (at 580 nm and 3 V bias) with ultra-fast response of 10 μsec (rise time). Transient measurements of Si/MoS2 heterojunction under the modulated light reveal that the devices can function up to 50 kHz. The Si/MoS2 heterojunction is found to be sensitive to broadband wavelengths ranging from visible to near-infrared light with maximum detectivity up to ≈1.4 × 1012 Jones (2 V bias). Reproducible low dark current and high responsivity from over 20 devices in the same wafer has been measured. Additionally, the MoS2/Si photodetectors exhibit excellent stability in ambient atmosphere. PMID:28281652

Two dimensional self-assembly zinc porphyrins and zinc phthalocyanines heterojunctions with record high power conversion efficiencies.

PubMed

Yu, Junting; Jiang, Zhou; Hao, Yifan; Zhu, Qianhong; Zhao, Mingliang; Jiang, Xue; Zhao, Jijun

2018-05-15

Compared to inorganic solar cells, the power conversion efficiencies (PCEs) of organic solar cells are much lower, but they are compensated by many merits such as lower cost, less weight, and tunable structures, making them prospective for further applications. Porphyrin and phthalocyanine are the two most significant materials for organic solar cells due to their strong light-absorbing properties and semiconductor characteristics. However, there is little research on the 2D heterojunction solar cells based on these two materials, meanwhile the PCEs of them are still low. Here we have self-assembled several 2D Zinc-porphyrins (ZnPors) and performed first-principles simulation to demonstrate their good stability, suitable light harvesting, and high charge carrier mobility. By perfectly matching lattice constants and band levels between those 2D ZnPors and our previous proposed ZnPcs, eleven type-II organic heterojunctions are constructed to further improve their charge separation capability. Those advantages endow 2D ZnPors and ZnPcs appreciable PCEs for solar cell. Among them, the theoretical PCE of 2D ZnPors/ZnPcs heterojunctions achieves as high as 19.84%, which prevails all reported organic solar cells, and even approaches the PCEs of inorganic solar cells. These results indicate that our 2D ZnPors and 2D ZnPcs are good candidate materials for future organic solar cells. © 2018 IOP Publishing Ltd.

A plate-on-plate sandwiched Z-scheme heterojunction photocatalyst: BiOBr-Bi2MoO6 with enhanced photocatalytic performance

NASA Astrophysics Data System (ADS)

Wang, Shengyao; Yang, Xianglong; Zhang, Xuehao; Ding, Xing; Yang, Zixin; Dai, Ke; Chen, Hao

2017-01-01

In this study, a direct Z-scheme heterojunction BiOBr-Bi2MoO6 with greatly enhanced visible light photocatalytic performance was fabricated via a two-step coprecipitation method. It was indicated that a plate-on-plate heterojunctions be present between BiOBr and Bi2MoO6 through different characterization techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and photoelectrochemical measurements. The crystal structure and morphology analysis revealed that the heterointerface in BiOBr-Bi2MoO6 occurred mainly on the (001) facets of BiOBr and (001) facets of Bi2MoO6. The photocatalytic activity of the BiOBr-Bi2MoO6 was investigated by degradation of RhB and about 66.7% total organic carbon (TOC) could be removed. Ciprofloxacin (CIP) was employed to rule out the photosensitization. It was implied that the higher activity of BiOBr-Bi2MoO6 could be attribute to the strong redox ability in the Z-scheme system, which was subsequently confirmed by photoluminescence spectroscopy (PL) and active spices trapping experiments. This study provides a promising platform for Z-scheme heterojunction constructing and also sheds light on highly efficient visible-light-driven photocatalysts designing.

Plasma treatment of p-GaN/n-ZnO nanorod light-emitting diodes

NASA Astrophysics Data System (ADS)

Leung, Yu Hang; Ng, Alan M. C.; Djurišic, Aleksandra B.; Chan, Wai Kin; Fong, Patrick W. K.; Lui, Hsien Fai; Surya, Charles

2014-03-01

Zinc oxide (ZnO) is a material of great interest for short-wavelength optoelectronic applications due to its wide band gap (3.37 eV) and high exciton binding energy (60 meV). Due to the difficulty in stable p-type doping of ZnO, other p-type materials such as gallium nitride (GaN) have been used to form heterojunctions with ZnO. p-GaN/n-ZnO heterojunction devices, in particular light-emitting diodes (LED) have been extensively studied. There was a huge variety of electronic properties and emission colors on the reported devices. It is due to the different energy alignment at the interface caused by different properties of the GaN layer and ZnO counterpart in the junction. Attempts have been made on modifying the heterojunction by various methods, such as introducing a dielectric interlayer and post-growth surface treatment, and changing the growth methods of ZnO. In this study, heterojunction LED devices with p-GaN and ZnO nanorods array are demonstrated. The ZnO nanorods were grown by a solution method. The ZnO nanorods were exposed to different kinds of plasma treatments (such as nitrogen and oxygen) after the growth. It was found that the treatment could cause significant change on the optical properties of the ZnO nanorods, as well as the electronic properties and light emissions of the resultant LED devices.

Probing π-π stacking modulation of g-C3N4/graphene heterojunctions and corresponding role of graphene on photocatalytic activity.

PubMed

Ma, Xinguo; Wei, Yang; Wei, Zhen; He, Hua; Huang, Chuyun; Zhu, Yongfa

2017-12-15

The photoelectrochemical properties of g-C 3 N 4 sheet are modified by the π-π stacking interaction with graphene, and the corresponding role of graphene on the surface chemical reactions is investigated by density functional theory. The calculated cohesive energies and the lattice mismatch energies indicate that g-C 3 N 4 and graphene are in parallel contact and can form a stable heterojunction. According to our calculated energy band structures and work functions of g-C 3 N 4 /graphene heterojunctions, the band edge modulations by graphene are discussed and corresponding photoinduced charge transfer processes are analyzed in detail. It is found that the incorporating of graphene into g-C 3 N 4 facilitates the separation of photoinduced e - /h + pairs and the oxidation capacity enhancement of the photoinduced holes with the downshifting of the valence band edge of g-C 3 N 4 layer. It is identified that the inhomogeneous onsite energies between interlayer and the band edge modulations are induced by the inhomogeneous charge redistribution between interlayer caused by graphene. Further, the initial dynamic reaction processes of oxygen atoms in g-C 3 N 4 /graphene heterojunctions also confirm the significant role of graphene on the surface chemical reactions. Copyright © 2017 Elsevier Inc. All rights reserved.

Graphite-like carbon nitride coupled with tiny Bi2S3 nanoparticles as 2D/0D heterojunction with enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

Zhu, Chengzhang; Gong, Tingting; Xian, Qiming; Xie, Jimin

2018-06-01

Novel well-dispersed tiny Bi2S3 nanoparticles (NPs) with an average sizes of approximately 16.2 nm were used to decorate layered g-C3N4 nanosheets (NSs), with the purpose of constructing highly efficient 0D/2D heterojunction photocatalyst by a simple hydrothermal method in one step. The fabricated Bi2S3/g-C3N4 heterostructures exhibited superior visible-light-driven photocatalytic activity toward methyl orange (MO) degradation in contrast to that of individual Bi2S3 and g-C3N4, which could be mainly ascribed to the synergistic effect of the tiny size effect of 0D Bi2S3 NPs and 2D g-C3N4 NSs, the matched energy level positions, and the abundant coupling heterointerfaces between two moieties. More importantly, the photodegradation of methylene blue (MB), rhodamine B (RhB) and colorless tetracycline (TC), ciprofloxacin (CIP) further revealed the broad-spectrum photodegradation capacities of the heterojunction materials. The possible photoinduced charge transfer and pollutant degradation process over Bi2S3/g-C3N4 heterojunctions under visible-light irradiation were proposed. This work may provide a platform for constructing new visible light 0D/2D intimate contact heterostructures with stable and efficient photocatalytic performance.

Two dimensional self-assembly zinc porphyrin and zinc phthalocyanine heterojunctions with record high power conversion efficiencies

NASA Astrophysics Data System (ADS)

Yu, Junting; Jiang, Zhou; Hao, Yifan; Zhu, Qianhong; Zhao, Mingliang; Jiang, Xue; Zhao, Jijun

2018-06-01

Compared to inorganic solar cells, the power conversion efficiencies (PCEs) of organic solar cells are much lower, but they are compensated by many merits such as lower cost, less weight, and tunable structures, making them prospective for further applications. Porphyrin and phthalocyanine are the two most significant materials for organic solar cells due to their strong light-absorbing properties and semiconductor characteristics. However, there is little research on the 2D heterojunction solar cells based on these two materials, meanwhile the PCEs of them are still low. Here we have self-assembled several 2D zinc porphyrins (ZnPors) and performed first-principles simulation to demonstrate their good stability, suitable light harvesting, and high charge carrier mobility. By perfectly matching lattice constants and molecular energy levels between those 2D ZnPors and our previous proposed zinc phthalocyanines (ZnPcs), 11 type-II organic heterojunctions are constructed to further improve their charge separation capability. Those advantages endow 2D ZnPors and ZnPcs appreciable PCEs for solar cells. Among them, the theoretical PCE of 2D ZnPors/ZnPcs heterojunctions achieves as high as 19.84%, which exceeds all reported organic solar cells, and even approaches the PCEs of inorganic solar cells. These results indicate that our 2D ZnPors and 2D ZnPcs are good candidate materials for future organic solar cells.

Stimulated emission within the exciplex band by plasmonic-nanostructured polymeric heterojunctions

NASA Astrophysics Data System (ADS)

Zhang, Xinping; Li, Hongwei; Wang, Yimeng; Liu, Feifei

2015-03-01

Organic heterojunctions have been extensively employed in the design of light-emitting diodes, photovoltaic devices, and thin-film field-effect transistors, which can be achieved by constructing a bilayer or a multi-layered thin-film deposition, or by blending two or more organic semiconductors with different charge-transport performances. Charge transfer excited states or exciplex may form on the heterointerfaces. Efficient light-emitting diodes have been demonstrated using exciplex emission. However, lasing or stimulated emission processes have not been observed with exciplex formation at organic heterojunctions. In this work, we demonstrate strong coherent interaction between photons and exciplex formation in the blends of poly-9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine (PFB) and poly-9,9'-dioctylfluorene-co-benzothiadiazole (F8BT), leading to transient stimulated exciplex emission. The responsible mechanisms involve plasmonic local-field enhancement and plasmonic feedback in a three-dimensional gold-nanoparticle matrix.Organic heterojunctions have been extensively employed in the design of light-emitting diodes, photovoltaic devices, and thin-film field-effect transistors, which can be achieved by constructing a bilayer or a multi-layered thin-film deposition, or by blending two or more organic semiconductors with different charge-transport performances. Charge transfer excited states or exciplex may form on the heterointerfaces. Efficient light-emitting diodes have been demonstrated using exciplex emission. However, lasing or stimulated emission processes have not been observed with exciplex formation at organic heterojunctions. In this work, we demonstrate strong coherent interaction between photons and exciplex formation in the blends of poly-9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine (PFB) and poly-9,9'-dioctylfluorene-co-benzothiadiazole (F8BT), leading to transient stimulated exciplex emission. The responsible mechanisms involve plasmonic local-field enhancement and plasmonic feedback in a three-dimensional gold-nanoparticle matrix. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00140d

A Co2 P/WC Nano-Heterojunction Covered with N-Doped Carbon as Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction.

PubMed

Gao, Ya; Lang, Zhongling; Yu, Feiyang; Tan, Huaqiao; Yan, Gang; Wang, Yonghui; Ma, Yuanyuan; Li, Yangguang

2018-03-22

The hydrogen evolution reaction (HER) produces clean hydrogen through an electrochemical process. However, new nonprecious-metal electrocatalysts for the HER are required to reduce the consumption of energy. Herein, we report a new Co 2 P/WC nano-heterojunction that consists of Co 2 P and WC composite phases coated with a few-layer N-doped graphitic carbon shells (Co 2 P/WC@NC). The composite was prepared by a one-step annealing of the polyoxometalate Na 9 (NH 4 ) 5 [{(B-α-PW 9 O 34 )Co 3 (OH)(H 2 O) 2 (Ale)} 2 Co]⋅35 H 2 O (Co 7 P 6 W 18 ) and dicyandiamide (DCA). The preparation method consisted of the simultaneous phosphorization of Co and carbonization of W in a confined space to isolate a Co 2 P/WC nano-heterojunction phase for the first time. Co 2 P/WC@NC facilitated the generation of hydrogen in the electrolysis process, which had an overpotential of only 91 mV at a current density of 10 mA cm -2 in the acid solution; an excellent HER performance (2 H + +2 e - →H 2 ) and Tafel slope (40 mV dec -1 ) as well as durability over a period of 50 h were achieved. Theoretical calculations showed that the Co 2 P, WC, and N pyridinic C dopants in the material synergistically promoted the HER activity rather than the individual constituents. Furthermore, Co 2 P/WC@NC nano-heterojunctions showed good HER performance in the whole pH range of electrolytes and considerable durability in acidic media containing transition metal ions, which may attract more attention for the exploration and optimization of nano-heterojunction catalysts for the HER. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrasonic-assisted pyrolyzation fabrication of reduced SnO2–x /g-C3N4 heterojunctions: Enhance photoelectrochemical and photocatalytic activity under visible LED light irradiation

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

Li, Kai; Zeng, Xiaoqiao; Gao, Shanmin

Novel SnO 2–x/g-C 3N 4 heterojunction nanocomposites composed of reduced SnO 2–x nanoparticles and exfoliated g-C 3N 4 nanosheets were prepared by a convenient one-step pyrolysis method. The structural, morphological, and optical properties of the as-prepared nanocomposites were characterized in detail, indicating that the aggregation of g-C 3N 4 nanosheets was prevented by small, well-dispersed SnO 2–x nanoparticles. The ultraviolet–visible spectroscopy absorption bands of the nanocomposites were shifted to a longer wavelength region than those exhibited by pure SnO 2 or g-C 3N 4. The charge transfer and recombination processes occurring in the nanocomposites were investigated using linear scan voltammetrymore » and electrochemical impedance spectroscopy. Under 30-W visible-light-emitting diode irradiation, the heterojunction containing 27.4 wt.% SnO 2–x exhibited the highest photocurrent density of 0.0468 mA·cm–2, which is 33.43 and 5.64 times larger than that of pure SnO 2 and g-C 3N 4, respectively. The photocatalytic activity of the heterojunction material was investigated by degrading rhodamine B under irradiation from the same light source. Kinetic study revealed a promising degradation rate constant of 0.0226 min-1 for the heterojunction containing 27.4 wt.% SnO 2–x, which is 32.28 and 5.79 times higher than that of pure SnO 2 and g-C 3N 4, respectively. The enhanced photoelectrochemical and photocatalytic performances of the nanocomposite may be due to its appropriate SnO 2–x content and the compact structure of the junction between the SnO 2–x nanoparticles and the g-C 3N 4 nanosheets, which inhibits the recombination of photogenerated electrons and holes.« less

Reliability of constricted double-heterojunction AlGaAs diode lasers

NASA Technical Reports Server (NTRS)

Botez, D.; Connolly, J. C.; Ettenberg, M.; Gilbert, D. B.; Hughes, J. J.

1983-01-01

Constricted double-heterojunction diode lasers have been life tested at 70 C heatsink temperature and 3-4 mW/facet in CW operation. A median life of 7800 h is obtained at 70 C, which extrapolates to 400,000 h median life at room temperature. The extrapolated mean time to failure at room temperature is in excess of 1,000,000 h. Single-longitudinal-mode CW operation is maintained after 10,000 h of accelerated aging at 70 C.

Unified planar process for fabricating heterojunction bipolar transistors and buried-heterostructure lasers utilizing impurity-induced disordering

NASA Astrophysics Data System (ADS)

Thornton, R. L.; Mosby, W. J.; Chung, H. F.

1988-12-01

We describe results on a novel geometry of heterojunction bipolar transistor that has been realized by impurity-induced disordering. This structure is fabricated by a method that is compatible with techniques for the fabrication of low threshold current buried-heterostructure lasers. We have demonstrated this compatibility by fabricating a hybrid laser/transistor structure that operates as a laser with a threshold current of 6 mA at room temperature, and as a transistor with a current gain of 5.

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.

Current- and lattice-matched tandem solar cell

DOEpatents

Olson, J.M.

1985-10-21

A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga/sub x/In/sub 1-x/P (0.505 equal to or less than x equal to or less than 0.515) top cell semiconductor lattice-matched to a GaAs bottom cell semiconductor at a low resistance heterojunction, preferably a p/sup +//n/sup +/ heterojunction between the cells. The top and bottom cells are both lattice-matched and current-matched for high efficiency solar radiation conversion to electrical energy.

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.

Facile fabrication of organic/inorganic nanotube heterojunction arrays for enhanced photoelectrochemical water splitting

NASA Astrophysics Data System (ADS)

Chen, Yingzhi; Li, Aoxiang; Yue, Xiaoqi; Wang, Lu-Ning; Huang, Zheng-Hong; Kang, Feiyu; Volinsky, Alex A.

2016-07-01

Organic/inorganic heterojunction photoanodes are appealing for making concurrent use of the highly photoactive organic semiconductors, and the efficient dielectric screening provided by their inorganic counterparts. In the present work, organic/inorganic nanotube heterojunction arrays composed of TiO2 nanotube arrays and a semiconducting N,N-(dicyclohexyl) perylene-3,4,9,10-tetracarboxylic diimide (PDi) layer were fabricated for photoelectrochemical water splitting. In this arrayed architecture, a PDi layer with a tunable thickness was coated on anodic TiO2 nanotube arrays by physical vapor deposition, which is advantageous for the formation of a uniform layer and an adequate interface contact between PDi and TiO2. The obtained PDi/TiO2 junction exhibited broadened visible light absorption, and an effective interface for enhanced photogenerated electron-hole separation, which is supported by the reduced charge transfer resistance and prolonged excitation lifetime via impedance spectroscopy analysis and fluorescence emission decay investigations. Consequently, such a heterojunction photoanode was photoresponsive to a wide visible light region of 400-600 nm, and thus demonstrated a highly enhanced photocurrent density at 1.23 V vs. a reversible hydrogen electrode. Additionally, the durability of such a photoanode can be guaranteed after long-time illumination because of the geometrical restraint imposed by the PDi aggregates. These results pave the way to discover new organic/inorganic assemblies for high-performance photoelectric applications and device integration.Organic/inorganic heterojunction photoanodes are appealing for making concurrent use of the highly photoactive organic semiconductors, and the efficient dielectric screening provided by their inorganic counterparts. In the present work, organic/inorganic nanotube heterojunction arrays composed of TiO2 nanotube arrays and a semiconducting N,N-(dicyclohexyl) perylene-3,4,9,10-tetracarboxylic diimide (PDi) layer were fabricated for photoelectrochemical water splitting. In this arrayed architecture, a PDi layer with a tunable thickness was coated on anodic TiO2 nanotube arrays by physical vapor deposition, which is advantageous for the formation of a uniform layer and an adequate interface contact between PDi and TiO2. The obtained PDi/TiO2 junction exhibited broadened visible light absorption, and an effective interface for enhanced photogenerated electron-hole separation, which is supported by the reduced charge transfer resistance and prolonged excitation lifetime via impedance spectroscopy analysis and fluorescence emission decay investigations. Consequently, such a heterojunction photoanode was photoresponsive to a wide visible light region of 400-600 nm, and thus demonstrated a highly enhanced photocurrent density at 1.23 V vs. a reversible hydrogen electrode. Additionally, the durability of such a photoanode can be guaranteed after long-time illumination because of the geometrical restraint imposed by the PDi aggregates. These results pave the way to discover new organic/inorganic assemblies for high-performance photoelectric applications and device integration. Electronic supplementary information (ESI) available: Additional structural characterization. See DOI: 10.1039/c5nr07893h

Hydrothermal synthesis of hierarchical CoO/SnO2 nanostructures for ethanol gas sensor.

PubMed

Wang, Qingji; Kou, Xueying; Liu, Chang; Zhao, Lianjing; Lin, Tingting; Liu, Fangmeng; Yang, Xueli; Lin, Jun; Lu, Geyu

2018-03-01

In this work, ethanol gas sensor with high performance was fabricated successfully with hierarchical CoO/SnO 2 heterojunction by two-steps hydrothermal method. The response value of CoO/SnO 2 sensor is up to 145 at 250 °C when exposed to 100 ppm ethanol gas, which is much higher than that (13.5) of SnO 2 sensor. These good sensing performances mainly attribute to the formation of the CoO/SnO 2 heterojunction, which makes great variation of resistance in air and ethanol gas. Thus, the combination of n-type SnO 2 and p-type CoO provides an effective strategy to design new ethanol gas sensors. The unique nanostructure also played an important role in detecting ethanol, due to its contribution in facilitating the transport rate of the ethanol gas molecules. Also, we provide a general two-step strategy for designing the heterojunction based on the SnO 2 nanostructure. Copyright © 2017 Elsevier Inc. All rights reserved.

Optimizing Performance Parameters of Chemically-Derived Graphene/p-Si Heterojunction Solar Cell.

PubMed

Batra, Kamal; Nayak, Sasmita; Behura, Sanjay K; Jani, Omkar

2015-07-01

Chemically-derived graphene have been synthesized by modified Hummers method and reduced using sodium borohydride. To explore the potential for photovoltaic applications, graphene/p-silicon (Si) heterojunction devices were fabricated using a simple and cost effective technique called spin coating. The SEM analysis shows the formation of graphene oxide (GO) flakes which become smooth after reduction. The absence of oxygen containing functional groups, as observed in FT-IR spectra, reveals the reduction of GO, i.e., reduced graphene oxide (rGO). It was further confirmed by Raman analysis, which shows slight reduction in G-band intensity with respect to D-band. Hall effect measurement confirmed n-type nature of rGO. Therefore, an effort has been made to simu- late rGO/p-Si heterojunction device by using the one-dimensional solar cell capacitance software, considering the experimentally derived parameters. The detail analysis of the effects of Si thickness, graphene thickness and temperature on the performance of the device has been presented.

T-Shaped Indan-1,3-dione derivatives as promising electron donors for bulk heterojunction small molecule solar cell

NASA Astrophysics Data System (ADS)

Adhikari, Tham; Solanke, Parmeshwar; Pathak, Dinesh; Wagner, Tomas; Bureš, Filip; Reed, Tyler; Nunzi, Jean-Michel

2017-07-01

We report on the photovoltaic performance of novel T-Shaped Indan-1,3-dione derivatives as donors in a solution processed bulk heterojunction solar cells. Small molecule bulk heterojunction solar cells of these molecules with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were fabricated and characterized. The preliminary characterization of these devices yielded a PCE of 0.24% and 0.33% for two separate derivatives. These low power conversion efficiencies were attributed to a high surface roughness with a large number of dewetting spots. Doping with 10% Polystyrene in the Indan-1,3-dione derivatives decreases surface roughness and dewetting spots thereby improving the efficiency of the devices. Efficiency of the devices was found as 0.39% and 0.51% for two derivatives after doping with polystyrene. The charge transfer mechanism was studied with photoluminescence quenching. The morphology and packing behavior of molecules were further studied using Atomic Force Microscopy (AFM) and X-ray diffraction (XRD).

Sulfur-doped Graphene Nanoribbons with a Sequence of Distinct Band Gaps

NASA Astrophysics Data System (ADS)

Du, Shi-Xuan; Zhang, Yan-Fang; Zhang, Yi; Berger, Reinhard; Feng, Xinliang; Mullen, Klaus; Lin, Xiao; Zhang, Yu-Yang; Pantelides, Sokrates T.; Gao, Hong-Jun

Unlike free-standing graphene, graphene nanoribbons (GNRs) can possess semiconducting band gap. However, achieving such control has been a major challenge in the fabrication of GNRs. Chevron-type GNRs were recently achieved by surface-assisted polymerization of pristine or N-substituted oligophenylene monomers. By mixing two different monomers, GNR heterojunctions can in principle be fabricated. Here we report fabrication and characterization of chevron-type GNRs by using sulfur-substituted oligophenylene monomers to achieve GNRs and related heterostructures for the first time. Importantly, our first-principles calculations show that the band gaps of GNRs can be tailored by different S configurations in cyclodehydrogenated isomers through debromination and intramolecular cyclodehydrogenation. This feature should open up new avenues to create multiple GNR heterojunctions by engineering the sulfur configurations. These predictions have been confirmed by Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS). The unusual sequence of intraribbon heterojunctions may be useful for nanoscale optoelectronic applications based on quantum dots

Comparison of carrier transport mechanism under UV/Vis illumination in an AZO photodetector and an AZO/p-Si heterojunction photodiode produced by spray pyrolysis

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

Shasti, M.; Mortezaali, A., E-mail: mortezaali@alzahra.ac.ir; Dariani, R. S.

2015-01-14

In this study, Aluminum doped Zinc Oxide (AZO) layer is deposited on p-type silicon (p-Si) by spray pyrolysis method to fabricate ultraviolet-visible (UV/Vis) photodetector as Al doping process can have positive effect on the photodetector performance. Morphology, crystalline structure, and Al concentration of AZO layer are investigated by SEM, XRD, and EDX. The goal of this study is to analyze the mechanism of carrier transport by means of current-voltage characteristics under UV/Vis illumination in two cases: (a) electrodes connected to the surface of AZO layer and (b) electrodes connected to cross section of heterojunction (AZO/p-Si). Measurements indicate that the AZO/p-Simore » photodiode exhibits a higher photocurrent and lower photoresponse time under visible illumination with respect to AZO photodetector; while under UV illumination, the above result is inversed. Besides, the internal junction field of AZO/p-Si heterojunction plays an important role on this mechanism.« less

p-GaN/n-ZnO heterojunction nanowires: optoelectronic properties and the role of interface polarity.

PubMed

Schuster, Fabian; Laumer, Bernhard; Zamani, Reza R; Magén, Cesar; Morante, Joan Ramon; Arbiol, Jordi; Stutzmann, Martin

2014-05-27

In this work, simulations of the electronic band structure of a p-GaN/n-ZnO heterointerface are presented. In contrast to homojunctions, an additional energy barrier due to the type-II band alignment hinders the flow of majority charge carriers in this heterojunction. Spontaneous polarization and piezoelectricity are shown to additionally affect the band structure and the location of the recombination region. Proposed as potential UV-LEDs and laser diodes, p-GaN/n-ZnO heterojunction nanowires were fabricated by plasma-assisted molecular beam epitaxy (PAMBE). Atomic resolution annular bright field scanning transmission electron microscopy (STEM) studies reveal an abrupt and defect-free heterointerface with a polarity inversion from N-polar GaN to Zn-polar ZnO. Photoluminescence measurements show strong excitonic UV emission originating from the ZnO-side of the interface as well as stimulated emission in the case of optical pumping above a threshold of 55 kW/cm(2).

Influence of Crystallinity and Energetics on Charge Separation in Polymer–Inorganic Nanocomposite Films for Solar Cells

PubMed Central

Bansal, Neha; Reynolds, Luke X.; MacLachlan, Andrew; Lutz, Thierry; Ashraf, Raja Shahid; Zhang, Weimin; Nielsen, Christian B.; McCulloch, Iain; Rebois, Dylan G.; Kirchartz, Thomas; Hill, Michael S.; Molloy, Kieran C.; Nelson, Jenny; Haque, Saif A.

2013-01-01

The dissociation of photogenerated excitons and the subsequent spatial separation of the charges are of crucial importance to the design of efficient donor-acceptor heterojunction solar cells. While huge progress has been made in understanding charge generation at all-organic junctions, the process in hybrid organic:inorganic systems has barely been addressed. Here, we explore the influence of energetic driving force and local crystallinity on the efficiency of charge pair generation at hybrid organic:inorganic semiconductor heterojunctions. We use x-ray diffraction, photoluminescence quenching, transient absorption spectroscopy, photovoltaic device and electroluminescence measurements to demonstrate that the dissociation of photogenerated polaron pairs at hybrid heterojunctions is assisted by the presence of crystalline electron acceptor domains. We propose that such domains encourage delocalization of the geminate pair state. The present findings suggest that the requirement for a large driving energy for charge separation is relaxed when a more crystalline electron acceptor is used. PMID:23524906

Electrospinning Nanofiber Based Organic Solar Cell

NASA Astrophysics Data System (ADS)

Yang, Zhenhua; Liu, Ying; Moffa, Maria; Nam, Chang-Yong; Pisignano, Dario; Rafailovich, Miriam

Bulk heterojunction (BHJ) polymer solar cells are an area of intense interest due to their potential to result in printable, inexpensive solar cells which can be processed onto flexible substrates. The active layer is typically spin coated from the solution of polythiophene derivatives (donor) and fullerenes (acceptor) and interconnected domains are formed because of phase separation. However, the power conversion efficiency (PCE) of BHJ solar cell is restricted by the presence of unfavorable morphological features, including dead ends or isolated domains. Here we MEH-PPV:PVP:PCBM electrospun nanofiber into BHJ solar cell for the active layer morphology optimization. Larger interfacial area between donor and acceptor is abtained with electrospinning method and the high aspect ratio of the MEH-PPV:PVP:PCBM nanofibers allow them to easily form a continuous pathway. The surface morphology is investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrospun nanofibers are discussed as a favorable structure for application in bulk-heterojunction organic solar cells. Electrospinning Nanofiber Based Bulk Heterojunction Organic Solar Cell.

Naphtho[2,1-b:3,4-b']dithiophene-based bulk heterojunction solar cells: how molecular structure influences nanoscale morphology and photovoltaic properties.

PubMed

Kim, Yu Jin; Cheon, Ye Rim; Back, Jang Yeol; Kim, Yun-Hi; Chung, Dae Sung; Park, Chan Eon

2014-11-10

Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1-b:3,4-b']dithiophene (NDT) derivatives blended with phenyl-C71-butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene-chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar-cell performances and their degree of crystallization was assessed. The grazing-incidence angle X-ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J-V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT-based polymers for use in bulk heterojunction solar cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Infrared to visible image up-conversion using optically addressed spatial light modulator utilizing liquid crystal and InGaAs photodiodes

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

Solodar, A., E-mail: asisolodar@gmail.com; Arun Kumar, T.; Sarusi, G.

2016-01-11

Combination of InGaAs/InP heterojunction photodetector with nematic liquid crystal (LC) as the electro-optic modulating material for optically addressed spatial light modulator for short wavelength infra-red (SWIR) to visible light image conversion was designed, fabricated, and tested. The photodetector layer is composed of 640 × 512 photodiodes array based on heterojunction InP/InGaAs having 15 μm pitch on InP substrate and with backside illumination architecture. The photodiodes exhibit extremely low, dark current at room temperature, with optimum photo-response in the SWIR region. The photocurrent generated in the heterojunction, due to the SWIR photons absorption, is drifted to the surface of the InP,more » thus modulating the electric field distribution which modifies the orientation of the LC molecules. This device can be attractive for SWIR to visible image upconversion, such as for uncooled night vision goggles under low ambient light conditions.« less

Effects of annealing gas and drain doping concentration on electrical properties of Ge-source/Si-channel heterojunction tunneling FETs

NASA Astrophysics Data System (ADS)

Bae, Tae-Eon; Wakabayashi, Yuki; Nakane, Ryosho; Takenaka, Mitsuru; Takagi, Shinichi

2018-04-01

Improvement in the performance of Ge-source/Si-channel heterojunction tunneling FETs (TFETs) with high on-current/off-current (I on/I off) ratio and steep subthreshold swing (SS) is demonstrated. In this paper, we experimentally examine the effects of gas ambient [N2 and forming gas (4% H2/N2)] and a doping concentration in the drain regions on the electrical characteristics of Ge/Si heterojunction TFETs. The minimum SS (SSmin) of 70.9 mV/dec and the large I on/I off ratio of 1.4 × 107 are realized by postmetallization annealing in forming gas. Also, the steep SSmin and averaged SS (SSavr) values of 64.2 and 78.4 mV/dec, respectively, are obtained in low drain doping concentration. This improvement is attributable to the reduction in interface state density (D it) in the channel region and to the low leakage current in the drain region.

Use of side-chain incompatibility for tailoring long-range p/n heterojunctions: photoconductive nanofibers formed by self-assembly of an amphiphilic donor-acceptor dyad consisting of oligothiophene and perylenediimide.

PubMed

Li, Wei-Shi; Saeki, Akinori; Yamamoto, Yohei; Fukushima, Takanori; Seki, Shu; Ishii, Noriyuki; Kato, Kenichi; Takata, Masaki; Aida, Takuzo

2010-07-05

To tailor organic p/n heterojunctions with molecular-level precision, a rational design strategy using side-chain incompatibility of a covalently connected donor-acceptor (D-A) dyad has been successfully carried out. An oligothiophene-perylenediimide dyad, when modified with triethylene glycol side chains at one terminus and dodecyl side chains at the other (2(Amphi)), self-assembles into nanofibers with a long-range D/A heterojunction. In contrast, when the dyad is modified with dodecyl side chains at both termini (2(Lipo)), ill-defined microfibers result. In steady-state measurements using microgap electrodes, a cast film of the nanofiber of 2(Amphi) displays far better photoconducting properties than that of the microfiber of 2(Lipo). Flash-photolysis time-resolved microwave conductivity measurements, in conjunction with transient absorption spectroscopy, clearly indicate that the nanofiber of 2(Amphi) intrinsically allows for better carrier generation and transport properties than the microfibrous assembly of 2(Lipo).

A dewetting route to grow heterostructured nanoparticles based on thin film heterojunctions.

PubMed

Li, Junjie; Yin, Deqiang; Li, Qiang; Chen, Chunlin; Huang, Sumei; Wang, Zhongchang

2015-12-21

Heterostructured nanoparticles have received considerable attention for their various applications due to their unique and tunable functionalities with respect to their individual bulk constituents. However, the current wet chemical synthesis of multicomponent heterostructured nanoparticles is rather complicated. Here, we report a simple and quick method to fabricate Co-Au dumbbell arrays by dewetting Co/Au heterojunctions on a Si substrate and demonstrate that the Co-Au dumbbells vary in size from 2 to 28 nm. We further show by chemical mapping that Co bells are covered by a pseudomorphic Au wetting layer of ∼4 Å, preventing the bells from oxidation. By controlling the thickness of metal heterojunctions and the annealing time, the morphology of the Co-Au nanoparticle is found to be transformed from the dumbbell to the core shell. This facile route is demonstrated to be useful for fabricating other metal-metal and metal-oxide heterostructures and hence holds technological promise for functional applications.

Enhancing the Efficiency of Bulk Heterojunction Solar Cells via Templated Self Assembly

NASA Astrophysics Data System (ADS)

Pan, Cheng; Li, Hongfei; Akgun, Bulent; Satijia, Sushil; Gersappe, Dilip; Zhu, Yimei; Rafailovich, Miriam

2013-03-01

Bulk Heterojunction (BHJ) polymer solar cells are an area of intense interest due to their flexibility and relatively low cost. The mixture of polythiophene derivatives (donor) and fullerenes (acceptor) is spin coated on substrate as the active layer, and are phase-separated into interconnected domains. However, due to the disordered inner structures in the active layer, donor or acceptor domains isolated from electrodes and long path conduction, the power conversion efficiency (PCE) of BHJ solar cell is low. Therefore, morphology control in bulk heterojunction (BHJ) solar cell is considered to be critical for the power conversion efficiency (PCE). Here, we present a novel approach that introduces non-photoactive polymer that organizes the poly(3-hexylthiophene) (P3HT) into columnar phases decorated by [6,6]-phenyl C61-butyric acid methyl ester (PCBM) at the interface. This structure represents a realization of an idealized morphology of an organic solar cell, in which, both exiciton dissociation and the carrier transport are optimized leading to increased power conversion efficiency.

Bulk heterojunction formation between indium tin oxide nanorods and CuInS2 nanoparticles for inorganic thin film solar cell applications.

PubMed

Cho, Jin Woo; Park, Se Jin; Kim, Jaehoon; Kim, Woong; Park, Hoo Keun; Do, Young Rag; Min, Byoung Koun

2012-02-01

In this study, we developed a novel inorganic thin film solar cell configuration in which bulk heterojunction was formed between indium tin oxide (ITO) nanorods and CuInS(2) (CIS). Specifically, ITO nanorods were first synthesized by the radio frequency magnetron sputtering deposition method followed by deposition of a dense TiO(2) layer and CdS buffer layer using atomic layer deposition and chemical bath deposition method, respectively. The spatial region between the nanorods was then filled with CIS nanoparticle ink, which was presynthesized using the colloidal synthetic method. We observed that complete gap filling was achieved to form bulk heterojunction between the inorganic phases. As a proof-of-concept, solar cell devices were fabricated by depositing an Au electrode on top of the CIS layer, which exhibited the best photovoltaic response with a V(oc), J(sc), FF, and efficiency of 0.287 V, 9.63 mA/cm(2), 0.364, and 1.01%, respectively.

18.4%-Efficient Heterojunction Si Solar Cells Using Optimized ITO/Top Electrode.

PubMed

Kim, Namwoo; Um, Han-Don; Choi, Inwoo; Kim, Ka-Hyun; Seo, Kwanyong

2016-05-11

We optimize the thickness of a transparent conducting oxide (TCO) layer, and apply a microscale mesh-pattern metal electrode for high-efficiency a-Si/c-Si heterojunction solar cells. A solar cell equipped with the proposed microgrid metal electrode demonstrates a high short-circuit current density (JSC) of 40.1 mA/cm(2), and achieves a high efficiency of 18.4% with an open-circuit voltage (VOC) of 618 mV and a fill factor (FF) of 74.1% as result of the shortened carrier path length and the decreased electrode area of the microgrid metal electrode. Furthermore, by optimizing the process sequence for electrode formation, we are able to effectively restore the reduction in VOC that occurs during the microgrid metal electrode formation process. This work is expected to become a fundamental study that can effectively improve current loss in a-Si/c-Si heterojunction solar cells through the optimization of transparent and metal electrodes.

Microcrystalline silicon growth for heterojunction solar cells

NASA Technical Reports Server (NTRS)

Leung, D. C.; Iles, P. A.; Fang, P. H.

1984-01-01

Microcrystalline Si (m-Si) films with a 1.7eV energy bandgap and crystal size of several hundred A were e-beam evaporated on single crystalline Si (c-Si) to form a heterojunction with the substrate, or a window layer to a single crystalline p-n junction (heteroface structure). The goal was to enhance Voc by such uses of the larger bandgap m-Si, with the intriguing prospect of forming heterostructures with exact lattice match on each layer. The heterojunction structure was affected by interface and shunting problems and the best Voc achieved was only 482mV, well below that of single crystal Si homojunctions. The heteroface structure showed promise for some of the samples with p m-Si/p-n structure (the complementary structure did not show any improvement). Although several runs with different deposition conditions were run, the results were inconsistent. Any Voc enhancement obtained was too small to compensate for the current loss due to the extra absorption and poor carrier transport properties of the m-Si film.

Raman study of bulk-heterojunction morphology in photoactive layers treated with solvent-vapor annealing

NASA Astrophysics Data System (ADS)

Onojima, Norio; Ishima, Yasuhisa; Izumi, Daisuke; Takahashi, Kazuyuki

2018-03-01

The effect of solvent-vapor annealing (SVA) on bulk-heterojunction morphology in photoactive layers composed of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was analyzed using Raman spectroscopy. We prepared the photoactive layers by electrostatic spray deposition (ESD) and fabricated organic photovoltaic devices with a conventional cell structure. Although postdeposition annealing can be omitted when the photoactive layer is deposited using ESD under dry condition, the surface is relatively rough owing to the existence of a number of droplet traces. The SVA treatment can eliminate such droplet traces, while excessive SVA resulted in a significant decrease in open-circuit voltage. The Raman study of the bulk-heterojunction morphology demonstrated the accumulation of P3HT molecules on the surface during SVA, which induced the recombination of photogenerated charges at the interface of the cathode/photoactive layer and thereby decreased the open-circuit voltage.

Metal-graphene heterojunction modulation via H{sub 2} interaction

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

Cadore, A. R., E-mail: alissoncadore@gmail.com, E-mail: lccampos@fisica.ufmg.br; Mania, E.; Lacerda, R. G.

2016-07-18

Combining experiment and theory, we investigate how a naturally created heterojunction (pn junction) at a graphene and metallic contact interface is modulated via interaction with molecular hydrogen (H{sub 2}). Due to an electrostatic interaction, metallic electrodes induce pn junctions in graphene, leading to an asymmetrical resistance in electronic transport for electrons and holes. We report that the asymmetry in the resistance can be tuned in a reversible manner by exposing graphene devices to H{sub 2}. The interaction between the H{sub 2} and graphene occurs solely at the graphene-contact pn junction and induces a modification on the electrostatic interaction between graphenemore » and metallic contacts. We explain the experimental data with theory providing information concerning the length of the heterojunction and how it changes as a function of H{sub 2} adsorption. Our results are valuable for understanding the nature of the metal-graphene interfaces and have potential application for selective sensors of molecular hydrogen.« less

Piezo-phototronic effect enhanced UV photodetector based on CuI/ZnO double-shell grown on flexible copper microwire.

PubMed

Liu, Jingyu; Zhang, Yang; Liu, Caihong; Peng, Mingzeng; Yu, Aifang; Kou, Jinzong; Liu, Wei; Zhai, Junyi; Liu, Juan

2016-12-01

In this work, we present a facile, low-cost, and effective approach to fabricate the UV photodetector with a CuI/ZnO double-shell nanostructure which was grown on common copper microwire. The enhanced performances of Cu/CuI/ZnO core/double-shell microwire photodetector resulted from the formation of heterojunction. Benefiting from the piezo-phototronic effect, the presentation of piezocharges can lower the barrier height and facilitate the charge transport across heterojunction. The photosensing abilities of the Cu/CuI/ZnO core/double-shell microwire detector are investigated under different UV light densities and strain conditions. We demonstrate the I-V characteristic of the as-prepared core/double-shell device; it is quite sensitive to applied strain, which indicates that the piezo-phototronic effect plays an essential role in facilitating charge carrier transport across the CuI/ZnO heterojunction, then the performance of the device is further boosted under external strain.

Mode characteristics of nonplanar double-heterojunction and large-optical-cavity laser structures

NASA Technical Reports Server (NTRS)

Butler, J. K.; Botez, D.

1982-01-01

Mode behavior of nonplanar double-heterojunction (DH) and large-optical-cavity (LOC) lasers is investigated using the effective index method to model the lateral field distribution. The thickness variations of various layers for the devices discussed are correlated with the growth characteristics of liquid-phase epitaxy over topographical features (channels, mesas) etched into the substrate. The effective dielectric profiles of constricted double-heterojunction (CDH)-LOC lasers show a strong influence on transverse mode operation: the fundamental transverse mode (i.e., in the plane perpendicular to the junction) may be laterally index-guided, while the first (high)-order mode is laterally index-antiguided. The analytical model developed uses a smoothly varying hyperbolic cosine distribution to characterize lateral index variations. The waveguide model is applied to several lasers to illustrate conditions necessary to convert leaky modes to trapped ones via the active-region gain distribution. Theoretical radiation patterns are calculated using model parameters, and matched to an experimental far-field pattern.

Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells.

PubMed

Huang, Yu-Ching; Tsao, Cheng-Si; Cho, Yi-Ju; Chen, Kuan-Chen; Chiang, Kai-Ming; Hsiao, Sheng-Yi; Chen, Chang-Wen; Su, Chun-Jen; Jeng, U-Ser; Lin, Hao-Wu

2015-09-04

The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells

NASA Astrophysics Data System (ADS)

Huang, Yu-Ching; Tsao, Cheng-Si; Cho, Yi-Ju; Chen, Kuan-Chen; Chiang, Kai-Ming; Hsiao, Sheng-Yi; Chen, Chang-Wen; Su, Chun-Jen; Jeng, U.-Ser; Lin, Hao-Wu

2015-09-01

The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

Tunable Synthesis of SiC/SiO2 Heterojunctions via Temperature Modulation

PubMed Central

Li, Wei; Yang, Daoyuan; Liu, Xinhong

2018-01-01

A large-scale production of necklace-like SiC/SiO2 heterojunctions was obtained by a molten salt-mediated chemical vapor reaction technique without a metallic catalyst or flowing gas. The effect of the firing temperature on the evolution of the phase composition, microstructure, and morphology of the SiC/SiO2 heterojunctions was studied. The necklace-like SiC/SiO2 nanochains, several centimeters in length, were composed of SiC/SiO2 core-shell chains and amorphous SiO2 beans. The morphologies of the as-prepared products could be tuned by adjusting the firing temperature. In fact, the diameter of the SiO2 beans decreased, whereas the diameter of the SiC fibers and the thickness of the SiO2 shell increased as the temperature increased. The growth mechanism of the necklace-like structure was controlled by the vapor-solid growth procedure and the modulation procedure via a molten salt-mediated chemical vapor reaction process. PMID:29748482

Magneto-electronic properties and spin-resolved I-V curves of a Co/GeSe heterojunction diode: an ab initio study

NASA Astrophysics Data System (ADS)

Makinistian, Leonardo; Albanesi, Eduardo A.

2013-06-01

We present ab initio calculations of magnetoelectronic and transport properties of the interface of hcp Cobalt (001) and the intrinsic narrow-gap semiconductor germanium selenide (GeSe). Using a norm-conserving pseudopotentials scheme within DFT, we first model the interface with a supercell approach and focus on the spin-resolved densities of states and the magnetic moment (spin and orbital components) at the different atomic layers that form the device. We also report a series of cuts (perpendicular to the plane of the heterojunction) of the electronic and spin densities showing a slight magnetization of the first layers of the semiconductor. Finally, we model the device with a different scheme: using semiinfinite electrodes connected to the heterojunction. These latter calculations are based upon a nonequilibrium Green's function approach that allows us to explore the spin-resolved electronic transport under a bias voltage (spin-resolved I-V curves), revealing features of potential applicability in spintronics.

A self-assembled microbonded germanium/silicon heterojunction photodiode for 25 Gb/s high-speed optical interconnects

PubMed Central

Tseng, Chih-Kuo; Chen, Wei-Ting; Chen, Ku-Hung; Liu, Han-Din; Kang, Yimin; Na, Neil; Lee, Ming-Chang M.

2013-01-01

A novel technique using surface tension to locally bond germanium (Ge) on silicon (Si) is presented for fabricating high performance Ge/Si photodiodes. Surface tension is a cohesive force among liquid molecules that tends to bring contiguous objects in contact to maintain a minimum surface energy. We take advantage of this phenomenon to fabricate a heterojunction optoelectronic device where the lattice constants of joined semiconductors are different. A high-speed Ge/Si heterojunction waveguide photodiode is presented by microbonding a beam-shaped Ge, first grown by rapid-melt-growth (RMG) method, on top of a Si waveguide via surface tension. Excellent device performances such as an operating bandwidth of 17 GHz and a responsivity of 0.66 and 0.70 A/W at the reverse bias of −4 and −6 V, respectively, are demonstrated. This technique can be simply implemented via modern complementary metal-oxide-semiconductor (CMOS) fabrication technologies for integrating Ge on Si devices. PMID:24232956

High-performance tandem organic light-emitting diodes based on a buffer-modified p/n-type planar organic heterojunction as charge generation layer

NASA Astrophysics Data System (ADS)

Wu, Yukun; Sun, Ying; Qin, Houyun; Hu, Shoucheng; Wu, Qingyang; Zhao, Yi

2017-04-01

High-performance tandem organic light-emitting diodes (TOLEDs) were realized using a buffer-modified p/n-type planar organic heterojunction (OHJ) as charge generation layer (CGL) consisting of common organic materials, and the configuration of this p/n-type CGL was "LiF/N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1'-biphenyl-4,4'-diamine (NPB)/4,7-diphenyl-1,10-phenanthroline (Bphen)/molybdenum oxide (MoOx)". The optimized TOLED exhibited a maximum current efficiency of 77.6 cd/A without any out-coupling techniques, and the efficiency roll-off was greatly improved compared to the single-unit OLED. The working mechanism of the p/n-type CGL was discussed in detail. It is found that the NPB/Bphen heterojunction generated enough charges under a forward applied voltage and the carrier extraction was a tunneling process. These results could provide a new method to fabricate high-performance TOLEDs.

Phosphorene/rhenium disulfide heterojunction-based negative differential resistance device for multi-valued logic

NASA Astrophysics Data System (ADS)

Shim, Jaewoo; Oh, Seyong; Kang, Dong-Ho; Jo, Seo-Hyeon; Ali, Muhammad Hasnain; Choi, Woo-Young; Heo, Keun; Jeon, Jaeho; Lee, Sungjoo; Kim, Minwoo; Song, Young Jae; Park, Jin-Hong

2016-11-01

Recently, negative differential resistance devices have attracted considerable attention due to their folded current-voltage characteristic, which presents multiple threshold voltage values. Because of this remarkable property, studies associated with the negative differential resistance devices have been explored for realizing multi-valued logic applications. Here we demonstrate a negative differential resistance device based on a phosphorene/rhenium disulfide (BP/ReS2) heterojunction that is formed by type-III broken-gap band alignment, showing high peak-to-valley current ratio values of 4.2 and 6.9 at room temperature and 180 K, respectively. Also, the carrier transport mechanism of the BP/ReS2 negative differential resistance device is investigated in detail by analysing the tunnelling and diffusion currents at various temperatures with the proposed analytic negative differential resistance device model. Finally, we demonstrate a ternary inverter as a multi-valued logic application. This study of a two-dimensional material heterojunction is a step forward toward future multi-valued logic device research.

Fabrication and characterization of a CuO/ITO heterojunction with a graphene transparent electrode

NASA Astrophysics Data System (ADS)

Mageshwari, K.; Han, Sanghoo; Park, Jinsub

2016-05-01

In this paper, we investigate the electrical properties of a CuO-ITO heterojunction diode with the use of a graphene transparent electrode by current-voltage (I-V) characteristics. CuO thin films were deposited onto an ITO substrate by a simple sol-gel spin coating method and annealed at 500 °C. The x-ray diffraction pattern of the CuO thin films revealed the polycrystalline nature of CuO and exhibited a monoclinic crystal structure. FESEM images showed a uniform and densely packed particulate morphology. The optical band gap of CuO thin films estimated using UV-vis absorption spectra was found to be 2.50 eV. The I-V characteristics of the fabricated CuO-ITO heterojunction showed a well-defined rectifying behavior with improved electrical properties after the insertion of graphene. The electronic parameters of the heterostructure such as barrier height, ideality factor and series resistance were determined from the I-V measurements, and the possible current transport mechanism was discussed.

Phosphorene/rhenium disulfide heterojunction-based negative differential resistance device for multi-valued logic

PubMed Central

Shim, Jaewoo; Oh, Seyong; Kang, Dong-Ho; Jo, Seo-Hyeon; Ali, Muhammad Hasnain; Choi, Woo-Young; Heo, Keun; Jeon, Jaeho; Lee, Sungjoo; Kim, Minwoo; Song, Young Jae; Park, Jin-Hong

2016-01-01

Recently, negative differential resistance devices have attracted considerable attention due to their folded current–voltage characteristic, which presents multiple threshold voltage values. Because of this remarkable property, studies associated with the negative differential resistance devices have been explored for realizing multi-valued logic applications. Here we demonstrate a negative differential resistance device based on a phosphorene/rhenium disulfide (BP/ReS2) heterojunction that is formed by type-III broken-gap band alignment, showing high peak-to-valley current ratio values of 4.2 and 6.9 at room temperature and 180 K, respectively. Also, the carrier transport mechanism of the BP/ReS2 negative differential resistance device is investigated in detail by analysing the tunnelling and diffusion currents at various temperatures with the proposed analytic negative differential resistance device model. Finally, we demonstrate a ternary inverter as a multi-valued logic application. This study of a two-dimensional material heterojunction is a step forward toward future multi-valued logic device research. PMID:27819264

Direct formation of InN-codoped p-ZnO/n-GaN heterojunction diode by solgel spin-coating scheme.

PubMed

Huang, Chun-Ying; Lee, Ya-Ju; Lin, Tai-Yuan; Chang, Shao-Lun; Lian, Jan-Tian; Lin, Hsiu-Mei; Chen, Nie-Chuan; Yang, Ying-Jay

2014-02-15

In this work p-ZnO/n-GaN heterojunction diodes were directly formed on the Si substrate by a combination of cost-effective solgel spin-coating and thermal annealing treatment. Spin-coated n-ZnO films on InN/GaN/Si wafers were converted to p-type polarity after thermal treatment of proper annealing durations. X-ray diffraction (XRD) analysis reveals that InN-codoped ZnO films have grown as the standard hexagonal wurtzite structure with a preferential orientation in the (002) direction. The intensity of the (002) peak decreases for a further extended annealing duration, indicating the greater incorporation of dopants, also confirmed by x-ray photoelectron spectroscopy and low-temperature photoluminescence. Hall and resistivity measurements validate that our p-type ZnO film has a high carrier concentration of 3.73×10¹⁷ cm⁻³, a high mobility of 210 cm²/Vs, and a low resistivity of 0.079 Ωcm. As a result, the proposed p-ZnO/n-GaN heterojunction diode displays a well-behaving current rectification of a typical p-n junction, and the measured current versus voltage (I-V) characteristic is hence well described by the modified Shockley equation. The research on the fabrication of p-ZnO/n-GaN heterojunctions shown here generates useful advances in the production of cost-effective ZnO-based optoelectronic devices.

Pyro-phototronic nanogenerator based on flexible 2D ZnO/graphene heterojunction and its application in self-powered near infrared photodetector and active analog frequency modulation.

PubMed

Sahatiya, Parikshit; Shinde, Akash; Badhulika, Sushmee

2018-08-10

Even though 2D ZnO has been utilized for enhanced self-powered sensing by strain modulation due to its piezoelectric property, study on utilizing the pyroelectric property of ZnO remains unexplored. The piezoelectric property of 2D ZnO works on mechanical strain, which disrupts the structure of ZnO leading to the failure of the device. For a pyroelectric nanogenerator, the temperature difference can be triggered by an external light source, which does not disrupt the ZnO structure and also avoids the need for physical bending/pressing, as in the case of a piezoelectric nanogenerator. This work represents the first demonstration of the fabrication of a flexible 2D ZnO/Gr pyro-phototronic diode where the pyro-potential generated in the 2D ZnO due to the near infrared (NIR) illumination adds to or subtracts from the built-in electric field of the heterojunction and modulates the depletion region of the heterojunction thereby enabling bias-free operation. Furthermore, the variation in the depletion width of the heterojunction was utilized as a variable capacitor in the frequency modulator, wherein, with the increasing intensity, the frequency of oscillations increased from 9.8 to 10.42 MHz. The work presented provides an alternative approach for a self-powered NIR photodetector and the utilization of the same at circuit level, having potential applications in the fields of optothermal detection, electronic tuning circuits, etc.

Double heterojunction nanowire photocatalysts for hydrogen generation.

PubMed

Tongying, P; Vietmeyer, F; Aleksiuk, D; Ferraudi, G J; Krylova, G; Kuno, M

2014-04-21

Charge separation and charge transfer across interfaces are key aspects in the design of efficient photocatalysts for solar energy conversion. In this study, we investigate the hydrogen generating capabilities and underlying photophysics of nanostructured photocatalysts based on CdSe nanowires (NWs). Systems studied include CdSe, CdSe/CdS core/shell nanowires and their Pt nanoparticle-decorated counterparts. Femtosecond transient differential absorption measurements reveal how semiconductor/semiconductor and metal/semiconductor heterojunctions affect the charge separation and hydrogen generation efficiencies of these hybrid photocatalysts. In turn, we unravel the role of surface passivation, charge separation at semiconductor interfaces and charge transfer to metal co-catalysts in determining photocatalytic H2 generation efficiencies. This allows us to rationalize why Pt nanoparticle decorated CdSe/CdS NWs, a double heterojunction system, performs best with H2 generation rates of ∼434.29 ± 27.40 μmol h(-1) g(-1) under UV/Visible irradiation. In particular, we conclude that the CdS shell of this double heterojunction system serves two purposes. The first is to passivate CdSe NW surface defects, leading to long-lived charges at the CdSe/CdS interface capable of carrying out reduction chemistries. Upon photoexcitation, we also find that CdS selectively injects charges into Pt NPs, enabling simultaneous reduction chemistries at the Pt NP/solvent interface. Pt nanoparticle decorated CdSe/CdS NWs thus enable reduction chemistries at not one, but rather two interfaces, taking advantage of each junction's optimal catalytic activities.

Photoreduction of CO2 on TiO2/SrTiO3 Heterojunction Network Film

NASA Astrophysics Data System (ADS)

Bi, Yongsheng; Zong, Lanlan; Li, Chen; Li, Qiuye; Yang, Jianjun

2015-08-01

Nanotube titanic acid (NTA) network film has a porous structure and large BET surface area, which lead them to possessing high utilization of the incident light and strong adsorption ability. We used NTA as the precursor to fabricate a TiO2/ SrTiO3 heterojunction film by the hydrothermal method. In the process of the reaction, part of NTA reacted with SrCl2 to form SrTiO3 nanocubes, and the remainder dehydrated to transform to the rutile TiO2. The ratio of TiO2 and SrTiO3 varied with the hydrothermal reaction time. SEM and TEM images indicated that SrTiO3 nanocubes dispersed uniformly on TiO2 film, and the particle size and crystallinity of SrTiO3 nanocubes increased with the reaction time prolonging. The TiO2/SrTiO3 heterojunction obtained by 1 h showed the best activity for CO2 photoreduction, where the mole ratio of TiO2 and SrTiO3 was 4:1. And the photo-conversion efficiency of CO2 to CH4 improved remarkably after the foreign electron traps of Pt and Pd nanoparticles were loaded. The highest photocatalytic production rate of CH4 reached 20.83 ppm/h cm2. In addition, the selectivity of photoreduction product of CO2 was also increased apparently when Pd acted as the cocatalyst on TiO2/SrTiO3 heterojunction film.

Controllable fabrication of Bi2O3/TiO2 heterojunction with excellent visible-light responsive photocatalytic performance

NASA Astrophysics Data System (ADS)

Huang, Yunfang; Wei, Yuelin; Wang, Jing; Luo, Dan; Fan, Leqing; Wu, Jihuai

2017-11-01

Three-dimensional Bi2O3/TiO2 hierarchical composites have been successfully prepared by a two-step hydrothermal method and subsequent calcination. The samples were characterized using XRD, SEM, TEM, EDS, BET and DRS. The measurement results signified that heterojunctions of various morphologies β-Bi2O3 growing on the three-dimensional hierarchical anatase TiO2 nanorods arrays on FTO glass were apparently formed. The morphology of Bi2O3 changed from three-dimension flower-like microstructures to the sphere-like nanoparticles as the Li(OH) dosage increased. The photocatalytic results showed that all samples exhibited much higher photocatalytic activities than that of pure Bi2O3 and TiO2 (P25) in photocatalytic degradation of methyl blue (MB) under visible-light irradiation. Whereas BTL4 sample exhibited the highest photoactivity with increasing the dosage of Li(OH) to 2 mmol. Furthermore, the absorption edge of the Bi2O3/TiO2 series composites displayed a broad-spectrum photoabsorption from UV to visible-light compared with the individual component. The as-synthesized Bi2O3/TiO2 composites possessed excellent photocatalytic activity and outstanding recyclability. The enhanced photocatalytic efficiency was mainly attributed to the Bi2O3/TiO2p-n heterojunctions and hierarchical nanostructure. The recombination of photogenerated electron-hole pairs was efficiently suppressed by the Bi2O3/TiO2p-n heterojunctions.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

PubMed Central

Ievskaya, Yulia; Hoye, Robert L. Z.; Sadhanala, Aditya; Musselman, Kevin P.; MacManus-Driscoll, Judith L.

2016-01-01

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics. PMID:27500923

Engineering graphene and TMDs based van der Waals heterostructures for photovoltaic and photoelectrochemical solar energy conversion.

PubMed

Li, Changli; Cao, Qi; Wang, Faze; Xiao, Yequan; Li, Yanbo; Delaunay, Jean-Jacques; Zhu, Hongwei

2018-05-08

Graphene and two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant interest due to their unique properties that cannot be obtained in their bulk counterparts. These atomically thin 2D materials have demonstrated strong light-matter interactions, tunable optical bandgap structures and unique structural and electrical properties, rendering possible the high conversion efficiency of solar energy with a minimal amount of active absorber material. The isolated 2D monolayer can be stacked into arbitrary van der Waals (vdWs) heterostructures without the need to consider lattice matching. Several combinations of 2D/3D and 2D/2D materials have been assembled to create vdWs heterojunctions for photovoltaic (PV) and photoelectrochemical (PEC) energy conversion. However, the complex, less-constrained, and more environmentally vulnerable interface in a vdWs heterojunction is different from that of a conventional, epitaxially grown heterojunction, engendering new challenges for surface and interface engineering. In this review, the physics of band alignment, the chemistry of surface modification and the behavior of photoexcited charge transfer at the interface during PV and PEC processes will be discussed. We will present a survey of the recent progress and challenges of 2D/3D and 2D/2D vdWs heterojunctions, with emphasis on their applicability to PV and PEC devices. Finally, we will discuss emerging issues yet to be explored for 2D materials to achieve high solar energy conversion efficiency and possible strategies to improve their performance.

Theoretical prediction of the band offsets at the ZnO/anatase TiO2 and GaN/ZnO heterojunctions using the self-consistent ab initio DFT/GGA-1/2 method.

PubMed

Fang, D Q; Zhang, S L

2016-01-07

The band offsets of the ZnO/anatase TiO2 and GaN/ZnO heterojunctions are calculated using the density functional theory/generalized gradient approximation (DFT/GGA)-1/2 method, which takes into account the self-energy corrections and can give an approximate description to the quasiparticle characteristics of the electronic structure of semiconductors. We present the results of the ionization potential (IP)-based and interfacial offset-based band alignments. In the interfacial offset-based band alignment, to get the natural band offset, we use the surface calculations to estimate the change of reference level due to the interfacial strain. Based on the interface models and GGA-1/2 calculations, we find that the valence band maximum and conduction band minimum of ZnO, respectively, lie 0.64 eV and 0.57 eV above those of anatase TiO2, while lie 0.84 eV and 1.09 eV below those of GaN, which agree well with the experimental data. However, a large discrepancy exists between the IP-based band offset and the calculated natural band offset, the mechanism of which is discussed. Our results clarify band alignment of the ZnO/anatase TiO2 heterojunction and show good agreement with the GW calculations for the GaN/ZnO heterojunction.

Self-assembled hybrid polymer-TiO2 nanotube array heterojunction solar cells.

PubMed

Shankar, Karthik; Mor, Gopal K; Prakasam, Haripriya E; Varghese, Oomman K; Grimes, Craig A

2007-11-20

Films comprised of 4 microm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction solid state solar cells.

Influence of the dynamic lattice strain on the transport behavior of oxide heterojunctions

NASA Astrophysics Data System (ADS)

Wang, J.; Hu, F. X.; Chen, L.; Zhao, Y. Y.; Lu, H. X.; Sun, J. R.; Shen, B. G.

2013-01-01

All-perovskite oxide heterojunctions composed of electron-doped titanate LaxSr1 - xTiO3 (x = 0.1, 0.15) and hole-doped manganite La0.67Ca0.33MnO3 films were fabricated on piezoelectric substrate of (001)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT). Taking advantage of the excellent converse piezoelectric effect of PMN-PT, we investigated the influence of the dynamic lattice strain on transport properties of the heterojunctions by applying external bias electric fields on the PMN-PT substrate. Photovoltaic experiments were carried out to characterize the interfacial barrier of the heterojunction. A linear reduction in the barrier height was observed with the increase of the bias field applied on PMN-PT. The value of the barrier height reduces from ˜1.55 (˜1.30) to 1.02 (1.08) eV as the bias field increases from 0 to 12 kV/cm for the junction of La0.10Sr0.9TiO3/La0.67Ca0.33MnO3 (La0.15Sr0.85TiO3/La0.67Ca0.33MnO3). The observed dependency of barrier height on external field can be ascribed to the increasing release of trapped carriers by strain modulation, which results in a suppression of the depletion layer and increases the opportunity for electron tunneling across the depletion area.

Single In x Ga1-x As nanowire/p-Si heterojunction based nano-rectifier diode.

PubMed

Sarkar, K; Palit, M; Guhathakurata, S; Chattopadhyay, S; Banerji, P

2017-09-20

Nanoscale power supply units will be indispensable for fabricating next generation smart nanoelectronic integrated circuits. Fabrication of nanoscale rectifier circuits on a Si platform is required for integrating nanoelectronic devices with on-chip power supply units. In the present study, a nanorectifier diode based on a single standalone In x Ga 1-x As nanowire/p-Si (111) heterojunction fabricated by metal organic chemical vapor deposition technique has been studied. The nanoheterojunction diodes have shown good rectification and fast switching characteristics. The rectification characteristics of the nanoheterojunction have been demonstrated by different standard waveforms of sinusoidal, square, sawtooth and triangular for two different frequencies of 1 and 0.1 Hz. Reverse recovery time of around 150 ms has been observed in all wave response. A half wave rectifier circuit with a simple capacitor filter has been assembled with this nanoheterojunction diode which provides 12% output efficiency. The transport of carriers through the heterojunction is investigated. The interface states density of the nanoheterojunction has also been determined. Occurrence of output waveforms incommensurate with the input is attributed to higher series resistance of the diode which is further explained considering the dimension of p-side and n-side of the junction. The sudden change of ideality factor after 1.7 V bias is attributed to recombination through interface states in space charge region. Low interface states density as well as high rectification ratio makes this heterojunction diode a promising candidate for future nanoscale electronics.

Excitonic processes at organic heterojunctions

NASA Astrophysics Data System (ADS)

He, ShouJie; Lu, ZhengHong

2018-02-01

Understanding excitonic processes at organic heterojunctions is crucial for development of organic semiconductor devices. This article reviews recent research on excitonic physics that involve intermolecular charge transfer (CT) excitons, and progress on understanding relationships between various interface energy levels and key parameters governing various competing interface excitonic processes. These interface excitonic processes include radiative exciplex emission, nonradiative recombination, Auger electron emission, and CT exciton dissociation. This article also reviews various device applications involving interface CT excitons, such as organic light-emitting diodes (OLEDs), organic photovoltaic cells, organic rectifying diodes, and ultralow-voltage Auger OLEDs.

Solvent additive effects on small molecule crystallization in bulk heterojunction solar cells probed during spin casting.

PubMed

Perez, Louis A; Chou, Kang Wei; Love, John A; van der Poll, Thomas S; Smilgies, Detlef-M; Nguyen, Thuc-Quyen; Kramer, Edward J; Amassian, Aram; Bazan, Guillermo C

2013-11-26

Solvent additive processing can lead to drastic improvements in the power conversion efficiency (PCE) in solution processable small molecule (SPSM) bulk heterojunction solar cells. In situ grazing incidence wide-angle X-ray scattering is used to investigate the kinetics of crystallite formation during and shortly after spin casting. The additive is shown to have a complex effect on structural evolution invoking polymorphism and enhanced crystalline quality of the donor SPSM. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Phase aggregation and morphology effects on nanocarbon optoelectronics.

PubMed

Xie, Yu; Lohrman, Jessica; Ren, Shenqiang

2014-12-05

Controllable morphology and interfacial interactions within bulk heterojunction nanostructures show significant effects on optoelectronic device applications. In this study, a nanocarbon heterojunction, consisting of single-walled carbon nanotubes (s-SWCNTs) and fullerene derivatives, is reported by assembling/blending its structures through solution-based processes. A uniform and dense graphene oxide hole transport layer is used to facilitate the photoconversion at a near infrared (NIR) wavelength. Effective interfacial interaction between the s-SWCNTs and fullerene is suggested by the redshifted photoabsorption and nanoscale/micron-scale fluorescence, which is associated with self-assembled nanocarbon morphology.

Visible GaAs/0.7/P/0.3/ CW heterojunction lasers

NASA Technical Reports Server (NTRS)

Kressel, H.; Olsen, G. H.; Nuese, C. J.

1977-01-01

The paper reports the first low-threshold red-light-emitting heterojunction laser diodes consisting of lattice-matched Ga(As,P)/(In,Ga)P heteroepitaxial layers. A room-temperature threshold current of 3400 A/sq cm was obtained at a wavelength of about 7000 A; this value is substantially lower than those achieved at this wavelength with (Al,Ga)As lasers. For the first time, continuous-wave laser operation at temperatures as high as 10 C has been obtained for GaAs(1-x)P(x).

Formulation strategies for optimizing the morphology of polymeric bulk heterojunction organic solar cells: a brief review

NASA Astrophysics Data System (ADS)

Vongsaysy, Uyxing; Bassani, Dario M.; Servant, Laurent; Pavageau, Bertrand; Wantz, Guillaume; Aziz, Hany

2014-01-01

Polymeric bulk heterojunction (BHJ) organic solar cells represent one of the most promising technologies for renewable energy with a low fabrication cost. Control over BHJ morphology is one of the key factors in obtaining high-efficiency devices. This review focuses on formulation strategies for optimizing the BHJ morphology. We address how solvent choice and the introduction of processing additives affect the morphology. We also review a number of recent studies concerning prediction methods that utilize the Hansen solubility parameters to develop efficient solvent systems.

Atomic Structure of Interface States in Silicon Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

George, B. M.; Behrends, J.; Schnegg, A.; Schulze, T. F.; Fehr, M.; Korte, L.; Rech, B.; Lips, K.; Rohrmüller, M.; Rauls, E.; Schmidt, W. G.; Gerstmann, U.

2013-03-01

Combining orientation dependent electrically detected magnetic resonance and g tensor calculations based on density functional theory we assign microscopic structures to paramagnetic states involved in spin-dependent recombination at the interface of hydrogenated amorphous silicon crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. We find that (i) the interface exhibits microscopic roughness, (ii) the electronic structure of the interface defects is mainly determined by c-Si, (iii) we identify the microscopic origin of the conduction band tail state in the a-Si:H layer, and (iv) present a detailed recombination mechanism.

Enhancement of the inverted polymer solar cells via ZnO doped with CTAB

NASA Astrophysics Data System (ADS)

Sivashnamugan, Kundan; Guo, Tzung-Fang; Hsu, Yao-Jane; Wen, Ten-Chin

2018-02-01

A facile approach enhancing electron extraction in zinc oxide (ZnO) electron transfer interlayer and improving performance of bulk-heterojunction (BHJ) polymer solar cells (PSCs) by adding cetyltrimethylammonium bromide (CTAB) into sol-gel ZnO precursor solution was demonstrated in this work. The power conversion efficiency (PCE) has a 24.1% increment after modification. Our results show that CTAB can dramatically influence optical, electrical and morphological properties of ZnO electron transfer layer, and work as effective additive to enhance the performance of bulk- heterojunction polymer solar cells.

Polymer-Polymer Förster Resonance Energy Transfer Significantly Boosts the Power Conversion Efficiency of Bulk-Heterojunction Solar Cells.

PubMed

Gupta, Vinay; Bharti, Vishal; Kumar, Mahesh; Chand, Suresh; Heeger, Alan J

2015-08-01

Optically resonant donor polymers can exploit a wider range of the solar spectrum effectively without a complicated tandem design in an organic solar cell. Ultrafast Förster resonance energy transfer (FRET) in a polymer-polymer system that significantly improves the power conversion efficiency in bulk heterojunction polymer solar cells from 6.8% to 8.9% is demonstrated, thus paving the way to achieving 15% efficient solar cells. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mixed ternary heterojunction solar cell

DOEpatents

Chen, Wen S.; Stewart, John M.

1992-08-25

A thin film heterojunction solar cell and a method of making it has a p-type layer of mixed ternary I-III-VI.sub.2 semiconductor material in contact with an n-type layer of mixed binary II-VI semiconductor material. The p-type semiconductor material includes a low resistivity copper-rich region adjacent the back metal contact of the cell and a composition gradient providing a minority carrier mirror that improves the photovoltaic performance of the cell. The p-type semiconductor material preferably is CuInGaSe.sub.2 or CuIn(SSe).sub.2.

Influence of Processing Additives on Charge-Transfer Time Scales and Sound Velocity in Organic Bulk Heterojunction Films.

PubMed

Kaake, Loren G; Welch, Gregory C; Moses, Daniel; Bazan, Guillermo C; Heeger, Alan J

2012-05-17

The role of processing additives in organic bulk heterojunction thin films was investigated by means of transient absorption spectroscopy. The rate of ultrafast charge transfer was found to increase when a small amount of diiodooctane was used during film formation. In addition, coherent acoustic phonons were observed, and their velocity was determined. A strong correlation between the sound velocity and the charge-transfer time scale was observed, both of which could be explained by a subtle increase in thin film density.

Fabrication and Characterization of a Long Wavelength InP HBT-Based Optical Receiver

NASA Technical Reports Server (NTRS)

Roenker, Kenneth P.

1997-01-01

Development of a high speed photodetector - the InP-based phototransistor (HPT) for use in optical receivers for microwave signal distribution for satellite phased array antennas is addressed. Currently, p-i-n photodetectors are used because of their compatibility with the heterojunction bipolar transistor (HBT), but their performance limits the bandwidth of these optical receivers. The HPT photodetector was investigated here as an alternative photodetector for monolithic integration with heterojunction bipolar transistor amplifiers in long wavelength (1.3 micron), gigahertz (GHz) frequency optical receivers.

Energy level alignment and sub-bandgap charge generation in polymer:fullerene bulk heterojunction solar cells.

PubMed

Tsang, Sai-Wing; Chen, Song; So, Franky

2013-05-07

Using charge modulated electroabsorption spectroscopy (CMEAS), for the first time, the energy level alignment of a polymer:fullerene bulk heterojunction photovoltaic cell is directly measured. The charge-transfer excitons generated by the sub-bandgap optical pumping are coupled with the modulating electric field and introduce subtle changes in optical absorption in the sub-bandgap region. This minimum required energy for sub-bandgap charge genreation is defined as the effective bandgap. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Deposition and characterization of ZnS/Si heterojunctions produced by vacuum evaporation

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.; Loferski, Joseph J.; Beaulieu, Roland

1988-01-01

Isotype heterojunctions of ZnS (lattice constant 5.41 A) were grown on silicon (lattice constant 5.43 A) p-n junctions to form a minority-carrier mirror. The deposition process was vacuum evaporation from a ZnS powder source onto a heated (450 C) substrate. Both planar (100) and textured (111) surfaces were used. A reduction of the minority-carrier recombination at the surface was seen from increased short-wavelength quantum response and increased illuminated open-circuit voltage. The minority-carrier diffusion length was not degraded by the process.

A Workshop on 3-5 Semiconductor: Metal Interfacial Chemistry and Its Effect on Electrical Properties, November 3-5, 1986,

DTIC Science & Technology

1986-11-05

band bending condition eliminated after metal deposition onto Ga203 * up to "𔃺.7 eY shift in EF occurs with sequential oxide and metal surface...and the tables of band- lineups to estimate the sign and magnitude of the effect. *Supported, in part, by ONR Contract No. N00014-85-C-0i35 ** Permanent...V1a,3. c SL. c93 1 Ill-V Interfaces: Schottky Barriers vs. Heterojunctions Giorgio Margaritondo University of Wisconsin HETE-ROJUNCTION BAND LINEUPS VS

Multi-level resistive switching behaviors and retention characteristics in ZnO/Nb:SrTiO3 heterojunction

NASA Astrophysics Data System (ADS)

Ren, Yong; Li, Jiachen; Zhang, Weifeng; Jia, Caihong

2017-10-01

Epitaxial ZnO thin films were grown on SrTiO3:Nb (NSTO) substrates by rf magnetron sputtering method. The multi-level resistance states were observed by applying different amplitudes and/or polarities of voltage pulses, which is supposed to be related to the drift of oxygen vacancies. Furthermore, the decay of retention is also corresponding to the migration of oxygen vacancies. The retention and cycle stability implies that the ZnO/Nb:SrTiO3 heterojunctions are promising for high density memory application.

Performance of RF sputtered p-Si/n-ZnO nanoparticle thin film heterojunction diodes in high temperature environment

NASA Astrophysics Data System (ADS)

Singh, Satyendra Kumar; Hazra, Purnima

2017-04-01

In this article, temperature-dependent current-voltage characteristics of n-ZnO/p-Si nanoparticle thin film heterojunction diode grown by RF sputtering technique are analyzed in the temperature range of 300-433 k to investigate the performance of the device in high temperature environment. The microstructural, morphological, optical and temptrature dependent electrical properties of as-grown nanoparticle thin film were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM), field emmision scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), variable angle ellipsometer and semiconductor device analyzer. XRD spectra of as-grown ZnO films are exhibited that highly c-axis oriented ZnO nanostructures are grown on p- Si〈100〉 substrate whereas AFM and FESEM images confirm the homogeneous deposition of ZnO nanoparticles on surface of Si substratewith minimum roughness.The optical propertiesof as-grown ZnO nanoparticles have been measured in the spectral range of 300-800 nm using variable angle ellipsometer.To measure electrical parameters of the device prototype in the temperature range of room temperature (300 K) to 433 K, large area ohmic contacts were fabricated on both side of the ZnO/Si heterostructure. From the current-voltage charcteristics of ZnO/Si heterojunction device, it is observed that the device exhibits rectifing nature at room temperature. However, with increase in temperature, reverse saturation current and barrier height are found to increase, whereas ideality factor is started decreasing. This phenomenon confirms that barrier inhomogeneities are present at the interface of ZnO/Si heterojunction, as a result of lattice constant and thermal coefficient mismatch between Si and ZnO. Therefore, a modified value of Richardson constant [33.06 Acm-2K-2] has been extracted from the temperature-dependent electrical characteristics after assuming the Gaussian distribution of special barrier height inhomogeneities across the Si/ZnO interface which is close to its theoretical value [32 Acm-2K-2]. This result indicates that regardless of presence of barrier height inmogeneities, ZnO/Si heterojunction diode still hasability to perform well in high temperature environment.

Solution-processed all-oxide bulk heterojunction solar cells based on CuO nanaorod array and TiO2 nanocrystals.

PubMed

Wu, Fan; Qiao, Qiquan; Bahrami, Behzad; Chen, Ke; Pathak, Rajesh; Tong, Yanhua; Li, Xiaoyi; Zhang, Tiansheng; Jian, Ronghua

2018-05-25

We present a method to synthesize CuO nanorod array/TiO 2 nanocrystals bulk heterojunction (BHJ) on fluorine-tin-oxide (FTO) glass, in which single-crystalline p-type semiconductor of the CuO nanorod array is grown on the FTO glass by hydrothermal reaction and the n-type semiconductor of the TiO 2 precursor is filled into the CuO nanorods to form well-organized nano-interpenetrating BHJ after air annealing. The interface charge transfer in CuO nanorod array/TiO 2 heterojunction is studied by Kelvin probe force microscopy (KPFM). KPFM results demonstrate that the CuO nanorod array/TiO 2 heterojunction can realize the transfer of photo-generated electrons from the CuO nanorod array to TiO 2 . In this work, a solar cell with the structure FTO/CuO nanoarray/TiO 2 /Al is successfully fabricated, which exhibits an open-circuit voltage (V oc ) of 0.20 V and short-circuit current density (J sc ) of 0.026 mA cm -2 under AM 1.5 illumination. KPFM studies indicate that the very low performance is caused by an undesirable interface charge transfer. The interfacial surface potential (SP) shows that the electron concentration in the CuO nanorod array changes considerably after illumination due to increased photo-generated electrons, but the change in the electron concentration in TiO 2 is much less than in CuO, which indicates that the injection efficiency of the photo-generated electrons from CuO to TiO 2 is not satisfactory, resulting in an undesirable J sc in the solar cell. The interface photovoltage from the KPFM measurement shows that the low V oc results from the small interfacial SP difference between CuO and TiO 2 because the low injected electron concentration cannot raise the Fermi level significantly in TiO 2 . This conclusion agrees with the measured work function results under illumination. Hence, improvement of the interfacial electron injection is primary for the CuO nanorod array/TiO 2 heterojunction solar cells.

Solution-processed all-oxide bulk heterojunction solar cells based on CuO nanaorod array and TiO2 nanocrystals

NASA Astrophysics Data System (ADS)

Wu, Fan; Qiao, Qiquan; Bahrami, Behzad; Chen, Ke; Pathak, Rajesh; Tong, Yanhua; Li, Xiaoyi; Zhang, Tiansheng; Jian, Ronghua

2018-05-01

We present a method to synthesize CuO nanorod array/TiO2 nanocrystals bulk heterojunction (BHJ) on fluorine-tin-oxide (FTO) glass, in which single-crystalline p-type semiconductor of the CuO nanorod array is grown on the FTO glass by hydrothermal reaction and the n-type semiconductor of the TiO2 precursor is filled into the CuO nanorods to form well-organized nano-interpenetrating BHJ after air annealing. The interface charge transfer in CuO nanorod array/TiO2 heterojunction is studied by Kelvin probe force microscopy (KPFM). KPFM results demonstrate that the CuO nanorod array/TiO2 heterojunction can realize the transfer of photo-generated electrons from the CuO nanorod array to TiO2. In this work, a solar cell with the structure FTO/CuO nanoarray/TiO2/Al is successfully fabricated, which exhibits an open-circuit voltage (V oc) of 0.20 V and short-circuit current density (J sc) of 0.026 mA cm‑2 under AM 1.5 illumination. KPFM studies indicate that the very low performance is caused by an undesirable interface charge transfer. The interfacial surface potential (SP) shows that the electron concentration in the CuO nanorod array changes considerably after illumination due to increased photo-generated electrons, but the change in the electron concentration in TiO2 is much less than in CuO, which indicates that the injection efficiency of the photo-generated electrons from CuO to TiO2 is not satisfactory, resulting in an undesirable J sc in the solar cell. The interface photovoltage from the KPFM measurement shows that the low V oc results from the small interfacial SP difference between CuO and TiO2 because the low injected electron concentration cannot raise the Fermi level significantly in TiO2. This conclusion agrees with the measured work function results under illumination. Hence, improvement of the interfacial electron injection is primary for the CuO nanorod array/TiO2 heterojunction solar cells.

Temperature-Dependent and Gate-Tunable Rectification in a Black Phosphorus/WS2 van der Waals Heterojunction Diode.

PubMed

Dastgeer, Ghulam; Khan, Muhammad Farooq; Nazir, Ghazanfar; Afzal, Amir Muhammad; Aftab, Sikandar; Naqvi, Bilal Abbas; Cha, Janghwan; Min, Kyung-Ah; Jamil, Yasir; Jung, Jongwan; Hong, Suklyun; Eom, Jonghwa

2018-04-18

Heterostructures comprising two-dimensional (2D) semiconductors fabricated by individual stacking exhibit interesting characteristics owing to their 2D nature and atomically sharp interface. As an emerging 2D material, black phosphorus (BP) nanosheets have drawn much attention because of their small band gap semiconductor characteristics along with high mobility. Stacking structures composed of p-type BP and n-type transition metal dichalcogenides can produce an atomically sharp interface with van der Waals interaction which leads to p-n diode functionality. In this study, for the first time, we fabricated a heterojunction p-n diode composed of BP and WS 2 . The rectification effects are examined for monolayer, bilayer, trilayer, and multilayer WS 2 flakes in our BP/WS 2 van der Waals heterojunction diodes and also verified by density function theory calculations. We report superior functionalities as compared to other van der Waals heterojunction, such as efficient gate-dependent static rectification of 2.6 × 10 4 , temperature dependence, thickness dependence of rectification, and ideality factor of the device. The temperature dependence of Zener breakdown voltage and avalanche breakdown voltage were analyzed in the same device. Additionally, superior optoelectronic characteristics such as photoresponsivity of 500 mA/W and external quantum efficiency of 103% are achieved in the BP/WS 2 van der Waals p-n diode, which is unprecedented for BP/transition metal dichalcogenides heterostructures. The BP/WS 2 van der Waals p-n diodes have a profound potential to fabricate rectifiers, solar cells, and photovoltaic diodes in 2D semiconductor electronics and optoelectronics.

ALD-Developed Plasmonic Two-Dimensional Au-WO3-TiO2 Heterojunction Architectonics for Design of Photovoltaic Devices.

PubMed

Karbalaei Akbari, Mohammad; Hai, Zhenyin; Wei, Zihan; Detavernier, Christophe; Solano, Eduardo; Verpoort, Francis; Zhuiykov, Serge

2018-03-28

Electrically responsive plasmonic devices, which benefit from the privilege of surface plasmon excited hot carries, have supported fascinating applications in the visible-light-assisted technologies. The properties of plasmonic devices can be tuned by controlling charge transfer. It can be attained by intentional architecturing of the metal-semiconductor (MS) interfaces. In this study, the wafer-scaled fabrication of two-dimensional (2D) TiO 2 semiconductors on the granular Au metal substrate is achieved using the atomic layer deposition (ALD) technique. The ALD-developed 2D MS heterojunctions exhibited substantial enhancement of the photoresponsivity and demonstrated the improvement of response time for 2D Au-TiO 2 -based plasmonic devices under visible light illumination. To circumvent the undesired dark current in the plasmonic devices, a 2D WO 3 nanofilm (∼0.7 nm) was employed as the intermediate layer on the MS interface to develop the metal-insulator-semiconductor (MIS) 2D heterostructure. As a result, 13.4% improvement of the external quantum efficiency was obtained for fabricated 2D Au-WO 3 -TiO 2 heterojunctions. The impedancometry measurements confirmed the modulation of charge transfer at the 2D MS interface using MIS architectonics. Broadband photoresponsivity from the UV to the visible light region was observed for Au-TiO 2 and Au-WO 3 -TiO 2 heterostructures, whereas near-infrared responsivity was not observed. Consequently, considering the versatile nature of the ALD technique, this approach can facilitate the architecturing and design of novel 2D MS and MIS heterojunctions for efficient plasmonic devices.

Enhanced photocatalytic performance and degradation pathway of Rhodamine B over hierarchical double-shelled zinc nickel oxide hollow sphere heterojunction

NASA Astrophysics Data System (ADS)

Zhang, Ying; Zhou, Jiabin; Cai, Weiquan; Zhou, Jun; Li, Zhen

2018-02-01

In this study, hierarchical double-shelled NiO/ZnO hollow spheres heterojunction were prepared by calcination of the metallic organic frameworks (MOFs) as a sacrificial template in air via a one-step solvothermal method. Additionally, the photocatalytic activity of the as-prepared samples for the degradation of Rhodamine B (RhB) under UV-vis light irradiation were also investigated. NiO/ZnO microsphere comprised a core and a shell with unique hierarchically porous structure. The photocatalytic results showed that NiO/ZnO hollow spheres exhibited excellent catalytic activity for RhB degradation, causing complete decomposition of RhB (200 mL of 10 g/L) under UV-vis light irradiation within 3 h. Furthermore, the degradation pathway was proposed on the basis of the intermediates during the photodegradation process using liquid chromatography analysis coupled with mass spectroscopy (LC-MS). The improvement in photocatalytic performance could be attributed to the p-n heterojunction in the NiO/ZnO hollow spheres with hierarchically porous structure and the strong double-shell binding interaction, which enhances adsorption of the dye molecules on the catalyst surface and facilitates the electron/hole transfer within the framework. The degradation mechanism of pollutant is ascribed to the hydroxyl radicals (rad OH), which is the main oxidative species for the photocatalytic degradation of RhB. This work provides a facile and effective approach for the fabrication of porous metal oxides heterojunction with high photocatalytic activity and thus can be potentially used in the environmental purification.

Selective isolation of the electron or hole in photocatalysis: ZnO-TiO2 and TiO2-ZnO core-shell structured heterojunction nanofibers via electrospinning and atomic layer deposition.

PubMed

Kayaci, Fatma; Vempati, Sesha; Ozgit-Akgun, Cagla; Donmez, Inci; Biyikli, Necmi; Uyar, Tamer

2014-06-07

Heterojunctions are a well-studied material combination in photocatalysis studies, the majority of which aim to improve the efficacy of the catalysts. Developing novel catalysts begs the question of which photo-generated charge carrier is more efficient in the process of catalysis and the associated mechanism. To address this issue we have fabricated core-shell heterojunction (CSHJ) nanofibers from ZnO and TiO2 in two combinations where only the 'shell' part of the heterojunction is exposed to the environment to participate in the photocatalysis. Core and shell structures were fabricated via electrospinning and atomic layer deposition, respectively which were then subjected to calcination. These CSHJs were characterized and studied for photocatalytic activity (PCA). These two combinations expose electrons or holes selectively to the environment. Under suitable illumination of the ZnO-TiO2 CSHJ, e/h pairs are created mainly in TiO2 and the electrons take part in catalysis (i.e. reduce the organic dye) at the conduction band or oxygen vacancy sites of the 'shell', while holes migrate to the core of the structure. Conversely, holes take part in catalysis and electrons diffuse to the core in the case of a TiO2-ZnO CSHJ. The results further revealed that the TiO2-ZnO CSHJ shows ∼1.6 times faster PCA when compared to the ZnO-TiO2 CSHJ because of efficient hole capture by oxygen vacancies, and the lower mobility of holes.

Flexible resistive switching device based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(4-vinylphenol) (PVP) composite and methyl red heterojunction

NASA Astrophysics Data System (ADS)

Hassan, Gul; Ali, Shawkat; Bae, Jinho; Lee, Chong Hyun

2017-04-01

To obtain a desired performance of non-volatile memory applications, heterojunction-based resistive switching devices have tremendous attractions. In this paper, we demonstrate resistive switching characteristics for heterojunction of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(4-vinylphenol) (PVP) composite and methyl red sandwiched in between bottom and top silver (Ag) electrodes. The proposed heterojunction layers are fabricated through spin coater at 3000 rpm for 60 s each, and the Ag electrodes are deposited through a commercialized inkjet printer DMP-3000 on polyethyleneterephthalate (PET) substrate. To verify the proposed device, the resistive switching on dual polarity voltage of ±10.2 V is measured over more than 500 endurance cycles. The paper also presents an R off/ R on ratio which can adjust through an active layer's area and a blending ratio of the PEDOT:PSS and PVP. By applying the area of 100 μm2 and the blending ratio of 3:1, we achieve the higher R off/ R on ratio of 121, and its high resistance state (HRS) and low resistance state (LRS) are observed as 3000 kΩ and 24.7 kΩ, respectively. To maintain a long retention time, the device is encapsulated with PDMS, which changes a little variations of 52 Ω for HRS 498 Ω for LRS over 60 days. For the flexible realization to be utilized in wearable applications, it can be easily applied on a plastic substrate using printed technologies.

The effects of solvent on photocatalytic properties of Bi2WO6/TiO2 heterojunction under visible light irradiation

NASA Astrophysics Data System (ADS)

Guo, Qiyao; Huang, Yunfang; Xu, Hui; Luo, Dan; Huang, Feiyue; Gu, Lin; Wei, Yuelin; Zhao, Huang; Fan, Leqing; Wu, Jihuai

2018-04-01

Bi2WO6/TiO2 heterojunction photocatalysts with two different microstructures were controllably fabricated via a facile two-step synthetic route. XRD, XPS, SEM, TEM, BET-surface, DRS, PL spectra, photoelectrochemical measurement (Mott-Schottky), and zeta-potential analyzer were employed to clarify structural and morphological characteristics of the obtained products. The results showed that Bi2WO6 nanoparticles/nanosheets grew on the primary TiO2 nanorods. The TiO2 nanorods used as a synthetic template inhibit the growth of Bi2WO6 crystals along the c-axis, resulting in Bi2WO6/TiO2 heterostructure with one-dimensional (1D) morphology. The photocatalytic properties of Bi2WO6/TiO2 heterojunction photocatalysts were strongly dependent on their shapes and structures. Compared with bare Bi2WO6 and TiO2, Bi2WO6/TiO2 composite have stronger adsorption ability and better visible light photocatalytic activities towards organic dyes. The Bi2WO6/TiO2 composite prepared in EG solvent with optimal Bi:Ti ratio of 2:12 (S-TB2) showed the highest photocatalytic activity, which could totally decompose Rhodamine B within 10 min upon irradiation with visible light (λ > 422 nm), and retained the high photocatalytic performance after five recycles, confirming its stability and practical usability. The results of PL indicated that Bi2WO6 and TiO2 could combine well to form a heterojunction structure which facilitated electron-hole separation, and lead to the increasing photocatalytic activity.

Black TiO2 nanobelts/g-C3N4 nanosheets Laminated Heterojunctions with Efficient Visible-Light-Driven Photocatalytic Performance

PubMed Central

Shen, Liyan; Xing, Zipeng; Zou, Jinlong; Li, Zhenzi; Wu, Xiaoyan; Zhang, Yuchi; Zhu, Qi; Yang, Shilin; Zhou, Wei

2017-01-01

Black TiO2 nanobelts/g-C3N4 nanosheets laminated heterojunctions (b-TiO2/g-C3N4) as visible-light-driven photocatalysts are fabricated through a simple hydrothermal-calcination process and an in-situ solid-state chemical reduction approach, followed by the mild thermal treatment (350 °C) in argon atmosphere. The prepared samples are evidently investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption, and UV-visible diffuse reflectance spectroscopy, respectively. The results show that special laminated heterojunctions are formed between black TiO2 nanobelts and g-C3N4 nanosheets, which favor the separation of photogenerated electron-hole pairs. Furthermore, the presence of Ti3+ and g-C3N4 greatly enhance the absorption of visible light. The resultant b-TiO2/g-C3N4 materials exhibit higher photocatalytic activity than that of g-C3N4, TiO2, b-TiO2 and TiO2/g-C3N4 for degradation of methyl orange (95%) and hydrogen evolution (555.8 μmol h−1 g−1) under visible light irradiation. The apparent reaction rate constant (k) of b-TiO2/g-C3N4 is ~9 times higher than that of pristine TiO2. Therefore, the high-efficient laminated heterojunction composites will have potential applications in fields of environment and energy. PMID:28165021

Au and Pt selectively deposited on {0 0 1}-faceted TiO2 toward SPR enhanced photocatalytic Cr(VI) reduction: The influence of excitation wavelength

NASA Astrophysics Data System (ADS)

Wang, Wei; Lai, Min; Fang, Jiaojiao; Lu, Chunhua

2018-05-01

Anatase TiO2 nanosheets with {0 0 1}-{1 0 1} surface heterojunction is employed as the typical photocatalyst to study surface plasmon resonance (SPR) enhanced photocatalytic Cr(VI) reduction with the help of selectively deposited Au and Pt nanoparticles. By employing an UV LED with central wavelength of 365 nm and a green LED with central wavelength of 530 nm as the light sources, results indicate the single green LED has little positive effect on driving the photocatalytic Cr(VI) reduction. In contrast, Au SPR can significantly improve the photocatalytic Cr(VI) reduction efficiency when both the UV LED and green LED are simultaneously irradiated. The {0 0 1}-{1 0 1} surface heterojunction and Pt nanoparticles can further improve the Cr(VI) reduction efficiency because of the facilitated hot electrons' transfer. Our findings suggest that the synergistic effect among {0 0 1}-{1 0 1} surface heterojunction, Au/Pt selective deposition, and excitation wavelength is important for SPR enhanced photocatalytic Cr(VI) reduction activity.

Determination of Acceptor Concentration, Depletion Width, Donor Level Movement and Sensitivity Factor of ZnO on Diamond Heterojunction under UV Illumination

PubMed Central

Saw, Kim Guan; Tneh, Sau Siong; Yam, Fong Kwong; Ng, Sha Shiong; Hassan, Zainuriah

2014-01-01

The concentration of acceptor carriers, depletion width, magnitude of donor level movement as well as the sensitivity factor are determined from the UV response of a heterojunction consisting of ZnO on type IIb diamond. From the comparison of the I-V measurements in dark condition and under UV illumination we show that the acceptor concentration (∼1017 cm−3) can be estimated from p-n junction properties. The depletion width of the heterojunction is calculated and is shown to extend farther into the ZnO region in dark condition. Under UV illumination, the depletion width shrinks but penetrates both materials equally. The ultraviolet illumination causes the donor level to move closer to the conduction band by about 50 meV suggesting that band bending is reduced to allow more electrons to flow from the intrinsically n-type ZnO. The sensitivity factor of the device calculated from the change of threshold voltages, the ratio of dark and photocurrents and identity factor is consistent with experimental data. PMID:24586707

The underlying micro-mechanism of performance enhancement of non-polar n-ZnO/p-AlGaN ultraviolet light emitting diode with i-ZnO inserted layer

NASA Astrophysics Data System (ADS)

Jiang, Fan; Chen, Jingwen; Bi, Han; Li, Luying; Jing, Wenkui; Zhang, Jun; Dai, Jiangnan; Che, Renchao; Chen, Changqing; Gao, Yihua

2018-01-01

Non-polar a-plane n-ZnO/p-AlGaN and n-ZnO/i-ZnO/p-AlGaN heterojunction film light-emitting diodes (LEDs) are fabricated with good crystalline quality. The optical measurements show obvious performance enhancement with i-ZnO layer insertion. Off-axis electron holography reveals a potential drop of ˜1.5 V across the heterojunctions with typical p-n junction characteristics. It is found that the electrostatic potentials are inclined and the corresponding electrostatic fields are opposite to each other in n-ZnO and p-AlGaN regions. The electrostatic fields are mainly attributed to strain induced piezoelectric polarizations. After an insertion of an i-ZnO layer into the p-n heterojunction, comparatively flat electrostatic potential generates in the intrinsic ZnO region and contributes to faster movements of the injected electrons and holes, making the i-ZnO layer more conductive to the radiative recombination with enhanced exciton recombination possibilities and at last the LED performance enhancement.

Exciton delocalization incorporated drift-diffusion model for bulk-heterojunction organic solar cells

NASA Astrophysics Data System (ADS)

Wang, Zi Shuai; Sha, Wei E. I.; Choy, Wallace C. H.

2016-12-01

Modeling the charge-generation process is highly important to understand device physics and optimize power conversion efficiency of bulk-heterojunction organic solar cells (OSCs). Free carriers are generated by both ultrafast exciton delocalization and slow exciton diffusion and dissociation at the heterojunction interface. In this work, we developed a systematic numerical simulation to describe the charge-generation process by a modified drift-diffusion model. The transport, recombination, and collection of free carriers are incorporated to fully capture the device response. The theoretical results match well with the state-of-the-art high-performance organic solar cells. It is demonstrated that the increase of exciton delocalization ratio reduces the energy loss in the exciton diffusion-dissociation process, and thus, significantly improves the device efficiency, especially for the short-circuit current. By changing the exciton delocalization ratio, OSC performances are comprehensively investigated under the conditions of short-circuit and open-circuit. Particularly, bulk recombination dependent fill factor saturation is unveiled and understood. As a fundamental electrical analysis of the delocalization mechanism, our work is important to understand and optimize the high-performance OSCs.

Plasmonic engineering of metal-oxide nanowire heterojunctions in integrated nanowire rectification units

NASA Astrophysics Data System (ADS)

Lin, Luchan; Zou, Guisheng; Liu, Lei; Duley, Walt W.; Zhou, Y. Norman

2016-05-01

We show that irradiation with femtosecond laser pulses can produce robust nanowire heterojunctions in coupled non-wetting metal-oxide Ag-TiO2 structures. Simulations indicate that joining arises from the effect of strong plasmonic localization in the region of the junction. Strong electric field effects occur in both Ag and TiO2 resulting in the modification of both surfaces and an increase in wettability of TiO2, facilitating the interconnection of Ag and TiO2 nanowires. Irradiation leads to the creation of a thin layer of highly defected TiO2 in the contact region between the Ag and TiO2 nanowires. The presence of this layer allows the formation of a heterojunction and offers the possibility of engineering the electronic characteristics of interfacial structures. Rectifying junctions with single and bipolar properties have been generated in Ag-TiO2 nanowire circuits incorporating asymmetrical and symmetrical interfacial structures, respectively. This fabrication technique should be applicable for the interconnection of other heterogeneous metal-oxide nanowire components and demonstrates that femtosecond laser irradiation enables interfacial engineering for electronic applications of integrated nanowire structures.

Efficient semitransparent perovskite solar cells for 23.0%-efficiency perovskite/silicon four-terminal tandem cells

DOE PAGES

Chen, Bo; Bai, Yang; Yu, Zhengshan; ...

2016-07-19

Here, we have investigated semi-transparent perovskite solar cells and infrared enhanced silicon heterojunction cells for high-efficiency tandem devices. A semi-transparent metal electrode with good electrical conductivity and optical transparency has been fabricated by thermal evaporation of 7 nm of Au onto a 1-nm-thick Cu seed layer. For this electrode to reach its full potential, MAPbI3 thin films were formed by a modified one-step spin-coating method, resulting in a smooth layer that allowed the subsequent metal thin film to remain continuous. The fabricated semi-transparent perovskite solar cells demonstrated 16.5% efficiency under one-sun illumination, and were coupled with infrared-enhanced silicon heterojunction cellsmore » tuned specifically for perovskite/Si tandem devices. A double-layer antireflection coating at the front side and MgF2 reflector at rear side of the silicon heterojunction cells reduced parasitic absorption of near-infrared light, leading to 6.5% efficiency after filtering with a perovskite device and 23.0% summed efficiency for the perovskite/Si tandem device.« less

Photovoltaic devices based on high density boron-doped single-walled carbon nanotube/n-Si heterojunctions

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

Saini, Viney; Li, Zhongrui; Bourdo, Shawn

2011-01-13

A simple and easily processible photovoltaic device has been developed based on borondoped single-walled carbon nanotubes (B-SWNTs) and n-type silicon (n-Si) heterojunctions. The single-walled carbon nanotubes (SWNTs) were substitutionally doped with boron atoms by thermal annealing, in the presence of B 2O 3. The samples used for these studies were characterized by Raman spectroscopy, thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The fully functional solar cell devices were fabricated by airbrush deposition that generated uniform B-SWNT films on top of the n-Si substrates. The carbon nanotube films acted as exciton-generation sites, charge collection andmore » transportation, while the heterojunctions formed between B-SWNTs and n-Si acted as charge dissociation centers. The current-voltage characteristics in the absence of light and under illumination, as well as optical transmittance spectrum are reported here. It should be noted that the device fabrication process can be made amenable to scalability by depositing direct and uniform films using airbrushing, inkjet printing, or spin-coating techniques.« less

Grooved nanowires from self-assembling hairpin molecules for solar cells.

PubMed

Tevis, Ian D; Tsai, Wei-Wen; Palmer, Liam C; Aytun, Taner; Stupp, Samuel I

2012-03-27

One of the challenges facing bulk heterojunction organic solar cells is obtaining organized films during the phase separation of intimately mixed donor and acceptor components. We report here on the use of hairpin-shaped sexithiophene molecules to generate by self-assembly grooved nanowires as the donor component in bulk heterojunction solar cells. Photovoltaic devices were fabricated via spin-casting to produce by solvent evaporation a percolating network of self-assembled nanowires and fullerene acceptors. Thermal annealing was found to increase power conversion efficiencies by promoting domain growth while still maintaining this percolating network of nanostructures. The benefits of self-assembly and grooved nanowires were examined by building devices from a soluble sexithiophene derivative that does not form one-dimensional structures. In these systems, excessive phase separation caused by thermal annealing leads to the formation of defects and lower device efficiencies. We propose that the unique hairpin shape of the self-assembling molecules allows the nanowires as they form to interact well with the fullerenes in receptor-ligand type configurations at the heterojunction of the two domains, thus enhancing device efficiencies by 23%. © 2012 American Chemical Society

Low cost, p-ZnO/n-Si, rectifying, nano heterojunction diode: Fabrication and electrical characterization.

PubMed

Kabra, Vinay; Aamir, Lubna; Malik, M M

2014-01-01

A low cost, highly rectifying, nano heterojunction (p-ZnO/n-Si) diode was fabricated using solution-processed, p-type, ZnO nanoparticles and an n-type Si substrate. p-type ZnO nanoparticles were synthesized using a chemical synthesis route and characterized by XRD and a Hall effect measurement system. The device was fabricated by forming thin film of synthesized p-ZnO nanoparticles on an n-Si substrate using a dip coating technique. The device was then characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The effect of UV illumination on the I-V characteristics was also explored and indicated the formation of a highly rectifying, nano heterojunction with a rectification ratio of 101 at 3 V, which increased nearly 2.5 times (232 at 3 V) under UV illumination. However, the cut-in voltage decreases from 1.5 V to 0.9 V under UV illumination. The fabricated device could be used in switches, rectifiers, clipper and clamper circuits, BJTs, MOSFETs and other electronic circuitry.

Strong and reversible modulation of carbon nanotube-silicon heterojunction solar cells by an interfacial oxide layer.

PubMed

Jia, Yi; Cao, Anyuan; Kang, Feiyu; Li, Peixu; Gui, Xuchun; Zhang, Luhui; Shi, Enzheng; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai

2012-06-21

Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure-Si heterojunction structures.

Synthesis of LaVO4/TiO2 heterojunction nanotubes by sol-gel coupled with hydrothermal method for photocatalytic air purification.

PubMed

Zou, Xuejun; Li, Xinyong; Zhao, Qidong; Liu, Shaomin

2012-10-01

With the aim of improving the effective utilization of visible light, the LaVO(4)/TiO(2) heterojunction nanotubes were fabricated by sol-gel coupled with hydrothermal method. The photocatalytic ability was demonstrated through catalytic removal of gaseous toluene species. The nanotube samples were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), surface photovoltage (SPV), Raman spectra and N(2) adsorption-desorption measurements. The characterization results showed that the samples with high specific surface areas were of typical nanotubular morphology, which would lead to the high separation and transfer efficiency of photo induced electron-hole pairs. The as-prepared nanotubes exhibited high photocatalytic activity in decomposing toluene species under visible light irradiation with fine photochemical stability. The enhanced photocatalytic performance of LaVO(4)/TiO(2) nanotubes might be attributed to the matching band potentials, the interconnected heterojunction of LaVO(4) versus TiO(2), and the large specific surface areas of nanotubes. Copyright © 2012 Elsevier Inc. All rights reserved.

Heterojunction photodetector based on graphene oxide sandwiched between ITO and p-Si

NASA Astrophysics Data System (ADS)

Ahmad, H.; Tajdidzadeh, M.; Thandavan, T. M. K.

2018-02-01

The drop casting method is utilized on indium tin oxide (ITO)-coated glass in order to prepare a sandwiched ITO/graphene oxide (ITO/GO) with silicon dioxide/p-type silicon (SiO2/p-Si) heterojunction photodetector. The partially sandwiched GO layer with SiO2/p-Si substrate exhibits dual characteristics as it showed good sensitivity towards the illumination of infrared (IR) laser at wavelength of 974 nm. Excellent photoconduction is also observed for current-voltage (I-V) characteristics at various laser powers. An external quantum efficiency greater than 1 for a direct current bias voltage of 0 and 3 V reveals significant photoresponsivity of the photodetector at various laser frequency modulation at 1, 5 and 9 Hz. The rise times are found to be 75, 72 and 70 μs for 1, 5 and 9 Hz while high fall times 455, 448 and 426 are measured for the respective frequency modulation. The fabricated ITO/GO-SiO2/p-Si sandwiched heterojunction photodetector can be considered as a good candidate for applications in the IR regions that do not require a high-speed response.

Lifetime improvement mechanism in organic light-emitting diodes with mixed materials at a heterojunction interface

NASA Astrophysics Data System (ADS)

Minagawa, Masahiro; Takahashi, Noriko

2016-02-01

To investigate the lifetime improvement mechanism caused by mixing at the heterojunction interface, organic light-emitting diodes (OLEDs) with stacked and mixed 4,4‧-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD)/tris(8-hydroxyquinoline)aluminum (Alq3) interfaces were fabricated, and changes in their displacement current due to continuous operation were measured. A decrease in accumulated holes at the α-NPD/Alq3 interface was observed in the stacked configuration devices over longer operations. These results indicate that the injected hole density was reduced during continuous operation, implying that the carrier balance became uneven in the emission region. However, few accumulated holes and changes in the displacement current due to continuous operation were observed in the devices having the mixed layer. Therefore, it was deduced that the number of holes concentrated between the α-NPD and Alq3 layers was decreased by mixing at the heterojunction interface, and that the change in the number of holes was smaller during continuous operation, resulting in less degradation.

Potential effect of CuInS2/ZnS core-shell quantum dots on P3HT/PEDOT:PSS heterostructure based solar cell

NASA Astrophysics Data System (ADS)

Jindal, Shikha; Giripunje, S. M.

2018-07-01

Nanostructured quantum dots (QDs) are quite promising in the solar cell application due to quantum confinement effect. QDs possess multiple exciton generation and large surface area. The environment friendly CuInS2/ZnS core-shell QDs were prepared by solvothermal method. Thus, the 3 nm average sized CuInS2/ZnS QDs were employed in the bulk heterojunction device and the active blend layer consisting of the P3HT and CuInS2/ZnS QDs was investigated. The energy level information of CuInS2/ZnS QDs as an electron acceptor was explored by ultra violet photoelectron spectroscopy. Bulk heterojunction hybrid device of ITO/PEDOT:PSS/P3HT: (CuInS2/ZnS QDs)/ZnO/Ag was designed by spin coating approach and its electrical characterization was investigated by solar simulator. Current density - voltage characteristics shows the enhancement in power conversion efficiency with increasing concentration of CuInS2/ZnS QDs in bulk heterojunction device.