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Band Alignment of MoTe <sub/>2</sub> /MoS <sub/>2</sub> Nanocomposite Films for Enhanced Nonlinear Optical Performance
摘要： Band alignment is a key issue for the optoelectronics based on 2D layered transition metal dichalcogenides (TMDs) heterostructures. Herein, band alignment of MoTe2/MoS2 mixed heterostructure is measured with high-resolution X-ray photoelectron spectroscopy. The MoTe2/MoS2 heterostructure belongs to type-II heterostructure with the conduction band offset of 0.46 eV and the valence band offset of 0.9 eV. The stronger saturable absorption is observed in MoTe2/MoS2 heterostructure film compared with that of pure MoTe2 and MoS2 nanofilms at the same condition. An energy-level model combined with Runge–Kutta algorithm is used to understand the enhancement mechanism. It is found that the interlayer transition from MoTe2/MoS2 heterojunction plays an important role in the nonlinear optical enhancement. Meanwhile, band structure of MoTe2/MoS2 heterostructure is calculated by the first principles. The contributions of the MoTe2 and MoS2 to the heterojunction are almost equal and the valence band maximum and conduction band minimum exist in MoTe2 and MoS2 separately. This structure can form the interlayer carriers easily. The results suggest that the band alignment of TMDs paves the way for the type-II heterostructure for enhanced nonlinear response in the development of optical modulator, ultrafast laser mode lockers, saturable absorbers, and optical switches.
关键词： molybdenum disulfide (MoS2),band alignment,saturable absorption,heterostructure,molybdenum telluride (MoTe2)
更新于2025-09-23 15:23:52
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Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu <sub/>2</sub> O Polyhedra Arising from Tunable Interfacial Band Alignment
摘要： ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity resulting from better charge carrier separation upon photoexcitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance (EPR) spectra agree with these experimental observations. Time-resolved photoluminescence (TRPL) profiles provide charge transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O (110)/ZnS (200) plane interface. A modified Cu2O–ZnS band diagram is presented. Density functional theory (DFT) calculations generating plane-specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing charge transfer across the Cu2O (110)/ZnS (200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.
关键词： interfacial charge transfer,zinc sulfide,cuprous oxide,facet-dependent properties,heterojunctions,band alignment
更新于2025-09-23 15:23:52
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Band Alignment of the CdS/Cu <sub/>2</sub> Zn(Sn <sub/>1-x</sub> Ge <sub/>x</sub> )Se <sub/>4</sub> Heterointerface and Electronic Properties at the Cu <sub/>2</sub> Zn(Sn <sub/>1-x</sub> Ge <sub/>x</sub> )Se <sub/>4</sub> surface: x = 0, 0.2, 0.4
摘要： The surface electronic properties of the light absorber and band alignment at the p/n heterointerface are key issues for high performance heterojunction solar cells. We investigated the band alignment of the heterointerface between cadmium sulfide (CdS) and Ge incorporated Cu2ZnSnSe4 (CZTGSe), with Ge/(Ge+Sn) ratios (x) between 0 and 0.4, by X-ray photoelectron, ultra-violet, and inversed photoemission spectroscopies (XPS, UPS, and IPES, respectively). In particular, we used interface-induced band bending in order to determine the conduction-band offset (CBO) and valence-band offset (VBO), which were calculated from the core-level shifts of each element in both the CdS overlayer and the CZTGSe bottom layer. Moreover, the surface electronic properties of CZTGSe were also investigated by laser-irradiated XPS. The CBO at the CdS/CZTGSe heterointerface decreased linearly, from +0.36 to +0.20 eV, as x was increased from 0 to 0.4; in contrast, the VBO at the CdS/CZTGSe heterointerface was independent of Ge content. Both UPS and IPES revealed that the Fermi level at the CZTGSe surface is located near the center of the bandgap. The hole concentration at the CZTGSe surface was of the order of 1011 cm-3, which is much smaller than that of the bulk (~1016 cm-3). We discuss the differences in hole deficiencies near the surface and in the bulk on the basis of laser-irradiated XPS, and conclude that hole deficiencies are due to defects distributed near the surface with densities that are lower than in the bulk, and the Fermi level is not pinned at the CZTGSe surface.
关键词： Solar cell,Kesterite,IPES,XPS,Band alignment,CZTGS,UPS
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE CPMT Symposium Japan (ICSJ) - Kyoto, Japan (2018.11.19-2018.11.21)] 2018 IEEE CPMT Symposium Japan (ICSJ) - Study on corundum-structured p-type iridium oxide thin films and band alignment at iridium oxide /gallium oxide hetero-junction
摘要： Corundum-structured iridium oxide, showing p-type conductivity, is a powerful candidate material for forming high-quality pn hetero-junctions with gallium oxide. We have succeeded in fabricating corundum-structured iridium oxide thin films on sapphire substrates. According to the optical transmittance measurement, the optical bandgap of iridium oxide was found to be approximately 3.0 eV. Furthermore, the band alignment at the iridium oxide /gallium oxide interface was investigated by X-ray photoemission spectroscopy, revealing a staggered-gap (type-Ⅱ) with the valence and conduction band offsets of 3.3 eV and 1.0 eV, respectively.
关键词： p-type oxide semiconductor,band alignment,gallium oxide
更新于2025-09-23 15:22:29
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Enhancement in the performance of nanostructured CuOa??ZnO solar cells by band alignment
摘要： In this study, we investigated the effect of cobalt doping on band alignment and the performance of nanostructured ZnO/CuO heterojunction solar cells. ZnO nanorods and CuO nanostructures were fabricated by a low-temperature and cost-effective chemical bath deposition technique. The band offsets between Zn1?xCoxO (x = 0, 0.05, 0.10, 0.15, and 0.20) and CuO nanostructures were estimated using X-ray photoelectron spectroscopy and it was observed that the reduction of the conduction band offset with CuO. This also results in an enhancement in the open-circuit voltage. It was demonstrated that an optimal amount of cobalt doping could effectively passivate the ZnO related defects, resulting in a suitable conduction band offset, suppressing interface recombination, and enhancing conductivity and mobility. The capacitance–voltage analysis demonstrated the effectiveness of cobalt doping on enhancing the depletion width and built-in potential. Through impedance spectroscopy analysis, it was shown that recombination resistance increased up to 10% cobalt doping, thus decreased charge recombination at the interface. Further, it was demonstrated that the insertion of a thin layer of molybdenum oxide (MoO3) between the active layer (CuO) and the gold electrode hinders the formation of a Schottky junction and improved charge extraction at the interface. The ZnO/CuO solar cells with 10% cobalt doped ZnO and 20 nm thick MoO3 buffer layer achieved the best power conversion efficiency of 2.11%. Our results demonstrate the crucial role of the band alignment on the performance of the ZnO/CuO heterojunction solar cells and could pave the way for further progress on improving conversion efficiency in oxide-based heterojunction solar cells.
关键词： nanostructured,solar cells,X-ray photoelectron spectroscopy,power conversion efficiency,molybdenum oxide,chemical bath deposition,band alignment,CuO–ZnO,cobalt doping
更新于2025-09-23 15:21:01
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Deep insights into interface engineering by buffer layer for efficient perovskite solar cells: a first-principles study; é?????é??é??????¤aé?3è????μ?±???-?????2?±????é?￠?·￥?¨?????·±??￥???è§￡: ????????§????????????;
摘要： Recent years have seen swift increase in the power conversion efficiency of perovskite solar cells (PSCs). Interface engineering is a promising route for further improving the performance of PSCs. Here we perform first-principles calculations to explore the effect of four candidate buffer materials (MACl, MAI, PbCl2 and PbI2) on the electronic structures of the interface between MAPbI3 absorber and TiO2. We find that MAX (X = Cl, I) as buffer layers will introduce a high electron barrier and enhance the electron-hole recombination. Additionally, MAX does not passivate the surface states well. The conduction band minimum of PbI2 is much lower than that of MAPbI3 absorber, which significantly limits the band bending of the absorber and open-circuit voltage of solar cells. On the other side, suitable bandedge energy level positions, small lattice mismatch with TiO2 surfaces, and excellent surface passivation make PbCl2 a promising buffer material for absorber/electron-transport-layer interface engineering in PSCs. Our results in this work thus provide deep understanding on the effects of interface engineering with a buffer layer, which shall be useful for improving the performance of PSCs and related optoelectronics.
关键词： perovskite solar cells,band alignment,interfacial defect passivation,buffer layer,interface engineering
更新于2025-09-23 15:21:01
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Decreasing Energy Loss and Optimizing Band Alignment for High Performance CsPbI3 Solar Cells through Guanidine Hydrobromide Post-Treatment
摘要： On account of the superior thermal stability and applicable band gap (~ 1.7 eV), the inorganic halide CsPbI3 perovskite solar cells (PSCs) have aroused intense interest in recent years. Nevertheless, the CsPbI3 PSCs are still facing a problem of high energy loss (Eloss) which leads to low open-circuit voltage (VOC). Herein, we developed efficient CsPbI3 PSCs through guanidine hydrobromide (GABr) post-treatment on the surface of CsPbI3 film. After optimizing, a supreme power conversion-efficiency (PCE) of 18.02% was obtained, which was higher than the original one (16.58%). By further studying, the characterization of passivation was found, which led to the reduced nonradiative recombination rate. Besides, the band alignment between CsPbI3 and interface layer is also optimized, leading to the decreased electron transport barrier for electron collection, and superb hole contact for furnishing a driving force in the hole transferring and forbidding electron to flow in the opposite direction.
关键词： energy loss,GABr,nonradiative recombination,CsPbI3,band alignment
更新于2025-09-23 15:21:01
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Mechanisms of LiF Interlayer Enhancements of Perovskite Light-Emitting Diodes
摘要： The use of LiF as a thin interlayer between the electron transport layer and cathode has played a pivotal role in remarkable advances in perovskite LEDs (PeLEDs); however, the mechanism behind the effect of LiF remains to be fully understood. Here we report a combined experimental and computational study from which we ascribe the benefits of a LiF interlayer to the migration of dissociated Li into the cathode and dissociated F into the anode. Electronic device simulations reveal that the former improves electron injection by lowering the Schottky barrier height, while the latter reduces the barrier width. These reduce turn-on voltage and improve current density and charge balance in LEDs. We fabricate PeLEDs with and without the LiF interlayer and link these materials and electronic phenomena to the device light-current-voltage characteristics. X-ray photoelectron spectroscopy obtained in sputter profiling of PeLEDs corroborates the dissociation of LiF.
关键词： LEDs,interface dipoles,metal-halide perovskites,photoelectron spectroscopy,band alignment
更新于2025-09-23 15:21:01
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Critical role of interface contact modulation in realizing low-temperature fabrication of efficient and stable CsPbIBr2 perovskite solar cells
摘要： CsPbIBr2 perovskite solar cells (PSCs) have received considerable concern due to their excellent stability. However, the interface defects and imperfect band alignment between electron transporting layer (ETL) and perovskite is one of the main reasons for hindering further efficiency improvement. Herein, we modulate the band alignment and perovskite crystallization of the ETL/perovskite interface by employing ZnO and SnO2 as ETL, which exhibit high electron mobility and can be fabricated at low temperature. Both ZnO and SnO2-based devices were fabricated at low temperature below 160 ℃. First, the effect of ZnO and SnO2 on the performance of CsPbIBr2 PSCs is systematically investigated. SnO2-based PSCs show a higher power conversion efficiency (PCE) of 10.81% as a consequence of improved Voc and fill factor (FF) as compared to 9.70% of ZnO counterpart, which is attributed to improved band alignment and perovskite crystallization, leading to enhanced electron extraction, reduced interface nonradiative recombination and improved carrier lifetimes. Remarkably, SnO2 ETL can also reduce hysteresis and improve device stability as compared to ZnO ETL. The present study unveils the critical role of interface contact modulation of CsPbIBr2 PSCs and provides an insightful strategy for preparing efficient and stable low-temperature inorganic PSCs.
关键词： Interface contact modulation,Perovskite solar cells,Band alignment,CsPbIBr2
更新于2025-09-23 15:21:01
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Highly Efficient Inorganic-Organic Heterojunction Solar Cells Based on Polymer and CdX (X=Se, Te) Quantum Dots: An Insight from a Theoretical Study
摘要： By using the density functional method, we explore the potentiality of recently synthesized CdX (X=Se, Te)QD/P3HT composites in solar energy conversion devices. Our study reveals that inorganic/organic hybrid CdXQD/P3HT nanocomposites with larger size of CdX QDs exhibit type-II band alignment, suggesting efficient charge separation upon photoexcitation. But for smaller size of QDs, the composites show type-I band alignment which are devoid of charge separation and thus are not suitable for solar cell applications. To remove this obstacle, we focus on chemical modification to polymer P3HT. The substitution of hydrogen at the beta position of each thiophene ring of polymer by electron withdrawing group (CN) results type-II band alignment and yield spatial charge separation even for smaller size of QDs. Finally, we calculated the powerconversion efficiency (PCE) of CdXQD and CN functionalized P3HT nanocomposites. The maximum calculated PCE value of 10.82% is achieved, which makes them immensely competitive with other reported heterojunction solar cells.
关键词： CdX (X=Se, Te)QD/P3HT composites,powerconversion efficiency,solar energy conversion,charge separation,type-II band alignment
更新于2025-09-23 15:21:01