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Role of hydrogen in modifying a-Si:H/c-Si interface passivation and band alignment for rear-emitter silicon heterojunction solar cells
摘要： Boosting the contact property of intrinsic hydrogenated amorphous silicon (a-Si:H(i)) film is pivotal to achieving high-efficiency silicon heterojunction (SHJ) solar cells. Here, the microstructure of a-Si:H(i) film is modified with hydrogen dilution ratio using hot wire chemical vapor deposition (HWCVD) for the application into rear-emitter SHJ solar cells. A higher hydrogen content associated with high valence band offset was found to decrease the fill factor FF for low dilution, while high interface defect densities related to epitaxial growth are responsible for the deterioration of both FF and open-circuit voltage VOC for high dilution. In particular, the most compact film prepared at a moderate dilution exhibits the most compact structure with most hydrogen located as isolated hydrogen rather than clustered hydrogen. Finally, high efficiency of SHJ solar cells up to 22.5% was yielded using the optimized a-Si:H(i) layer thanks to a significant enhancement of FF, which is attributed to improved passivation quality and rational band alignment at the a-Si:H(i)/c-Si interface. This work clearly interpreted the correlation between SHJ device parameters and a-Si:H(i)/c-Si interface properties, which might guide the design of a-Si:H passivation layers in pursuit of high-efficiency SHJ solar cells.
关键词： HWCVD,hydrogen dilution,SHJ solar cells,a-Si:H(i),passivation,band alignment
更新于2025-09-23 15:21:01
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In Situ SiO <sub/>2</sub> Passivation of Epitaxial (100) and (110)InGaAs by Exploiting TaSiO <sub/><i>x</i> </sub> Atomic Layer Deposition Process
摘要： In this work, an in situ SiO2 passivation technique using atomic layer deposition (ALD) during the growth of gate dielectric TaSiOx on solid-source molecular beam epitaxy grown (100)InxGa1?xAs and (110)InxGa1?xAs on InP substrates is reported. X-ray reciprocal space mapping demonstrated quasi-lattice matched InxGa1?xAs epitaxy on crystallographically oriented InP substrates. Cross-sectional transmission electron microscopy revealed sharp heterointerfaces between ALD TaSiOx and (100) and (110)InxGa1?xAs epilayers, wherein the presence of a consistent growth of an ～0.8 nm intentionally formed SiO2 interfacial passivating layer (IPL) is also observed on each of (100) and (110)InxGa1?xAs. X-ray photoelectron spectroscopy (XPS) revealed the incorporation of SiO2 in the composite TaSiOx, and valence band offset (ΔEV) values for TaSiOx relative to (100) and (110)InxGa1?xAs orientations of 2.52 ± 0.05 and 2.65 ± 0.05 eV, respectively, were extracted. The conduction band offset (ΔEC) was calculated to be 1.3 ± 0.1 eV for (100)InxGa1?xAs and 1.43 ± 0.1 eV for (110)InxGa1?xAs, using TaSiOx band gap values of 4.60 and 4.82 eV, respectively, determined from the fitted O 1s XPS loss spectra, and the literature-reported composition-dependent InxGa1?xAs band gap. The in situ passivation of InxGa1?xAs using SiO2 IPL during ALD of TaSiOx and the relatively large ΔEV and ΔEC values reported in this work are expected to aid in the future development of thermodynamically stable high-κ gate dielectrics on InxGa1?xAs with reduced gate leakage, particularly under low-power device operation.
关键词： in situ SiO2 passivation,atomic layer deposition,InxGa1?xAs,band alignment,TaSiOx,gate dielectric
更新于2025-09-23 15:21:01
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Ternary Hierarchical Cu <sub/>7</sub> S <sub/>4</sub> /TiO <sub/>2</sub> /CoCr-LDH Heterostructured Nanorod Arrays with Multiphase Reaction Interfaces for More Efficient Photoelectrochemical Water Splitting
摘要： Fabricating hierarchical and highly matched heterostructure with large surface areas and multiple interfaces is an effective approach to enhancing the photoelectrochemical performance. Here, well-aligned hierarchical Cu7S4/TiO2/CoCr-layered double hydroxide (LDH) nanorod arrays are reported, aiming at accelerating charge separation and transfer kinetics. The modifications of Cu7S4 and CoCr-LDH based on TiO2 have endowed the photoanode a surprising enhancement in both ultraviolet light absorption and charge separation efficiency due to highly matched band alignment. The formation of heterojunction is an effective strategy to prevent photocorrosion of Cu7S4 by attaching protective layers on Cu7S4. Moreover, other than the hierarchical morphology with enlarged active surface areas would provide sufficient active sites for the water oxidation processes and pore channels for the gas escaping, owing to the special band alignment of three components, multiple reaction interfaces are produced and involved in the water splitting process, since the photoinduced holes for water oxidation are simultaneously distributed in CoCr-LDH and Cu7S4. As expected, this synergistic effect in this ternary Cu7S4/TiO2/CoCr-LDH heterogeneous photoanode gives rise to a largely enhanced photoconversion efficiency (0.58% at 0.6 V) and photocurrent density (2.04 mA cm?2 at 1.23 V).
关键词： 3D hierarchical nanorod arrays,Cu7S4/TiO2/CoCr-LDH,ternary heterostructure,highly matched band alignment,photoelectrochemical water splitting
更新于2025-09-23 15:21:01
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Polarization-Sensitive Self-Powered Type-II GeSe/MoS2 Van der Waals Heterojunction Photodetector
摘要： Polarization-sensitive photodetectors are highly desirable for high performance optical signal capture and stray light shielding in order to enhance the capability for detection and identification of targets in the dark, haze and other complex environments. Usually, filters and polarizers are utilized for conventional devices to achieve polarization-sensitive detection. Herein, to simplify the optical system, a 2-D self-powered polarization-sensitive photodetector is fabricated based on a stacked GeSe/MoS2 van der Waals (vdWs) heterojunction which facilitates efficient separation and transportation of the photogenerated carriers, due to type-II band alignment. Accordingly, a high performance self-powered photodetector is achieved with merits of a very large on-off ratio photocurrent at zero bias of currently 104 and a high responsivity (Rλ) of 105 mA/W with the external quantum efficiency (EQE) of 24.2%. Furthermore, a broad spectral photoresponse is extended from 380 nm to 1064 nm owing to the high absorption coefficient in a wide spectral region. One of the key benefits from these highly anisotropic orthorhombic structures of layered GeSe is self-powered polarization sensitive detection with a peak/valley ratio up to 2.95. This is realized irradiating with a 532 nm wavelength laser with which a maximum photoresponsivity of up to 590 mA/W is reached when the input polarization is parallel to the armchair direction. This work provides a facile route to fabricate self-powered polarization-sensitive photodetectors from GeSe/MoS2 vdW heterojunctions for integrated optoelectronic devices.
关键词： polarization sensitive photodetector,self-powered,type-II band alignment,GeSe/MoS2 heterojunction,broad spectral photoresponse
更新于2025-09-23 15:19:57
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Diluted nitride type-II superlattices: Overcoming the difficulties of bulk GaAsSbN in solar cells
摘要： We demonstrate type-II GaAsSb/GaAsN superlattices (SL) as a suitable structure to form the lattice-matched 1.0–1.15 eV subcell that would allow the implementation of the optimum monolithic multi-junction solar cell design. The separation of Sb and N atoms during growth leads to an improved composition homogeneity and a lower defect density than in the bulk GaAsSbN counterparts. The type-II band alignment SLs provide long radiative lifetimes that facilitate carrier collection as compared to equivalent type-I SLs. Moreover, the radiative lifetime can be controllably tuned through the period thickness, which is not possible in type-I SLs. A reduced period thickness results in enhanced absorption due to increased wavefunction overlap, as well as in a change in the transport regime from diffusive to quasiballistic, providing improved carrier extraction efficiency. As a result, the short period SL single-junction solar cells show an enhanced power conversion efficiency of 134% over the equivalent bulk devices.
关键词： Strain-balanced,GaAsSbN,Type-II band Alignment,Multi-junction solar cells,Superlattices,1 eV bandgap
更新于2025-09-23 15:19:57
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Properties of Thermally Evaporated Titanium Dioxide as an Electron-Selective Contact for Silicon Solar Cells
摘要： Recently, titanium oxide has been widely investigated as a carrier-selective contact material for silicon solar cells. Herein, titanium oxide ?lms were fabricated via simple deposition methods involving thermal eVaporation and oxidation. This study focuses on characterizing an /TiO2 electron-selective passivated contact layer with this oxidized method. Subsequently, the SiO2 stack was examined using high-resolution transmission electron microscopy. The phase and chemical composition of the titanium oxide ?lms were analyzed using X-ray di?raction and X-ray photoelectron spectroscopy, respectively. The passivation quality of each layer was con?rmed by measuring the carrier lifetime using quasi-steady-state photoconductance, providing an implied open circuit voltage of 644 mV. UV–vis spectroscopy and UV photoelectron spectroscopy analyses demonstrated the band alignment and carrier selectivity of the TiO2 layers. Band o?sets of ~0.33 and ~2.6 eV relative to the conduction and valence bands, respectively, were con?rmed for titanium oxide and the silicon interface.
关键词： carrier-selective contact cell,band alignment,titanium oxide,electron-selective contact
更新于2025-09-23 15:19:57
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A Comparative Study on the Photovoltaic Properties of ZnX (X=S, Se, Te) QD/CNT Inorganic/Organic Hybrid Nanocomposites
摘要： Designing the efficient inorganic/organic hybrid light harvesting systems through understanding of charge generation, separation and recombination dynamics is an important pathway for improvement of power conversion efficiency (PCE) of photovoltaic cell. Using density functional method, we explored the photovoltaic performance of recently synthesized ZnX (X=S, Se, Te) QD/carbon nanotube (CNT) nanocomposites. Interestingly, ZnX QD/CNT nanocomposites exhibit type-II band alignment, where hole and electron charge carriers are localized on ZnX QD and CNT, respectively. However, the energy difference between highest occupied molecular orbital of ZnXQD and conduction band minimum of CNT is very small (0.09-0.26 eV), implying huge possibilities of electron-hole recombination at ZnX:CNT interface. To overcome such unpleasant situation, we focus on chemical modification of CNT. The CNT is hydrogenated by attachment of atomic hydrogen and next the hydrogenated CNT is functionalized by electron withdrawing group (-CN) in part. We found that ZnX QD and CN functionalized hydrogenated CNT nanocomposites exhibit intended type-II band alignment and achieve high PCEs in the range of 6.73-8.38%, making them exceptionally competitive with other previously reported hybrid solar cells.
关键词： inorganic/organic hybrid nanocomposites,power conversion efficiency,ZnX QD/CNT,type-II band alignment,photovoltaic properties
更新于2025-09-23 15:19:57
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Interlayer interactions in 2D WS <sub/>2</sub> /MoS <sub/>2</sub> heterostructures monolithically grown by <i>in situ</i> physical vapor deposition
摘要： The understanding of the interlayer interactions in vertical heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is essential to exploit their advanced functions for next-generation optoelectronics and electronics. Here we demonstrate a monolithic stacking of TMDC heterostructures with 2D MoS2 and WS2 layers via in situ physical vapor deposition. We find that the kinetically sputtered atoms are able to overcome the interlayer van der Waals forces between the vertical layers, leading to a substantial number of randomly oriented stacks with various twist angles. Our X-ray photoelectron spectroscopy results reveal a type II heterojunction for 2D WS2/MoS2, showing a band alignment with a conduction band offset of 0.41 eV and a valence band offset of 0.25 eV. In particular, we observed a remarkable interlayer coupling and associated exciton relaxation at the hetero-interface due to the misoriented stacks. By analyzing the band structures and charge densities of the vertical stacks using first-principles calculations, we reveal that the interlayer coupling is a function of the interlayer distance and is relatively insensitive to the angle of misorientation.
关键词： band alignment,2D materials,physical vapor deposition,interlayer coupling,heterostructures
更新于2025-09-19 17:15:36
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Energy Band Alignment of a Monolayer MoS <sub/>2</sub> with SiO <sub/>2</sub> and Al <sub/>2</sub> O <sub/>3</sub> Insulators from Internal Photoemission
摘要： Internal photoemission of electrons (IPE) from large area one monolayer 2H-MoS2 films synthesized on top of amorphous (a-) SiO2 or Al2O3 is used to determine the energy of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). This allows us to compare the VB top energy in MoS2 to that of the (100)Si substrate crystal at the interface with the same insulator. Despite the CB in a–Al2O3 is found to be ~1 eV below that in SiO2 as measured relative to the Si VB edge, the authors observe nearly no shift of the spectral threshold in the case of IPE from the MoS2 VB. This observation indicates violation of electroneutrality at the MoS2/a–Al2O3 interface causing an increase in barrier by ~1 eV. This conclusion is supported by the much weaker field dependence of the IPE threshold at the MoS2/a–Al2O3 interface compared to the MoS2/a–SiO2 one, suggesting the presence of negative charges and/or interface dipoles. Therefore, the commonly accepted electron affinity rule (EAR) appears to be not appropriate to describe the band alignment at 2D/insulator interfaces.
关键词： internal photoemission spectroscopy,MoS2,electron affinity,electron barrier,band alignment
更新于2025-09-19 17:15:36
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Effect of Na doping on the performance and the band alignment of CZTS/CdS thin film solar cell
摘要： Alkali doping can suppress deleterious antisite defects in kesterite Cu2ZnSnS4 (CZTS) and improve the open-circuit voltage. In this study, the effects of light Na-doping on the performance and the band alignment of CZTS/CdS thin-film solar cells were investigated. CZTS:Na thin films were fabricated by the spin coating with 10% Na doping on the surface of CZTS. The Na-doping led to the narrower FWHM and larger grain size. The hole concentration and the conductivity were improved due to the NaZn shallow acceptor defects. In addition, Na-doping can improve the band alignment of absorber/buffer interface and inhibit SRH recombination by the Na passivation effect and the suppression of SnZn defects. The typical cliff-like conduction band offset (CBO) was reduced from 0.25 eV in CZTS:Na/CdS to 0.1 eV in CZTS/CdS heterojunction. CZTS:Na device exhibited a higher Voc of 653 mV than that of CZTS/CdS device. The maximum conversion efficiency reached 7.46%, increased by 44% after Na-doping. These results clarify the effect of Na-doping on the band structure of the heterojunction in CZTS solar cells and support a new aspect that synthesis of a surface-doping CZTS:Na absorber has great potential for future research.
关键词： Conduction band offset,Na-doping,Cu2ZnSnS4,Band alignment,Cliff-like
更新于2025-09-19 17:13:59