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This study investigates the band alignment of the Zn0.8Mg0.2O/Sb2Se3 interface structure to improve solar cell performance. Sb2Se3 is a promising absorber material. However, Sb2Se3 solar cells exhibit a lower conversion efficiency than CuInGaSe2 and CdTe solar cells. The lower efficiency of Sb2Se3 solar cells is attributed to the severe open‐circuit voltage loss caused by the band structure at the buffer/Sb2Se3 interface. Sb2Se3 solar cells typically employ CdS as the buffer layer, and the CdS/Sb2Se3 interface exhibits a cliff structure, which results in interfacial recombination. By contrast, a ZnMgO buffer layer can form a spike structure with Sb2Se3 at their interface, which reduces recombination and, as a result, enhances conversion efficiency. Therefore, this study employs the ZnMgO buffer layer and analyzes their material properties with various Mg contents and band structure at buffer/absorber layer interface. A ZnMgO buffer layer is sputter‐deposited on Sb2Se3. The optical bandgap of ZnMgO is 3.3–3.72 eV, corresponding to an Mg content of 0–0.35 at%. The carrier concentration indicates an appropriate doping level ranging from 1014 to 1016 cm−3. The Zn0.8Mg0.2O/Sb2Se3 interface is characterized via interface‐induced band bending. The Zn0.8Mg0.2O/Sb2Se3 interface exhibits a spike structure with a positive delta conduction band offset of +0.193 eV. [ABSTRACT FROM AUTHOR]

Using a one-dimensional solar cell capacitance simulator (SCAPS-1D), the initial simulation study is carried out by using inorganic Pb-free RbGeI3-based perovskite layer along with 2,2′,7,7′- tetrakis [N, N-di4-methoxyphenylamino]-9,9′-spirobifluorene (Spiro-OMeTAD) as a hole transport layer (HTL) and titanium dioxide (TiO2) as an electron transport layer (ETL), which shows a device efficiency of 13.11%. In addition, we investigated the impact of the conduction band offset (CBO) between the ETL and absorber layer, and the valence band offset (VBO) between the absorber and HTL. Band offsets play a critical role in carrier recombination at the interfaces, which determines the open-circuit voltage (Voc). Our study found that extremely negative and positive band offsets lead to reduced PV performance. The optimum position of CBO with respect to the perovskite layer is found to be − 0.2 to − 0.1 eV, while the optimum position of VBO is found to be − 0.1 to 0.0 eV. When ETL is replaced by ZnSe and HTL by CuSCN, the device shows an improved power conversion efficiency (PCE) of 15.82%, as predicted by band offset engineering. The effect of thickness and defect density of perovskite layer, back contact work function, series resistance, shunt resistance, and temperature on the performance of perovskite solar cell (PSC) has been analyzed. The optimized device exhibited a PCE of 17.93%, fill factor (FF) of 74.96%. Thus, the proposed simulation study promotes RbGeI3 as a promising candidate for the absorbing layer and provides significant insight that will help to find out the suitable ETL and HTL combination. [ABSTRACT FROM AUTHOR]

Computational analysis of triple absorber‐based solar cell structure is undertaken. This solar cell device configuration allows better utilization of the incident solar spectrum. Three different absorbers with a band gap in the range 1–1.5 eV are sandwiched between high‐doped p+ and n+ regions in descending order of electron affinity to form an energy‐matched multiple absorber device. A comprehensive analysis of key device parameters influencing performance, including band gap, conduction band alignment, interfacial defects, and thickness, is presented. The optimized triple absorber device shows beyond Shockley–Queisser limit (SQ limit) performance under the constraint of passivated interfaces with defect density below 1013 cm−2. Wide spectrum coverage leads to high short circuit current and an efficiency of 40.3%, which is higher than the SQ limit for single band gap solar cell. [ABSTRACT FROM AUTHOR]

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µFE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆EC) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆EC of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs. [ABSTRACT FROM AUTHOR]

ZnO–Cu2O composites were made as photocatalysts in a range of different amounts using an easy, cheap, and environment-friendly coprecipitation method due to their superior visible light activity to remove pollutants from the surrounding atmosphere. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) have demonstrated that ZnO–Cu2O catalysts are made of highly pure hexagonal ZnO and cubic Cu2O. X-ray photoelectron spectroscopy has confirmed that there is a substantial interaction between the two phases of the resultant catalyst. The optical characterizations of the synthesized ZnO–Cu2O composite were done via UV–vis reflectance spectroscopy. Due to the doping on ZnO, the absorption range of the ZnO–Cu2O catalyst is shifted from the ultraviolet to the visible region due to diffuse reflection. The degradation efficiency is affected by the Ratio of ZnO: Cu2O and ZnO–Cu2O composite with a proportion of 90:10 exhibited the most prominent photocatalytic activity on Acid Red 114, with a pseudo-first-order rate constant of 0.05032 min−1 that was 6 and 11 times greater than those of ZnO and Cu2O, respectively. The maximum degradation efficiency is 97 %. The enhanced photocatalytic activity of the composite is caused by the synergistic interaction of ZnO and Cu2O, which improves visible light absorption by lowering band gap energy and decreasing the rate at which the electron-hole pairs recombine. The scavenging experiment confirmed that hydroxyl radical was the dominant species for the photodegradation of Acid Red 114. Notably, the recycling test demonstrated the ZnO–Cu2O photocatalyst was highly stable and recyclable. These results suggest that the ZnO–Cu2O mix might be able to clean up environmental pollutants when it meets visible light.

This work elucidates the intricate interplay between the structural complexity of double absorber layered perovskite solar cells and the presence of defects, offering crucial insights for advancing the field of photovoltaics. The study systematically investigates the impact of a heterostructure featuring two perovskite absorber layers on device efficiency and highlights the challenges associated with defects. Our comprehensive analysis underscores the significance of a precisely tuned conduction band offset within the heterostructure, a parameter critical for achieving superior charge transport properties and overall device performance. Moreover, deliberate introduction of acceptor defects emerges as a strategic avenue for enhancing the structural integrity and photovoltaic output of the solar cell. This research contributes to the evolving understanding of defect engineering in perovskite solar cells, providing an intricate perspective on defect dynamics to improve device functionality. The identified parameters and insights presented in this study facilitate and guide the design and fabrication of advanced perovskite solar cells, emphasizing the importance of tailored heterostructure configurations and defect management strategies.

Benefiting from the advantages of a high absorption coefficient, a long charge diffusion length, excellent carrier mobility, and a tunable bandgap, three-dimensional (3D) metal halide perovskites exhibit great potential for application in solar cells. However, 3D perovskite solar cells (PSCs) often suffer from poor long-term stability against moisture, heat, and light. To address this issue, reducing the dimension of perovskite and forming two-dimensional (2D) perovskites can be effective in slowing down the oxidation of the perovskite film and significantly improving device stability. In this study, 2D PSCs were designed with glass/FTO/TiO2/Dion–Jacobson (DJ) perovskite/NiOx/Au structures, based on the solar cell simulation software SCAPS. The absorption layers employed in the study included PeDAMA2Pb3I10, PeDAMA3Pb4I13, PeDAMA4Pb5I16, and PeDAMA5Pb6I19. The influence of the conduction band offset (CBO) variation in the range of −0.5 to 0.5 eV on cell performance was explored through a numerical simulation. The simulation results indicate that the open-circuit voltage and fill factor continue to increase, whereas the short-circuit current density remains almost unchanged when the CBO increases from −0.5 eV to 0 eV. The devices exhibit better performance when the value of the CBO is positive and within a small range. For DJ PSCs, controlling the CBO within 0.1–0.4 eV is conducive to better cell performance. [ABSTRACT FROM AUTHOR]

Copper antimony selenium (CuSbSe2) is considered a promising candidate for manufacturing flexible thin film solar cells. However, inappropriate band offset deteriorates the properties of CuSbSe2 solar cell devices. In this work, the effects of Cd1−xZnxS and ZnOyS1−y buffer layers on the performance of CuSbSe2 solar cells were studied with SCAPS simulation. The preliminary structure was designed, and the influence of Zn/(Zn + Cd) ratio, O/(O + S) ratio, thickness, and donor density of Cd1−xZnxS and ZnOyS1−y buffer layers on the performance of the solar cell was then investigated. The conduction band offset (CBO) of the interface between buffer layer and absorber layer was optimized. Efficiency values of 7.81% and 10.26% were obtained for the CuSbSe2 devices with Zn/(Zn + Cd) = 0.5 and O/(O + S) = 0.6, and the thickness of Cd1−xZnxS and ZnOyS1−y buffer layers was 20 nm and 30 nm, respectively. [ABSTRACT FROM AUTHOR]

• Devices with cliff conduction band offset are sensitive to interface defects. • Minimum depletion width has been identified as an important interface parameter. • Inflection in N CV -W curves in reverse bias is due to 0.55 eV deep acceptors. • Midgap neutral defects, deep acceptors and interface defects decrease V OC. • Decrease in OVC ionized acceptors and increase in back contact barrier decrease V OC. • All modeling results corroborated with experimental stress testing results. A parametric study of the effect of bulk and interface properties on device characteristics as a function of heat and light stress under open-circuit and short-circuit conditions is developed for Cu(In,Ga)(S,Se) 2 solar cells using SCAPS-1D simulator. The variables and interdependencies modeled include: (1) conduction band offset (CBO) between buffer and absorber; (2) buffer ionized donor density; (3) CIGS shallow acceptor density; (4) CIGS deep acceptor density; (5) CIGS shallow donor density; (6) ionized acceptor concentration in the ordered vacancy compound (OVC) CIGS/buffer interface; and (7) back contact work-function. An increase in absorber shallow acceptor or a decrease in shallow donor density results in an increase in net carrier density and open-circuit voltage (V OC). A decrease in V OC is observed with an increase in the deep acceptors or neutral midgap defects in the CIGS due to higher charge carrier recombination. A change of CBO from spike to cliff condition is a dominant mechanism of decreasing V OC with an interface defect density of 1012 cm−2. The minimum depletion width is found to be specifically sensitive to CBO and interface defect density. An inflection in the capacitance–voltage curves (in reverse bias) is observed with simultaneous increase in bulk deep acceptor density and shallow donor density near the back contact. [ABSTRACT FROM AUTHOR]

Solar energy is the most used renewable energy source. CZTSSe uses earth-abundant elements and has promising optoelectronic properties, resulting in becoming a viable alternative to thin film PV. This work provides design guidelines for CZTSSe-based solar cells, where CZTSSe has a tunable affinity and energy gap. The analysis is based on incorporating a ternary compound material to serve as an electron transport material (ETM). In this regard, CdZnS is a potential candidate that can be utilized as an electron transport layer whose affinity and energy gap can be tuned to adjust the band alignment at the ETL/CZTSSe interface. In order to design a high-efficiency solar cell, one has to tune both the ETL and absorber layers to have a suitable conduction band offset (CBO), thereby minimizing the non-radiative recombination which, in turn, boosts the power conversion efficiency (PCE). Thus, in our presented simulation study, we provide a codesign of alloy compositions of both the CZTSSe photoactive layer and the CdZnS ETL using SCAPS-1D simulation. It is found that using the codesign of alloy compositions of the ternary compound ETL and the absorber enhances the PCE by about 2% and, more importantly, overcomes the main issue in CZTSSe which is its open-circuit voltage (VOC) deficit. Furthermore, upon optimizing the thickness and doping of both the ETL and absorber layer, as well as the bulk defect of the absorber layer, a PCE of 17.16% is attained in this study, while the calibrated PCE based on a previously published experimental work was 12.30%. [ABSTRACT FROM AUTHOR]

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µFE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆EC) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆EC of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs.

The power conversion efficiency (PCE) of thin-film solar cells (TFSCs) has drastically increased in the last few years. In this regard, perovskite solar cells (PSCs) come on the top thanks to their bandgap tunability, lower fabrication cost, and high absorption coefficient. In this work, a comprehensive simulation study is presented in which methylammonium-free PSCs are analyzed and designed. Also, the design of the presented solar cell structure is based on using a hole transport layer (HTL)-free. So, the design is carried out in such a way as to prevent the instability and cost issues associated with the organic materials, usually incorporated in HTLs, as well as methylammonium (MA) which limits the device operation stability. Next, the conduction band offset between the perovskite as an absorber and the electron transport layer (ETL) is controlled to provide a spike-like band offset that is more desirable by selecting appropriate materials serving as ETLs. The work function of the back contact is also investigated, and it is found that using Carbon, which has a lower cost than gold, is beneficial to get high efficiency. An enhanced performance has been achieved by combining the different steps of the design. This is reflected in the PCE which performs 25.35% instead of the initial calibrated cell which shows a PCE of 20.7%. The PCE could further be boosted to 27.8% if reduced absorber and interface defects are included. The calibration and simulation of the presented PSCs were done by utilizing SCAPS one-dimensional simulator, based on practical material parameters, at AM1.5 illumination.

Perovskite solar cells (PSCs) play a pivotal role in advancing renewable energy to achieve United Nation's Sustainable Development Goal 7 (SDG 7), which aims to ensure universal access to affordable, sustainable, reliable and modern energy services. Aiming to enhance the performance of PSCs by replacing the typically used electron transport layers (ETLs: TiO 2 , SnO 2 , ZnO etc.), we theoretically investigated the viability of tungsten oxide (WO X) as a promising ETL for PSCs. Moreover, the effect of altering the energy levels of WO X on cell performance has also been analyzed through simulation. Initially, 12 (twelve) PSC structures having the combination of different perovskite (PSK: CsPbBr 3 , CsPbI 3 , FAPbBr 3 , FAPbI 3) absorber layers with different organic hole transport layers (HTLs: Spiro-OMeTAD, P3HT, PEDOT:PSS) and a fixed ETL of WO X were optimized numerically for comparing their performance. As CsPbBr 3 -based PSCs showed the best performance, further simulations were performed by varying some WO X /CsPbBr 3 interface properties such as interface defect density, conduction band offset (CBO) between WO X and CsPbBr 3 , energy bandgap (E g) of WO X etc. Finally, the best-performed PSCs were found for the E g = 3.5 eV of WO X and the CBO of - 0.5 eV confirming the conduction band minimum (CBM) of WO X is lower than that of CsPbBr 3 by 0.5 eV. A properly chosen WO X layer enhanced the efficiency of CsPbBr 3 -based PSCs up to 14.65 %, 14.52 % and 16.09 %, aproaching the Shockley-Queisser (S-Q) limit (16.37% for CsPbBr 3 -based solar cell) from the initial values of 11.39 %, 11.27 %, and 12.49 %, respectively. This study ensures WO X is a promising ETL for which a proper PSC structure having a suitable PSK and an HTL can improve cell performance. Moreover, the importance of modifying energy levels of ETL material in enhancing the performance of PSCs is explored. As a result, this study opens a path for the researchers to develop WO X having suitable CBM and E g , so that it can be well-suited with a properly matched PSK material resulting in enhanced cell performance. • PSCs consisting of Cs and FA-based different perovskites and WO X as ETL are studied theoretically. • CsPbBr 3 -based PSCs having WO X as ETL exhibit the best performances. • WO X /CsPbBr 3 interface properties are varied to study their effect on cell performances. • The position of the conduction band minimum and energy band gap of WO X are optimized. • The identified optimum value conduction band offset at the WO X /CsPbBr 3 interface is −0.5 eV. [ABSTRACT FROM AUTHOR]

The present work investigated numerically, using SCAPS software, the impact of conduction band alignment between the absorber and electron transport layer (ETL) on the perovskite solar cell performance. The conduction band alignment was tailored by inserting an interfacial thin layer between the absorber and ETL. The architecture of the proposed structure consists of CdS as an electron transport layer, MAPbI3 as an absorber layer, and the spiroOMeTAD as a hole transport layer (HTL). Before inserting the interfacial layer, an adjustment of the doping density of ETL and HTL and the thickness of the perovskite solar layers have been optimized to obtain the best PSC performance. It was found that the best power conversion efficiency of 18 % was obtained at a doping density of 1022 cm−3 for ETL and 1019 cm−3 for HTL and thickness of 250 nm, 400 nm, and 200 nm for ETL, absorber, and HTL respectively. Individual interfacial layers, with different electron affinities, are sandwiched between the CdS/Perovskite layers to achieve different conduction band alignments. Based on the electron affinity of inserted layer, different structures from spike and cliff in the conduction band alignment were achieved. The results reveal that the inserted interfacial layer improved the solar cell performance when the inserted layer produce a spike-cliff conduction band offset at the absorber-interfacial layer interface and interfacial layer-ETL interface respectively.

An SnS/CdS heterostructure-based solar cell has been simulated and evaluated for possible solar cell application. SnS being an earth-abundant, nontoxic, stable inorganic material with suitable optoelectronic properties, is potential material for solar cell application. A three-step optimization process has been undertaken to improve the performance of SnS-based solar cells. Initially, SnS/CdS junction is modified to a p–i–n structure by introducing an intrinsic layer in between SnS/CdS. The introduction of an intrinsic layer increases the efficiency from 1.32 to 6.85%. Further, the structure has been optimized by employing a conduction band offset at the p–n interface. Following this process, the efficiency further improved to 7.05%. Finally, the heterostructure has been optimized by adding back surface field in the device configuration. The final simulated heterostructure after all three optimizations shows efficiency enhancement up to 8.15% from its benchmarked 1.32% value. The optimized device configuration p+-SnS/SnS/i/CdS/ZnO presents a crucial guideline for experimentalist to fabricate high-efficiency SnS solar cells. [ABSTRACT FROM AUTHOR]

The copper zinc tin sulphide (CZTS) is a promising candidate for solar cell application. The CZTS/ZnS-based heterojunction provides a high conduction band offset at the junction. The three types of conduction band offset (spike, flat, and cliff) are discussed in the study, and the comparison of cell output variation is also discussed. In this simulation-based study, we have performed optimisation of the device for layer thickness, carrier mobility, defects, front contact transmission profile, and both the series and shunt resistance. A high acceptor type defect density in CZTS increases open-circuit voltage by shifting the Fermi level towards the valance band maximum. The introduction of CuI as a hole transport layer (HTL) offers a low Schottky barrier and delivers high efficiency compared to the same without the CuI layer, while a higher CuI thickness produce a barrier to back reflection. The finally optimised cell gives the highest power conversion efficiency of 15.53% for a spike like conduction band offset of 0.06 eV. This simulation paves a way to fabricate realistic CZTS solar cells based on the present cell model. [Display omitted] • Variation of solar cell performance on conduction band offset is performed. • The open-circuit voltage variation due to two different CZTS defects is studied. • Optimisation of the device is done for different layer parameters. • The effect of the nature of front contact on device performance is studied. • The device shows an enhanced power conversion efficiency of 15.53% with HTL. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study of the current-voltage (I-V) and capacitance-voltage (C-V) measurements made on a CdS/CdTe based solar cell by numerical modeling. Implementation of the simulated cell having a superstrate configuration was done with the help of SCAPS program using defect density model. The I-V characterisation includes window and absorber layer optimisation based on various factors including the impurity doping concentration, thickness and defect density. The energy band diagram, spectral response and currentvoltage plot of the optimised cell configuration are shown. C-V characterisation (Mott-Schottky analysis) of the solar cell is conducted at different low frequencies to determine the flatband potential, carrier concentration and to validate the reliability of the results. The optimum device performance was obtained when the active layer was 2 μm thick with a doping level of 1×1015/cm3.

2D perovskite passivation strategies effectively reduce defect-assisted carrier nonradiative recombination losses on the perovskite surface. Nonetheless, severe energy losses are causing by carrier thermalization, interfacial nonradiative recombination, and conduction band offset still persist at heterojunction perovskite/PCBM interfaces, which limits further performance enhancement of inverted heterojunction PSCs. Here, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (5FTPP) is introduced between 3D/2D perovskite heterojunction and PCBM. Compared to tetraphenylporphyrin without electron-withdrawing fluoro-substituents, 5FTPP can self-assemble with PCBM at interface into donor-acceptor (D-A) complex with stronger supramolecular interaction and lower energy transfer losses. This rapid energy transfer from donor (5FTPP) to acceptor (PCBM) within femtosecond scale is demonstrated to enlarge hot carrier extraction rates and ranges, reducing thermalization losses. Furthermore, the incorporation of polystyrene derivative (PD) reinforces D-A interaction by inhibiting self-π-π stacking of 5FTPP, while fine-tuning conduction band offset and suppressing interfacial nonradiative recombination via Schottky barrier, dipole, and n-doping. Notably, the multidentate anchoring of PD-5FTPP with FA + , Pb 2+ , and I - mitigates the adverse effects of FA + volatilization during thermal stress. Ultimately, devices with PD-5FTPP achieve a power conversion efficiency of 25.78% (certified: 25.36%), maintaining over 90% of initial efficiency after 1000 h of continuous illumination at the maximum power point (65 °C) under ISOS-L-2 protocol., (© 2024 Wiley‐VCH GmbH.)

The valence and conduction band offset in FeNiO/CuNiO bilayer film are studied utilizing X‐ray photoelectron spectroscopy and UV–vis spectroscopy. The bilayer film is grown on Si substrate employing ion beam sputtering technique using a mixture of argon and oxygen gases at 25% oxygen partial pressure. From the precise knowledge of the valence band maxima energies and core‐level energy positions in the single‐layer film and the corresponding shifts in the bilayer film, the valence and conduction band offsets are estimated to be 0.8 and 0.3 eV, respectively. From the computed band offset data, a type‐I band alignment is identified at the interface of the grown bilayer film, which facilitates the knowledge of carrier transport mechanism and is highly attractive for the realization of efficient room‐temperature optoelectronic device. [ABSTRACT FROM AUTHOR]

In order to mitigate the current global energy and environmental challenges associated with the use of fossil fuels, there is a need for better energy alternatives such as the inexhaustible solar energy. Of great interest is the design and fabrication of low-cost photovoltaic devices which are the epitome of efficient solar energy harvesting. Herein, we report inexpensive hole transport layer (HTL)-free dye-sensitized solar cell architecture with robust photovoltaic (PV) performance. In the proposed solar cell model, expensive hole transport layers, CuI, CuSCN, Spiro-OMeTAD, and PEDOT:PSS, are not required, but instead, a metallic layer is used for dye regeneration. A thorough analysis of the effect of series and shunt resistances, conduction band offset, Schottky barriers, working temperature, the metal work function of the back contact, and the electron affinities of the electron transport layers (ETLs) on the performance of the proposed solar cell is presented. The Solar Capacitance Simulator (SCAPS-1D) is used to perform the numerical simulations of the proposed solar cell design. The study focused on modeling HTL-free dye-sensitized solar cells with the configuration: FTO/ETL/N719 dye/Au. The performance of two ETLs—ZnOS and TiO2 are critically examined. The optimized model cell performance for the FTO/ZnOS/N719 dye/Au architecture gave an optimal power conversion efficiency (PCE) of 11.54%, 62.71% as the fill factor (FF), short circuit current (Jsc) of 18.50 mAcm−2, and an open-circuit voltage (Voc) of 0.99 V. On the other hand, the cell architecture FTO/TiO2/N719 dye/Au gave an optimized performance of 10.22% as the PCE, 63.58% as the FF, a Voc of 0.97 V, and 16.50 mAcm−2 as the Jsc. Based on these results, ZnOS is a suitable ETL material that has better PV performance of the solar cell device under consideration. ZnOS is earth-abundant, has a tunable band gap, is less toxic, and is, therefore, a promising candidate to replace TiO2 ETL in future designs and manufacture of HTL-free DSSCs for commercial production. [ABSTRACT FROM AUTHOR]

• The CuSb(S,Se) 2 solar cells with a structure of contact/CuSb(S,Se) 2 /buffer layer/i-nO/ZnO:Al/contact was studied. • CuSbS 2 solar cell based on an experimental device (ɳ=3.2%) has been modeled. • Conventional CdS buffer layer replaced by Zn(O,S) buffer layers. • The influence of Se/(Se + S) ratio in the CuSb(S 1-x, Se x) 2 absorber layer and oxygen content in the buffer layer on the performance of the solar cell was investigated. • The influence of carrier concentration of both CuSb(S 1-x ,Se x) 2 absorber and buffer layers was investigated. An initial structure was designed based on CuSbS 2 experimental data. Afterward, an investigation on the performance of contact/CuSb(S 1-x ,Se x) 2 alloy/buffer layer/i-ZnO/ZnO:Al/contact has been carried out. The conventional CdS layer was replaced by Zn(O 1-y ,S y) layer, and the influence of Se/(Se + S) ratio in the CuSb(S 1-x, Se x) 2 absorber layer and oxygen content in the buffer layer on the performance of the solar cell were investigated. The influence of carrier concentration of both CuSb(S 1-x ,Se x) 2 absorber and buffer layers are studied to enhance the output performance of CuSb(S 1-x ,Se x) 2 thin-film solar cells. After optimizing the Se content in the absorber layer and oxygen content in the buffer layer, the best device is delivered 5.85% efficiency. However, after optimization of donor concentration in buffer layer the conversion efficiency is further increased to 7.19% for CuSbS 2 absorber and donor concentration of 1019 cm−3. [ABSTRACT FROM AUTHOR]

Compared with the traditional structure, the new Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cell without ZnO window layer has a larger short-circuit current reduction. Due to the poor band matching, serious interface recombination exists at the CZTSSe/CdS heterojunction interface. We have designed a strategy for the preparation of CdS(In) buffer layers by In ion doping to increase the depletion layer width, enhance the carrier concentration in the CdS(In) buffer layer, and improve the energy band alignment problem at the interface of the CZTSSe/CdS heterojunction, which in turn reduces the J SC loss caused by the removal of the ZnO layer. The energy band alignment of the CZTSSe/CdS heterojunction was modulated by finely controlling the doping amount of In ions, which decreased the conduction band offset (CBO) from 0.32 eV to 0.28 eV. Good band alignment is more conducive to carrier separation and transport, and reducing the nonradiative charge recombination at the CZTSSe/CdS heterojunction interface can effectively improve the J SC. Based on the contribution of device electrical parameters to photoelectric conversion efficiency (PCE), the contributions of J SC , open-circuit voltage, and fill factor were calculated to be 107.56%, -6.89%, and -0.67%, respectively, which indicates that the method significantly improves short-circuit currents and reduces the loss of J SC due to the absence of ZnO layer. This study provides a method to achieve high-efficiency CZTSSe solar cells by optimizing the energy band matching of CZTSSe/CdS heterojunctions from 7.07% PCE in conventional cells to 9.01% PCE in novel cells. [Display omitted] • New Cu 2 ZnSn(S, Se) 4 (CZTSSe) cell structure with ZnO removal based on DMF system. • The width of depletion layer is increased by adjusting the amount of In doping in CdS. • The CdS band gap is increased, the band arrangement is adjusted, and the conduction band offset is reduced. • The short circuit current density is effectively increased by increasing the CdS carrier concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel kesterite solar cell was designed and analyzed by SCAPS 1D. • Replacement of Mo by ITO reduces the Schottky barrier height. • Back surface field enhances minority carrier life time and diffusion length. • Alternative buffer produces an offset of 0 eV at buffer/absorber interface. • A systematic optimization of cell design boosted the efficiency up to 20%. Among the several obstacles which impede efficiency enhancement of CZTS solar cells, the sub-optimized Mo back contact and the unfavorable conduction band offset at CZTS/CdS interface are the critical ones, contributing largely to high surface recombination and low open circuit voltage. In this article, a numerical simulation model was used for device structure analysis and performance optimization. A substrate configuration of CZTS solar cell was considered. Benchmarking study of the reference cell gives a conversion efficiency of 8.3% which matches well with the reported experimental value, validating the accuracy of our simulation model. Thereafter, we have implemented several modifications in the experimental device structure including an alternative back contact, a back surface passivation layer, a Cd-free buffer layer with tunable conduction band minimum, and a wide band gap ZnO-based alloy material which enhances the spectral response to shorter wavelength contributing to higher efficiency. A systematic optimization of device structure results in the increase of J SC and V OC due to the increment in diffusion length and optimal free carrier collection which ultimately increases the power efficiency from 8.4 to 20.6%. [ABSTRACT FROM AUTHOR]

The solution based on dimethylformamide (DMF) has shown promising application prospects in the fabrication of high-efficiency Cu 2 ZnSnS 4 solar cells. However, due to the high boiling temperature of the solvent, it is difficult to completely volatilize DMF during the evaporation process after spin coating, leading to remains of C and O atoms at grain boundaries, which severely restricts the photoelectric performance of solar cells. In this study, ethyl acetate (EA) with green character was used as an additive to optimize the film formation process of DMF-based CZTS precursor. The experimental results showed that using a small amount of EA additives could effectively improve morphology, crystallinity, composition distribution and electrical properties of the CZTS absorber. In addition, the CZTS and CdS heterojunctions exhibited a cliff-like energy band structure, and the optimized conduction band offset increased the activation energy required for the carrier recombination path, consequently reducing the carrier recombination. Compared with the pure DMF precursor solution, the photoelectric conversion efficiency of CZTS solar cells with an EA addition ratio of 10% was improved by 42%, and the open circuit voltage of the device reached 601 mV. [ABSTRACT FROM AUTHOR]

We investigated the working mechanisms of CdTe solar cells in which a second absorber-layer (defined as A2) with a lower bandgap was added through SCAPS simulation. The results show various positions and bandgap values of A2 are applicable at particular parameters, and the details are analyzed. We explored the essence of the improved cell performances via adding A2 for different occasions and provided some principles and models. Some new cognition for real cells was also presented. Additionally, we studied how the parameters of the wider-gap first absorber-layer influence the cell performances and its function as 439a back highly-resistant layer. [ABSTRACT FROM AUTHOR]

• Cu 2 Sn 1−x Ge x S 3 (CTGS) solar cells are fabricated. • Zn 1−x Mg x O (ZMO) was applied as second buffer layer. • E g of ZMO is increased to 3.55 eV, yielding improved conduction band offset. • Interface recombination in CTGS solar cell is reduced by using ZMO second buffer. • Efficiency of CTGS cell is enhanced to 4.5% with E g of 3.55 eV for ZMO buffer. Zn 1−x Mg x O (ZMO) second buffer was applied to replace conventional ZnO second buffer layer of Cu 2 (Sn,Ge)S 3 (CTGS) solar cells to reduce interface carrier recombination and open-circuit voltage deficit (V OC, def). Structure of the solar cell is glass/Mo/CTGS/CdS first buffer/ZMO second buffer/ZnO:Al (AZO)/Ni-Al. Bandgap energy (E g) of the ZMO films is changed from 3.20 to 3.65 eV by varying Mg/(Mg + Zn) ratio from 0 (for pure ZnO) to 0.26. The increase in the E g of ZMO films is attributable to the move of conduction band minimum (E C). It is determined that ZMO second buffer with increase in E g from 3.20 to 3.55 eV yields the smoothing conduction band offset (CBO) at ZMO/CdS interface varying from −0.26 to +0.09 eV. Saturation current density (J 0) is therefore reduced to the lowest value, and activation energy of recombination (E A) is the closet to the E g of the CTGS absorber layer, implying the lowest interface carrier recombination (reduced V OC, def), and thereby increasing conversion efficiency (η) to 4.5% (E g of ZMO: 3.55 eV). On the other hand, the ZMO second buffer with E g larger than 3.55 eV results in the CBO at ZMO/CdS interface of +0.19 eV (E g of ZMO: 3.65 eV), making the well of E C structure in ZMO/CdS/CTGS stacking layers, thus increasing interface carrier recombination, and severely decreasing the η to about 0.2%. [ABSTRACT FROM AUTHOR]

Solar cell research has always been an attraction by virtue of its clean and green status. However, to overcome the implications of high cost and moderate efficiency, there has always been fierce competition to search alternative approach for designing efficient solar cells with optimal performance-cost ratio. Recently, antimony sulfide (Sb 2 S 3) has received substantial attention as an absorber in thin film solar cells due to earth abundance, low cost, non-toxic property and high optical absorption. Still, its performance could not match Si based cells. In this work, we adopted two-stage simulation approach to design Sb 2 S 3 absorber based heterojunction solar cell to enhance efficiency. Initial simulation for configuration optimization was done considering thickness, defect density, recombination (radiative, Auger) effect, carrier density of the Sb 2 S 3 absorber layer. Buffer layer thickness and absorption coefficient optimization was taken up. Further, series and shunt resistance of the device as well as conduction band offset (CBO) at absorber/buffer interface was also optimized at initial stage only. In the next level of simulation, efficiency enhancement was achieved by optimizing optimal back contact metal work function, absorber layer band gap grading and temperature. The aforesaid two-stage optimization yielded efficiency ~24.81%, which is higher than conventional thin film solar cell. The optimal solar cell structure configuration, for Sb 2 S 3 absorber solar cell, suggested a positive CBO of 0.26 eV (e.g.; ZnS buffer layer), a back contact metal work function of 5.1 eV (e.g.; Mo, Au) and band gap grading window ~1.31 to 1.62 eV. [ABSTRACT FROM AUTHOR]

• Fabrication of CZTS:Na/CdS with Na doping on the surface using spin coating method. • The typical cliff-like CBO were obtained to 0.25 eV for CZTS/CdS heterojunction and 0.1 eV for CZTS:Na/CdS. • Sodium doping improves the performance of CZTS solar cells. Alkali doping can suppress deleterious antisite defects in kesterite Cu 2 ZnSnS 4 (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 Na Zn 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 Sn Zn 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. [ABSTRACT FROM AUTHOR]

SnS x Se 1−x films can be fabricated by adjusting the Se/(Se + S) ratio by using two different source materials (SnS + SnSe or S + Se). However, maintaining a uniform composition throughout the film can be challenging when using conventional double-source methods. Here, we have developed a single-source vapor-transport-deposition (VTD) method to deposit highly compact and uniform SnS x Se 1−x alloy films with a Se/(Se + S) compositional ratio of 0.3. Furthermore, we fabricate thin-film solar cell (TFSC) devices with varying evaporation durations ranging from 3 to 7 h. By increasing the evaporation duration from 3 to 7 h, the thickness of the SnS 0.7 Se 0.3 absorber layer nearly doubled from around 1.05 µm to approximately 2.0 µm. As a result, the solar cell device (SLG/Mo/SnS 0.7 Se 0.3 /CdS/i-ZnO/AZO/Al) fabricated with a 5-h evaporation duration, which had an absorber thickness of approximately 1.55 µm and a bandgap of 1.18 eV, achieved a highest efficiency of 3.59%. In addition, its V OC , J SC , and FF were 0.284 V, 24.50 mA cm−2, and 51.3%, respectively. Furthermore, the band alignment at the SnS 0.7 Se 0.3 /CdS interface was investigated to determine the conduction band offset (CBO) and valence band offset (VBO). The results confirmed a cliff-like CBO of −0.07 eV at the SnS 0.7 Se 0.3 /CdS interface. The optimized device retained almost 99.9% of its initial efficiency after 6 months of storage in the air. [Display omitted] • Single-source vapor transport deposition of SnS x Se 1−x thin films. • Structural and morphological study of SnS x Se 1−x via varied evaporation durations. • Optimization of SnS x Se 1−x /CdS TFSCs with a competitive efficiency of 3.59% • Revealing band alignment at the SnS 0.7 Se 0.3 /CdS heterojunction interface [ABSTRACT FROM AUTHOR]

We have investigated the simulation approach of a one-dimensional online simulator named A Device Emulation Program and Tool (ADEPT2.1) and the device performances of a thin film solar cell based on Cu2ZnSn(S,Se)4 (CZTSSe) absorber have been measured. Initiating with a thin film photovoltaic device structure consisting of n-ZnO:Al/i-ZnO/Zn1-xSnxOy (ZTO)/CZTSSe/Mo/SLG stack, a graded space charge region (SCR) and an inverted surface layer (ISL) were inserted between the buffer and the absorber. The cadmium (Cd) free ZTO buffer, a competitive substitute to the CdS buffer, significantly contributes to improve the open-circuit voltage, Voc without deteriorating the short-circuit current density, Jsc. The optimized solar cell performance parameters including Voc, Jsc, fill factor (FF), and efficiency (η) were calculated from the current density-voltage curve, also known as J–V characteristic curve. The FF was determined as 73.17%, which in turns, yields a higher energy conversion efficiency of 14.09%.

• Cu(In,Ga)Se 2 solar cell based on an experimental device (ɳ = 17.6%) has been modeled. • Traditional CdS buffer layer replaced by (Zn,Sn)O in CIGS solar cells. • Study the effect of Ga and Sn concentration in CIGS and (Zn,Sn)O on the PCE. • AlZnO/i:ZnO/Zn 0.8 Sn 0.2 O /CuGaSe 2 is the optimized cell. • A final photovoltaic conversion efficiency of 25.36% can be achieved. The conventional CdS layer in Cu(In 1−x ,Ga x)Se 2 based solar cells replaced by (Zn 1−y ,Sn y)O as a buffer layer and the solar performance analyzed. An initial model based on an experimental device has been established. The dependence of solar cells performance on the change of Ga concentrations in CIGS absorber and Sn concentrations ZnSnO (band gap of ZnSnO) buffer layer was investigated. The optimum values of Ga and Sn concentrations were found at x = 1 and y = 0.2, leading to a conversion efficiency of 25.36%. [ABSTRACT FROM AUTHOR]

[Display omitted] • CAS-CdS-ZnO photocatalysts were synthesized by simple rapid microwave irradiation synthesis. • The photocatalytic activity of CAS-CdS-ZnO photocatalyst was investigated. • The effects of adjusting band alignment to photocatalyst were in-depth discussion with characterization and DFT calculation. • A method of adjusting band alignment to reduce interfacial recombination and improve photocatalytic performance was proposed. Photocatalytic technology based on heterojunction structure has been proved to be an effective way to solve environmental pollution and energy crisis. The effective carrier concentration plays an important role in improving the performance of heterojunction photocatalyst. In this work, CuSbS 2 (CAS)-CdS-ZnO was prepared by simple 3-steps microwave irradiation method to reveal the influence of energy band structure on photocatalytic performance. Adding CdS could regulate band alignment to translate the "cliff-like" conduction band offset of CAS-ZnO to "spike-like". That could effectively reduce the carrier recombination rate to improve the photocatalytic degradation activity, which could completely degraded Rhodamine B (RhB) after 80 min under a solar simulation, highest rate constant (0.02028 min−1) and good stability. Furthermore, the transformation of charge transfer mechanism from the Z-type to Ⅱ-type by adding CdS were confirmed by experiments and density functional theory (DFT) calculations. This change could raise the energy level of photoelectrons, resulting in CAS-CdS-ZnO with a certain photocatalytic hydrogen evolution capacity (42.37 μmol g−1 h−1). This work reveals the important role of band structure in photocatalytic properties and applications of heterojunction. [ABSTRACT FROM AUTHOR]

Abstract The effects of the conduction band offset (CBO) between the electron selective layer (ESL) and the perovskite layer in planar-heterojunction perovskite solar cells (PSCs) have been systematically investigated for the first time. To obtain different values of CBO, Magnesium doped zinc oxide (Zn 1-x Mg x O (ZMO)) thin films with a tunable conduction band energy level were employed as a model ESL in planar PSCs. We found that the charge recombination at the interface between the ESL and perovskite is strongly dependent on the CBO values: When the cliff structure is formed, i.e., when the conduction band minimum (CBM) of the ESL is lower than that of the perovskite, the interface recombination became dominant, and the open-circuit voltage (V oc) worsened. When the spike structure is formed, i.e., when the CBM of the ESL is higher than that of the perovskite, the interfacial recombination is largely suppressed, which leads to an increased V oc of the solar cells. Additionally, we found that an appropriate amount of Mg doping in ZnO to form ZMO reduced carrier concentration and improved carrier mobility, thereby enhancing the charge collection efficiency of the photoexcited electrons by the FTO electrode and, consequently, the short-circuit current density (J sc). Using transient absorption (TA) measurements, we have revealed for the first time that the electron injection from photoexcited MAPbI 3 to FTO through a ZMO compact layer occurs in the timescale of a few nanoseconds in planar PSCs. PSCs based on the optimized Zn 0.9 Mg 0.1 O-ESL exhibited a considerable increase (~ 35%) in power conversion efficiencies (PCE) compared with that of the control device. Graphical abstract In planar-structure perovskite solar cells (PSCs), a spike structure is formed between the perovskites and the electron selective layer (ESL), i.e., the energy level of the conduction band of the ESL is higher than that of the perovskite absorber. This spike structure can lead to less photovoltage loss for the PSCs while maintaining high electron injection, which results in a higher open-circuit voltage and a greater short-circuit current, as well as a higher efficiency for planar PSCs. fx1 Highlights • The effects of the conduction band offset have been systematically investigated in planar PSCs for the first time. • The conduction band offset adjustment was essential to reduce the interfacial recombination. • The photoexcited electron transfer rate from perovskite to electrode in the planar PSCs were revealed. [ABSTRACT FROM AUTHOR]

Abstract Cu 2 ZnSn(S,Se) 4 (CZTSSe) is an interesting absorber material for thin film solar cells. However, one of the key challenges for the kesterite-based solar cells is to improve the open-circuit voltage (V oc) deficit, which is resultant of recombination at the interface of buffer/absorber. In this work, Cd-free n -type buffer layers with two different Mg-doped ZnO layers (Mg 0.26 Zn 0.74 O, Mg 0.30 Zn 0.70 O) have been examined using ultraviolet photoelectron spectroscopy. The most important electronic properties which are essential for the band offset study, ie. fermi level location, valence and conduction band offsets at the interface in the CZTSSe substrate, have been determined. The conduction band offset values for Mg 0.26 Zn 0.74 O, Mg 0.30 Zn 0.70 O buffer layers has been calculated experimentally. We have also established the correlation between device parameters and performances for dual ion beam sputtered ZnO buffer/CZTSSe-based heterojunction solar cells as a function of conduction band offset and the energy distribution of interface defects, to gain deeper understanding about the V oc -deficit behavior from a high recombination rate at the buffer/kesterite interface using simulation study. From the simulation study, the values of the solar cell efficiency with Mg 0.26 Zn 0.74 O and Mg 0.30 Zn 0.70 O buffer layers are 10.18 and 10.25%, respectively, which are higher in comparison to those obtained by using conventional CdS buffer layer. Highlights • The band gap of 3.90 and 3.94 eV for Mg.26 Zn.74 O, Mg.30 Zn.70 O respectively using spectroscopic ellipsometry measurement. • The conduction band offset of 0.29 and 0.34 eV for Mg.26 Zn.74 O, Mg.30 Zn.70 O buffer layers have been obtained respectively. • The relationship between device parameters and performances for (Zn,Mg)O/CZTSSe-based solar cells has been established. • Solar cells with buffer layer of Mg.26 Zn.74 O and Mg.30 Zn.70 O has achieved efficiency of 10.18% and 10.25% respectively. [ABSTRACT FROM AUTHOR]

In the CZTS structure, ZnMgO alloy can be a promising alternative buffer layer candidate to toxic cadmium sulphide (CdS) material. The effects of conduction band offset (CBO) at ZnMgO/CZTS interface are investigated by numerical approach. The main factor examined is the Mg concentration of ZnMgO and at high values of this parameter, a significantly higher barrier is observed, leading to a distortion in the current-voltage curve (S-shape). This phenomenon caused by degraded open circuit voltage (V oc ) and fill factor (FF) parameters leads to overall poor performance. Zn 1-x Mg x O with 20% Mg concentration decreases maximally the CBO and eliminates the S-shape while increasing the conversion efficiency. The suggested design by ultimately replacing both CdS buffer and ZnO window layers by a single layer of ZnMgO leads to an optimised CZTS based solar cell exhibiting a conversion efficiency of 11.50% with Voc = 0.78 V, Jsc = 22.37 mA/cm² and FF = 66.11%. [ABSTRACT FROM AUTHOR]

Ternary zinc tin oxide (ZTO) is one of the few environmental compatible buffer materials with the potential of replacing the n-CdS buffer in Cu(In,Ga)Se2 (CIGS) solar cells and other photovoltaic systems once its properties are fully understood and optimized. In this work, ZTO films were grown by atomic layer deposition and were logically characterized with the aim of understanding the correlations between compositional changes and film properties. The ZnO:SnO2 pulse ratio significantly affected the growth rate, crystal structure, morphology, and band gap of the ZTO films. By controlling the Sn/(Sn + Zn) atomic ratio, the optical band gap of the ZTO films was tuned between 3.05 and 3.36 eV. Integrating the ZTO films as buffer layers in CIGS solar cells, we observed that films with Sn concentrations of 9 to 16 at.% yielded photo-conversion efficiency close to 14%, which was very comparable to efficiency attained with the commonly used CdS buffer. Furthermore, using X-ray photoelectron spectroscopy analysis, we correlated the current-voltage behavior of the cells to the conduction band offset at the ZTO/CIGS interface. [ABSTRACT FROM AUTHOR]

This paper analyzes various high-κ dielectrics for low leakage AlGaN (Aluminium Gallium Nitride)/GaN (Gallium Nitride) MIS-HEMT (Metal Insulator Semiconductor—High Electron Mobility Transistor) device. The investigation is carried out by examining different attributes such as the dielectric constant, conduction band offset, and energy band gap of the dielectric which are crucial for a good dielectric-AlGaN interface. This work also computes the values of band offsets of different dielectrics to AlGaN analytically. The selection of the most promising dielectric is done using three different multi-criteria decision making methods (MCDM) namely the Ashby, VIKOR (VIseKriterijumska Optimizacija I Kompromisno Resenje in Serbian, meaning Multicriteria Optimization and Compromise Solution) and TOPSIS (Technique for Order Preference by Similarity to Ideal Solution). All the analyses point to La2O3 as the best gate dielectric for AlGaN/GaN MIS-HEMT device. [ABSTRACT FROM AUTHOR]

We investigated limitation factors of high efficiency Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells, where the CZTSSe absorbers were made by using sulfo-selenization process. CZTSSe absorbers with two S/(S+Se) ratios, ~ 0.12 (Se-rich) and ~ 0.22 (S-increased), were prepared by varying the sulfo-selenization temperature. The Se-rich CZTSSe solar cells were found to have larger conduction band offset (CBO) between the absorber and the buffer, which was reflected in the kinked J-V curves at low temperatures. Considering that the larger CBO prevents electron transport from absorber to buffer and resultantly reduces short circuit current and fill factor, it could be possible limitation factor of the high efficiency solar cell. Contrary to Se-rich solar cells, S-increased solar cells showed reduced CBO and no kinked J-V curve. However, deep defects were found to be generated, which induced defect centers of charge recombination both at interface and in bulk of the absorber. The larger CBO in Se-rich CZTSSe solar cell and deep defects in S-increased CZTSSe solar cell are observed even in ~ 12% efficiency solar cells. Thus, we believe that these possible limitation factors should be resolved to achieve high efficiency kesterite CZTSSe solar cell above 12%. [ABSTRACT FROM AUTHOR]

We fabricated kesterite Cu 2 ZnSnSe 4 (CZTSe) solar cells and studied device characteristics, where CZTSe absorbers were made by using two-step process. First, we deposited precursor CZTSe films with spin-coating or sputtering, and performed sulfurization and subsequent selenization. To complete the device, we applied In 2 S 3 as a buffer layer. We obtained power conversion efficiency (PCE) of 4.18% with spin-coated CZTSe absorber and 5.60% with sputtered CZTSe absorber. Both devices showed deep defects in the bulk and strong interface recombinations near the pn junction. In addition, we observed red-kinks in the current density-voltage (J-V) curves for both devices under the filtered light illumination (>660 nm), which is attributed to large conduction band offset (CBO) between the CZTSe absorber and the buffer layer and defect states in the buffer/CZTSe absorber or in the buffer. The red-kink was also observed in CZTSe (PCE of 7.76%) solar cell with CdS buffer. Hence, to enhance the PCE with CZTSe absorber, along with suppression of deep defects which act as recombination center, optimization of CBO between absorber and buffer is also required. [ABSTRACT FROM AUTHOR]

Numerical modeling of conduction band offset (Δ E ) between an n-type CdSO window layer and a p-type CdTe absorption layer on the effect of the cadmium telluride (CdTe) solar cells was studied through simulation. The simulation results show that a slightly positive Δ E yields high efficiency because the surface recombination rate at the CdSO/CdTe interface can be substantially reduced, leading to higher open-circuit voltage ( V ) and fill factor. Further increase in Δ E (≥ 0.4 eV) will impose an energy barrier against the photo-generated electrons under forward bias. We demonstrated the mechanistic picture of this effect using thermionic emission. However, if intra-band tunneling is considered in the simulation, a large Δ E shows negligible influence on the performance of CdTe solar cells. Our simulation results suggest that an Δ E of 0.3 eV is an optimal conduction band offset for high-efficiency CdTe solar cells. [ABSTRACT FROM AUTHOR]

Enhancing the performance of antimony selenide (Sb 2 Se 3) solar cells is significantly influenced by the optimization of the absorber/buffer junction. A wider bandgap buffer layer is suggested as a substitute for the traditional CdS buffer layer, for achieving this purpose. To enhance the short-circuit current density (J sc) and mitigate parasitic absorption of Sb 2 Se 3 cells, this study introduces zinc tin oxide (Zn,Sn)O as a substitute buffer layer instead of the narrow-bandgap and toxic CdS material. This study focuses on the simulation and numerical analysis of Sb 2 Se 3 solar cells with (Zn,Sn)O buffer layer using the SCAPS (Solar Cell Capacitance Simulator) software. The photovoltaic performance was evaluated by investigating the impact of different fractions of x = Sn/(Zn + Sn) in the Zn 1-x Sn x O layer. The reduction of interface recombination and improvement of open-circuit voltage (V oc) can be attained by optimizing the band alignment through the Zn 1-x Sn x O layer. The most favorable interface between the Sb 2 Se 3 and Zn 1-x Sn x O layers is attained when x = 0.2. In a traditional Sb 2 Se 3 /TiO 2 /CdS cell, the interface between the absorber and buffer layers has a −0.4 eV conduction band offset (CBO). The utilization of a Zn 0.8 Sn 0.2 O buffer layer causes an upward shift of the conduction band and a reduction of the negative CBO to −0.16 eV. Consequently, due to the wider gap between the conduction band of the Zn 0.8 Sn 0.2 O and the valence band of the Sb 2 Se 3 , interface recombination is reduced. According to the simulation results, the efficiency of the simulated Sb 2 Se 3 /TiO 2 /Zn 0.8 Sn 0.2 O cell is increased to 14.6%, representing a significant improvement compared to the conventional Sb 2 Se 3 /TiO 2 /CdS cell. • Sb 2 Se 3 solar cell with (Zn,Sn)O buffer layer was simulated by the SCAPS software. • The purpose is optimizing the conduction band offset at junction in Sb 2 Se 3 cells. • Efficiency of simulated Sb 2 Se 3 /TiO 2 /(Zn,Sn)O cells was improved by optimization of Sn content. • Optimized Sn content [Sn/(Zn + Sn)] in the Zn 1-x Sn x O was determined to be 0.2. • Efficiency of simulated Sb 2 Se 3 solar cells was improved from 9.3% to 14.6%. [ABSTRACT FROM AUTHOR]