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The importance and breadth of applications of the family of quaternary chalcogenides with the formula Cu2ZnSnSxSe(4−x) (CZTS/Se) where x = 0–4 are steadily expanding due to the tunable optoelectronic properties of these compounds and the Earth abundance of the elements in their composition. These p-type semiconductors are viewed as a viable alternative to Si, gallium arsenide, CdTe, and CIGS solar cells due to their cost effectiveness, Earth's crust abundance, and non-toxic elements. Additionally, CZTS/Se compounds have demonstrated notable capabilities beyond solar cells, such as photoelectrochemical CO2 reduction, solar water splitting, solar seawater desalination, hydrogen production, and use as an antibacterial agent. Various routes have been explored for synthesizing pure CZTS/Se nanomaterials and significant efforts have been dedicated to reducing the occurrence of secondary phases. This review focuses on synthetic approaches for CZTS/Se nanomaterials, with emphasis on controlling the size and morphology of the nanoparticles and their recent application in solar energy harvesting and beyond, highlighting challenges in achieving the desired purity required in all these applications. [ABSTRACT FROM AUTHOR]

Kesterite-based copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) thin films have attracted considerable attention as promising materials for sustainable and cost-effective thin-film solar cells. However, the successful integration of these materials into photovoltaic devices is hindered by the coexistence of secondary phases, which can significantly affect device performance and stability. This review article provides a comprehensive overview of recent progress and challenges in controlling secondary phases in kesterite CZTS and CZTSe thin films. Drawing from relevant studies, we discuss state-of-the-art strategies and techniques employed to mitigate the formation of secondary phases. These include a range of deposition methods, such as electrodeposition, sol-gel, spray pyrolysis, evaporation, pulsed laser deposition, and sputtering, each presenting distinct benefits in enhancing phase purity. This study highlights the importance of employing various characterization techniques, such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, for the precise identification of secondary phases in CZTS and CZTSe thin films. Furthermore, the review discusses innovative strategies and techniques aimed at mitigating the occurrence of secondary phases, including process optimization, compositional tuning, and post-deposition treatments. These approaches offer promising avenues for enhancing the purity and performance of kesterite-based thin-film solar cells. Challenges and open questions in this field are addressed, and potential future research directions are proposed. By comprehensively analyzing recent advancements, this review contributes to a deeper understanding of secondary phase-related issues in kesterite CZT(S/Se) thin films, paving the way for enhanced performance and commercial viability of thin-film solar cell technologies. [ABSTRACT FROM AUTHOR]

A tandem structure efficiently boosts solar cell efficiency because it uses a larger spectrum of solar radiation and minimizes photon energy thermalization. High-performance tandem solar cells have historically been difficult to produce due to a shortage of high-performance, low-bandgap cells. The proposed design is based on the CH3NH3GeI3 (1.9 eV) as a wide band gap absorber layer and FAMASnGeI3 (1.4 eV) as a narrow band gap perovskite layer with CZTSe as HTL. This research investigates the effect of different ETLs, perovskite layer thicknesses and their doping concentration on the device's photovoltaic parameters. Furthermore, the effect of tunnel junction thickness and front contact work function on the solar cell performance has also been simulated. It has been noted that the PCBM presents a better efficiency device than the other ETLs. The Voc of different ETLs has been related to Vbi. Moreover, the optimized thicknesses of both perovskite absorber layers are 450 nm and 400 nm for MAGeI3 and FAMASnGeI3, respectively. The optimal doping density is found to be E14 cm−3. It has been observed that the tunnel junction's thickness and the front contact's work function also play an important role in optimized device efficiency. The tunnel junction thickness is 4 nm for lead-free mixed cation perovskite/CZTSe tandem solar cells. However, the work function of the front electrode of 4.4 eV is optimum for this structure. The proposed lead-free mixed cation perovskite/CZTSe tandem device shows significant performance parameters, i.e., Voc= 0.970 V, Jsc = 28.46 mAcm−2, FF = 84.43 % and PCE= 23.32 %

Cu2ZnSnSe4 thin films have been synthesized by employing two magnetron-sputtering depositions, interlaced with two sequential post-deposition heat treatments in low vacuum, Sn+Se and Se–rich atmospheres at 550 °C. By employing successive structural analysis methods, namely Grazing Incidence X–Ray Diffraction (GIXRD) and Raman Spectroscopy, secondary phases such as ZnSe coexisting with the main kesterite phase have been identified. SEM peered into the surface morphology of the samples, detecting structural defects and grain profiles, while EDS experiments showed off–stoichiometric elemental composition. The optical bandgaps in our samples were calculated by a widely used extrapolation method from recorded transmission spectra, holding values from 1.42 to 2.01 eV. Understanding the processes behind the appearance of secondary phases and occurring structural defects accompanied by finding ways to mitigate their impact on the solar cells’ properties is the prime goal of the research beforehand.

Cu2ZnSnSe4 thin films have been synthesized by employing two magnetron-sputtering depositions, interlaced with two sequential post-deposition heat treatments in low vacuum, Sn+Se and Se–rich atmospheres at 550 °C. By employing successive structural analysis methods, namely Grazing Incidence X–Ray Diffraction (GIXRD) and Raman Spectroscopy, secondary phases such as ZnSe coexisting with the main kesterite phase have been identified. SEM peered into the surface morphology of the samples, detecting structural defects and grain profiles, while EDS experiments showed off–stoichiometric elemental composition. The optical bandgaps in our samples were calculated by a widely used extrapolation method from recorded transmission spectra, holding values from 1.42 to 2.01 eV. Understanding the processes behind the appearance of secondary phases and occurring structural defects accompanied by finding ways to mitigate their impact on the solar cells' properties is the prime goal of the research beforehand. [ABSTRACT FROM AUTHOR]

The importance and breadth of applications of the family of quaternary chalcogenides with the formula Cu2ZnSnSxSe(4−x) (CZTS/Se) where x = 0–4 are steadily expanding due to the tunable optoelectronic properties of these compounds and the Earth abundance of the elements in their composition. These p-type semiconductors are viewed as a viable alternative to Si, gallium arsenide, CdTe, and CIGS solar cells due to their cost effectiveness, Earth’s crust abundance, and non-toxic elements. Additionally, CZTS/Se compounds have demonstrated notable capabilities beyond solar cells, such as photoelectrochemical CO2 reduction, solar water splitting, solar seawater desalination, hydrogen production, and use as an antibacterial agent. Various routes have been explored for synthesizing pure CZTS/Se nanomaterials and significant efforts have been dedicated to reducing the occurrence of secondary phases. This review focuses on synthetic approaches for CZTS/Se nanomaterials, with emphasis on controlling the size and morphology of the nanoparticles and their recent application in solar energy harvesting and beyond, highlighting challenges in achieving the desired purity required in all these applications.

In the present work, we studied the optimization of annealing temperature on the formation of Cu2ZnSnSe4 (CZTSe) thin films and its impact on the film properties. The CZTSe films were deposited on Mo/SLG substrate by the thermal evaporation method. All the elements of the compound were deposited in the stack using its pellets. After the successful deposition of the films, the composition of the as deposited film was measured, then it was proceeded further for two steps annealing. The annealing parameter is one of the crucial steps for obtaining good quality kesterite-based absorber layer. In the present work, we have utilized two-step annealing to achieve the absorber layer suitable for device fabrication. The annealing in Se atmosphere were carried out at 230 °C for 10 min in first step followed by another 10 min annealing in second step with a temperature variation from 430 to 490 °C. The final temperature was varied to investigate the influence of annealing temperature on the absorber layer (CZTSe) film properties and its optimization. The films annealed between 470 and 490 °C are showing better structural, optical, electrical and morphological properties for further processing. [ABSTRACT FROM AUTHOR]

Kesterite-based copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) thin films have attracted considerable attention as promising materials for sustainable and cost-effective thin-film solar cells. However, the successful integration of these materials into photovoltaic devices is hindered by the coexistence of secondary phases, which can significantly affect device performance and stability. This review article provides a comprehensive overview of recent progress and challenges in controlling secondary phases in kesterite CZTS and CZTSe thin films. Drawing from relevant studies, we discuss state-of-the-art strategies and techniques employed to mitigate the formation of secondary phases. These include a range of deposition methods, such as electrodeposition, sol-gel, spray pyrolysis, evaporation, pulsed laser deposition, and sputtering, each presenting distinct benefits in enhancing phase purity. This study highlights the importance of employing various characterization techniques, such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, for the precise identification of secondary phases in CZTS and CZTSe thin films. Furthermore, the review discusses innovative strategies and techniques aimed at mitigating the occurrence of secondary phases, including process optimization, compositional tuning, and post-deposition treatments. These approaches offer promising avenues for enhancing the purity and performance of kesterite-based thin-film solar cells. Challenges and open questions in this field are addressed, and potential future research directions are proposed. By comprehensively analyzing recent advancements, this review contributes to a deeper understanding of secondary phase-related issues in kesterite CZT(S/Se) thin films, paving the way for enhanced performance and commercial viability of thin-film solar cell technologies.

• A novel hybrid structure of HTL/Perovskite/CZTSe/CdS/ZnO is proposed in this research. • Perovskite (CH 3 NH 3 Pb 3−x Cl x) and CZTSe act as absorber layer to absorb high energy and low energy photons respectively. • Solar Cell performance is observed by varying thickness, doping density, defects, and temperature. • A high efficiency of 30.9% is achieved which is much higher than other solar cells. • Short Circuit Current Density (J SC), Open Circuit Voltage (V OC), Fill-Factor (FF %) show interesting characteristics. With newer developments, the solar cells in the market need to be more efficient, affordable, stable, and environment friendly. The perovskite solar cells have already shown very impressive progress in performance since their inception. It has already reached 26 % efficiency and is expected to reach more, owing to its stupendous photovoltaic nature. On the other hand, even with a very high absorption coefficient, the CZTSe solar cell has not crossed the 15 % efficiency mark. Looking at the characteristics of both the materials and considerable differences in band gap, a novel hybrid structure, HTL/Perovskite/CZTSe/CdS/ZnO, has been proposed in this work to implement Perovskite (CH 3 NH 3 Pb 3−x Cl x) and CZTSe layer to absorb higher energy and lower energy photons respectively. In this context, choosing a proper Perovskite material becomes more crucial to have the required band alignment for the easy transportation of the excitons. The performance of the cell has been observed in varying parameters like thickness, doping, defects, and temperature. A high efficiency of 30.9 % is achieved which is much higher than the contemporary solar cells. Several other output parameters like Short Circuit Current Density (J SC), Open Circuit Voltage (V OC), Fill-Factor (FF%) characteristics have also been discussed. [ABSTRACT FROM AUTHOR]

In this work, Ag-doped Cu2ZnSnSe4 (CZTSe) thin films were deposited on FTO substrate by thermal evaporation method. The structural, morphological, optical and electrical properties of the (Cu1-xAgx)2ZnSnSe4 thin films were analyzed. The XRD analysis shows tetragonal crystal structure for CZTSe thin films, and the peak shift reveals the incorporation of the Ag into CZTSe crystal structure. Raman spectra show the presence of binary phases. SEM images show irregular shaped particles, and EDS spectra show non-stoichiometric nature. The optical spectra reveal good optical absorption in the visible region, and it is increased for Ag-doped films. Hall effect analysis shows p-type conductivity for CZTSe, whereas Ag-doped CZTSe sample provokes n-type conductivity. The result is also supported by the Mott–Schottky plots. The film x = 0.5 Ag doping concentration exhibits higher band bending in the dark which is essential for increasing Voc of the photoelectrochemical cell. The carrier concentration is found to be 1018 –1020 cm−3 for (Cu1-xAgx)2ZnSnSe4 thin films. The photoelectrochemical performance of the films was analyzed. Among the films, x = 0.5 Ag-doped film shows 3.02% photoconversion efficiency (PCE). The solar cells Glass/FTO/(Cu1−xAgx)2ZnSnSe4/Cu2ZnSnSe4/Ag were fabricated, and their PCE has been analyzed. [ABSTRACT FROM AUTHOR]

Kesterite Cu2ZnSnSxSe4−x (CZTSSe) is among the most promising inorganic Earth‐abundant thin‐film photovoltaic technologies, although currently, the larger voltage deficit compared with more mature chalcogenide technologies is hampering solar‐to‐electricity conversion efficiency progress in these materials. Most of the latest reports agree on the CZTSSe defect structure as the main limitation for the open‐circuit voltage. Small atom doping is suggested as an interesting strategy to reduce the concentration of defects without affecting secondary phase formation. Herein, an innovative approach based on the introduction of LiAlH4 and its further decomposition during the selenization process of CZTSe precursors, as a pathway for hydrogen and lithium/alkali transient doping, is explored. This process shows a strong beneficial influence on the crystal growth and solar cell device performance, especially with a significant improvement in Voc and fill factor. A reduction of nonradiative recombination and a remarkable fourfold increase in the carrier lifetime correlating with the reduction of the open‐circuit voltage (Voc) deficit below 330 mV is demonstrated. A mechanism on how small atoms (Li and H) interact to reduce the concentration of SnZn recombination centers while keeping doping relatively unchanged is proposed, opening fundamental perspectives for the simple and universal transient doping of thin‐film chalcogenide compounds. [ABSTRACT FROM AUTHOR]

In this work, an ultra-thin (0.815 μm) lead-free all-inorganic novel PV cell structure consisting of solid-state layers with the configuration SnO2/ZnOS/CsGeI3/CZTSe/Au has been optimized using SCAPS-1D simulator. ZnOS electron transport layer (ETL) has been deployed and various hole transport layer (HTL) material candidates have been considered to find the most suitable one in order to get the maximum possible power conversion efficiency (PCE). The simulation begins with the optimization of the thickness of the ZnOS buffer layer, followed by an analysis of HTL and ETL doping concentrations, thickness and bandgap optimization of absorber layer. The maximum permissible defect density at the ZnOS/CsGeI3 interface and the bulk defect density of the absorber layer (CsGeI3) are also investigated. It is also found that when the temperature rises, short circuit current density (Jsc) rises by 1.43 mA/K and open-circuit voltage (Voc) degrades by 2 mV/K. The optimized structure results in a PCE of 26.893% with Jsc, Voc, and fill factor (FF) of 28.172 mA cm−2, 1.0834 V, and 88.107% respectively. The cell performance parameters outperform those found in the recent literature. The simulated results of the proposed configuration are expected to be a helpful reference for the future implementation of a cost-effective and efficient all-inorganic perovskite PV cell.

In this work, a two-step method for preparation of CZTSe (Cu2ZnSnSe4) single crystals was demonstrated for the first time by recrystallization of a polycrystalline material in a KI-KCl meltsolution in a temperature gradient. At the first step, a polycrystalline material consisting of a mixture of metal selenides was synthesized by direct fusion of elemental Cu, Zn, Sn, and Se at 1000°C. Next, recrystallization process was carried out at a temperature gradient of 100°C, while the temperature of the cold zone was 750°C. The phase and chemical composition of the crystals were studied by energy dispersive X-ray and Raman spectroscopy. It was shown that the charge composition does not affect the composition of the obtained crystals. According to the amount of the remaining charge in the hot zone, one can speak of a very low recrystallization rate and a low product yield. Analysis of the elemental composition of crystals from the cold zone revealed a high inhomogeneity even in one experiment, which indicates the need to optimize the experimental parameters. On the other hand, according to the full line width at half height of the main peak, it can be argued that the obtained samples have a high degree of order in the structure and are suitable for measuring of physical characteristics. [ABSTRACT FROM AUTHOR]

Here we investigated a novel layer-based optimization technique to improve the performance of a CZTSe solar cell. By using this technique, the optical behavior and electrical properties of the proposed solar cell improved significantly as a result of the changes in the layer specifications and the layer materials. The structure of the cell consisted of an absorber laid on a conducting layer and covered by Indium Tin Oxide (ITO), with ZnO on its top surface. Due to the employment of the CSLO technique, a p+pn junction was formed between the absorber and window layers, which provided a lower recombination rate by transmitting more electrons and holes to the contacts. In addition, the main important parameters affecting the solar cell's performance such as layer thickness, carrier lifetime, and total effect density were investigated. According to the results, the proposed CZTSe solar cell achieved a 32.6% and 79.5% efficiency and fill factor, respectively—which in comparison to a conventional solar cell is remarkable. Moreover, hybrid structures made by utilizing CZTS-based, Ge-based Cu2ZnGeSe4, and Si-based Cu2ZnSiSe4 with the proposed CZTSe-based solar cell were implemented and better results were achieved, yielding an efficiency of about 42, 50, and 34% and a fill factor of 66, 55, and 42%, respectively, due to the materials' properties. [ABSTRACT FROM AUTHOR]

The self‐seed inducing grain growth mechanism for a Cu2ZnSnSe4 (CZTSe) thin film is explored via the existence of the fine‐grain CZTSe synthesized spontaneously at a relatively low soft‐selenization temperature of 300°C. Fine control over the elementary proportion and distribution of metal precursors is an important approach for obtaining the self‐seed inducing effect after soft selenization. Herein, a multiple‐cycle metal stack precursor, prepared by a weighting method, is developed to control the elementary proportion and distribution. By shortening the diffusion distance to produce a self‐seed inducing effect at soft selenization, the formation of detrimental intrinsic defects and secondary phases is effectively suppressed, contributing to the optimization of the CZTSe absorber back contact and surface. Consequently, the conductivity of the grain interiors and boundaries of the absorber layer is enhanced, the electric potential and roughness of the surface are reduced considerably, and the minority carrier lifetime of the layer is increased. When the number of stacked cycles increases from 1 to 7, the champion efficiency of CZTSe solar cell improves from 2.97% to 8.05% with a significant decrease in the open circuit voltage deficit from 0.831 to 0.617 V. These results may prove useful for developing a wider range of multinary compound semiconductor devices. [ABSTRACT FROM AUTHOR]

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu 2 ZnSnS 4 , Cu 2 ZnSnSe 4 , and their solid solution Cu 2 ZnSn(S x Se 1 − x ) 4 , where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials. [ABSTRACT FROM AUTHOR]

A comparative study of the thin layer based on copper zinc tin sulphide Cu2ZnSnS4 (CZTS) and that based on copper zinc tin selenide Cu2ZnSnSe4 (CZTSe) was made in order to assess the structural, morphological, optical and electrical qualities. for better use in improving performance of CZTS, CZTSe or CZTSSe based solar cell. CZTS and CZTSe thin films prepared by the spray pyrolysis technique were characterized by X-ray diffraction (XRD) which confirmed their kesterite structure in the tetragonal crystal phase. In addition, the analysis of the surfaces of the thin layers with the scanning electron microscope SEM, showed compact grains, well agglomerated and of appreciable sizes. UV-visible spectroscopy measured the quality of light absorption and located the bandgap energy values between 1.16 eV for CZTSe and 1.69 eV for CZTS i.e. in the range of potential absorbers for CZTS and CZTSe based thin film solar cells.

• Performance evaluation of Kesterite solar cell without defects and trap charges. • Analysis of kesterite solar cell in presence of Defect densities and trap charges. • Performance analysis of solar cell under Tail and Gaussian Distributions of defects. • Analysis of efficiency and quantum efficiency of solar cell. Kesterite materials Cu 2 ZnSn(S x Se 1−x) 4 , Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 have received considerable attention as absorber layers for photovoltaic cell applications. But they exhibit efficiencies lower than 12%. In this work, different possible loss mechanisms that affect the solar cell performance are analysed. Numerical investigation is made on the influence of different loss mechanisms such as radiative recombination, presence of traps and defect densities on the performance of the device. A comparative between results on solar cells based on Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 absorber layers is presented. The recombination mechanisms are found to play a vital role in degrading the performance of the solar cell. Additionally, trap centers and density of defect states are distributed to the absorber layer. It is observed that efficiency of the solar cell is severely affected and degraded by 10 % in the presence of defect states. [ABSTRACT FROM AUTHOR]

• Simulation of highly efficient CZTS solar cell. • Introduce CZTSe back surface field (BSF) layer to reduce back contact recombination. • Marked enhancement in PCE achieved. • Effect of back contact metals analyzed and Mo, Ni, Au, and Pt proposed as back contacts. • Detail analysis presented to guide the cells grower. Copper Zinc Tin Sulphide (CZTS) thin film solar cell achieved a great attention of researchers due to its optimum direct energy gap, higher absorption coefficient and good electronic properties. In this work, the CZTS/CdS based solar cell structure with and without back surface field (BSF) layer has been investigated numerically by using SCAPS-1D. Firstly, a basic experimentally reported structure (FTO/ZnO/CdS/CZTS/Mo) without BSF layer is considered and replicated. Then, by inserting p-CZTSe material as BSF layer in between the absorber and back contact, a new device structure (FTO/ZnO/CdS/CZTS/CZTSe/Mo) has been proposed. The performance of both structures; with and without BSF layer, have been analyzed with respect to different layer parameters like: thickness, carrier concentration, and defect densities (N t). A negative effect on cell performance has been observed with working temperature. From these analyses the optimum conversion efficiency of CZTS based PV cell without BSF layer has been found to be around 8.55% using CZTS absorber. The cell with CZTSe BSF layer (FTO/ZnO/CdS/CZTS/CZTSe/Mo) gives an overall conversion efficiency of 22.03%. The efficiency of both cells improved by replacing back contact metal with higher work function. This study gives the highest efficiency of about 29.86% for FTO/ZnO/CdS/CZTS/CZTSe/Pt structure. These simulation results could be an important guideline to a researcher for fabricating cost effective, non-toxic, and highly efficient CZTS solar cells. [ABSTRACT FROM AUTHOR]

• ALD V2Ox HTL in CZTSe-based solar cell in order to obtain semi-transparent devices. • CZTSe-based solar cells reveal efficiency up to 3.9% for devices annealed at 225 °C. • Notable 10mΩcm2 contact resistivity between the V 2 O x -based contact and CZTSe absorber. • Novel cleaning procedure based in diluted HF dips to improve CTZSe surface. This work explores the use of very thin transparent vanadium oxide films deposited by atomic layer deposition (ALD) technique as hole transport layer for CZTSe solar cells as alternative of opaque molybdenum based contacts. Contact resistivity between the CZTSe absorber and the ALD V 2 O x contact was measured. In order to improve contact quality, a cleaning bath using hydrofluoric acid (HF) dip, was also analyzed and its influence on kesterite surface was studied. Elementary material characterization and composition analysis of the V 2 O x layers was performed. Contact quality was assessed yielding contact resistivity values below 9 and 30 mΩcm2 for ALD and thermal evaporated V 2 O x films respectively. The proposed ALD V 2 O x based hole transport layer was deposited onto a glass covered with a transparent conductive oxide forming part of the rear contact scheme of a vertical CZTSe solar cell with a conventional ITO/CdS stack as electron transport layer. The impact of subsequent thermal post-annealing treatments in the cell performance was also analyzed yielding efficiency up to 3.9% on a semi-transparent CZTSe solar cell without any additional optimization process. In this way, a CZTSe solar cell with both transparent electrodes has been demonstrated paving the way to obtain in the future high efficiency bifacial and/or semitransparent Building –integrated photovoltaic devices. [ABSTRACT FROM AUTHOR]

In this work, the computational analysis on use of nanostructures to both III-Nitride and Kesterite solar cell are presented and compared. The scope behind the comparative analysis of III-nitride and kesterite material based solar cells is due to their excellent material properties, which made them suitable as an absorber for solar cells. In III-nitride based solar cells, stress induced polarization charges play an important role in carrier dynamics of cell, whereas, kesterite based cells suffer from detrimental effect due to its in-house defects. Here, an analysis is carried out to understand the above mentioned important effects, i.e., carrier transport mechanisms under the influence of polarization charges in III-nitride materials and in presence of defects in kesterite materials with nanostructures. It is anticipated that, nanostructures provide lots of advantages over bulk layer in order to overcome the detrimental effects in solar cells. A detailed comparative analysis of both type of solar cells are carried out. Finally, quantum efficiency measurement is carried out in order to observe the range of light absorption in each structures. It is quite interesting to observe that nanostructure doesn't boost the performance of the solar cell unless until the device is engineered properly. It is purely depends on carrier recovery and transport from the nanostructures.

We present an optical simulation of a solar cell employing core (Si) /shell (Kesterite Cu2ZnSnS4 (CZTS) or/and Cu2ZnSnSe4 CZTSe) vertically-aligned nanowire array. The method of the simulation is rigorous coupled wave analysis. In the first stage, we studied the case where the shell is composed of only CZTS or CZTSe. A larger absorptance of CZTSe led to a larger value of the ideal short circuit current (41 mA/cm2) in the case of CZTSe solar cell than in the case of CZTS solar cell (24 mA/cm2). In the second stage, to avoid the heat losses in CZTSe solar cell without reducing the current, we proposed a shell composed of a 3 µm of CZTS in the upper part and a 6 µm of CZTSe in the lower part. The maximum ideal current value in this structure is almost twice as large as that of a planar solar cell with the same amounts of used materials. Furthermore, the variation of this maximal ideal current with the incident angle of the sunlight shows that the investigated solar cell still has good performance as long as the incident angle doesn't exceed 60°. [ABSTRACT FROM AUTHOR]

[Display omitted] • A single junction CdS(n)/(Ag x Cu 1–x) 2 ZnSnSe 4 (p)/Cu 2 ZnSnSe 4 (p +) solar cell is presented. • Photoconversion efficiency of 18.63% is achieved from the optimized cell including different recombination mechanisms. • A relative improvement of ~47.6% in the performance of selenium rich low bandgap CZTSe solar cell is reported. • (Ag x Cu 1–x) 2 ZnSnSe 4 (ACZTSe) is used as the main absorber for better cationic ordering. • ITO is used as the back electrode to improve band bending and Schottky contact. • CZTSe is used as the back-surface field layer to prevent surface recombination. Direct bandgap Cu 2 ZnSnSe 4 (CZTSe) material is a promising absorber for thin film photovoltaics due to its affordable production cost and ecofriendly constituents. However, bulk defects, small grain size, short minority carrier lifetime and band bending at CZTSe/Mo (back contact) interface limit the performance of CZTSe solar cells. To overcome these issues, we design a single junction CdS(n)/ (Ag x Cu 1–x) 2 ZnSnSe 4 (p) /Cu 2 ZnSnSe 4 (p +) solar cell where we use (Ag x Cu 1–x) 2 ZnSnSe 4 (ACZTSe) as the main absorber layer. We have chosen the carrier density of each layer in a such way that ACZTSe becomes depleted and generated minority are collected efficiently. In our design, we utilize CZTSe as the back surface field layer to prevent surface recombination and indium doped tin oxide (ITO) as the back electrode to avoid band bending and increase the open circuit voltage. Additionally, we optimize the thicknesses of different layers and achieve a maximum efficiency of 18.63% including Shockley-Read-Hall, radiative and surface recombination mechanisms. The photo conversion efficiency (PCE) of our designed solar cell is 6 % higher (12.6% vs 18.63%) than that of the best reported selenium rich CZTSe solar cell. The design concept proposed in this work would help in harvesting solar energy efficiently from next generation CZTSe solar cells. [ABSTRACT FROM AUTHOR]

This work reports on a numerical modeling of Cu2ZnSnSe4 (CZTSe) thin film based solar cells using Solar Cell Capacitance Simulator (SCAPS). First, a conventional CZTSe/CdS/ZnO solar cell structure has been proposed and optimized. The optimal output parameters (power conversion efficiency PCE = 24.50%, short circuit current density Jsc = 47.732 mA/cm2, fill factor FF = 80.478% and open circuit voltage Voc = 0.639 V) have been obtained for ZnO, CdS and CZTSe layer thicknesses closed to 0.02 μm, 0.02 μm and 1.5 μm, respectively. Next, to improve on the conventional solar cell performance, three cell structures with different highly P-doped materials as back surface field (BSF) layers, such as P+-CZTSe, P+-Cu2O and P+-CZTS, have been proposed and optimized. In comparison to the conventional cell, devices with BSF layer have shown improvements of all the photovoltaic parameters. The CZTS/CZTSe/CdS/ZnO device has provided the highest performance (PCE = 25.83%, Jsc = 51.04 mA/cm2, FF = 78.14% and Voc = 0.646 V) for ZnO, CdS, CZTSe and P+-CZTS thicknesses closed to 0.02 μm, 0.02 μm, 1.5 μm and 0.4 µm, respectively. Additionally, the generation rate is no affected by the BSF layer; however, the recombination rate has decreased in the bulk and back surface of the CZTSe absorber. Finally, the insertion of the BSF layer has caused an increase of external quantum efficiency (EQE) up to 94.5% and a slight red shift of absorption in the long-wavelength region near the band edge. [ABSTRACT FROM AUTHOR]

Here we investigated a novel layer-based optimization technique to improve the performance of a CZTSe solar cell. By using this technique, the optical behavior and electrical properties of the proposed solar cell improved significantly as a result of the changes in the layer specifications and the layer materials. The structure of the cell consisted of an absorber laid on a conducting layer and covered by Indium Tin Oxide (ITO), with ZnO on its top surface. Due to the employment of the CSLO technique, a p+pn junction was formed between the absorber and window layers, which provided a lower recombination rate by transmitting more electrons and holes to the contacts. In addition, the main important parameters affecting the solar cell’s performance such as layer thickness, carrier lifetime, and total effect density were investigated. According to the results, the proposed CZTSe solar cell achieved a 32.6% and 79.5% efficiency and fill factor, respectively—which in comparison to a conventional solar cell is remarkable. Moreover, hybrid structures made by utilizing CZTS-based, Ge-based Cu2ZnGeSe4, and Si-based Cu2ZnSiSe4 with the proposed CZTSe-based solar cell were implemented and better results were achieved, yielding an efficiency of about 42, 50, and 34% and a fill factor of 66, 55, and 42%, respectively, due to the materials’ properties.

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu2ZnSnS4, Cu2ZnSnSe4, and their solid solution Cu2ZnSn(SxSe1−x)4, where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials.

One-step method for the electrodeposition of thin Cu2ZnSnSe4 (CZTSe) film onto a polyaniline/FTO/glass substrate was developed. Polyaniline film was preliminary obtained also by electrochemical deposition onto the FTO/glass substrate. The nucleation of CZTSe in the course of the film formation on the polyaniline surface was studied by chronoamperometry method. This process can be described by the instantaneous crystallization model. According to SEM data, the films consist of 25–50 nm nanocrystals which can form large crystallites. Photocurrent was established to increase up to 20 times in the CZTSe/polyaniline/FTO/glass heterojunction in comparison with the polyaniline free structure. In the heterojunction, polyaniline acts as a hole transport layer improving the charge transfer to the FTO electrode and preventing circuit shorting because of porosity of the CZTSe film. Graphical abstract [ABSTRACT FROM AUTHOR]

• CZTSe absorber patterning using sacrificial templated assisted UV lithography process. • CZTSe micro-cuboids are introduced on flat CZTSe layer over an area of 20 mm2. • The patterned CZTSe showed an average ~28% increase in optical absorbance. • Increased absorption due to increased surface area, multiple and internal reflections. Thin-film solar absorber layer presenting its surface with periodically patterned structures or with random roughness are considered one of the ways to increase the incident light absorption and thereby enhance the performance of the solar cell. This surface modification in the absorber layer reduces the reflection loss and leads to multiple reflections of the photons that fall on the absorber layer, leading to improved absorbance. In this present work, optical lithography process has been adapted to achieve periodic micro patterning of Cu 2 ZnSnSe 4 (CZTSe) solar absorber thin film surface and the changes in optical absorbance is studied. Optimization of the lithography process is undertaken to upscale the area of patterning up to (~20 mm × 20 mm) in CZTSe absorber thin films. CZTSe films were grown using e-beam evaporation and surface patterning is integrated through lithography process. Patterning integrity was examined through optical and scanning electron microscopes. Phase integrity was studied using XRD and Raman spectroscopy tools. The optical absorbance of the flat and patterned CZTSe thin films are measured using UV–Vis-NIR spectrophotometer. [ABSTRACT FROM AUTHOR]

The fabrication of kesterite CZTSe solar cells via an electrodeposition method provides an attractive approach for the low‐cost and environment‐friendly energy supply, yet the highest conversion efficiency for such solar cells (around 9%) is still far away from the highest efficiency of Cu‐based kesterite solar cells. Herein, a 10.54% efficient CZTSe solar cell (0.28 cm2 active sized area, without an antireflection layer) is developed by introducing electrodeposited Cu–Ge alloy layer at the bottom of metal precursor. It is found that the presence of Ge element within the bottom of the film can promote downward diffusion of Sn element. Consequently, the distribution of Sn is relatively homogeneous during the annealing process; thus, the formation of undesirable defect clusters is inhibited and the band alignment of the CdS/CZTSe interface is optimized. As a result, the conversion efficiency of CZTSe thin‐film solar cells is increased from 6.74% to 10.54%, which is the highest efficiency reported for electrochemically fabricated CZTSe solar cells. [ABSTRACT FROM AUTHOR]

A CZTS/CZTSe tandem solar cell with copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) absorber layers for the top and bottom cell, respectively, is proposed. The effects of different interconnect layers such as graphene, fluorine-doped tin oxide (FTO), indium tin oxide (ITO), and a p+–n+ tunnel junction consisting of CZTS and CdS on the performance of the cell are investigated, revealing that the p+–n+ tunnel junction results in the best performance. The impact of adding a thin SnS layer under the absorber layers to reduce recombination is also examined, revealing a significant improvement in cell performance. The optimized thicknesses of the buffer and absorber layers are obtained in all cases. The maximum efficiency of 26.21% is achieved in the optimum tandem device including the SnS layer and p+–n+ tunnel junction, being much higher than results for previous structures. Finally, the effect of the absorber bandgap energy on the performance of the tandem cells is investigated. [ABSTRACT FROM AUTHOR]

New solar cells with Ag/C60/MAPbI3/Cu2ZnSnSe4 (CZTSe)/Mo/FTO multilayered structures on glass substrates have been prepared and investigated in this study. The electron-transport layer, active photovoltaic layer, and hole-transport layer were made of C60, CH3NH3PbI3 (MAPbI3) perovskite, and CZTSe, respectively. The CZTSe hole-transport layers were deposited by magnetic sputtering, with the various thermal annealing temperatures at 300 °C, 400 °C, and 500 °C, and the film thickness was also varied at 50~300 nm The active photovoltaic MAPbI3 films were prepared using a two-step spin-coating method on the CZTSe hole-transport layers. It has been revealed that the crystalline structure and domain size of the MAPbI3 perovskite films could be substantially improved. Finally, n-type C60 was vacuum-evaporated to be the electronic transport layer. The 50 nm C60 thin film, in conjunction with 100 nm Ag electrode layer, provided adequate electron current transport in the multilayered structures. The solar cell current density–voltage characteristics were evaluated and compared with the thin-film microstructures. The photo-electronic power-conversion efficiency could be improved to 14.2% when the annealing temperature was 500 °C and the film thickness was 200 nm. The thin-film solar cell characteristics of open-circuit voltage, short-circuit current density, fill factor, series-resistance, and Pmax were found to be 1.07 V, 19.69 mA/cm2, 67.39%, 18.5 Ω and 1.42 mW, respectively.

• The effective back-contact barrier of CZTSe: nanoscale Ge is improved and characterized. • The mechanism of the back-contact improvement is demonstrated with device models. • The model of MoSe 2 interface defect at back-contact agrees with the empirical data. • The efficiency is improved up to 8.3% by including nanolayer Ge at back contact. Using temperature-dependent measurements and device modeling, we systematically study the effective back-contact barrier of CZTSe devices to improve the property of the back-contact interface. By comparing with CZTSe devices with various nanoscale Ge configurations, CZTSe nanoscale Ge bi-layers devices show the improved power conversion efficiency by 1.1%. DC magnetron sputtering is used to fabricate CZTSe: nanolayer Ge devices. Critical device parameters are characterized to understand the impact of nanoscale Ge films on the back-contact device characteristics. Based on empirical results, modeling is performed for the influence of MoSe 2 defects on the effective back-contact barrier. Analysis of experimental results of Ge bi-layers devices with the improved back-contact barrier makes a good agreement with modeling and Sentaurus TCAD simulation at the 95% confidence-level. The conversion efficiency of CZTSe: nanoscale Ge bi-layers devices is improved up to 8.3%. [ABSTRACT FROM AUTHOR]

In CZTSe thin film solar cell, CZTSe/CdS as absorber/buffer layer has been used and ZnO is used as a window layer. CdS as buffer layer have high efficiency but it is toxic due to cadmium. So to reduce the cadmium usage, a hybrid buffer layer of ZnO/CdS is proposed and the numerical study has been performed using SCAPS-1D simulator. The thickness of ZnO/CdS buffer layer has been optimized at ZnO-15 nm/CdS-65 nm, for maximum solar cell efficiency. The solar cell with hybrid buffer layer of ZnO/CdS exhibits more efficiency compared to the solar cell using only CdS or only ZnO as buffer layers. The solar cell efficiency variation with temperature has been studied for CdS, ZnO and CdS/ZnO buffer layer and observed that the variations are almost same for all the three layers. [ABSTRACT FROM AUTHOR]

A MASnI 3 -based perovskite solar cell with structure CZTSe / MASnI 3 / TiO 2 / FTO was proposed in this work. To accomplish this task, first, the effect of different kesterite and stannite CZTS , CBTS , CFTS , CMTS , CNTS , CZTSe compounds as hole transport layer HTL simulations were performed in a solar cell capacitance simulator. All simulations were performed in 1.5 G 1 sun light spectrum. From the results it was found that valance band offset of the absorber/ HTL interface affects the performance of the solar cell, and among different HTL , CZTSe is proven to be a suitable candidate for HTL. After selection of CZTSe as HTL for a MASnI 3 solar cell, device optimization was performed by analyzing the absorber and HTL thicknesses and doping concentrations on device performance. After analysis, improved functional parameters were attained with a conversion efficiency of 19.52%, short-circuit current of 29.45 mA / cm 2 open circuit voltage of 0.86 V and fill factor of 76.74%. The concept presented in this work for modeling of MASnI 3 -based devices, will categorically provide ways for the feasible fabrication of a high-efficiency solar cell. [ABSTRACT FROM AUTHOR]

We reported the growth of CZTSSe thin films on Mo-coated SLG substrates by the two-step approach which includes the deposition of precursor films by the magnetron sputtering method at room temperature followed by selenization of the precursor films at 560∘C. Formation of CZTSSe films with the kesterite structure was confirmed by XRD and Raman spectroscopy analyses. The films are slightly Cu-rich and Zn-deficient. SEM study shown that the films have uniform surface morphology and densely packed structure without any voids and cracks. [ABSTRACT FROM AUTHOR]

This paper presents new photovoltaic solar cells with Cu2ZnSnSe4/CH3NH3PbI3(MAPbI3)/ZnS/IZO/Ag nanostructures on bi-layer Mo/FTO (fluorine-doped tin oxide) glasssubstrates. The hole-transporting layer, active absorber layer, electron-transporting layer, transparent-conductive oxide layer, and top electrode-metal contact layer, were made of Cu2ZnSnSe4, MAPbI3 perovskite, zincsulfide, indium-doped zinc oxide, and silver, respectively. The active absorber MAPbI3 perovskite film was deposited on Cu2ZnSnSe4 hole-transporting layer that has been annealed at different temperatures. TheseCu2ZnSnSe4 filmsexhibitedthe morphology with increased crystal grain sizesand reduced pinholes, following the increased annealing temperature. When the perovskitefilm thickness was designed at 700 nm, the Cu2ZnSnSe4 hole-transporting layer was 160 nm, and the IZO (indium-zinc oxide) at 100 nm, and annealed at 650 °C, the experimental results showed significant improvements in the solar cell characteristics. The open-circuit voltage was increased to 1.1 V, the short-circuit current was improved to 20.8 mA/cm2, and the device fill factor was elevated to 76.3%. In addition, the device power-conversion efficiency has been improved to 17.4%. The output power Pmax was as good as 1.74 mW and the device series-resistance was 17.1 Ω.

Kesterite-structured Cu2ZnSnSe4 (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, the control over substrate temperature (i.e., growth temperature) is very important in terms of the deposition of high-quality CZTSe films. In this regard, the effects of growth temperatures on the CZTSe film morphology were investigated. The suitable temperature range to deposit CZTSe films with Cu-poor and Zn-rich compositions was 380−480 °C. As the temperature increased, the surface roughness of the CZTSe film decreased, which could improve p/n junction properties and associated device performances. Particularly, according to capacitance-voltage (C-V) and derived-level capacitance profiling (DLCP) measurements, the density of interfacial defects of CZTSe film grown at 480 °C showed the lowest value, of the order of ~3 × 1015 cm−3. Regardless of applied growth temperatures, the formation of a MoSe2 layer was rarely observed, since the growth temperature was not high enough to have a reaction between Mo back contact layers and CZTSe absorber layers. As a result, the photovoltaic (PV) device with CZTSe film grown at 480 °C yielded the best power conversion efficiency of 6.47%. It is evident that the control over film growth temperature is a critical factor for obtaining high-quality CZTSe film prepared by one-step process.

Abstract This work studies the influence of various conductive substrates such as Al, Cu and Ag on the optical and photoconductive behavior of Cu 2 ZnSnSe 4 (CZTSe) thin films prepared using thermal evaporation method. The XRD analysis indicates that the deposited CZTSe films are tetragonal structure for all substrates, however, the compound prepared using glass substrates shows some secondary phases. The SEM images show spherical particles for all the films. The films show dense and uniform surface and no voids are observed. EDX analysis witnesses for the deposition compound that exhibits near stoichiometric values. CZTSe thin films show the absorption coefficient about 104 cm−1 and the band-gap is found to be about 1.15 eV, 1.32 eV, 1.4 eV and 1.19 eV for CZTSe films deposited on glass, Al, Cu and Ag substrates respectively. From, the Mott-Schottky Plot, the CZTSe thin films confirms p-type conductivity and the J-V plot of CZTSe thin films shows the photoactivity. The CZTSe films deposited on Al substrates show higher PCE. Highlights • Cu 2 ZnSnSe 4 (CZTSe) thin films prepared thermal evaporation method on different conductive substrates. • The film deposited on Cu substrate shows higher optical conductivity in the region 300–550 nm. • Mott-Schottky Plot, the CZTSe thin films confirm p type conductivity. • J-V plot of CZTSe thin films shows the photo activity. • The CZTSe films deposited on Cu substrates shows higher PCE. [ABSTRACT FROM AUTHOR]

Abstract Cu 2 ZnSnSe 4 (CZTSe) nanocrystals were prepared by a solvo-thermal method using elemental copper, zinc, tin and selenium powders as precursors and ethylenediamine as a stabilizer and chelating medium. The particles were synthesized at 180 °C after which they were annealed at 300 °C and 400 °C for 1 h. The influence of annealing the nanocrystals, on the crystal structure, particle size, morphology, composition and optical properties has been investigated. As-grown particles were found to contain secondary phases, which subsequently transformed into CZTSe nanocrystals upon annealing. XRD and Raman results confirmed that the samples recrystallized into kesterite CZTSe on annealing at 400 °C. SEM studies show that the as-grown material has a platelet like morphology, and after annealing at 400 °C, freshly formed nanosized particles (10–20 nm) appear. TEM studies reveal that the grain size of CZTSe nanoparticles is about 5–10 nm. Optical studies show that the band gap energy exhibits a blue shift in the range 1.3–1.6 eV, indicative of quantum confinement of electrons. Highlights • Single step nanocrystalline growth of Cu 2 ZnSnSe 4 nanoparticles by solvothermal method. • XRD and Raman studies reveal single phase growth of CZTSe. • Stochiometric growth of material confirmed by EDAX analysis. [ABSTRACT FROM AUTHOR]

Polycrystalline powder samples of eight very far off‐stoichiometric Cu2ZnSnSe4 (CZTSe) compounds (off‐stoichiometry types A–D) are grown using the solid‐state reaction method in evacuated silica tubes. An additional thermal annealing is performed, in order to study the influence of annealing on the phase content and stoichiometry of the CZTSe phases formed under these conditions. The structural characterization of the synthesized materials before as well as after annealing is carried out by powder X‐ray diffraction (PXRD), paying a special attention to the possibility of minimization the content of secondary phases. Wavelength dispersive X‐ray spectroscopy (WDX) is used to determine the chemical composition of the obtained phases, paying a special attention to the phase constituents as well as the evolution of the CZTSe phases after the additional annealing. A comparative study of the phase content of very far off‐stoichiometric CZTSe compounds is presented. The possible limits of the existence region of the kesterite CZTSe are discussed. [ABSTRACT FROM AUTHOR]

Kesterite Cu 2 ZnSn( S x Se 1 − x ) 4 is an attractive earth-abundant material for low-cost thin film photovoltaics with the capability to achieve power production in the terawatt range and therefore to supply a significant part of the global electricity needs. Despite its advantageous optical and electrical properties for photovoltaic applications, the large band tailing causes voltage losses that limit the efficiency of kesterite-based devices. Here we show that the band-tailing originates mainly from band-gap fluctuations attributable to chemical composition variations at nanoscale; while electrostatic fluctuations play a lesser role. Absorption measurement reveal that the Cu-Zn disorder, always present in kesterite Cu 2 ZnSn( S x Se 1 − x ) 4 , is not the main source of the large band tailing. Instead defect clusters having a significant impact on the band-edge energies, e.g. [2 Cu Zn − + Sn Zn 2 + ], are proposed as the main origin for the kesterite band tail. [ABSTRACT FROM AUTHOR]