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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]

• 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]

The traditional sulfur selenization process in Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cell fabrication often results in the creation of localized anion vacancies ( V S and V Se (CZTSe) solar cells. Our investigation, utilizing current-voltage ( 2 ZnSnSe 4 ) and admittance spectroscopy measurements, provides clear insights. We observed notable improvements in carrier collection efficiency and a discernible reduction in defect states. Furthermore, there was a significant decrease in the activation energy required within the solar cell device, dropping from 184 to 145 meV. To delve deeper into the structural and compositional aspects, we employed synchrotron-based X-ray nanoprobes. Through nanoscale X-ray fluorescence and hard X-ray beam-induced current measurements, we can directly observe and document the relationship between the local compositional distribution and photocurrent activity in operando. These comprehensive results furnish strong evidence that mitigating anion vacancies in the CZTSe layer can substantially improve the power conversion efficiency of the CZTSe solar cells. This advancement not only sheds light on the critical role of anion vacancies in solar cell performance but also underscores the effectiveness of the HAS process in enhancing overall device efficiency.I - V ) and admittance spectroscopy measurements, provides clear insights. We observed notable improvements in carrier collection efficiency and a discernible reduction in defect states. Furthermore, there was a significant decrease in the activation energy required within the solar cell device, dropping from 184 to 145 meV. To delve deeper into the structural and compositional aspects, we employed synchrotron-based X-ray nanoprobes. Through nanoscale X-ray fluorescence and hard X-ray beam-induced current measurements, we can directly observe and document the relationship between the local compositional distribution and photocurrent activity in operando. These comprehensive results furnish strong evidence that mitigating anion vacancies in the CZTSe layer can substantially improve the power conversion efficiency of the CZTSe solar cells. This advancement not only sheds light on the critical role of anion vacancies in solar cell performance but also underscores the effectiveness of the HAS process in enhancing overall device efficiency.

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.

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.

[Display omitted] • A MEA-DMF based S free solution for preparing CZTSe was successfully developed. • Phase evolution of CZTSe thin film during selenization was studied. • A device efficiency of 7.53% was obtained by using the MEA-DMF solution method. Most precursor solutions for preparing Cu 2 ZnSn(S,Se) 4 thin films use sulfur containing groups to complex metal ions. However, solutions with sulfur containing groups are always toxic and harmful gases, such as H 2 S and SO x , will be released when drying precursor films. Based on the excellent chelating ability of ethanolamine, a stable molecular precursor solution without using sulfur based complexing agent was successfully developed. Cu-Sn alloy phase is formed in the precursor film, which makes the phase evolution of the absorber during selenization similar to that of Cu 2 ZnSnSe 4 film grown from metallic precursor. Impacts of selenization time on compositional, morphological and photovoltaic properties of the Cu 2 ZnSnSe 4 film were studied. Finally, a Cu 2 ZnSnSe 4 solar cell with conversion efficiency of 7.53% was obtained by using the ethanolamine-dimethyl formamide based solution. [ABSTRACT FROM AUTHOR]

Most reported solution processed Cu 2 ZnSn(S,Se) 4 thin film solar cells are fabricated from precursor solution with sulfur source. However, the use of sulfur-containing solution is undesirable from the viewpoint of environment and security due to the release of sulfur-containing harmful gases when drying precursors. Here, a novel sulfur/selenium-free solution method using ethanolamine-dimethyl formamide as solvent was developed for the preparation of Cu 2 ZnSnSe 4 thin films. It was found that Cu-Sn alloy phases were formed in precursor during drying process. The formation and phase transition mechanisms of the Cu-Sn phases were illustrated. The aggregation level of the alloy phases and their distribution in the precursor depend on the drying time. Effects of different drying time on structural, morphological and photoelectric properties of the resulted Cu 2 ZnSnSe 4 films were systematically investigated. The Cu 2 ZnSnSe 4 absorbers exhibit a sandwiched structure or a four-layer structure, which is determined by the drying time of precursor, implying two different grain growth mechanisms. The devices with drying time of 6 min show larger grain size, longer carrier life time, higher external quantum efficiency and better average photovoltaic performance. [Display omitted] • A S/Se free pure solution method was developed for growing CZTSe thin films. • Formation and phase transition mechanisms of Cu-Sn alloys in precursor were investigated. • Short drying time of precursor leads to carbon-rich surface of CZTSe thin film. • Aggregation level of Cu-Sn phase affects absorber morphology and device performance. [ABSTRACT FROM AUTHOR]

• A two-steps non-hydrazine synthesis technique was used to fabricate CZTSe thin film. • Growth of high-quality CZTSe thin film with monoethanolamine and ethanol mixture solvent was investigated. • Optical and electrical characterisations were conducted to confirm the high-quality CZTSe thin film. • SCAPS-1D and 3D FDTD numerical simulations were carried out to investigate the electrical effects and optics of the device. • Optimised CZTSe solar cell estimates a conversion efficiency of 18.5%. This article reports on Cu 2 ZnSnSe 4 (CZTSe) thin film preparation via a nonhydrazine, nonpyridine and environmentally friendly low-cost solution process method. CZTSe fabrication through a solution-based process has not yet been suitably demonstrated given the impediments to addressing the presence of selenium in solutions. In this study, we introduced a two-step CZTSe fabrication method that used monoethanolamine as the chelating agent/co-solvent and ethanol as the main solvent. Selenization was then conducted. In this process, we successfully avoided the use of hydrazine to synthesise CZTSe thin films. Material characterisations (e.g. UV–VIS–NIR, scanning electron microscopy, electron dispersive spectroscopy, X-ray diffractometry and Fourier transform infrared spectroscopy) confirmed the high quality of the deposited thin films. The deposited CZTSe thin film showed high crystallinity without carbon residues, indicating its potential application as a photovoltaic absorber. Hence, we investigated the photovoltaic parameters of the CZTSe-based solar cells on the basis of the deposited thin film's optoelectronic properties. We utilised Solar Cell Capacitance Simulator to examine the electrical effects of CZTSe solar cells and used three-dimensional finite-difference time-domain optical simulations to investigate the optics of the solar cells. We estimated that the realistic power conversion efficiency of the CZTSe solar cells could reach 18.5% with a short-circuit current density of 30 mA/cm2. [ABSTRACT FROM AUTHOR]

In the present work, in order to study the effect of Germanium (Ge) thin layer incorporation on the CZTSe films, the Ge thin layer was deposited on the backside of the CZTSe as well as in between the CZTSe. The films were prepared with the help of thermal evaporation technique in stack format using all the constituents. Subsequently, the films were subjected to selenization process in order to obtain the Germanium doped CZTSe films. The properties such as structural, morphological, optical and electrical of the undoped CZTSe and Ge doped CZTSe absorber layer with change in Ge thin layer incorporation position was investigated. The major peak of the CZTSe film is shifted towards right due to change in position of Ge thin layer in CZTSe. It was noticed that the position of Ge thin layer affects the properties of CZTSe film. [ABSTRACT FROM AUTHOR]