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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]

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]

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]

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]

Copyright of Chemical Bulletin of Kazakh National University is the property of Al-Farabi Kazakh National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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]

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]

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]

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]

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]

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]

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]

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]

Abstract: Double layer distribution exists in Cu2SnZnSe4 (CZTSe) thin films prepared by selenizing the metallic precursors, which will degrade the back contact of Mo substrate to absorber layer and thus suppressing the performance of solar cell. In this work, the double‐layer distribution of CZTSe film is eliminated entirely and the formation of MoSe2 interfacial layer is inhibited successfully. CZTSe film is prepared by selenizing the precursor deposited by electrodeposition method under Se and SnSex mixed atmosphere. It is found that the insufficient reaction between ZnSe and Cu‐Sn‐Se phases in the bottom of the film is the reason why the double layer distribution of CZTSe film is formed. By increasing Sn content in the metallic precursor, thus making up the loss of Sn because of the decomposition of CZTSe and facilitate the diffusion of liquid Cu2Se, the double layer distribution is eliminated entirely. The crystallization of the formed thin film is dense and the grains go through the entire film without voids. And there is no obvious MoSe2 layer formed between CZTSe and Mo. As a consequence, the series resistance of the solar cell reduces significantly to 0.14 Ω cm2 and a CZTSe solar cell with efficiency of 7.2% is fabricated. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S1−xSex)4 solar cells are well suited for roll-to-roll mass production since they are formed mainly by non-toxic and earth-abundant elements. Polyimide (PI) has proved to be a promising roll-to-roll compatible substrate yielding very high efficiency devices for Cu(In,Ga)Se2. In this work, we demonstrate the feasibility of using PI as a low-weight and flexible alternative to soda-lime glass for Cu2ZnSnSe4 (CZTSe) solar cells. Two main concerns arise when working with PI. Firstly, its low thermal robustness limits process temperatures below 500°C. The second concern is the lack of alkali in PI in contrast to conventional soda-lime glass fundamental for high efficiency devices. This work tackles both issues. First, different alkali doping strategies are investigated for the incorporation of Na and K into CZTSe absorbers prepared on PI substrates by sequential precursor sputtering and selenization at 470°C: pre-absorber synthesis and post-deposition treatment. Post-deposition treatment does not lead to an improvement of performance. Pre-absorber synthesis effectively dopes the CZTSe absorbers increasing the solar cell performance and carrier concentration of the devices. Cu2ZnSnSe4 devices are then fabricated on glass and PI at different temperatures (450°C-490°C). A detrimental SnSe2 secondary phase is detected in most of these devices. The formation of this phase is proved to be strongly related to process temperature. Despite this, a 6.4% efficiency device is achieved at 490°C on glass. Finally, through further experimentation and the addition of a Ge nanolayer, we report a 4.9% efficiency flexible device on PI setting a new record for kesterite solar cells on a polymer substrate. [ABSTRACT FROM AUTHOR]

The thin-film photovoltaic absorber Cu2ZnSn(S,Se)4 (CZTSSe) holds considerable promise for large scale conversion of sunlight into electricity. CZTSSe is composed of Earth-abundant elements that exhibit low-toxicities, but improvements in device efficiency have been hampered by difficulties in increasing open circuit voltages ( VOC) due, at least in part, to disorder induced band tailing. We present a method to increase VOC through direct modification of the back contact; our approach involves the separation of fully functioning devices from their Mo/glass substrate to reveal the back CZTSSe surface. Formation of a new back contact consisting of a thermally deposited high work function material (MoO3), together with a higly reflective (Au) capping layer, creates an electrostatic field that drives electrons to the front p-n junction and leads to a decrease in electron-hole recombination. Model simulations indicating an increase in VOC with decreasing absorber thickness are borne out by experiments with devices of varying thicknesses (0.7-2.0 μm). We report VOC increases of up to 49 mV for a 1 μm thick absorber, with even greater increases up to 61 mV when the back CZTSSe surface is etched with bromine-methanol. [ABSTRACT FROM AUTHOR]

In this work, quaternary chalcogenide CuZnSnSe (CZTSe) was synthesized using a mechanochemical ball milling process and its thermoelectric properties were studied by electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. The synthesis process comprises three steps viz., wet ball milling of the elemental precursors, vacuum annealing, and densification by hot pressing. The purpose of this is to evaluate the feasibility of introducing wet milling in place of vacuum melting in solid state synthesis for the reaction of starting elements. We report the structural characterization and thermoelectric studies conducted on samples that were milled at 300 rpm and 500 rpm. X-ray diffraction (XRD) analysis showed the existence of multiple phases in the as-milled samples, indicating the requirement for heat treatment. Therefore, the ball milled powders were cold pressed and vacuum annealed to eliminate the secondary phases. Annealed samples were hot pressed and made into dense pellets for further investigations. In addition to XRD, energy dispersive spectroscopy (EDS) studies were performed on hot pressed samples to study the composition. XRD and EDS studies confirm CZTSe phase formation along with ZnSe secondary phase. Electrical resistivity and Seebeck coefficient measurements were done on the hot pressed samples in the temperature range 340-670 K to understand the thermoelectric behaviour. Thermal conductivity was calculated from the specific heat capacity and thermal diffusivity values. The thermoelectric figure of merit zT values for samples milled at 300 rpm and 500 rpm are ∼0.15 and ∼0.16, respectively, at 630 K, which is in good agreement with the values reported for solid state synthesized compounds. [ABSTRACT FROM AUTHOR]

We obtained Raman spectra of a co-evaporated Cu2ZnSnSe4 (CZTSe) thin film under pressures of up to 5.56 GPa using a gasketed diamond anvil cell. Each spectrum was carefully resolved into Lorentzian peaks to analyze the observed phonons. Six Raman peaks were observed at 1 atm. These Raman peaks appeared at 174, 193, 196, 220, 234, and 248 cm−1 and were attributed to the vibration modes of kesterite CZTSe with B (or A), E, A, E, B, and B symmetries, respectively. Also, two Raman modes with a frequency of approximately 260 cm−1 emerged at 1.27 GPa. A small additional peak with a 220 cm−1 Raman shift was visible at pressures higher than 3.55 GPa. The origins of these peaks are also discussed. [ABSTRACT FROM AUTHOR]

The influence of the conditions of electrochemical deposition of Cu-Zn-Sn-Se precursor thin films from solutions containing lactic acid on their optical and electrophysical properties was studied. It was found that an additional annealing step of precursor films in a selenium atmosphere at 550 °C is necessary for the preparation of single-phase polycrystalline photoconducting Cu-Zn-Sn-Se films with a band gap energy equal to ~1 eV. The obtained semiconductor CZTSe materials satisfy the composition and property requirements imposed on absorbing layers in solar panels. [ABSTRACT FROM AUTHOR]

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Cu2ZnSnSe4 solar cell absorbers are synthesized by large-area electrodeposition of metal stack precursors followed by selenization. A champion solar cell exhibits 8.2% power conversion efficiency, a new record for Cu2ZnSnSe4 solar cells prepared from electrodeposited metallic precursors. Significant improvements of device performance are achieved by the application of two etching procedures and buffer layer optimization. These results validate electrodeposition as a credible alternative to vacuum processes (sputtering, co-evaporation) for earth-abundant thin-film solar cell fabrication at low cost. [ABSTRACT FROM AUTHOR]

The influence of a prealloying process on the formation of MoSe2 and thus on the performance of Cu2ZnSnSe4 (CZTSe) solar cells is investigated using sputtering deposition and post-annealing approaches. The dense alloy layer, which is made by a low-temperature prealloying process, acts as a temporary Se diffusion barrier during a subsequent high-temperature selenization process. The formation of thick interfacial MoSe2 can be suppressed effectively by this temporary barrier, cooperating with subsequent quick formation of compact CZTSe layer. The thickness of interfacial MoSe2 layer in CZTSe solar cells can be tailored by adjusting the preannealing process during selenization. As a consequence, the series resistance of CZTSe solar cells is reduced to a low level (≈0.6 Ω cm2), and the performance of CZTSe solar cells is improved significantly. A CZTSe solar cell with efficiency of 8.7% is fabricated. [ABSTRACT FROM AUTHOR]

This work reports the synthesis of photovoltaic-grade Cu2ZnSnSe4 thin films with Zn-poor compositions (Zn/Sn < 1) prepared by selenization of sputter deposited metallic precursors. This contrasts with most other reports where up to now fabrication of photovoltaic-grade Cu2ZnSnSe4 requires Cu-poor and Zn-rich compositions, which often favor the formation the ZnSe secondary phase. Synthesis of Zn-poor or stoichiometric films opens up prospects for preparing device-grade films while minimizing formation of common secondary phases. While the maximum device efficiency is modest (2.5%), it is notable because it falls outside the optimum compositional range. Annealing conditions including temperature, chalcogen source, and system pressure were varied to determine their influence on film and device properties. Phase characterization confirms that Cu2ZnSnSe4 is the main phase present. Reasons for the formation of device-grade films outside the ideal compositional range are discussed, including the fact that initial film growth is under Zn-rich conditions, and that films are Cu-poor in relation to Zn (Cu/Zn < 2), both of which may potentially give rise to the necessary electronic defects for a photovoltaic-grade absorber layer. Finally, the importance reporting other compositional ratios, especially Cu/Zn and Cu/Sn, instead of the more common ratio Cu/(Zn + Sn), is expounded for this class of materials. [ABSTRACT FROM AUTHOR]

This paper reports the formation of CZTSe absorber layers at temperatures between 380-550°C using a two-stage process. Energy dispersive X-ray spectroscopy (EDS) analysis identified the presence of Cu rich and Zn rich regions that are consistent with the presence of secondary phases. These phases could evolve at lower temperatures during the formation of the CZTSe phase. The absorber layers exhibit an evolution in the morphology with conversion temperature, with the highest temperature yielding the largest and most compact grains. In the past, Cu-Zn alloys have been identified in the sputtered metallic precursor produced with our baseline process. In this study, we investigate the selenisation of Cu-Zn precursors under the same conditions as used for the CZTSe in order to understand and identify the formation of potential secondary phases that might form in our CZTSe absorber layers. The results showed that Cu1·8Se and ZnSe were formed as separate phases. There is evidence to suggest that the Cu1·8Se evolves into the Cu2Se phase as the temperature increases above 520°C. This provides an insight into the phases formed during processing and their possible influence on kesterite formation. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 solar cells were synthesized by electrodeposition of metal stack precursors followed by selenization, a high potential process for industry, leading to conversion efficiencies above 5%. An additional selenium-capping layer deposited on the precursor before annealing showed improved uniformity and morphology of CZTSe layers compared to other selenization routes. Two different atmospheric annealing systems were used: a closed graphite box in a tubular furnace and a three-chamber dynamic rapid thermal processing furnace. The RTP system gave larger grains and more compact layers, whereas CZTSe selenized in tube furnace had smaller grains and a higher series resistance. Both annealing systems gave best cells power conversion efficiencies over 5%. We will discuss the device photoelectric properties and their relation to material structures and processing. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) thin films were synthesized on transparent conducting oxide glass substrates via a simple, non-toxic, and low-cost process using a precursor solution paste. A three-step heating process (oxidation, sulfurization, and selenization) was employed to synthesize a CZTSe thin film as an absorber layer for use in thin-film solar cells. In particular, we focused on the effects of sulfurization conditions on CZTSe film formation. We found that sulfurization at 400 °C involves the formation of secondary phases such as CuSe2 and Cu2SnSe3, but they gradually disappeared when the temperature was increased. The formed CZTSe thin films showed homogenous and good crystallinity with grain sizes of approximately 600 nm. A solar cell device was tentatively fabricated and showed a power conversion efficiency of 2.2% on an active area of 0.44 cm² with an open circuit voltage of 365 mV, a short current density of 20.6 mA/cm², and a fill factor of 28.7%. [ABSTRACT FROM AUTHOR]

ABSTRACT Zn-rich Cu2ZnSnSe4 (CZTSe) films were prepared by a two-step process consisting in the DC-magnetron sputtering deposition of a metallic stack precursor followed by a reactive anneal under a Se + Sn containing atmosphere. Precursor composition and annealing temperature were varied in order to analyze their effects on the morphological, structural, and optoelectronic properties of the films and solar cell devices. Raman scattering measurements show the presence of ZnSe as the main secondary phase in the films, as well as the presence of SnSe at the back absorber region of the films processed with lower Zn-excess values and annealing temperatures. The ZnSe phase is found to accumulate more towards the surface of the absorber in samples with lower Zn-excess and lower temperature annealing, while increasing Zn-excess and annealing temperature promote its aggregation towards the back absorber region of the devices. These measurements indicate a strong dependence of these process variables in secondary phase formation and accumulation. In a preliminary optimization of both the composition and reactive annealing process, a solar cell with 4.8% efficiency has been fabricated, and potential mechanisms limiting device efficiency in these devices are discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, single-kesterite-phase Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) nanocrystallines have been synthesized by a simple solvothermal route. Scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorbance and Raman scattering spectroscopy were used to characterize the optical and micro-structure properties of the as-synthesized samples. The bandgap of CZTS could be tuned in a large range by incorporating a few Se atoms. Both the CZTS and CZTSe exhibited the similar temperature dependence of the Raman "A" modes, including a monotonic redshift in peak position and an irregular variation in peak linewidth. Such a behavior might be due to the cumulative effect of thermal expansion and small crystalline sizes. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4(CZTSe) films were formulated by the selenization of Cu(Zn, Sn) (CZT) metal precursors. The CZT precursor was prepared by depositing zinc onto a Cu-Sn layer co-sputtered on molybdenum-coated soda-lime glass substrates. Selenium was evaporated thermally onto the CZT precursor. The resulting CZTSe film was then annealed at 450 °C for various annealing times (1, 3, 5, 10 and 15 min) using a rapid thermal process (RTP). Crystallization of the CZTSe film as a function of the annealing time was observed by X-ray diffraction (XRD). The XRD patterns of the films annealed over 3 min were well matched to those of a CZTSe single crystal. The lattice parameters of the CZTSe films annealed over 5 min werea= 5.639 Å andc= 11.356 Å. These values were reasonably close to the lattice parameters of a single crystal of Cu2ZnSnSe4(a= 5.693 Å andc= 11.333 Å). The energy gap of the CZTSe films was 1.14 eV. [ABSTRACT FROM AUTHOR]

In this study, a novel sequential electrodeposition of Cu-Zn-Sn-Se and Cu-Sn-Se layers was applied for fabrication of a Cu2ZnSnSe4 (CZTSe) thin film. The desired Cu-Zn-Sn-Se/Cu-Sn-Se bilayer was obtained at a selected applied potential from electrolytes containing corresponding metal and selenium ions. Annealing of the bilayer film under argon (Ar) flow induced significant losses of Sn and Se components due probably to evaporation of the SnSe compound. Suppression of these losses could be realized by introduction of Se vapor during the annealing: as a result, a CZTSe thin film with an ideal Cu-poor/Zn-rich composition for solar cell application was obtained. The solar cell with a device with the structure of glass/Mo/CZTSe/CdS/ZnO/AZO derived from thus-obtained CZTSe film exhibited a conversion efficiency of 1.1%, while the device still possessed a significant leakage current and a high series resistance. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

This paper reports the preparation of Cu2ZnSnSe 4 (CZTSe) nanocrystals from elemental sources through the application of various coordinating solvents. The CZTSe nanocrystals were synthesized by mixing metals in oleylamine (OLA) and isophorondiamine (IPDA) at a ratio of 1:3 as well as a Se solution in trioctylphosphine (TOP) under N 2 flow at atmospheric pressure at a reaction temperature of 235 °C. X-ray diffraction and Raman spectroscopy were used to track the reaction mechanisms associated with various solvents. A growth mechanism, distinct from that associated with TOP/OLA, promoted the formation of nanoparticles and improved the reactivity provided by the addition of IPDA solvent through double N-chelation. The reaction mechanism involved in stannite Cu2ZnSnSe 4 phase crystallization from Cu2SnSe3 and ZnSe is supported by theoretical analysis. The monodispersed CZTSe nanocrystals are polycrystalline and 20–30 nm in size. Optical measurements revealed a direct band gap of 1.42 eV. This study presents a relatively simple, low cost coordinating solvent route for the synthesis of CZTSe nanoparticles, applicable to the fabrication of low-cost thin-film solar cells. [ABSTRACT FROM PUBLISHER]

Cu(Zn, Sn)(CZT) metal precursors were deposited on glass substrates by an RF-magnetron sputtering method for use in CZT-based solar cells. Recently, researches have shown that CZT-based solar cell films prepared with a metal precursor with a rough surface morphology produce a low conversion efficiency. A single layer of tin (Sn) grown on a substrate has a rough surface morphology. In this study, the co-sputtering method was used, wherein Zn, Cu, and Sn layers were deposited on co-sputtered layers of Cu-Sn, Zn-Sn, and Cu-Zn, respectively. From an atomic force microscopy analysis, the root-mean-square surface roughness of the Zn/Cu-Sn layer was found to be 12.3∼14.3 times smaller than that of the other layers precursors, Cu/Zn-Sn, and Sn/Cu-Zn. [ABSTRACT FROM PUBLISHER]

A Cu2ZnSnSe4 (CZTSe) film was formed by the selenization of Cu(Zn, Sn) (CZT) alloy precursors. The CZT precursor was prepared by depositing zinc onto a layer of Cu-Sn co-sputtered on molybdenum-coated soda-lime glass. Selenium was evaporated on the CZT precursor. The CZTSe film was then annealed for a minute at various substrate temperatures ranging from 350°C to 650°C in steps of 50°C in a rapid thermal process using tungsten halogen lamps. The lattice parameters of the CZTSe annealed at temperatures over 500°C were found to be a = 5.709 Å and c = 11.351 Å. We also found that the energy gap of the CZTSe was 1.137 eV, which was independent of the annealing temperature. [ABSTRACT FROM PUBLISHER]

The compositional distribution of elements is known to be significant for the high conversion efficiency of CZTSe solar cells. As detailed understanding of the Cu/(Zn+Sn) ratio in the light absorption layer is important, CuZnSnSe (CZTSe) films grown via the co-evaporation process under different copper fluxes were characterized. It is difficult to evaluate the Cu content effect on the properties of CZTSe films grown using a co-evaporation process with Cu, Zn, Sn, and Se elemental effusion sources because the Cu flux variation during the process also induces other element ratio changes. Furthermore, the Zn/Sn ratio shows significant correlation to the Cu/(Zn+Sn) ratio variation in CZTSe thin films. Replacing the zinc metal effusion source with the ZnSe compound source resulted in less fluctuation in the Zn/Sn variation according to Cu flux change during the CZTSe co-evaporation. This can be useful in evaluating the effect of the different Cu ratios on the CZTSe solar cell characteristics. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

The dependence of carrier concentration on copper content in Cu2−xZnSnSe4 single crystals, grown without fluxing agents, is presented over the composition range Cu/(Zn + Sn) of 0.77–0.93 and Zn/Sn from 1.3 (low Cu content) to 1.3 (high Cu content). Single phase mono‐crystals with facets up to 5 mm are synthesized from high‐purity elements and validated using Laue diffraction. A direct optical band gap of 0.98 eV is observed for a crystal with Cu/(Zn + Sn) = 0.85. Van der Pauw–Hall resistance analysis shows decreasing hole concentration, from 1019 cm−3 to 2 × 1015 cm−3, with decreasing copper content over the composition range. Hole mobility varies from 50 cm2 V−1 s−1 to 160 cm2 V−1 s−1, with no dependence on copper concentration. A linear temperature dependence of the Seebeck coefficient is found for all crystals. The Seebeck coefficient–carrier concentration dependence is used to determine the valence band density of states, NV, and corresponding effective mass, μh*. Crystals with Cu/(Zn + Sn) < 0.9 have NV = 4 × 1018 cm−3 and μh* = 0.4 m0 while crystals with elevated copper concentration, Cu/(Zn + Sn) > 0.9, exhibit higher density of states, NV = 3 × 1019 cm−3 and hole effective mass μh* = 0.9 m0. The increased valence band density of states at elevated copper composition is consistent with more Cu–Zn exchange sites contributing to bulk defects and band edge fluctuations. Temperature‐dependent conductivity measurements indicate a transition from metallic‐type to semiconductor‐type conduction at Cu/(Zn + Sn) < 0.9. At lower copper content, for a crystal with Cu/(Zn + Sn) = 0.83 and p = 1017 cm−3 the activation energy for intrinsic conduction is 60 meV. This behavior is attributed to the copper vacancy defect, VCu, and is comparable to reported values obtained in thin films and by first‐principles predictions. [ABSTRACT FROM AUTHOR]

The performance‐boosting effect of alkali treatments is well known for chalcogenide thin‐film solar cells based on Cu(In,Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe–kesterite) absorbers. In contrast to heavier alkali elements, lithium is expected to alloy with the kesterite phase leading to the solid solution (LixCu1−x)2ZnSn(S,Se)4 (LCZTSSe), which offers a way of tuning the semiconductor bandgap by changing the ratio Li/(Li+Cu). Here is presented an experimental series of solution‐processed LCZTSSe with lithium fraction Li/(Li+Cu) ranging from x = 0 to 0.12 in the selenized absorber as measured by means of inductively coupled plasma mass spectrometry. The proportional increase in lattice parameter a and bandgap from 1.05 to 1.18 eV confirms the lithium alloying in the kesterite phase. Increase in grain size is observed for x up to 0.07, whereas a higher lithium fraction leads to a porous absorber morphology due to an inhomogeneous distribution of Li‐containing compounds in the kesterite layer. An increase of the photoluminescence quantum yield is observed as the Li fraction increases in the absorber layer. A champion device exhibits a remarkable efficiency of 11.6% (12.2% active area) for x = 0.06, close to the world record value of 12.6% demonstrating the effectiveness of lithium alloying. In contrast to the other alkali elements, Li can alloy in the mixed (LixCu1−x)2ZnSn(S,Se)4 kesterite phase by substituting for Cu, hence widening the bandgap. For an optimal Li fraction of Li/(Li+Cu) = 0.06, a solar cell with a maximum efficiency of 11.6% (illuminated area) is obtained. [ABSTRACT FROM AUTHOR]

In article number 1402178, Yi Zhang, Yun Sun, and co‐workers present a simple method to tailor the formation of the MoSe2 interface in Cu2ZnSnSe4 (CZTSe) thin film solar cells without an additional barrier. The ohm contact between the absorber layer and back contact is realized by the controlling thickness of the MoSe2 interface. The results make it possible to create an excellent current collection process from the CZTSe absorber to the Mo back contact. [ABSTRACT FROM AUTHOR]