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Integrating both electrical and light-modulated multi-type neuromorphic functions in a single synaptic memristive device holds the most potential for realizing next-generation neuromorphic systems, but is still challenging yet achievable. Herein, a simple bi-terminal optoelectronic synaptic memristor is newly proposed based on kesterite Cu2ZnSnS4, exhibiting stable nonvolatile resistive switching with excellent spatial uniformity and unique optoelectronic synaptic behaviors. The device demonstrates not only low switching voltage (−0.39 ± 0.08 V), concentrated Set/Reset voltage distribution (<0.08/0.15 V), and long retention time (>104 s) but also continuously modulable conductance by both electric (different width/interval/amplitude) and light (470–808 nm with different intensity) stimulus. These advantages make the device good electrically and optically simulated synaptic functions, including excitatory and inhibitory, paired-pulsed facilitation, short-/long-term plasticity, spike-timing-dependent plasticity, and "memory-forgetting" behavior. Significantly, decimal arithmetic calculation (addition, subtraction, and commutative law) is realized based on the linear conductance regulation, and high precision pattern recognition (>88%) is well achieved with an artificial neural network constructed by 5 × 5 × 4 memristor array. Predictably, such kesterite-based optoelectronic memristors can greatly open the possibility of realizing multi-functional neuromorphic systems. [ABSTRACT FROM AUTHOR]

Realizing the graded bandgap in absorber layer is very essential for high efficient thin film solar cells. However, such bandgap modification in kesterite-structured Cu2ZnSnSe4 is normally realized via high temperature sulfurization process (above 500°C), which is not only difficult to control the sulfurization depth, but also introduces additional deep defects because of the decomposition of absorber layer at such high temperature. In this study, a low-temperature sulfurization process (150°C) is developed. Such process not only inhibits the decomposition of Cu2ZnSnSe4 films and controls the elemental distribution very well, but also increase the surface bandgap of the absorber layer and form a gradient energy bandgap. Also, the density of deep-level defects in the Cu2ZnSnSe4 layer is reduced. As a consequence, the open circuit voltage of the solar cell is improved by 60 mV. This study paves the way towards the high efficient kesterite solar cell and other solar cells. [ABSTRACT FROM AUTHOR]

Realizing the graded bandgap in absorber layer is very essential for high efficient thin film solar cells. However, such bandgap modification in kesterite-structured Cu2ZnSnSe4 is normally realized via high temperature sulfurization process (above 500°C), which is not only difficult to control the sulfurization depth, but also introduces additional deep defects because of the decomposition of absorber layer at such high temperature. In this study, a low-temperature sulfurization process (150°C) is developed. Such process not only inhibits the decomposition of Cu2ZnSnSe4 films and controls the elemental distribution very well, but also increase the surface bandgap of the absorber layer and form a gradient energy bandgap. Also, the density of deep-level defects in the Cu2ZnSnSe4 layer is reduced. As a consequence, the open circuit voltage of the solar cell is improved by 60 mV. This study paves the way towards the high efficient kesterite solar cell and other solar cells. [ABSTRACT FROM AUTHOR]

Optoelectronic memristors hold the most potential for realizing next-generation neuromorphic computation; however, memristive devices that can integrate excellent resistive switching and both electrical-/light-induced bio-synaptic behaviors are still challenging to develop. In this study, an artificial optoelectronic synapse is proposed and realized using a kesterite-based memristor with Cu2ZnSn(S,Se)4 (CZTSSe) as the switching material and Mo/Ag as the back/top electrode. Benefiting from unique electrical features and a bi-layered structure of CZTSSe, the memristor exhibits highly stable nonvolatile resistive switching with excellent spatial uniformity, concentrated Set/Reset voltage distribution (variation <0.08/0.02 V), high On/Off ratio (>104), and long retention time (>104 s). A possible mechanism of the switching behavior in such a device is proposed. Furthermore, these memristors successfully achieve essential bio-synaptic functions under both electrical and various visible light (470–655 nm) stimulations, including electrical-induced excitatory postsynaptic current, paired pulse facilitation, long-term potentiation, long-term depression, spike-timing-dependent plasticity, as well as light-stimulated short-/long-term plasticity and learning-forgetting-relearning process. As such, the proposed neotype kesterite-based memristor demonstrates significant potential in facilitating artificial optoelectronic synapses and enabling neuromorphic computation. [ABSTRACT FROM AUTHOR]

Optoelectronic memristors hold the most potential for realizing next-generation neuromorphic computation; however, memristive devices that can integrate excellent resistive switching and both electrical-/light-induced bio-synaptic behaviors are still challenging to develop. In this study, an artificial optoelectronic synapse is proposed and realized using a kesterite-based memristor with Cu2ZnSn(S,Se)4 (CZTSSe) as the switching material and Mo/Ag as the back/top electrode. Benefiting from unique electrical features and a bi-layered structure of CZTSSe, the memristor exhibits highly stable nonvolatile resistive switching with excellent spatial uniformity, concentrated Set/Reset voltage distribution (variation <0.08/0.02 V), high On/Off ratio (>104), and long retention time (>104 s). A possible mechanism of the switching behavior in such a device is proposed. Furthermore, these memristors successfully achieve essential bio-synaptic functions under both electrical and various visible light (470–655 nm) stimulations, including electrical-induced excitatory postsynaptic current, paired pulse facilitation, long-term potentiation, long-term depression, spike-timing-dependent plasticity, as well as light-stimulated short-/long-term plasticity and learning-forgetting-relearning process. As such, the proposed neotype kesterite-based memristor demonstrates significant potential in facilitating artificial optoelectronic synapses and enabling neuromorphic computation. [ABSTRACT FROM AUTHOR]

Cd‐free high‐bandgap Cu2ZnSnS4 (CZTS) solar cells are expected to offer green and low‐cost solutions to single‐junction and tandem photovoltaic markets. Despite attracting considerable attention in past years, reported certified efficiency has yet to exceed the 10% threshold. Sn‐related defects, especially those originating from Sn2+ oxidation states, lead to severe recombination loss and limit device performance. Here, the formation of these detrimental defects is suppressed by creating a more benign chemical environment during sulfurization annealing. With dominant Sn4+ states in the source material and the precursor, the oxidation state of Sn remains primarily in its native Sn4+ state during annealing and in the final film. Engineering the Sn‐related defects leads to shallower tail states in bulk CZTS and fewer interfacial defects. As a result, both radiative and non‐radiative recombination losses are alleviated, contributing to a certified 10.7% efficiency of the Cd‐free high‐bandgap CZTS solar cell. This strategy may advance various kesterite materials and other technologies with multivalent constituents. [ABSTRACT FROM AUTHOR]

Tandem solar cells have the potential to be more efficient than the Shockley–Queisser limit imposed on single junction cells. In this study, optical and electrical modeling based on experimental data were used to investigate the possibility of boosting the performance of kesterite/c-Si tandem solar cells by inserting an alternative nontoxic TiO2 buffer layer into the kesterite top subcell. First, with SCAPS-1D simulation, we determined the data reported for the best kesterite (CZTS (Eg = 1.5 eV)) device in the experiments to be used as a simulation baseline. After obtaining metric parameters close to those reported, the influence on the optoelectronic characteristics of replacing CdS with a TiO2 buffer layer was studied and analyzed. Different top subcell absorbers (CZTS0.8Se0.2 (Eg = 1.4 eV), CZTS (Eg = 1.5 eV), CZTS (Eg = 1.6 eV), and CZT0.6Ge0.4S (Eg = 1.7 eV)) with different thicknesses were investigated under AM1.5 illumination. Then, to achieve current matching conditions, the c-Si bottom subcell, with an efficiency at the level of commercially available subcells (19%), was simulated using various top subcells transmitting light calculated using the transfer matrix method (TMM) for optical modeling. Adding TiO2 significantly enhanced the electrical and optical performance of the kesterite top subcell due to the decrease in parasitic light absorption and heterojunction interface recombination. The best tandem device with a TiO2 buffer layer for the top subcell with an optimum bandgap equal to 1.7 eV (CZT0.6Ge0.4S4) and a thickness of 0.8 µm achieved an efficiency of approximately 20%. These findings revealed that using a TiO2 buffer layer is a promising way to improve the performance of kesterite/Si tandem solar cells in the future. However, important optical and electrical breakthroughs are needed to make kesterite materials viable for tandem applications. [ABSTRACT FROM AUTHOR]

Featured Application: This work has the potential to have a great impact on wastewater treatment plants. The currently adopted methods for the degradation of emerging water micropollutants, such as Diclofenac, are not efficient enough, leading to only 20–40% degradation. Our photocatalyst is a cheap and sustainable tool that allows for up to 90% degradation over 120 min, even when just using visible light sources, meaning it is superior to the dangerous UV-driven photolysis typically observed for this class of compounds. Dangerous emerging water micropollutants like Diclofenac are harming ecosystems all over the planet, and immediate action is needed. The large bandgap photocatalysts conventionally used to degrade them need to be more efficient. Cu2ZnSnS4, a well-known light absorber in photovoltaics with a bandgap of 1.5 eV, can efficiently harvest an abundant portion of the solar spectrum. However, its photocatalytic activity has so far only been reported in relation to the degradation of organic dyes, and it is usually used as a benchmark to assess the activity of a photocatalyst without testing its actual potential on a hazardous water micropollutant conventionally encountered in primary and secondary waters. Here, we report the promising photocatalytic activity of Cu2ZnSnS4 nanoparticles in the degradation of Diclofenac, chosen as a benchmark for dangerous emerging water micropollutants. [ABSTRACT FROM AUTHOR]

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study. [ABSTRACT FROM AUTHOR]

Flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is attracting much attention because of their enormous application prospects. However, current flexible CZTSSe solar cells with Mo foil as substrate still suffer from severe back interface problems due to the complexity of substrate surfaces. Herein, a facile approach to tailor the surface of the flexible substrate and modify the back interface between CZTSSe and Mo foil is proposed. The study discloses that a simple polishing can not only improve the wettability of the precursor solution on the substrate unexpectedly and thus improve the quality of the CZTSSe film, but also increase the mechanical stability of the absorber layer grown on Mo foil. The subsequent UV‐ozone treatment helps to form a favorite MoO3 layer for efficient CZTSSe devices. Surprisingly, the quasi‐ohmic contact is formed between CZTSSe/Mo foil by such combined treatments and thus promoting the carrier collection. Consequently, the efficiency of the flexible CZTSSe solar cell is significantly improved from 4.94% to 10.32% without anti‐reflection layer. The bending durability of the cell fabricated on the treated Mo foil is increased greatly. This work discloses that back contact interface is very important for the carrier collection and thus the highly efficient flexible thin film solar cells. [ABSTRACT FROM AUTHOR]

It has been validated that enhancing crystallinity and passivating the deep‐level defect are critical for improving the device performance of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Coordination chemistry interactions within the Cu‐Zn‐Sn‐S precursor solution play a crucial role in the management of structural defects and the crystallization kinetics of CZTSSe thin films. Therefore, regulating the coordination environment of anion and cation in the precursor solution to control the formation process of precursor films is a major challenge at present. Herein, a synergetic crystallization modulation and defect passivation method is developed using P2S5 as an additive in the CZTS precursor solution to optimize the coordination structure and improve the crystallization process. The alignment of theoretical assessments with experimental observations confirms the ability of the P2S5 molecule to coordinate with the metal cation sites of CZTS precursor films, especially more liable to the Zn2+, effectively passivating the Zn‐related defects, thereby significantly reducing the defect density in CZTSSe absorbers. As a result, the device with a power conversion efficiency of 14.36% has been achieved. This work provides an unprecedented strategy for fabricating high‐quality thin films by anion‐coordinate regulation and a novel route for realizing efficient CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

To accurately determine the Schottky barrier characteristics and elucidate the consequent impacts, it is imperative to possess a comprehensive understanding of the conduction pathways within a Schottky barrier. The objective of this study was to examine the structural and electrical characteristics of a Schottky junction composed of an aluminum (Al) electrode, a p-type copper zinc tin sulfide (CZTS) thin film, and a molybdenum (Mo) substrate. The structural characterization of the material was conducted through the utilization of SEM analysis and EDX Spectra. On the other hand, the electrical characterization was accomplished by analyzing the current–voltage (I–V) characteristics. A significant part of the study is dedicated to validating the obtained CZTS solar cell parameters by simulating the I–V characteristic using extracted parameters and comparing them to experimental data. A comparative analysis of experimental and fitted I–V characteristics is presented, showcasing the effectiveness of the GA method in parameter extraction. The findings of this research contribute to the broader understanding of solar cell parameter optimization and offer a robust methodology for future applications in the field. [ABSTRACT FROM AUTHOR]

A Kesterite CZTS semiconductor contains earth-abundant elements and has been recognized as a promising absorber layer for highly efficient and low-cost thin-film solar cells. We present a numerical approach for analyzing the performance of CZTS-based photovoltaic cell with a non-toxic ZTO buffer layer through the use of a solar cell capacitance simulator. The performance of the p-CZTS/n-ZTO device has been examined in terms of ZTO buffer layer parameters such as thickness, donor concentration, mid-gap defect density, electron affinity and bandgap. The maximum cell efficiency obtained for the conduction band offset was 0.2 eV, which shows a small spike at the interface between the absorber and the buffer layers. In the optimized cell, the efficiency and fill factor were found to be 17.48% and 82.53%, respectively, which is the highest value reported so far. There are different kinds of current–voltage distortions observed, such as crossover and red-kink behavior, and the reason behind these distortions have been discussed. The results of this study provide valuable insights into the development of Cd-free highly efficient solar cells based on CZTS. [ABSTRACT FROM AUTHOR]

This work presents a copper zinc tin sulfide (CZTS)-based solar cell structure (AI/ITO/C60/CZTS/SnS/Pt) with C60 as a buffer layer, developed using the SCAPS-1D simulator by optimizing each parameter to calculate the output. Optimizing the parameters, the acceptor concentration and thickness were altered from 6.0 × 1015 cm−3 to 6.0 × 1018 cm−3 and 1500 nm to 3000 nm, respectively. Although, in this simulator, we can tune the value for the acceptor concentration to 6.0 × 1022, higher doping might present an issue regarding adjustment in the physical experiment. Thus, tunable parameters need to be chosen according to the reliability of the experimental work. The defect density varied from 1.0 × 1014 cm−3 to 1.0 × 1017 cm−3 and the auger hole/electron capture coefficient was determined to be 1.0 × 10−26 cm6 s−1 for the maintenance of the minorities in theoretical to quasi-proper experimental measurements. Although the temperature was intended to be kept near room temperature, this parameter was varied from 290 K to 475 K to investigate the effects of the temperature on this cell. The optimization of the proposed structure resulted in a final acceptor concentration of 6.0 × 1018 cm−3 and a thickness of 3000 nm at a defect density of 1.0 × 1015 cm−3, which will help to satisfy the desired experimental performance. Satisfactory outcomes (VOC = 1.24 V, JSC = 27.03 mA/cm2, FF = 89.96%, η = 30.18%) were found compared to the previous analysis. [ABSTRACT FROM AUTHOR]

Solution‐processed kesterite (copper zinc tin sulfide [CZTS]) solar cells attract significant attention owing to their low cost, ease of large‐scale production, and earth‐abundant elemental composition, which make these devices promising to fulfill the ever‐increasing demand of the photovoltaic (PV) industry. Compared to the performances of expensive vacuum‐based techniques, colloidal nanocrystal kesterite solar cells garner substantial interest due to their economical and rapid processing. Led by the hot‐injection method, organic solvent‐based techniques are widely adopted to realize CZTS nanocrystal inks. With organic solvents, ligand‐stabilized nanoparticles are formed leading to dispersive and homogenous kesterite inks. However, the presence of carbon‐rich ligands around the nanocrystal surface often leads to the formation of a fine‐grain layer that is rich in carbon content. The organic ligands decompose into amorphous carbon residues during a high‐temperature annealing process and hinder the grain growth process. The carbon‐rich fine‐grain (CRFG) layer generally poses a negative influence on the PV performance of the kesterite solar cell; however, few reports maintain their disposition about CRFG as innocuous. In this review study, a detailed discussion on CRFG is presented, aiming to understand the insights about its formation and impact on the device's performance. [ABSTRACT FROM AUTHOR]

Advancements in solar cell research are constantly pushing the boundaries of energy efficiency and sustainability. Kesterite materials have gained attention for their positive environmental impact and are being considered as promising candidate for renewable energy. These materials show potential for improving efficiency through creative structural modifications. Quantum well (QW) solar cells, utilizing kesterite materials, provide a combination of high efficiency, cost‐effectiveness, and environmental sustainability. These materials have a wide range of applications, from residential and commercial solar panels to portable and flexible devices, building‐integrated photovoltaics, off‐grid systems, and even space applications. This study investigates the improvement of solar cell efficiency by incorporating kesterite‐based nanostructures with quantum confinement technology. The key aspects of the analysis are measure performance of solar cell with variation in S/Se mole fraction of CZTSSe absorber layer. The special care is given to analyze behavior of QW structures with CZTSSe as the well material. Additionally, the study is expanded to an analysis of broad range of mole fraction variation in CZTSSe. Finally, the structure is optimized by adjusting the well width. Moreover, a remarkable efficiency of 31.33% is achieved with well width of 20 nm and the mole fraction of 0.8. This finding highlights the importance of customizing composition and nanostructure in solar cell design to improve efficiency and push forward renewable energy technologies. [ABSTRACT FROM AUTHOR]

The lack of attractive n-type thermoelectric materials greatly restricts their applications because most high-performance materials are p-type conductors, such as the kesterite compound Cu2ZnSnS4. This study reports high-quality n-type kesterite (Cu1−xAgx)2ZnSnS4 (CAZTS) single crystals that exhibit a record high dimensionless figure of merit value of 1.1 at approximately 800 K, primarily owing to Ag alloying, cation compositional optimization, and intrinsic low thermal conductivity. An n-type CAZTS-based single-leg device was fabricated using a Mo-barrier layer. The device exhibited a thermoelectric conversion efficiency of 3.4% at a temperature gradient of 473 K. This study provides insights into developing thermoelectric modules using environmentally friendly kesterite materials. [ABSTRACT FROM AUTHOR]

Herein, the 1D Solar Cell Capacitance Simulator software is used to perform numerical analysis of thin‐film solar cells with Cu2ZnSnS4, Cu2BaSnS4, Cu2FeSnS4, and Cu2MnSnS4 absorber layers. The main goal is to investigate the impact of parameters, such as absorber layer thickness, acceptor density, buffer layer, bandgap, and donor density, on the efficiency of these solar cells. The absorber layer investigation entails varying the thickness and the acceptor density to evaluate their influence on the efficiency of the solar cell. A new zinc oxide sulfide (Zn(O,S)) buffer layer is also introduced instead of the conventional cadmium sulfide (CdS) buffer layer. The Zn(O,S) bandgap and its donor density, which are investigated in terms of how they affect the efficiency of the solar cells, have been varied. The optimal values for the thickness of the absorber layer, acceptor density, and the bandgap of the buffer layer are calculated. Subsequently, the donor density is evaluated to find any potential defects that may affect the efficiency of the solar cell. These results confirm that Zn(O,S) can be utilized as a buffer layer. This study concludes that Cu2ZnSnS4, Cu2BaSnS4, and Cu2MnSnS4 absorber layers have superior efficiency in comparison with Cu2FeSnS4. [ABSTRACT FROM AUTHOR]

Pertaining to the optimal band alignment of ZnO and CZTS, the heterostructure was fabricated with CZTS as the absorber layer and ZnO being the buffer layer coated on the FTO glass for photovoltaic application. Both the layers were deposited by using sol–gel spin coating technique. The results revealed the polycrystalline nature of both ZnO and CZTS films with distinct phase formations, with ZnO exhibiting prominent diffraction peaks at 31.77, 34.31, 36.20, 47.47, and 56.59° corresponding to (100), (002), (101), (102), and (110) planes, while CZTS showed diffraction peaks at (112), (220), and (312) planes. ZnO thin films demonstrated high optical transmittance (∼90%) and exhibited a wide band gap of 3.24 eV, while CZTS demonstrated a band gap of 1.44 eV. AFM images showed smooth surfaces with favorable topography for both films. Hall effect measurements indicated differences in electrical properties of the two films. Raman spectroscopy revealed vibrational energy patterns in both films. Additionally, current–voltage (I-V) characteristics revealed the electrical behavior of the ZnO/CZTS heterojunction, shedding light on its diode characteristics under both dark and illuminated conditions. With CZTS’s ideal band gap of 1.44 eV, sunlight is easily absorbed, and ZnO’s high electron mobility makes it an effective layer for electron transport. As a result, power conversion efficiency can be improved. [ABSTRACT FROM AUTHOR]

The built‐in field (Ebi) is a key factor for the dynamic of carrier transport in the heterojunction interface, thus determining the photovoltaic performance of the solar cell, such as Cu2ZnSn(S,Se)4 (CZTSSe) cell. It is critical to improve the carriers' transport across the pn heterojunction for the fabrication of highly efficient solar cells. In this work, the large electric field of ferroelectric BaTiO3 nanoparticles (BTO NPs) is used to tailor the carrier transport in the CZTSSe solar cells by embedding BTO NPs into the interface of CZTSSe/CdS heterojunction. It is very surprising that a polarization electric field (EP) with the same direction of Ebi synergically enhances carrier transport greatly and increases the PCE by 20.6%. Further study on the mechanism discloses that BTO NPs reduce the work function of CZTSSe and CdS and form interfacial dipoles at their interface, which is conducive to the photogenerated electrons to be collected by the electron transport layer. This strategy also works well on other thin film solar cells and gives a new aspect of strengthening the carrier transport between p–n heterojunction. [ABSTRACT FROM AUTHOR]

In this research, a front layer of indium tin oxide (ITO) is added on the top surface of copper zinc tin sulfide (CZTS)/zinc oxide (ZnO) thin film solar cell. The goal of this paper is to improve the absorption values against the angle of incidence through visible wavelengths. The transfer matrix approach and the finite element method were extensively used in the design and simulation process. The numerical findings are investigated with the help of COMSOL multiphysics software as well. Recently, it has been found that the angle of incidence significantly reduces the solar cell absorption. To prevent such increment of absorption losses as the angle of incidence rises, the numerical findings have deduced that it may therefore be of interest to include an anti-reflecting coating of ternary one-dimensional photonic crystals on a single unit cell. Meanwhile, the anti-reflective coating is designed with three different geometries: planar, convex, and concave. The investigated results demonstrated that the concave geometry is efficient in controlling the absorption losses of the designed CZTS/ZnO thin film solar cell against the increase in the angle of incidence. In this regard, for an angle of incidence less than 50°, the solar cell absorption values remain greater than 0.9055 all over the visible spectrum. Therefore, a relatively high performance of this cell is strongly expected. [ABSTRACT FROM AUTHOR]

The perovskite crystals formed by methylammonium lead iodide (MAPbI3) have garnered growing interest owing to their exceptional photovoltaic capabilities, economical production process, and ability to be processed in solution. A multitude of techniques have been devised to produce dense and uniform perovskite thin coatings, which are critical for the proper functioning of electronic devices. In order to promote the development of CH3NH3PbI3 perovskite thin films that are uniform, dense, and exceptionally smooth, we present an additive-assisted method utilizing Copper zinc tin sulfide Cu2ZnSnS4 (CZTS) nanoparticles. The surface, optical, morphological, and structural properties were subsequently determined. The mechanisms by which the additive improves the quality of the material during the formation of CH3NH3PbI3 perovskite films are elucidated in this study. These processes are postulated to characterize the crystallization of the films. Using this beneficial technique, a high-quality CH3NH3PbI3 film with a grain size significantly larger than 1.6 μm was effectively manufactured. Additionally, the doping process resulted in enhancements in both absorption and photoluminescence intensity. The addition of CZTS NPs elevated the crystal structures and morphologies of the CH3NH3PbI3 layer to a degree that was comparatively favorable. This was evidenced by the crystallite size of 83 nm and an optical bandgap (Eg) of 1.63 eV, both of which attest to the enhanced quality of the film. With the structure of glass/FTO/TiO2/CH3NH3PbI3:CZTS NPs/spiro-oMeTAD/Au ,the power conversion efficiency (PCE) of the best cell was 15.13% with a fill factor of 66.07%. The results of this study indicate that doping CH3NH3PbI3 solar cells with CZTS NPs is a dependable method for enhancing photovoltaic performance and promoting crystal growth. [ABSTRACT FROM AUTHOR]

In recent years, the primary reasons for low efficiency Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells have been attributed to Sn Zn defects and related defect clusters, as well as the balance of absorption layer bandgap for short-circuit current density (J sc) and open-circuit voltage (V oc). Ge gradient has been theoretically proven to be an effective strategy to change traditional flat bandgap structure and suppress Sn Zn defects and related defect clusters for improving the device performance of CZTSSe solar cells. However, the potential of Ge gradient has not been fully verified. In this work, Ge doping effectively reduces the formation of Sn Zn defects and [2Cu Zn + Sn Zn ] defect clusters in the CZTSSe absorption layer. In addition, it can be found that the construction of the V-type bandgap is the best solution for balancing between V oc and J sc. By using the bandgap grading strategy, the disparity between the recombination barrier of the junction and the optical bandgap's minimum value is widened, thereby obtaining a large V oc. The V-type doped device has the highest efficiency when V oc is 0.45 V, which can reach 8.03%. This Ge graded substitution method provides an alternative absorption layer structure for improving V oc and the preparation of future high-efficiency kesterite photovoltaic devices. [ABSTRACT FROM AUTHOR]

Abstract It has been validated that enhancing crystallinity and passivating the deep‐level defect are critical for improving the device performance of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Coordination chemistry interactions within the Cu‐Zn‐Sn‐S precursor solution play a crucial role in the management of structural defects and the crystallization kinetics of CZTSSe thin films. Therefore, regulating the coordination environment of anion and cation in the precursor solution to control the formation process of precursor films is a major challenge at present. Herein, a synergetic crystallization modulation and defect passivation method is developed using P2S5 as an additive in the CZTS precursor solution to optimize the coordination structure and improve the crystallization process. The alignment of theoretical assessments with experimental observations confirms the ability of the P2S5 molecule to coordinate with the metal cation sites of CZTS precursor films, especially more liable to the Zn2+, effectively passivating the Zn‐related defects, thereby significantly reducing the defect density in CZTSSe absorbers. As a result, the device with a power conversion efficiency of 14.36% has been achieved. This work provides an unprecedented strategy for fabricating high‐quality thin films by anion‐coordinate regulation and a novel route for realizing efficient CZTSSe solar cells.

Concernin the crucial interfacial issues in multi-layered kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, (NH4)2S treatment has been proven to be effective in eliminating surface secondary phases. While for the CZTSSe absorbers without impurity phases, what can the low-temperature (NH4)2S treatment do to the absorbers, thus to the device performance? Herein, the chloride-fabricated CZTSSe absorbers are surface treated with the (NH4)2S solution at room temperature, and its influence on the device performance is investigated in detail. Surprisingly, such treatment can make the absorbers' surface become nearly super-hydrophilicity, greatly decreasing the surface wetting angle from 63.1° ± 3.4° to 7.3° ± 0.6° after 50 min-treating, and thus lead to marked differences in the interfacial properties of the CdS/CZTSSe heterojunctions deposited in a chemical bath. Consequently, for the best-performing CZTSSe cells, combining the passivated interfacial defects, increased carrier concentration, reduced carrier recombination, and prolonged minority lifetime, the efficiency is improved from 6.54% to 9.88%, together with the 37 mV and 7.9% increase in VOC and FF, respectively. This study confirms the newfound results that the (NH4)2S treatment can effectively adjust the wettability of the absorbers to form high-quality heterojunctions to boost the device efficiency, which would be valuable for an in-depth understanding of the intrinsic mechanisms of interfacial processing. [ABSTRACT FROM AUTHOR]

The use of kesterite materials in photovoltaic solar cells holds great promise due to their abundance, non-toxic nature, cost-effectiveness, and excellent optoelectronic properties. However, the power conversion efficiency of kesterite solar cells remains considerably below the Shockley-Queisser limit efficiency. This underscores the need for continuous development of new cell designs to maximize kesterite's potential for solar energy conversion. In this study, we presented a novel design for a kesterite solar cell incorporating semi-ellipsoidal nanostructures into the active layer to overcome its limitations and achieve higher efficiencies. Comprehensive simulations were conducted to study the effect of these nanostructures on solar cell performance. An extensive parametric study was also performed to identify the design parameters for the best performance. The results revealed that the presence of nanostructures significantly enhances power conversion efficiency, reaching a remarkable 17.6%, overcoming many challenging obstacles facing kesterite solar cells and making them more competitive in the ever-expanding solar cell market.

Charge loss at grain boundaries of kesterite Cu2ZnSn(S, Se)4 polycrystalline absorbers is an important cause limiting the performance of this emerging thin-film solar cell. Herein, we report a Pd element assisted reaction strategy to suppress atomic vacancy defects in GB regions. The Pd, on one hand in the form of PdSex compounds, can heterogeneously cover the GBs of the absorber film, suppressing Sn and Se volatilization loss and the formation of their vacancy defects (i.e. VSn and VSe), and on the other hand, in the form of Pd(II)/Pd(IV) redox shuttle, can assist the capture and exchange of Se atoms, thus contributing to eliminating the already-existing VSe defects within GBs. These collective effects have effectively reduced charge recombination loss and enhanced p-type characteristics of the kesterite absorber. As a result, high-performance kesterite solar cells with a total-area efficiency of 14.5% (certified at 14.3%) have been achieved. Charge loss at grain boundaries of kesterite polycrystalline absorbers limits the performance of thin film solar cells. Here, authors report the use of Pd(II)/Pd(IV) redox shuttle to assist the capture and exchange of Se atoms and eliminate vacancy defects, realizing certified efficiency of 14.3%. [ABSTRACT FROM AUTHOR]

The unsatisfactory material quality of absorber is an important factor limiting the development of Cu2ZnSn(S,Se)4 (CZTSSe) thin‐film solar cells, including poor crystallization, multi‐layer structure, and various defects. Here, an effective strategy to enhance the quality of kesterite absorber and improve the performance of solar cells is proposed by tailoring the additional sequence of metal ions in precursor solution. With an addition sequence S─Sn─Cu─Zn (STCZ), higher values of Cu+/Cu2+ and Sn4+/Sn2+ ratios are obtained, and the surface grain growth is modulated into an inclined growth mode. Consequently, the decomposition of CZTSSe bulk is suppressed and its final morphology presents mainly as large grains spanning across the absorber. The quality of absorber and its interface is enhanced with activating the desirable shallow acceptor and reducing recombination center defects. An encouraging efficiency of over 12% for CZTSSe solar cells with increased short‐circuit current density and fill factor is realized. This novel strategy provides insight into crystallization mechanism of kesterite photovoltaic material and has guiding significance for further improving material crystallization and absorber quality. [ABSTRACT FROM AUTHOR]

The majority of numerical research on kesterite tandem solar cells has predominantly focused on a two‐terminal (2T) configuration that utilizes an ideal tunnel junction. Herein, the performance of kesterite tandem solar cells by introducing a photonic crystal structure (1DPC) as intermediate layer in both three‐terminal (3T) and four‐terminal (4T) configurations is investigated. The photonic crystal (1DPC) is designed by stacking ITO and SiO2 layers with the terminal layer consisting of NiO. Optical properties of the 1DPC are modeled. This innovative approach offers several advantages. 1) The 1DPC selectively reflects lower wavelengths, effectively enhancing the short‐circuit current density (Jsc) of the top subcell, while the solar irradiance spectrum at higher‐wavelength optimum for the subcell is not affected. 2) The 1DPC serves as an intermediate electrode, needed for the 3T or 4T configuration. 3) Replacing the conventional Mo back contact with a NiO layer significantly boosts the open‐circuit voltage (Voc) of the top subcell. The findings demonstrate that these configurations exhibit higher performance compared to previously reported results. Furthermore, the utilization of 3T and 4T configurations, incorporating the 1DPC as an electrical beam splitter, provides an effective and accurate design compared to the 2T configuration using ideal tunnel junctions. [ABSTRACT FROM AUTHOR]

The fabrication of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin‐film solar cells using the electrochemical deposition (ED), which is valued for its industrial feasibility, offers a cost‐effective and environmentally friendly approach to the carbon‐free and clean energy production. However, the reported power conversion efficiency of approximately 10 % for electrodeposited CZTSSe thin‐film solar cells is lower compared to the alternative methods like sputtering and spin‐coating, which is mainly attributed to the phase inhomogeneity and the rough morphology generated during the ED process. Ensuring the microscopic and macroscopic uniformity of the electrodeposited films is crucial for the improvement of the film quality and the device performances. In this review, strategies to address these challenges including the intrinsic film control such as the deposition mode, pH, concentration of metal ions, and complexing agents, as well as the extrinsic approaches such as doping, substitution of metal elements, and the introduction of interfacial layers. In addition, the prospects for the electrochemically deposited CZTSSe solar cells were presented, focusing on the promising applications in tandem, flexible, and solar water‐splitting devices. Finally, this review will provide technical insights into the ED process for preparing CZTSSe solar cells, outlining a perspective for the future development of highly efficient CZTSSe thin film solar cells. [ABSTRACT FROM AUTHOR]

Despite its growing popularity as a solar material, there is no comprehensive reference to aid with determining various polymorphs of copper zinc tin sulfide (CZTS) in the lab. Understanding the diverse electronic, optical and vibrational properties of these polymorphs is crucial to further enhance the conversion efficiency of CZTS solar cells. Here, findings are presented that suggest the effective hole mass in a monoclinic polymorph, that is likely to form along with the more commonly reported tetragonal variations, is about 10 times heavier than that of its tetragonal counterparts, thereby affecting key attributes such as carrier transport and concentration. Among tetragonal polymorphs, the so‐called primitive mixed CuAu (PMCA) arrangement is likely to undergo a direct‐indirect gap transition due to internal strains. Optical absorption between different polymorphs could also vary by up to 90% in the visible spectrum. Finally, accurate Raman footprint of each polymorph is predicted to help establish a definitive method for their detection. From a modeling perspective, Becke‐Lee‐Yang‐Parr with spin‐orbit coupling is shown to be a superior yet 100X faster alternative to hybrid functionals when applied to studying electronic structure of CZTS. [ABSTRACT FROM AUTHOR]

Kesterite is an earth‐abundant energy material with high predicted power conversion efficiency, making it a sustainable and promising option for photovoltaics. However, a large open circuit voltage Voc deficit due to non‐radiative recombination at intrinsic defects remains a major hurdle, limiting device performance. Incorporating Ge into the kesterite structure emerges as an effective approach for enhancing performance by manipulating defects and morphology. Herein, how different amounts of Ge affect the kesterite growth pathways through the combination of advanced microscopy characterization techniques are systematically investigated. The results demonstrate the significance of incorporating Ge during the selenization process of the CZTSSe thin film. At high temperature, the Ge incorporation effectively delays the selenization process due to the formation of a ZnSe layer on top of the metal alloys through decomposition of the Cu‐Zn alloy and formation of Cu‐Sn alloy, subsequently forming of Cu‐Sn‐Se phase. Such an effect is compounded by more Ge incorporation that further postpones kesterite formation. Furthermore, introducing Ge mitigates detrimental "horizontal" grain boundaries by increasing the grain size on upper layer. The Ge incorporation strategy discussed in this study holds great promise for improving device performance and grain quality in CZTSSe and other polycrystalline chalcogenide solar cells. [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]

This work presents a facile hydrothermal synthesis method for fabricating a multifunctional composite of copper zinc tin sulfide (CZTS) nanoparticles coated onto sepiolite fibers. Morphological analysis confirms the firm attachment of approximately 10 nm CZTS nanoparticles onto the sepiolite surface. Elemental analysis verifies the presence of constituent elements from both CZTS and sepiolite, with a slight deficiency in Cu and an abundance of Zn observed. The compositional formula of CZTS in the composite is estimated as Cu1.93Zn1.05Sn0.98S4.04. Notably, the material exhibits a narrow band gap of 1.5 eV, enabling effective utilization of the entire visible light spectrum, making it promising for photocatalytic applications. BET nitrogen adsorption/desorption measurements reveal a substantial surface area of approximately 85.720 m²/g, confirming the composite's versatility and applicability, particularly in photocatalysis and adsorption processes. Additionally, X-ray diffraction analysis indicates reflections consistent with the crystal structures of kasterite CZTS and sepiolite, further confirming the composite's composition. The multifunctional CZTS/Sepiolite composite demonstrates exceptional potential for simultaneous photocatalytic degradation and adsorption of organic pollutants, presenting a promising avenue for sustainable water treatment applications. [ABSTRACT FROM AUTHOR]

Third-generation solar cells have emerged as a potential solution to the effectiveness and stability issues encountered in conventional solar technology. This study focuses on the characteristics of copper-zinc-tin-sulfide (CZTS) thin films inside this innovative architectural framework, which is an important step toward improving third-generation solar cells by incorporating a p-type silicon layer. This integrated method provides a versatile and manageable setting for film deposition, underscoring the effort put into creating high-quality CZTS thin films. Using X-ray diffraction (XRD), the study assessed the structural change of CZTS films after annealing, finding that kesterite phases were dominant. Images captured by a scanning electron microscope (SEM) reveal the microstructure and surface morphology of CZTS-coated Silicon nanowires (Si-NWs). A detailed analysis of the current-voltage characteristics provides evidence of the operational potential of the Si-NWs-CZTS coated solar cell. Significant performance parameters observed include a Voc value of 0.45 ± 0.02V, Isc value of 8.25 ± 0.30 mA/cm², FF value of 24 ± 2%, and η value of 1.0 ± 0.1%. The encouraging results indicate the capacity of using P-type silicon to enhance the performance of third-generation solar cells. [ABSTRACT FROM AUTHOR]

Kesterite solar cells often suffer from low open‐circuit voltage due to interface recombination. To address this, a passivation approach is explored using a dielectric layer between the absorber and buffer layer, coupled with a point contact structure. In this method, carrier transport is enabled through point contacts while effectively passivating regions covered by oxide. In this study, although forming point contacts on the front surface poses processing challenges, a novel solution is presented. Herein, in situ formed ZnS nanoparticles (NPs) during Cu2ZnSn(S, Se)4 (CZTSSe) absorber fabrication is utilized as a nanomask for front surface point contacts. A thin TaOx layer, acting as the passivation layer, is deposited over the CZTSSe surface with ZnS NPs by using atomic layer deposition (ALD). The selective removal of these NPs by deionized water soaking creates size‐controlled point contacts without damaging the absorber surface. In this approach, the first successful implementation of TaOx in enhancing CZTSSe solar cell efficiency, which jumps from 6.17% to 9.02% due to this strategy, is marked. The passivation mechanism involves sodium attraction during ALD, reduced interface defects, and the generation of positive fixed oxide charges. In this innovative method, not only solar cell efficiency is improved but new insights are also provided into using secondary phases as nanomasks in interface engineering. [ABSTRACT FROM AUTHOR]

In the era of green sustainable energy, the quest for lead-free and nontoxic materials is driven by the need to meet the increasing energy demands of the twenty-first century. In this scenario, copper zinc tin sulfide (CZTS)-based solar cells could be a viable option due to their suitable band alignment and cost-effectiveness. This study investigates CZTS-based solar cells through the use of five potential electron transport layers (ETLs) via the SCAPS-1D simulation software and modeling framework. Initially, all possible combinations, namely In2S3/CZTS, WS2/CZTS, CdS/CZTS, ZnS/CZTS, and SnS2/CZTS, and their generation–recombination (GR) profiles were considered in order to analyze the efficiency of the solar cells. Additionally, calibration of the device was performed to analyze the performance of the solar cells, while considering several electrical and optical factors including acceptor density and interfacial defect density. The study investigated the influence of series and shunt resistance on the performance of SnS2/CZTS solar cells among the five studied configurations. Results showed that the performance of solar cells is influenced by temperature, leading to variations in the output parameters over a temperature range from 300 K to 400 K. Finally, the findings of the study demonstrate that the utilization of SnS2 as the ETL material in conjunction with CZTS as the absorber layer material yielded maximum efficiency of 21.89%, open-circuit voltage (Voc) of 0.97 V, short-circuit current density (Jsc) of 26.53 mA/cm2, and fill factor (FF) of 84.86%. These findings demonstrate significant potential in advancing the production of CZTS-based solar cells characterized by high efficiency, affordability, and environmental safety. [ABSTRACT FROM AUTHOR]

This review emphasizes the recent advancements and prospects of thin-film kesterite-based photovoltaic (PV) applications using magnesium, iron and nickel. The quest for novel materials employed in solar cells has resulted in incorporating these elements into the composition of kesterite as substitutes or modifiers (dopants) for zinc. This integration has induced notable repercussions on the structural, optoelectronics and morphological properties, which are reviewed. The first section of this paper offers a comprehensive review of the general characteristics of kesterite minerals. These crucial materials exhibit a high absorption coefficient (104 cm–1) and an optical band gap of 1.0–1.8 eV. Moreover, they are free of critical raw materials, non-toxic and sustainable. The second section depicts the substitution or modification of zinc by magnesium in kesterite. Additionally, this paper provides a comprehensive review of the quaternary and pentanary systems Cu2MgSn(S,Se)4 and Cu2Zn1– x Mg x SnS4, highlighting their advantages and drawbacks. In the last section, a review of the quaternary or pentanary systems is conducted, namely Cu2Zn x Fe1– x SnS4 and Cu2Zn x Ni1– x SnS4, along with their effects on optoelectronic properties. In conclusion, various methods for obtaining modified or substituted kesterite materials using magnesium, iron and nickel have demonstrated sustainability, scalability for industrial production and potential candidacy as substitutes for conventional PV materials. The prospects for pentanary materials (Cu2Zn1‑xMgxSnS4, Cu2Zn1‑xFexSnS4 and Cu2Zn1‑xNixSnS4) are to overcome the efficiency record of kesterite reported in 2014, which was 12.6 % for Cu2ZnSn(S,Se)4, and to enhance its optoelectronic properties through synthesis conditions that comply with the principles of green chemistry. [ABSTRACT FROM AUTHOR]

Thermogravimetry coupled with thermal analysis and quadrupole mass spectroscopy TGA/DTA-QMS were primarily used to assess the oxidation susceptibility of a pool of nanocrystalline powders of the semiconductor kesterite Cu2ZnSnS4 for prospective photovoltaic applications, which were prepared via the mechanochemically assisted synthesis route from two different precursor systems. Each system, as confirmed by XRD patterns, yielded first the cubic polytype of kesterite with defunct semiconductor properties, which, after thermal annealing at 500 °C under neutral gas atmosphere, was converted to the tetragonal semiconductor polytype. The TGA/DTA-QMS determinations up to 1000 °C were carried out under a neutral argon Ar atmosphere and under a dry, oxygen-containing gas mixture of O2:Ar = 1:4 (vol.). The mass spectroscopy data confirmed that under each of the gas atmospheres, a distinctly different, multistep evolution of such oxygen-bearing gaseous compounds as sulfur oxides SO2/SO3, carbon dioxide CO2, and water vapor H2O was taking place. The TGA/DTA changes in correlation with the nature of evolving gases helped in the elucidation of the plausible chemistry linked to kesterite oxidation, both in the stage of nanopowder synthesis/storage at ambient air conditions and during forced oxidation up to 1000 °C in the dry, oxygen-containing gas mixture. [ABSTRACT FROM AUTHOR]

Incorporating substitutional elements from groups I, II and IV is an important approach to improve the quality of kesterite thin films. Among the elements, Ag and Ge are most effective in promoting the performance of Cu2ZnSn(S,Se)4 solar cells. Although several theoretical and experimental studies have been conducted on the Ag/Ge-alloyed kesterite, there are significant differences in the reported morphological characteristics, photovoltaic performance and even the optimal Ag/Ge substitution ratio due to different preparation processes utilized, which leads to difficulties in comparing the Ag-incorporated and Ge-incorporated kesterite solar cells. Currently, there is little literature on the comparative study concerned. Herein, we fabricated Ag-alloyed and Ge-alloyed kesterite solar cells based on the same solution method and process conditions, and laterally compared the effects of Ag substitution and Ge substitution on the phase compositions, morphologies, optical bandgaps, minority carrier lifetime and device performance of kesterite Cu2ZnSn(S,Se)4 thin films. [ABSTRACT FROM AUTHOR]

Dangerous emerging water micropollutants like Diclofenac are harming ecosystems all over the planet, and immediate action is needed. The large bandgap photocatalysts conventionally used to degrade them need to be more efficient. Cu2ZnSnS4, a well-known light absorber in photovoltaics with a bandgap of 1.5 eV, can efficiently harvest an abundant portion of the solar spectrum. However, its photocatalytic activity has so far only been reported in relation to the degradation of organic dyes, and it is usually used as a benchmark to assess the activity of a photocatalyst without testing its actual potential on a hazardous water micropollutant conventionally encountered in primary and secondary waters. Here, we report the promising photocatalytic activity of Cu2ZnSnS4 nanoparticles in the degradation of Diclofenac, chosen as a benchmark for dangerous emerging water micropollutants.

Tandem solar cells have the potential to be more efficient than the Shockley–Queisser limit imposed on single junction cells. In this study, optical and electrical modeling based on experimental data were used to investigate the possibility of boosting the performance of kesterite/c-Si tandem solar cells by inserting an alternative nontoxic TiO2 buffer layer into the kesterite top subcell. First, with SCAPS-1D simulation, we determined the data reported for the best kesterite (CZTS (Eg = 1.5 eV)) device in the experiments to be used as a simulation baseline. After obtaining metric parameters close to those reported, the influence on the optoelectronic characteristics of replacing CdS with a TiO2 buffer layer was studied and analyzed. Different top subcell absorbers (CZTS0.8Se0.2 (Eg = 1.4 eV), CZTS (Eg = 1.5 eV), CZTS (Eg = 1.6 eV), and CZT0.6Ge0.4S (Eg = 1.7 eV)) with different thicknesses were investigated under AM1.5 illumination. Then, to achieve current matching conditions, the c-Si bottom subcell, with an efficiency at the level of commercially available subcells (19%), was simulated using various top subcells transmitting light calculated using the transfer matrix method (TMM) for optical modeling. Adding TiO2 significantly enhanced the electrical and optical performance of the kesterite top subcell due to the decrease in parasitic light absorption and heterojunction interface recombination. The best tandem device with a TiO2 buffer layer for the top subcell with an optimum bandgap equal to 1.7 eV (CZT0.6Ge0.4S4) and a thickness of 0.8 µm achieved an efficiency of approximately 20%. These findings revealed that using a TiO2 buffer layer is a promising way to improve the performance of kesterite/Si tandem solar cells in the future. However, important optical and electrical breakthroughs are needed to make kesterite materials viable for tandem applications.

The double gradient bandgap absorber has the potential to enhance carrier collection, improve light collection efficiency, and make the performance of solar cells more competitive. However, achieving the double gradient bandgap structure is challenging due to the comparable diffusion rates of cations during high‐temperature selenization in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) films. Here, it has successfully achieved a double gradient bandgap in the CZTSSe absorber by spin‐coating the K2S solution during the preparation process of the precursor film. The K2S insertion serves as an additional S source for the absorber, and the high‐affinity energy of K‐Se causes the position of the spin‐coated K2S solution locally Se‐rich and S‐poor. More importantly, the position of the bandgap minimum (notch) and the depth of the notch can be controlled by varying the concentration of K2S solution and its deposition stage, thereby avoiding the electronic potential barrier produced by an inadvertent notch position and depth. In addition, the K─Se liquid phase expedites the selenization process to the elimination of the fine grain layer. The champion CZTSSe device achieved an efficiency of 13.70%, indicating the potential of double gradient bandgap engineering for the future development of high‐efficiency kesterite solar cells. [ABSTRACT FROM AUTHOR]

In this study, CZTS (Copper Zinc Tin Sulfide) thin films were fabricated using the pulse laser deposition (PLD) technique. Pellets formed under a pressure of 5 tons were ablated with a Nd:YAG laser at a pulse energy of 700 mJ. The resulting plasma plume was generated through a range of pulse counts--200, 250, 300, 350, and 400--at a consistent frequency of 6 Hz. The structural properties of the films were investigated via X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD analysis revealed a polycrystalline tetragonal structure of the CZTS thin films, with an increase in peak quantity correlating to higher pulse counts. Concurrently, variations in grain size, strain, dislocation density, and lattice constants (a,c) manifested an irregular pattern as a function of pulse count. AFM assessments--comprising parameters such as root-mean-square (RMS) roughness, average diameter, and arithmetic mean height--indicated a peak in surface roughness at the maximum pulse quantity of 400. Optical properties were characterized using a UV-Visible Spectrophotometer (2700) across a spectrum ranging from 300 to 1100 nm. An increment in absorbance was noted with the rise in pulse number, whereas the direct bandgap exhibited a decrease from 3.6 to 2.8 eV. The films demonstrated exceptional potential for sensor applications, evidenced by transmittance levels exceeding 90%. Optical constants, including refractive index and extinction coefficient, were derived from the spectral data. The comprehensive analysis suggests that by manipulating the pulse count during PLD, not only can the structural properties of CZTS thin films be tailored, but their optical attributes can be optimized, paving the way for advanced applications in photonic sensors and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

This comparative numerical simulation study investigates the electrical characteristics of two heterojunction thin-film solar cells based on Kësterites Copper Zinc Tin Sulfide. The study compared two solar cells with different structures, Zinc Oxide ZnO/Cadmium Sulfide CdS/Kësterites CZTS/Molybdenum Mo and Zinc Oxide ZnO/Zinc Sulfide ZnS/Kësterites CZTS/Molybdenum Mo, to determine which is more efficient in achieving maximum photovoltaic efficiency. The results showed that the ZnO/ZnS/CZTS/Mo solar cell is the better option, outperforming the CdS/CZTS/Mo solar cell in terms of short-circuit current density Jsc, open-circuit voltage Voc, form factor FF, and photovoltaic efficiency η. The study also investigated the effect of doping and layer thickness of CZTS and ZnS on photovoltaic parameters. The optimized ZnS/CZTS solar cell achieved an efficiency of 16.29% for ZnS and CZTS layer thicknesses of 0.02µm and 4μm, respectively, and doping concentrations of 1018 and 1016cm-3, respectively. Overall, this study provides valuable insights for designing more efficient solar cells and optimizing their photovoltaic efficiency using Kësterites CZTS, CdS, and ZnS materials. [ABSTRACT FROM AUTHOR]

CZTSSe is composed of earth abundant, relatively inexpensive and non-toxic metal with an intermediate chalcogenide structure. Direct bandgap metal chalcogenide thin film has the potential to reduce production costs for both raw materials and processing requirements. CZTSSe has received greater attention in the field of solar cells due to its tunable bandgap for different S to Se ratio varying for pure selenide (Eg = 1.1) and pure sulfide (Eg = 1.45). The current study describes the synthesis of CZTSSe nanocrystals using a simple and cost-effective solvothermal method. This method not only reduces cost but also prevents the usage of toxic solvents and avoids the selenization route. Aniline has been used as both solvent and stabilizing agent for the formation of nanocrystals. The obtained nanocrystals were studied for their structural, morphological and optical properties using XRD, HRTEM, UV-Vis spectroscopy and XPS. The XRD and HRTEM patterns of the synthesized nanocrystals confirms the kesterite structure of CZTSSe. The UV-Vis spectra of the nanocrystal confirms the direct bandgap of about 1.187 eV. This band gap energy is very near to the ideal value for an absorber in a photovoltaic solar cell. [ABSTRACT FROM AUTHOR]

Recently, a record open‐circuit voltage (1.1 V) is obtained for wide‐bandgap Cu2ZnGeS4 (CZGS) thin‐film solar cells with a Zn1−xSnxOy (ZTO) buffer grown by atomic layer deposition (ALD) (N. Saini et al. Sol. RRL 2021, 2100837). However, a low short‐circuit current and a small variation in device performance with ZTO properties are observed, suggesting similar interface properties. Since the CZGS absorber cannot be etched due to peeling, it is suggested that the presence of an oxide interlayer can influence the device performance. Here, the chemical and electronic properties of the near‐surface region of CZGS absorber and its interface with ZTO buffers with varying properties (bandgap and thickness) are studied nondestructively by employing excitation‐dependent X‐ray photoelectron spectroscopy. The formation of Ge oxide species is indicated at the absorber surface during device fabrication, which is preserved during ALD. Further, it is shown that the ZTO/CZGS interface properties are similar and not influenced by variations in ZTO properties, which can explain the small variation in device performance. Thus, attention shall be given to possible absorber surface cleaning treatment typically applied before the buffer deposition for Ge‐containing CZGS, and an optimization of the ALD ZTO buffer layer growth shall be considered for a non‐etched absorber. [ABSTRACT FROM AUTHOR]

Achieving a high-quality heterojunction interface (HEI) and absorber is crucial for the efficient Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, an alternative and feasible passivation strategy aiming to harness synergistic passivation effects (SPE) by introducing CuAlO2 (CAO) into HEI is developed. During the selenization process, interdiffusion of HEI elements occurs between absorber and CAO, resulting in the anticipated inversion of electrical properties from p- to n-type in the shallow bulk of absorber and enabling the construction of a homogeneous field passivation. Moreover, the Cu-poor characteristic of CAO promotes the formation of a thicker Cu-deficient shallow bulk, thereby facilitating the increased Na diffusion from soda lime glass substrate to both absorber and HEI. This behavior contributes to passivating dangling bonds within absorber grain boundaries and HEI, as well as promoting grain growth and reducing local potential fluctuations. Consequently, carrier recombination at absorber and HEI is depressed simultaneously, leading to a more than 10% efficiency device with a remarkably low open-circuit voltage deficit of ≈ 0.3 V. The impact of SPE and mechanism underpinning device performance improvement are comprehensively investigated. The findings provide valuable insights for achieving high-quality HEI and absorbers with effectively suppressed recombination, thus enabling efficient CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

In the ongoing few years, electricity cost is bound to increase so as a result, innovations in the photovoltaic industry are worth promising. One of the new ventures, kesterite (Cu2ZnSnS4) plays a significant role in fulfilling the energy demands due to its high earth abundance, non-toxicity, and low-cost processing characteristics. This semiconductor thin film can be considered as an alternative to CIGS where the expensive and scarce resources such as indium (In) and gallium (Ga) are replaced with cost-effective and abundant zinc (Zn) and tin (Sn). In this paper, the variations in the concentration of precursors of kesterite– copper, zinc, tin, and sulfur, and their influence on structural and optoelectrical characteristics of kesterite thin films have been reviewed and their effects are discussed. [ABSTRACT FROM AUTHOR]

In this work we present а comparative study of two photovoltaic cells based on n-type CZTS (Cu2ZnSnS4) kesterite-type thin films, using (a) an undoped pristine CZTS absorber and (b) doped with Li CZTS absorber, both integrated into photovoltaic (PV) cells, incorporating CdS thin film as an n-type buffer layer. The morphological, structural, compositional, optical, and electrical properties of both absorbers CZTS and CZTS:Li were studied by SEM-EDX, XRD, Vis-NIR spectroscopy, Hall-effect, and four-point probe measurements, revealing the impact on the Li-doping. The evaluation of the band gap was made using Taucplots. The influence of Li-doping in the CZTS films was scrutinized through the comparative study of the IV characteristics of PV cells. The results showed that the Li-doped CZTS yields better efficiency η=0,83% versus 0,53% for pristine CZTS absorber and better cell parameters, except for the Fill-Factor. [ABSTRACT FROM AUTHOR]