Cu2SnS3 Thin Film Solar Cells Research Articles

Theoretical exploration of high VOC in Cu2SnS3 thin film solar cells towards high efficiency

This article manifests the outstanding performance of copper-tin-sulphide (Cu2SnS3)-based double-heterojunction (DH) photovoltaic cell. The n-type ZnSe as window and the p+-type CGS (CuGaSe2) as back surface field (BSF) layer have been used for the p-type Cu2SnS3 base layer. The SCAPS-1D simulator is used for the simulation of this photovoltaic cell and demonstrating the effects of each layer. The n-ZnSe/p-Cu2SnS3 heterojunction has displayed a power conversion efficiency (PCE) of 17.69 % with JSC = 32.39 mA/cm2, VOC = 0.60 V, and FF = 80.58 %, when functioning alone. An enrichment of PCE to 38.14 % has been observed, owing to the addition of CGS as aBSF layer in the proposed structure. The VOC also develops enormously to 1.22 V in dual-heterojunctions, which boosts the PCE. The effective band alignment between ZnSe/Cu2SnS3 and Cu2SnS3/CuGaSe2 interfaces produces greater built-in potential that is liable to generate high VOC. The built-in potential of the device is 1.54 V according to the C-V study. These outcomes imply that the n-ZnSe/p-Cu2SnS3/p+-CGS device would be a viable alternative for harvesting solar energy in the era of thin film solar cells.

Investigation on photovoltaic performance of Cu2SnS3 thin film solar cells fabricated by RF-sputtered In2S3 buffer layer

A two-step process was used to prepare Cu2SnS3 films in this study: first, precursor stacks were deposited using a magnetron sputtering technique, and then the stacks were annealed in sulfur-containing atmosphere at various times. Utilizing a variety of characterization techniques, it was thoroughly examined how sulfurization time affected the films’ structural, morphological, optical, and electrical characteristics. X-ray diffraction and Raman spectroscopy measurements indicated that two structural polymorphs (tetragonal and monoclinic) of Cu2SnS3 co-existed in the films. Surface and cross-sectional images obtained by scanning electron microscopy showed that the microstructures of the films were entirely changed to well-grown crystal structures at 30 min and 40 min sulfurization times. In2S3/Cu2SnS3 stacks were prepared by the deposition of In2S3 films on the absorber layers sulfurized for 30 and 40 min by RF magnetron sputtering method. The fabrication of Ni/Al/Ni/AZO/i:ZnO/In2S3/Cu2SnS3/Mo/SLG-structured devices was done using both thermally annealed and non-annealed In2S3/Cu2SnS3 stacks. Secondary ion mass spectroscopy studies of the devices revealed that the indium diffused from In2S3 layer into the Cu2SnS3 absorber to a certain depth. The efficiency values of the devices were found to have been slightly enhanced with the annealing of the In2S3/Cu2SnS3 stacks. The solar cell with the maximum efficiency (η) of 3.12 %, open-circuit voltage (VOC) of 0.265 mV, short-circuit current (JSC) of 37.90 mA/cm2, and fill factor (FF) of 0.31 was produced by thermally annealed In2S3/Cu2SnS3 stack with an absorber layer sulfurized for 40 min.

Effect of annealing temperature on p–n junction formation in Cu2SnS3 thin-film solar cells fabricated via the co-evaporation of elemental precursors

Cu2SnS3 (CTS) thin-film solar cells were fabricated by the co-evaporation of the precursors, and the effect of annealing in N2 atmosphere on their photovoltaic properties was investigated by varying the annealing temperature after the chemical bath deposition of CdS. The characteristics of the solar cells improved as the annealing temperature was increased in the 250 °C–275 °C range (annealing time: 30 min). However, annealing temperatures exceeding 275 °C caused the deterioration of the device characteristics. Therefore, annealing in the 250 °C–275 °C range after CdS deposition is important for forming an optimum p–n junction at the CTS/CdS interface for manufacturing the CTS solar cells evaluated in this study. The best-performing solar cell fabricated using a CTS film annealed at 275 °C after CdS deposition exhibited an open circuit voltage of 0.181 V, with a short circuit current density of 20.9 mA cm−2, fill factor of 0.462, and power conversion efficiency of 1.74%.

Effect of Ag doping on the performance of Cu2SnS3 thin-film solar cells

For the promising next-generation thin-film solar cells, Cu2SnS3 (CTS) solar cells still suffer from low open circuit voltage (VOC) and so resulting an unsatisfactory power conversion efficiency. Herein, Ag was introduced in solution-processed CTS thin films via adding AgNO3 into precursor solution for photovoltaic devices. Compared with CTS, the VOC deficit for CuxAg2−xSnS3 (CATS) based cells could be effectively reduced for about 10 mV, together with the increased short circuit current density (JSC) and fill factor (FF), a power conversion efficiency of 3.99% was achieved. Such improved performance of CATS cells could be attributed to the improved crystallization, reduced shunting channels and the decreased band-gap of CATS films.

Effect of sulfurization process on the properties of solution-processed Cu2SnS3 thin film solar cells

Cu2SnS3 (CTS) based thin film solar cells were successfully fabricated through a facile solution processes followed by a post-sulfurization treatment. The influence of sulfurization temperature and time on the structural, compositional, morphological, optical and also the electrical properties of the solar cells were systematically studied. The results showed that the CTS thin films sulfurized at 580 °C would be a void-free and densely packed absorber layer with the grain size to be microns, having the band gap of ~ 1.01 eV. Furthermore, the sulfurization time is the key factor to influence the electronic properties of CTS absorber layer, and thus resulting in the best device performance of PCE = 2.41% by 20 min sulfurization process.

The effect of metal-chelate complex in Cu2SnS3 thin film solar cells and their characteristics, photovoltaic performance, and defect analysis

Hybrid inks with a chelating agent were prepared and coated by a spin-coating method to form Cu2SnS3 (CTS) thin films. After the coating, a subsequent sulfurizing process via rapid thermal annealing was performed. During the sulfurization, the Cu and Sn precursors in the hybrid inks exist in complex forms with chelates and these complexes help to form the CTS thin films by controlling the reaction rate of the metal precursors. Additionally, even though the complexes with chelates were formed, the oxidation numbers of the metal precursors were affected by the ionization tendency of each metal in the hybrid inks to form the semiconducting CTS thin films. After obtaining the optimum sulfurizing condition by controlling the reaction pressure and temperature, the CTS thin films were characterized and CTS solar cells were fabricated under these conditions. The best conversion efficiency of the fabricated cells was 2.953% and the temperature-dependent photovoltaic performances were also examined to investigate the carrier transport mechanisms of the devices. According to admittance spectroscopy, the dominant defect energy level was determined as 0.09 eV above the valence band minimum, which accords with the copper vacancy (VCu) level. In addition, capacitance–voltage measurements and drive-level capacitance profiling were applied to demonstrate the carrier densities and defect behaviors.

Fabrication of Cu2SnS3 thin film solar cells by sulphurization of sequentially sputtered Sn/CuSn metallic stacked precursors

In this present work, we report a novel fabrication technique of ternary Cu2SnS3 (CTS) thin films by sulphurization of sequentially sputtered Sn/CuSn (elemental/alloy) stacked metallic precursors. The focal aim of our investigation is on the impact of metallic precursors’ Cu/Sn ratio on the overall material properties of CTS films, which in turn, influence the photovoltaic device performance. All CTSs exhibited polycrystalline films with a mixture monoclinic CTS and orthorhombic SnS compound, p-type conductivity, and optical band gap in the range of 0.84–0.90 eV. Metallic precursor with Cu/Sn ratio of 1.09 produced optimum CTS film with post-sulphurization Cu/Sn ratio of 1.98 and highest conversion efficiency of 0.71%, respectively, despite exhibiting pronounced formation of SnS secondary phase. The correlation between XRD, Raman, and SEM-EDX outcomes revealed that CTS films from metallic precursors with Cu/Sn ratio higher than 1.09 undergo severe microstructural degradation due to Sn-loss through decomposition of volatile SnS phase and consequently, resulted in poorer absorber layer quality and lower device performance. Finally, several efficiency impeding factors are discussed and practical propostions to overcome them are presented.

Effects of different precursors on Cu2SnS3 thin film solar cells prepared by sputtering method

In this work, the impacts of different precursors on Cu2SnS3 thin film solar cells were investigated in detail. The two kinds of precursors of CuS/Sn and Cu/Sn were deposited on Mo-coated soda lime glasses by magnetron sputtering. Cu2SnS3 (CTS) films based on different precursors were fabricated by soft annealing and following sulfurization in S vapor. The crystal structure, phase purity, composition, surface morphology and cross section images of CTS films from different precursors were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectrometry (EDS) and scanning electron microscope (SEM) respectively. Meanwhile, the optical-electrical properties of CTS thin films were detected by using UV–vis–INR Spectrophotometer and Hall measurement. As a result, the CTS thin films with smooth surface and uniform compositional ratio distribution were obtained from the precursors of CuS/Sn. The best conversion efficiency of the fabricated CTS film solar cell based on CuS/Sn precursors was 1.18% with a high open-circuit voltage of 299 mV.

Impact of post-deposition annealing in Cu2SnS3 thin film solar cells prepared by doctor blade method

In this work, post-deposition annealing is done at three different temperatures on Cu2SnS3 (CTS) thin film solar cells prepared by doctor blade technique. Structural and electrical characteristics are determined from scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence spectroscopy (ED-XRF), X-ray diffraction (XRD), Hall Effect and I-V characteristics studies to enlighten the mechanisms by which solar cells performance varies. The highest efficiency gain is obtained 1.14%. It is concluded that the optimum post-deposition annealing temperature for CTS is 400 °C for 30 min in the sulfur atmosphere.

Effect of sodium addition on Cu2SnS3 thin-film solar cells fabricated on alkali-free glass substrates

Cu2SnS3 (CTS) p-type semiconductors are expected to be applied as a light absorption material for low-cost thin-film solar cells due to their advantageous physical properties. The influence of sodium addition to CTS thin films was investigated by comparing Na-free CTS and Na-doped CTS fabricated on alkali-free glass substrates. Grain growth for Na-free CTS, which has a Cu/Sn composition ratio of approximately 2.0, did not occur below 570 °C. In contrast, the addition of sodium to the CTS increased the grain sizes with an increase in the annealing temperature. Even with Na-free and Na-doped CTS, the grain sizes increased with a decrease in the Cu/Sn composition ratio. These results show that an excess of Sn combined with the presence of sodium accelerate the grain growth of CTS. Photovoltaic cells using the Na-doped CTS with a Cu/Sn ratio of 1.81 exhibited an open-circuit voltage of 242 mV, a short-circuit current density of 26.5 mA/cm2, a fill factor of 0.523, and a conversion efficiency of 3.35%. The cells using CTS without sodium did not exhibit good photovoltaic characteristics due to the small grain sizes.

Fabrication of Cu2SnS3 thin-film solar cells with oxide precursor by pulsed laser deposition

In this paper, Cu2SnS3 (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO2 target. XRD and Raman analyses indicate a pure monoclinic Cu2SnS3 phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm−2.

Fabrication of Cu2SnS3 thin film solar cells using Cu/Sn layered metallic precursors prepared by a sputtering process

As an alternative to Cu(In,Ga)(S,Se)2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTS)-based thin film solar cells (TFSCs), the ternary chalcogenide semiconductor Cu2SnS3 (CTS) is an emerging material with suitable optical band gap energy ranging from 0.93 to 1.77eV and high absorption coefficients (>104cm−1). In this study, we report the preparation of high-quality CTS thin films by the annealing of the sputtered Cu-Sn metallic precursor under S vapor atmosphere in a graphite box using the RTA process. Furthermore, the influence of different S vapor partial pressures in the graphite box during annealing on the properties of the CTS thin films has been investigated systematically. It is observed that the properties and photovoltaic performance of the CTS thin films are strongly dependent on the S vapor partial pressure during annealing. The monoclinic crystal structure is observed from X-ray diffraction (XRD) of the (112), (220), and (312) planes, and it is further confirmed using Raman spectroscopy by the presence of Raman peaks at 295 and 354cm−1. The direct band gap energy is found to be 0.91eV by extrapolation from external quantum efficiency (EQE) measurement of a CTS thin film annealed using 60mg of S powder. The preliminary best power conversion efficiency (PCE) of 2.21% with a short circuit current density of 29.7mA/cm2, an open circuit voltage of 179.5mV, and a fill factor of 41% have been obtained for a CTS thin film annealed using 60mg of S powder, although the processing parameters have not been optimized.

Fabrication of Cu2SnS3 thin-film solar cells with power conversion efficiency of over 4%

Cu2SnS3 (CTS) thin films were produced by the co-evaporation of Cu, Sn, and cracked sulfur, followed by annealing. The as-deposited films were then annealed at 570 °C for 5 min in the presence of 100 mg of sulfur lumps in a rapid thermal processing furnace filled with N2 gas at atmospheric pressure. Solar cells were then fabricated using the CTS films as absorber layers, and their efficiency was evaluated for different Cu/Sn compositional ratios. The largest grain size was found for films with a slightly Sn-rich composition. The highest performance was obtained for solar cells containing a CTS thin film with a Cu/Sn ratio of about 1.9. A cell with a Cu/Sn ratio of 1.87 exhibited an open-circuit voltage of 258 mV, a short-circuit current density of 35.6 mA/cm2, a fill factor of 0.467, and a power conversion efficiency of 4.29%.

Cu2SnS3 thin-film solar cells fabricated by sulfurization from NaF/Cu/Sn stacked precursor

Cu2SnS3 thin films were prepared by crystallization in a sulfur/tin mixing atmosphere from stacked NaF/Cu/Sn precursors deposited by the sequential evaporation of Sn, Cu elements, and NaF. The NaF mole ratio was changed at (x = 0 to 0.12). From X-ray diffraction patterns and Raman spectra, the Cu2SnS3 thin films were considered to have a monoclinic structure. The grain size of the Cu2SnS3 thin films decreased with increasing NaF/Cu mole ratio. The band-gap energies of the Cu2SnS3 thin films determined from quantum efficiency spectra were 0.93 and 1.02 eV. The solar cell with x = 0.075 demonstrated the best performance, namely, Voc = 283 mV, Isc = 37.3 mA/cm2, FF = 0.439, and η = 4.63%.