First-principles study of novel Cs3SCl anti-perovskite and performance assessment of solar cell structures with different hole transport layers and back contact metals.

Anti-perovskite materials have recently gained special importance for environmentally friendly, lead-free, and low-cost renewable energy technologies. In this study, the structural, electronic, dynamic, thermodynamic, mechanical, optical, and photovoltaic properties of Cs3SCl anti-perovskite are analyzed in detail by density functional theory (DFT) and an SCAPS-1D simulator. The results show that Cs3SCl is thermodynamically, dynamically, and mechanically stable, with a ductile nature due to its B/G ratio of 2.03. The electronic band structure analysis identified the compound as a direct bandgap semiconductor, with bandgaps of 1.185 eV and 2.051 eV obtained by GGA-PBE and HSE06 methods, respectively. This suitable bandgap is highly favorable for visible light absorption. Optical analysis shows that Cs3SCl exhibits high absorption coefficients of about (2.6-0.2) × 105 cm-1 in the ultraviolet, visible, and near-infrared regions. In addition, its favorable refraction, low reflectivity, and excellent dielectric properties further strengthen its potential for solar energy harvesting, charge-carrier generation, and optoelectronic applications. A fully lead-free Al/FTO/SnS2/Cs3SCl/HTL/Se solar cell was designed and optimized to evaluate the photovoltaic potential of the material. After systematic optimization of the hole transport layer (HTL), back-contact metal, device temperature, absorber layer thickness, defect density, and shallow acceptor density, the Cu2Te-based device exhibited the highest performance. At a 0.750 µm absorber layer thickness, 1 × 1015 cm-3 defect density, and 1 × 1017 cm-3 shallow acceptor density, the device achieves an open-circuit voltage of 0.752 V, a short-circuit current density of 39.23 mA cm-2, a fill factor of 84.43%, and a power conversion efficiency of 24.92%. Overall, these results indicate that Cs3SCl is a highly promising material for future generations of high-efficiency, environmentally friendly solar cells, visible-light-dependent photocatalytic technologies, and advanced optoelectronic devices.