Computational optimization of Cs0.5Sn0.5GeI3 perovskite solar cells: A comprehensive performance analysis using SCAPS-1D simulation with a ZnO0.3S0.7 ETL

• Tin-based perovskites offer efficient, eco-friendly solar energy alternatives. • Cs0.5Sn0.5GeI3 combines high efficiency and stability for photovoltaics. • ZnO0.3S0.7 ETL reduces recombination with tunable bandgap and mobility. • Optimized device achieves 31.13% efficiency via SCAPS-1D simulation. • Structural and material variations enhance photovoltaic performance. Tin-based perovskite solar cells are an emerging photovoltaic technology designed to replace lead in traditional perovskite devices, offering a less toxic and more environmentally friendly alternative for next-generation solar energy harvesting. Cs 0.5 Sn 0.5 GeI 3 (cesium tin germanium iodide) perovskites represent a paradigm shift in solar technology, combining exceptional efficiency with enhanced stability. Meanwhile, zinc oxy-sulfide (ZnO 1-x S x ) has emerged as a promising electron transport layer (ETL) material due to its tunable bandgap (2.7 to 3.8 eV), high electron mobility, and ability to reduce recombination rates. In this work, we propose an optimized FTO/ZnO 0.3 S 0.7 /Cs 0.5 Sn 0.5 GeI 3 /Cu 2 O/Au structure, developed through numerical simulation using SCAPS-1D. To maximize performance, we analyze the effects of Cs 0.5 Sn 0.5 GeI 3 thickness, acceptor density, and defect density variations, along with adjustments to HTL and ETL thicknesses and their respective acceptor and donor concentrations. Additionally, back metal work function and temperature were evaluated. Various ETL materials, including Cu 2 O, CuSCN, Spiro-OMeTAD, MoOx, CuI, CuSbS 2 , NiO as well as HTL materials such as IGZO, PCBM, C 60 , and WS 2 , were investigated at the device's optimal point. The best-optimized ZnO 0.3 S 0.7 /Cs 0.5 Sn 0.5 GeI 3 /Cu 2 O structure achieved a short-circuit current density of 26.24 mA/cm 2 , an open-circuit voltage of 1.31 V, a fill factor of 90.36%, and a power conversion efficiency of 31.13%. These results highlight the significance of strategic material selection and systematic investigations in advancing high-efficiency innovations for tin-based perovskite solar cells as sustainable alternatives to lead-based counterparts.