Abstract
This study presents a comprehensive first-principles and device-level investigation into the structural, electronic, optical, and photovoltaic properties of vacancy-ordered lead-free perovskites Cs(2)SnZ(6) (Z = Cl, Br, I) for next-generation solar energy conversion. Using density functional theory (DFT), we examined the structural stability, band structure, density of states, and optical response of Cs(2)SnCl(6), Cs(2)SnBr(6), and Cs(2)SnI(6). The calculated direct bandgaps are 2.652 eV for Cs(2)SnCl(6), 1.358 eV for Cs(2)SnBr(6), and 0.228 eV for Cs(2)SnI(6), demonstrating significant tunability through halide substitution. Optical analyses reveal strong absorption in the visible spectrum, with a redshift in absorption onset from Cl to I, enhancing light-harvesting capabilities. To assess device performance, SCAPS-1D simulations were employed with four different electron transport layers (ETLs): CdS, IGZO, SnS(2), and ZnS. The Cs(2)SnBr(6)-based PSC with IGZO ETL achieved the highest power conversion efficiency (PCE) of 26.22%, driven by optimal band alignment and balanced charge transport. Meanwhile, Cs(2)SnI(6), despite exhibiting ultrahigh short-circuit current densities (J (SC) > 70 mA cm(-2)) due to its narrow bandgap, showed poor performance with ZnS ETL due to mismatched energy levels. These results highlight the potential of Cs(2)SnZ(6) perovskites as promising lead-free absorber materials and emphasize the critical role of ETL compatibility and absorber optimization in achieving high-efficiency solar cells.