Optimizing CsSnI <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si51.svg" display="inline" id="d1e2842"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> perovskites with Al and In doping for

Lead-free perovskite solar cells offer a sustainable pathway for next-generation photovoltaics. This study employs a combined Density Functional Theory (DFT) and SCAPS-1D approach to investigate the structural, electronic, optical, and photovoltaic properties of pristine and Al/In-doped CsSnI 3 . Using the Quantum ESPRESSO package with PBE-GGA, DFT calculations reveal that 3.7% Al 3＋ or In 3 + doping enhances the structural stability of CsSnI 3 , with In-doped systems exhibiting optimal Goldschmidt tolerance ( t = 0 . 86 ) and octahedral factors ( μ = 0 . 53 ). The direct bandgap increases from 0.46 eV (pristine) to 1.23 eV (Al-doped) and 1.65 eV (In-doped), with a Fermi level shift promoting p-type conductivity and introducing localized states near band edges. Optical properties calculations indicate strong sub-gap absorption and free-carrier effects in the doped systems, manifested as dramatically enhanced low-energy extinction coefficient, absorption coefficient, and reflectivity, together with increased static dielectric constant and refractive index due to intraband contributions from p-type doping at the Sn site. SCAPS-1D simulations, conducted for pristine CsSnI 3 under AM1.5G illumination, evaluate three device configurations (e.g., FTO/PCBM/CsSnI 3 /Cu 2 O/Au), achieving power conversion efficiencies up to 27.96% at an optimal absorber thickness of 1100–1200 nm. These results underscore the potential of Al and In doping to enhance CsSnI 3 stability and optoelectronic properties, while the SCAPS-1D analysis provides a robust framework for optimizing pristine CsSnI 3 -based solar cells, paving the way for efficient, eco-friendly photovoltaic technologies.