Enhancing the photovoltaic potential of lead-free CsSnCl3 perovskite via Al/In doping: A combined DFT and SCAPS-1D study

The pursuit of high-efficiency, environmentally friendly photovoltaics has intensified the search for lead-free perovskite solar cells (PSCs). This study comprehensively investigates the potential of inorganic cesium tin chloride (CsSnCl${}_3$) as a stable, non-toxic absorber material via a combined computational approach. To address the inherent instability of Sn${}^{2+}$, we propose strategic doping with aluminum (Al) and indium (In). First-principles density functional theory (DFT) calculations reveal that doping successfully widens the band gap from 0.95 eV to 1.63 eV (Al) and 1.95 eV (In), induces beneficial p-type conductivity, enhances optical absorption, and improves structural stability. Subsequently, device-level performance is evaluated through SCAPS-1D simulations of pristine CsSnCl${}_3$ in three novel heterojunction architectures: FTO/ZnO/CsSnCl3/Spiro-OMeTAD/Au, FTO/C$60$/CsSnCl${}_3$/CuSCN/Au, and FTO/WS${}_2$/CsSnCl${}_3$/P3HT/Au. These configurations yield high power conversion efficiencies (PCEs) of 24.89%, 24.53%, and 23.03%, respectively, at an 800 nm absorber thickness. The ZnO/Spiro-OMeTAD structure achieves superior performance due to optimal band alignment and minimized recombination losses. Further optimization of the absorber thickness boosts the PCE to 25.00% for the leading device. All configurations exhibit exceptional quantum efficiency, exceeding 99%. Our findings not only validate doped CsSnCl${}_3$ as a highly promising lead-free absorber but also underscore the critical importance of synergistic materials engineering and device architecture optimization in developing efficient and sustainable PSCs.