Defect and Temperature Effects in MASnI3 Perovskite Solar Cells: A SCAPS-1D Simulation Study with Interface and Recombination Analysis

Tin-based perovskite solar cells (PSCs), particularly methylammonium tin triiodide (MASnI3), have emerged as promising lead-free alternatives to conventional lead-based devices. However, their performance is significantly limited by defect-induced recombination and thermal instability. In this work, a systematic SCAPS-1D simulation study is conducted to investigate the coupled effects of absorber thickness, bulk defect density, interface defect states, band alignment, and operating temperature on device performance. The simulation model is constructed using experimentally reported material parameters and benchmarked against literature-reported efficiency ranges (5–9%) to ensure physical relevance. Results indicate that an optimal absorber thickness of 600 nm yields a power conversion efficiency (PCE) of 17.31%, representing a balance between optical absorption and carrier transport. Bulk defect density is identified as the dominant performance-limiting factor, with PCE decreasing sharply from 25.05% to 4.47% as defect density increases from 10⁹ to 10¹⁶ cm⁻³ due to enhanced Shockley–Read–Hall recombination. Interface analysis reveals that the MASnI3/Spiro-OMeTAD junction is more sensitive to defect states than the TiO2/MASnI3 interface, leading to significant degradation in fill factor and current density at high trap densities. Band alignment optimization indicates that small positive offsets (0 to +0.20 eV) can suppress interfacial recombination while maintaining efficient charge extraction. Temperature-dependent analysis demonstrates performance improvement up to ~400 K, followed by degradation due to increased recombination and bandgap narrowing. Although the study is based on numerical simulation without direct experimental validation, the results are consistent with experimentally observed trends and provide semi-quantitative insights. The findings therefore offer practical design guidelines rather than absolute performance predictions, highlighting critical defect thresholds and interface engineering strategies for improving MASnI3 solar cell performance.