Numerical Investigation of CsSnI₃ Absorber Layer Parameters Toward Efficient Tin-Based Perovskite Solar Cells

Lead-free tin-based perovskites, particularly CsSnI₃, offer a promising route toward environmentally benign photovoltaics, yet their device performance still lags behind lead-based counterparts. In this work, we perform a systematic SCAPS-1D simulation study on a planar heterojunction CsSnI₃ solar cell with a TiO₂ electron transport layer and a P3HT hole transport layer. We focus on the interplay between absorber-layer properties, acceptor doping concentration, thickness, defect density, carrier mobility, and parasitic resistances. Our results reveal that an optimal acceptor density around 10¹⁹ cm^-3 balances built-in potential enhancement against Shockley-Read-Hall recombination, yielding the highest efficiency. Thicker absorbers improve light harvesting but aggravate bulk recombination, while defect densities above 10¹⁶ cm^-3 cause catastrophic performance collapse. High carrier mobility (>1 cm²/V·s) is essential for efficient collection, and series resistance must be kept below 2 Ω·cm² to avoid fill factor degradation. Under optimized conditions, the device achieves a theoretical efficiency exceeding 27%, demonstrating the critical role of co-optimizing absorber parameters for high-performance, lead-free perovskite solar cells.