Defect-Dominated Performance Limits in FASnI₃ Perovskite Solar Cells: A Thickness-Dependent Simulation Study

Abstract

The performance of lead-free tin-based perovskite solar cells remains fundamentally constrained by defect-induced recombination losses, limiting their competitiveness with lead-based counterparts. In this work, a physically calibrated numerical investigation of an inverted (p–i–n) FASnI₃ perovskite solar cell is performed using the SCAPS-1D simulation framework. The model incorporates experimentally consistent material parameters, including bulk and interface defect states, as well as series and shunt resistive losses, enabling realistic reproduction of non-ideal device behaviour. A baseline power conversion efficiency of 14.02% is achieved, with an open-circuit voltage of 1.073 V, short-circuit current density of 27.48 mA/cm², and fill factor of 47.56%. A systematic thickness-dependent analysis (100–1000 nm) reveals a counterintuitive decline in device performance with increasing absorber thickness. While optical absorption improves marginally, enhanced Shockley–Read–Hall recombination and transport limitations dominate, leading to reduced carrier collection efficiency. Notably, the open-circuit voltage remains largely invariant, indicating a recombination-limited regime, whereas both current density and fill factor degrade with thickness. The optimal absorber thickness is identified within the range of 100–300 nm, where the balance between photogeneration and recombination losses is maximized. These findings demonstrate that device performance in FASnI₃ solar cells is fundamentally governed by carrier preservation rather than photon absorption. The study establishes a physically grounded framework for thickness optimization and highlights the critical role of defect passivation and interface engineering in advancing high-efficiency, lead-free perovskite solar cells.