Thickness-dependent performance optimization of lead-free FASnI3 perovskite solar cells: Interplay between optical absorption and charge recombination

Perovskite solar cells (PSCs) have emerged as a promising photovoltaic technology due to their high efficiency and low-cost fabrication. However, the development of stable, lead-free alternatives remains a critical challenge. Tin-based perovskites, such as FASnI 3 , offer available solution but suffer from oxidation-related instability and suboptimal charge transport. This study addresses these challenges by investigating the impact of perovskite absorber thickness (450–1650 nm) on the performance of a novel CuI/FASnI 3 /CeO 2 /FTO solar cell architecture. Using numerical simulations (SCAPS-1D) and electrochemical impedance spectroscopy (EIS), we systematically investigate the interplay between light absorption, charge transport, and recombination dynamics. Our results reveal that an optimal thickness of 1050 nm achieves the highest power conversion efficiency up to (25.8 %) by balancing enhanced light harvesting (Jsc = 26 mA/cm 2 ) with reduced bulk recombination (relaxation frequency f 2 = 10 5 Hz) and stable interfacial properties (f 1 = 1–10 Hz). Thinner films (<800 nm) exhibit insufficient absorption, while thicker layers (>1200 nm) suffer from increased recombination losses and reducing V oc by 30 mV. Impedance analysis confirms that the CuI/FASnI 3 and FASnI 3 /CeO 2 interfaces effectively suppresses bulk recombination, unlike conventional architectures. These findings provide a new way for optimizing Sn-based PSCs through precise thickness control and interfacial engineering, advancing the development of efficient, lead-free photovoltaics.