Simulation-Guided Optimization of FA–Cs Perovskite Solar Cells Achieving Over 28% Efficiency

Perovskite solar cells (PSCs) have emerged as a competitive alternative to silicon-based photovoltaics due to their remarkable efficiency, tunable bandgap, and low fabrication cost. Among lead-based perovskites, the mixed-cation, mixed-halide compound FA₀.₈₅Cs₀.₁₅Pb(I₀.₈₅Br₀.₁₅)₃ stands out for its enhanced thermal stability and suppressed halide migration. In this study, we present a detailed numerical investigation using SCAPS-1D to optimize the device architecture FTO/ETL/FA-Cs perovskite/CZTSe/Pt. Four electron transport layers (ETLs)—LBSO, SnO₂, SnS₂, and ZnS—are comparatively analyzed, while CZTSe is employed as a stable inorganic hole transport layer (HTL). Key device parameters including layer thickness, defect density, doping concentration, bandgap, work function, and operating temperature are systematically varied to maximize performance.Among the configurations studied, the SnO₂/CZTS-based device demonstrates superior alignment and charge transport characteristics, achieving a record simulated power conversion efficiency (PCE) of 28.4%, with V _OC = 1.05 V, J _SC = 30.29 mA/cm², and fill factor = 84.29%. Temperature and resistance analysis further validate the thermal robustness and charge transport stability of the optimized structure. These results underscore the potential of interface-engineered FA₀.₈₅Cs₀.₁₅Pb(I₀.₈₅Br₀.₁₅)₃-based PSCs for next-generation photovoltaics. The findings offer a promising route for experimental realization using scalable, low-temperature deposition techniques, paving the way for high-efficiency, cost-effective, and stable perovskite devices.