Numerical Simulation of a Lead-Free FASnI₃ Perovskite Solar Cell with CeO₂ Electron Transport Layer Achieving 22.29% Power Conversion Efficiency Using SCAPS-1D

This paper presents a physics-based simulation of a lead-free FASnI₃ Perovskite Solar Cell (PSC) using Solar Cell Capacitance Simulator One-Dimension (SCAPS-1D). Six device parameters were systematically investigated: the absorber band gap, the layer thickness, bulk defect density (Nt), the operating temperature, the series resistance (Rs) and the shunt resistance (Rsh). The device Short-circuit Current Density (Jsc) was determined to be 28.73 mA/cm², Open-circuit Voltage (Voc) = 0.9862 V, Fill Factor (FF) = 78.68%, and Power Conversion Efficiency (PCE) = 22.29%. A conduction band cliff of −0.60 eV at the CeO₂/FASnI₃ interface and a valence band cliff of −0.19 eV at the FASnI₃/NiO interface were found, which promote interfacial recombination and limit the FF; the effect of the interface band offsets and interface defect density on the device performance was quantified. It was observed that bulk defect density is the most critical parameter limiting the device performance, with PCE = 7.72% at Nt = 10²⁰ cm-3; it is evident that Nt needs to be reduced below 10¹⁶ cm-3 for PCE > 20%. Voc varied by only 5.1 mV (0.9828–0.9879 V) and the PCE changed over 280–310 K, whereas the PCE was degraded significantly at Rsh < 1000 Ω·cm² and Rs > 2 Ω·cm². The absorption edge was confirmed by quantum efficiency, which is around 855 nm. The targets for improvement are: FASnI₃/NiO interface passivation, reduction of Nt, and electron transport layer (ETL) work-function engineering (χ = 4.2–4.3 eV).