One-dimensional drift-diffusion assessment of interfacial defect reduction and PEA2SnI4 transport in a FA(Sn0.75Ge0.25)I3 perovskite solar cell with ZnMgO/CuSCN selective contacts

Lead-free perovskite absorbers are attractive for near-term photovoltaic development, but their performance remains sensitive to interface recombination, absorber thickness, and contact selectivity. This study presents a 300 K numerical design-screening assessment of an FTO/Zn 0.8 Mg 0.2 O/PEA 2 SnI 4 /FA(Sn 0.75 Ge 0.25 )I 3 /CuSCN/carbon solar cell. The calculations were performed with SIMsalabim v5.36, which solves the coupled Poisson and electron/hole continuity equations in a one-dimensional drift-diffusion framework. The reference condition uses a 650 nm-thick absorber and a carbon contact with a work function of 5.05 eV. Wavelength-resolved transfer-matrix generation and explicit defect, band-offset, thickness, and work-function sensitivities were evaluated under AM1.5 G illumination. Reducing the defect density in a 3 nm interfacial region increases the modeled PCE from 13.17% to 19.28%, primarily through improved open-circuit voltage and fill factor. In contrast, explicit PEA 2 SnI 4 layers with the assumed 0.30 eV electron barrier are transport-limiting. The results are presented as a numerically verified sensitivity study, not as experimentally calibrated device predictions.