<p>The expansion of renewable energy applications is essential for reducing carbon emissions. To promote environmentally friendly photovoltaic technologies, this study optimizes the performance of lead-free FASnI₃ perovskite solar cells by introducing ZnO nanowires (NW) as the electron transport layer (ETL). Based on SCAPS-1D simulations, the effects of four key parameters—absorber thickness, bulk defect density, interfacial defect density, and ETL doping concentration-were systematically analyzed. The optimized device, with an absorber thickness of 300 nm, achieves a power conversion efficiency (PCE) of 17.21%, balancing light absorption and carrier transport. As the bulk defect density increases beyond 4.0 × 10¹⁷cm⁻³, device performance deteriorates rapidly, and the efficiency drops to 2.14% at 4.0 × 10¹⁹cm⁻³. The impact of interfacial defects is relatively small, with a PCE loss of less than 10%, underscoring the importance of bulk defect passivation. Moderate ETL doping concentrations (10¹⁷-10¹⁸cm⁻³) enhance carrier extraction, whereas excessive doping (&gt; 10¹⁹cm⁻³) causes band misalignment and recombination losses. Replacing planar ZnO or TiO₂/SnO₂ ETLs with ZnO nanowires further improves charge extraction, reduces interfacial recombination, and enables low-temperature, lead-free processing compatibility. These findings highlight the synergistic effects of structural and electronic optimization and provide theoretical guidance for designing high-efficiency, stable, and environmentally sustainable perovskite solar cells.</p>