This study presents a comprehensive numerical investigation of lead-free perovskite solar cells (PSCs) employing methylammonium bismuth iodide (MA₃Bi₂I₉) as the absorber material in an FTO/ETL/MA₃Bi₂I₉/Cu₂O/Ni device architecture. Using SCAPS-1D simulation software, the photovoltaic performance of three electron transport layers (ETLs), TiO₂, SnO₂, and ZnO was analysed under identical absorber thickness (1.4 µm) and defect density (1 × 1012 cm⁻3). The resulting power conversion efficiencies (PCEs) were 16.16% for TiO₂, 14.82% for SnO₂, and 16.23% for ZnO, with all devices achieving high open-circuit voltages (Voc ≈ 1.44 V). All three ETLs yield a CBO of + 0.26 eV and a VBO of –0.95 eV, both within the literature-reported optimal thresholds (CBO < 0.30 eV and VBO < 0.2 eV) for achieving high efficiency. This alignment enables efficient hole extraction and creates an ideal spike-and-cliff band structure that reduces interfacial recombination while maintaining effective carrier flow. Therefore, the overall band alignment in all configurations supports favorable operation, and the remaining performance disparities stem from charge transport and interface quality. This work promotes MA₃Bi₂I₉ as a stable, non-toxic absorber and validates Cu₂O/Ni contacts as effective, low-cost alternatives to spiro-OMeTAD/Au.