This study numerically investigates a lead-free dual-absorber perovskite solar cell (PSC) architecture employing RbGeI \(_{3}\) and CsSnGeI \(_{3}\) absorbers within the SCAPS-1D framework. Device optimization was carried out through a systematic evaluation of electron transport layers (ETLs) and hole transport layers (HTLs), with absorber parameters held constant to isolate transport layer effects. The influence of band offsets, specifically the conduction band offset and the valence band offset were analyzed. The analysis identified BaSnO \(_{3}\) as the most effective ETL due to favorable conduction band alignment, while Cu \(_{2}\) O was determined to be the optimal HTL, enabling efficient hole extraction and improved charge transport. Additional parametric studies explored the effects of absorber thickness, transport layer properties, doping concentrations, bulk and interface defect densities, series and shunt resistances, back-contact metal work functions, and temperature variations. The optimized configuration, Au/Cu \(_{2}\) O/RbGeI \(_{3}\) /CsSnGeI \(_{3}\) /BaSnO \(_{3}\) /FTO, with absorber thicknesses of 1300 nm for RbGeI \(_{3}\) and 100 nm for CsSnGeI \(_{3}\) , achieved a power conversion efficiency of 31.12%, with an open-circuit voltage of 1.079 V, short-circuit current density of 33.907 mA/cm \(^{2}\) , and fill factor of 85.08%. These findings provide valuable insights into material selection and interface engineering, highlighting the potential of lead-free dual-absorber perovskite architectures for next generation, eco friendly solar energy technologies.
