Lead toxicity in perovskite solar cells (PSCs) presents a major challenge for their broader commercialization. The leading organic hole transport layer (HTL) material, spiro-OMeTAD, is costly due to its complex synthesis process. This research involves a comprehensive device simulation of inorganic \(\hbox {RbGeI}_{{3}}\) -based PSCs, examining various copper-based materials for the HTL, such as copper barium thiostannate (CBTS), copper iron tin sulfide (CFTS), \(\hbox {Cu}_{{2}}\) O, CuI, CuO, \(\hbox {CuCrO}_{{2}}\) , \(\hbox {CuInSe}_{{2}}\) , and CuSCN, using the SCAPS-1D simulator. The study systematically varies parameters related to the absorber layer, including thickness, doping density, and defect density, to evaluate their effects on device performance. It also investigates how changes in the doping density and thickness of both the electron transport layer (ETL) and HTL, interface defect densities, series resistance, shunt resistance, and temperature fluctuations influence PSC performance. The main goal of this research is to optimize critical design parameters to improve the efficiency of solar cell power conversion. The parametric analysis shows significant performance enhancements, with the optimized device achieving short-circuit current density (Jsc) of 33.90 mA/ \(\hbox {cm}^{2}\) , open-circuit voltage (Voc) of 0.815 V, a fill factor (FF) of 80.93%, and power conversion efficiency (PCE) of 22.36%.
