This study optimizes all-inorganic Pb-free CsGeI3-based perovskite solar cells. CsGeI3 forms four structures with four electron transport layers (ZnOS, BaSnO3, PC61BM, and ZnSe) and one hole transport layer of Copper Tin Ferrite Sulfide (CFTS). The thickness of the absorber layer is optimized by assessing the effects of the electron transport layer and hole transport layer thicknesses, along with the acceptor and defect densities in the absorbers, donor and defect densities in the electron transport layers, and acceptor and defect densities in the hole transport layers. After optimization, the FTO/ZnOS/CsGeI3/CFTS/Au configuration achieved optimal performance with a VOC of 1.07 V, JSC of 24.39 mA/cm², FF of 82.49 % and efficiency of 21.72 %. The influences of series and shunt resistance, temperature, voltage-current density, quantum efficiency, and generation and recombination rates are examined to determine structural stability. This study aims to improve understanding of CsGeI3-based perovskite solar cell’s experimental research potential.