Abstract: In recent years, there has been a concerted effort to explore novel lead-free inorganic perovskite materials with the aim of matching the performance of lead-based perovskite solar cells. In this work, relatively high quality lead-free inorganic Cs₃Bi₂I₉ films were successfully prepared for the first time using a layered alternating evaporation technique for BiI₃ and CsI films. By doping KI into the Cs₃Bi₂I₉ films through vacuum evaporation, it results in a reduced bandgap and an increased exciton lifetime. The above two thin-films were used as active layers to fabricate solar cells with the structure of ITO/CuPc/active layer/C60/Al. In order to improve the performance of this type of solar cell, numerical simulations of devices based on Cs₃Bi₂I₉ thin-films were conducted using the SCAPS-1D solar cell simulation software to obtain the optimal device parameters. After optimizing the thickness of each functional layer of the simulated device and increasing the doping concentration of the donor in the active layer, only a modest maximum power conversion efficiency of 8.62% was achieved. Subsequently, other suitable hole and electron transport materials were chosen to optimize the device structure. The best simulated device exhibited a power conversion efficiency of 25.66%. This work provides theoretical guidance for the subsequent experimental preparation of Cs₃Bi₂I₉ thin-film solar cells.