Environmentally friendly tin and germanium-based halide perovskite materials are promising candidates attracting more attention as lead-free halide perovskite solar cells. However, the limited power conversion efficiency of these perovskites is an important issue in the solar cells field. Therefore, in the present study, a different lead-free perovskite was used to reach higher power conversion efficiency. Devices with an indium tin oxide/electron transport layer/perovskite/hole transport layer/Ag structure but different absorber layers were simulated. Simulation was done using the Solar Cell Capacitance Simulator (SCAPS-1D) to investigate the photovoltaic performance of solar cells with CsGeI3 and CsSnI3 perovskites as the absorber layer.Method. Simulation was done by using the SCAPS software, which is a one-dimensional solar cell simulation platformdeveloped at the Department of Electronics and Information Systems of theUniversity ofGent, Belgium.Main results. The effect of the absorber layer thickness was investigated, and a maximum power conversion efficiency of 10.51% was obtained for 1000 nm thick CsGeI3, while the maximum value of 12.83% was obtained for 400 nm thick CsGeI3. Then, to further increase the efficiency, devices with an alternative lead-free CsSn0.5Ge0.5I3 perovskite including a planar ZnO layer and ZnO nanorod arrays as electron transport layers was used in the simulation, and the thickness of the absorber layer was optimized for both devices. For the maximum power conversion efficiency of the devices, the values of 17.56% and 22.61% were achieved for devices with a ZnO layer and ZnO nanorods, respectively. It is noted that the simulation results of this study could provide a perspective towards fabricating an environmentally friendly perovskite-based solar cell. Practical significance. The main significance of the present work is obtaining a significant power conversion efficiency of 22.61% for a device based on environmentally friendly perovski
