Performance optimization of a CsGeI3-based solar device by numerical simulation

•A Numerical simulation of a CsGeI3-based solar device using SCAPS-1D software to understand device behavior and save time and resources.•Examination of various CTLs to select those with good alignment with the perovskite for improved performance.•Optimization of properties including CuI, SnO2, and CsGeI3 thickness, CTLs and CsGeI3 doping density, and Nt at the absorber's interfaces.•Investigation of the impact of temperature, shunt resistance, and series resistance on solar cell performance.•Development of a fully inorganic CsGeI3-based solar device (FTO/SnO2/CsGeI3/CuI/Ag) achieving an impressive efficiency of 15.68% at room temperature, providing insights for future PSC design and fabrication. Germanium-based halide perovskites (CsGeI3) are good absorbers materials for eco-friendly perovskite solar devices. In this work, a numerical analysis via SCAPS-1D software, is done to enhance the performance of a device already experimentally realized (FTO/TiO2/CsGeI3/Spiro-OMeTAD/Ag). After selecting SnO2 and CuI as best Charge transport materials (CTMs) in front of others, we have optimized their thicknesses, we investigated the impact of: CsGeI3 thickness, its defect density (Nt), its acceptor concentration, CuI doping density, SnO2 doping density, SnO2/CsSnI3 defect density, CsSnI3/CuI defect density, also the impact of shunt resistance, series resistance, and temperature. Finally, we have achieved a new solar device based on CsGeI3, with a fully inorganic FTO/ SnO2/CsGeI3/CuI/Ag structure. The final output parameters are PCE = 15.68 %, FF = 73.45 %, JSC = 22.56 mA/cm2 and VOC = 0.946 V at room temperature. The results are beneficial for the design and manufacture of CsGeI3-based solar devices.