Abstract: It is an important task for the future green development of perovskite solar cells (PSCs) to reducing or replacing the use of lead (Pb) with the premise of ensuring the power conversion efficiency (PCE) and stability. Herein, a PSCs hired a germanium-based n-methylammonium germanium iodide/p-methylammonium germanium iodide (n-MAGeI₃/p-MAGeI₃) perovskite homojunction as light absorbing layer, Cd_0.5Zn_0.5S as electron transport layer (ETL) and methylammonium tin bromide (MASnBr₃) as hole transport layer (HTL) was designed. SCAPS-1D software was used to simulate the photoelectric performance of the device. It was found that the n-MAGeI₃/p-MAGeI₃ homojunction structure show a superior photo-carriers dissociation and transportation than the single MAGeI₃ absorb layer. The use of Cd_0.5Zn_0.5S as an ETL has a more matched energy level position than traditional TiO₂ ETL. The MASnBr₃ HTL can realize the dual functions of hole transportation and supplement absorb the unabsorbed photons of the perovskite layer to generate electron-hole pairs, and thus improving the device performance. After optimization of the device structure and defect density of perovskite layer, we got a high-performance germanium-based PSCs with a voltage open circuit (V_OC) of 1.9069 V, short circuit current density (J_SC) of 15.1388 mA/cm², fill factor (FF) of 88.69% and photoelectric conversion efficiency (PCE) of 25.60%. While the control device with the TiO₂/MAGeI₃/2,2',7,7'-tetraN,N-di(4-methoxyphenyl)amino-9,9'-spirobifluorene (Spiro-OMeTAD) structure only show a PCE of 23.47%, and the Cd_0.5Zn_0.5S/MAGeI₃/MASnBr₃ device show a PCE of 25.33%.