The lead-free Cs3Sb2Br9/Si tandem solar cell (TSC) has been successfully explored to improve power conversion efficiency (PCE). In the presented work, the 2-T Cs3Sb2Br9/Si TSC has been investigated by using SCAPS-1D. First, the current-matching between the top and bottom subcells is obtained by varying the top absorber’s thickness. The identical current density (JSC) in both subcells is obtained at the optimum thickness of Cs3Sb2Br9 of 1.325 μm with a JSC of 14.26 mAcm−2. Finally, the proposed 2-T Cs3Sb2Br9/Si TSC exhibits the simulation results as PCE of 22.94% followed by open-circuit voltage (VOC) of 1.90 V, JSC of 14.26 mAcm−2, and fill factor (FF) of 84.66%. The result and analysis of this study highlight the feasibility of lead-free Cs3Sb2Br9 perovskite material, to attain a cost-effective and high PCE tandem device. Thus, it can be concluded that the proposed Cs3Sb2Br9/Si TSC offers a highly viable lead-free substitute for photovoltaic technologies.