Herein, a solar cell device simulation study is performed using the solar cell capacitance simulator 1D tool to assess the performance parameters of a monolithic two-terminal (2-T) and a mechanically stacked four-terminal (4-T) tandem solar cell with a top perovskite subcell and a bottom subcell consisting of a perovskite material FA_0.83Cs_0.17PbI_1.5Br_1.5 and a kesterite photovoltaic material Cu₂ZnSnSe₄ as the light-harvesting material, respectively. The 2-T tandem device design furnishes a open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency (PCE) of 1.81 V, 18.18 mA cm⁻², 66.18%, and 31.15%, respectively, while establishing the condition of matching the short-circuit current density between the top perovskite and bottom kesterite cells. The 4-T device furnishes a high PCE of 37.49% when the filtered spectrum is used for modeling the bottom subcell. Further, the optimization of the input parameters of the light active layers of the top and bottom cells leads to an increase in PCE of the 4-T tandem device to 37.84%.