In this study, we discuss a simulation model for a tandem device with MAPbSnI3 as a bottom subcell having bandgap of 1.2 eV and MACsPb(I0.6Br0.4) as a top subcell having bandgap of 1.8 eV. These perovskite material-based top and bottom cells are first examined under standalone condition. Simulation result shows the efficiency of standalone MAPbSnI3 and MACsPb(I0.6Br0.4) devices to be 15.34% and 12.74% respectively. These results are consistent with previously reported experimental findings. We have also analyzed the effect of defect density, perovskite thickness and contact work function on overall efficiency of the solar cell. It has been found that defect density in the perovskite layer should be smaller than 1013 cm−3 and the optimal work function for the front contact of the perovskite solar cell was found to be 5.44 eV, while for the back contact it is 4.22 eV for optimal performance of the solar cell. The matching of tandem stacks is investigated in terms of the equal short-circuit currents of subcells. This condition is met at perovskite thicknesses of 400 nm and 150 nm for MAPbSnI3 and MACsPb(I0.6Br0.4), respectively. Finally, to evaluate tandem solar cell performance, the top cell was operated under the standard AM 1.5 spectrum retaining perovskite thickness at 400 nm, while the bottom cell efficiency was calculated in a filtered spectrum. Improved efficiency of 20% is obtained for the MACsPb(I0.6Br0.4)/MAPbSnI3 tandem solar cell. The analysis and findings reported in this work give a potential route for tandem solar cell design.