Minimizing optical losses of the incident light at the window layers is one of the effective strategies for high photoresponse to achieve highly efficient perovskite/silicon tandem cells. The enhancement of the photoresponse of monolithic tandem cells via rationally controlling their window layers consisting of C-60 and indium tin oxide (ITO) is reported. The optical simulation and experimental results are consistent that employing thinner C-60 and ITO layers would reduce the optical losses caused by absorption/reflection of the incident, which should lead to the increased photocurrent density. However, it is found that the enhanced optical properties have to be balanced with the changes in the electrical and structural properties. The thickness of layers is optimized to function as charge collection and protection (during sputtering process) layers. As a result, the optimum design of the window layers maximizes the photoresponse without degrading the device performances, leading to a highly efficient two-terminal perovskite/silicon tandem solar cell with a power conversion efficiency of 25.63%.