The tunable bandgap properties of perovskite materials allow attaining highly efficient tandem solar cells. An optimum bandgap for tandem solar cells can be reached by tuning the composition of halide elements in the perovskite material systems. However, realizing efficient tandem solar cells is complex, which needs a considerable understanding of device geometry and associated materials as compared to the single-junction solar cells. In this study, planar perovskite/perovskite and perovskite/silicon tandem solar cells are designed by considering realistic interface morphologies and device geometries, which can exhibit energy conversion efficiencies 30%. Herein, the optics and optimization of solar cells are investigated by finite-difference time-domain (FDTD) simulations in three dimensions. Contact materials used in the nanophotonic design of tandem solar cells were prepared by the atomic layer deposition (ALD) of zinc oxide films. Investigated solar cells are compared in terms of their quantum efficiencies, short-circuit current densities and calculated power densities. A detailed discussion on nanophotonic device designs is provided.