In this study, an optimized quasi-periodic intermediate structure has been introduced to enhance the performance of perovskite/Si tandem solar cells. The proposed FC(3,3) intermediate structure consists of seven alternating layers of SiO2 and TiO2 with a total thickness of 1150 nm. The results obtained by the transfer matrix method and the finite difference time domain analysis are in good agreement and prove that the proposed intermediate structure enhances the conversion efficiency of the device by 5%. Also, the absorption efficiency of the bottom cell (thin-film Si layer) with reduced thickness to 5 mu m has been improved by the implementation of Ag nanoparticles with optimized radius of 125 nm. Short current density enhancement of similar to 88% has been obtained for the thin-film Si cell after applying the proposed intermediate structure and Ag nanoparticles.