Inorganic perovskite materials (IPMs) seem to overcome the limitation of the stability of organic perovskites to a large extent. Herein, we discuss the design and the development of periodic nanophotonic structure (PNS)-based two-terminal IPM/Si tandem solar cells through the optical optimization process, computed using rigorous coupled-wave analysis. The IPM taken as the top active layer is cesium lead iodide (CsPbI₃), as it perfectly matches with the top cell requirements to design with a bottom Si-based tandem cell. The PNS is designed on to the tandem cell’s top layer. The top cell IPM layer thickness is kept fixed at 100 nm to limit the problems associated with thicker perovskite layers’ depositions and all the required tandem cell parameters are then optimized accordingly. To highlight the effectiveness of the proposed design, it is comparatively analyzed with Lambertian limiting values and bare and planar tandem structures. The results predict a notable performance enhancement for the planned design that accounts for around 40% comparative short-circuit current density increase. The complete spectral analysis presented provides insight for quantitative performance enhancement of the CsPbI₃ cell due to PNS that leads to overall tandem cell performance improvement. The absorption enhancement is credited to the PNS at the top as it leads to better index matching, reduction in reflections, and better trapping of full-spectrum photons.