Due to the high-efficiency potential over 40%, the two-terminal (2T) perovskite/c-Si tandem solar cell becomes a desirable and promising candidate for solar cells. The photovoltaic materials and devices (PVMD) group in TU Delft has developed the c-Si solar cell using poly-SiOx as carrier-selective passivating contacts. The utilization of poly-SiOx as carrier selective passivating contacts is relatively new and very interesting to be analyzed as its bandgap can be varied by changing its oxygen content. This can be used in the solar cell to increase the Jsc. In this work, the 2T perovskite/c-Si tandem solar cells' optimization has been conducted by means of optical and electrical simulations. Optical simulations of the 2T, 3T and 4T perovskite/c-Si tandem solar cells in GenPro4 are presented. The main objective is to show the new type of bottom cell's optical performance in the 2T, 3T, and 4T tandem solar cell. Furthermore, the two-terminal (2T) perovskite/c-Si tandem solar cell's electrical modeling framework with the new type of the bottom cell has been developed. In this model, the optical generation profile from GenPro4 was successfully imported into the semiconductor simulations software called Sentaurus TCAD. The perovskite and c-Si solar cells have been optimized separately. The perovskite solar cell optimization was conducted by changing parameters such as contact resistance, surface recombination velocity and thickness of each layer. This leads to the increase in the perovskite solar cell efficiency from 15.83% to 21.50%. This top cell was combined with a c-Si bottom cell with an efficiency of 25% to form a two-terminal (2T) tandem solar cell. The two-terminal (2T) perovskite/c-Si was further optimized by optimizing the tunnel recombination junction. The optimization of TRJ was done by varying the doping concentration of indium tin oxide (ITO) and spiro-OMeTAD, respectively. As a result, the 33.70% efficiency of the two-terminal (2T) perovskite/c-Si tandem solar cell was obtained.