Within the PVMD group at TU Delft, the study of perovskite/c-Si tandem solar cells is being researched. A comprehensive study is performed through advanced optical and electrical simulations to understand the tandem’s characteristics and operative behavior. We use GenPro4 and Sentaurus TCAD to perform the optical and electrical simulations, respectively. From the previous research, the developed J-V simulations revealed an indication of extra current collection from the tandem’s supporting layers. This extra current density makes the tandem’s short circuit current density J_SC higher than the current-matched J_ph of each perovskite and c-Si absorber layer. Because only J-V curves that could be simulated and not the EQE curves, it remained a mystery of which supporting layers in the tandem that contribute to the extra current collection. In this thesis project, a new EQE simulation methodology was developed to help to solve this mystery of extra current collection from the supporting layers. By performing the EQE simulation, we find that SnO2, TiO2, and Spiro-OMeTAD layers contribute to a total potential extra current collection of 2.50 mA/cm2 to 2.79 mA/cm2. A further study of the extra current collection is also conducted by modifying the simulation method that considers the absorbed photons’ energy in respect to the material’s energy bandgap. Under this further study, only absorbed photons with energy higher than the material’s energy bandgap can generate electron-hole pairs. After considering the absorbed photons’ energy in the simulation, only SnO2 and TiO2 layers that contribute to the significantly lower extra current collection of 0.07 mA/cm2.