Optical simulations of 4-terminal hybrid tandem modulescombining high-efficiency crystalline silicon(c-Si) cells with three different thin-film top cells respectively are presented. We considered three types of thin film PV cells: 1. Enlarged-bandgap oxygenated amorphous silicon (a-SiO:H) cells, 2. Wide-bandgap chalcopyrite (CuGaSe2) cells, and 3. Perovskite (CH3NH3PbI3) cells. A methodology for evaluating the efficiency gain of the 4-terminal hybrid tandem module is proposed and used to show how the efficiency of aninterdigitated back contact (IBC)c-Si module with an efficiency of about 19.5% can significantly be increased through this 4-terminal tandem concept. In our model we also included the change in electrical output parameters by the color-filtering effect of the top cells.