An efficient double junction InGaN/CIGS solar cell can be simulated using Silvaco ATLAS software. In this study, a thin CdS top cover layer is used as the anti-reflector layer. To reach the current matching condition, changing the thickness of this CdS layer, we can enhance the short-circuit currents of both the top and bottom cells. To gain a desired efficiency, different design parameters, such as the doping concentrations and the thicknesses of the various layers of the cell are optimized. This cell is designed to be used in a real environmental situation. Considering the proposed structure and the simulation results, an optimum efficiency of 41.87% is achieved and also the obtained fill factor is equal to 75.16%.