Indium Phosphide (InP) and Silicon(Si) based multi junction thin solar cell is one of the most competent devices in PV community which have the potential to fulfill the energy demand of present era with minimum material consumption. Through this study we try to develop different types of designs and evaluate the efficiency of InP/Si based multi-junction solar cells through various opto-electronics simulation studies. During this investigation we achieved more than 18% efficiency of solar cell using optimized doping profile of both materials with 12 µm substrate thickness. Further the electrical model was validated by different optical studies and found its competency in that domain also.