The band-gap of InxGa1−xN can cover a wide range of electromagnetic radiation of the solar spectrum and offers a method for using it in photovoltaic solar cells. A solar cell structure consisting of InxGa1−xN/GaN superlattice (SL) piled up between p-GaN and n-GaN is modeled and simulated. The impact of variations in the indium mole fraction and step graded SL having different quantum well thicknesses are analyzed. The results indicate that high indium content leads to lattice mismatch, decrement of fill factor, and development of strain in the quantum wells that reduce the overall efficiency. To increase the efficiency of the solar cell, a step graded 20 SL with a 5 nm quantum well thickness is introduced, and the highest efficiency of 22.6% is obtained. The use of a step graded SL InGaN cell allows for constructing real structures with the possibility of obtaining the enhanced power conversion efficiency compared with a conventional quantum well solar cell using SILVACO TCAD.