The optical properties of Λ-graded indium gallium nitride (InGaN) solar cells are studied. Graded InGaN well structures with the indium composition increasing to x_max and then decreasing in a Λ-shaped pattern have been designed. Through polarization doping, this naturally creates alternating p- and n-type regions. Separate structures are designed by varying the indium alloy profile from GaN to maximum indium concentrations ranging from 20% to 90%, while maintaining a constant overall structure thickness of 100 nm. The solar cell parameters under fully strained and relaxed conditions are considered. The results show that a maximum efficiency of ≅5.5  %   under fully strained condition occurs for x_max  =  60  %  . Solar cell efficiency under relaxed conditions increases to a maximum of 8.3% for x_max  =  90  %  . Vegard’s law predicts the bandgap under relaxed conditions, whereas a Vegard-like law is empirically determined from the output of nextnano™ for varying indium compositions to calculate the solar cell parameters under strain.