  The optical properties of V graded InGaN solar cells are studied. Graded
InGaN well structures with the indium composition increasing then decreasing in
a V shaped pattern have been designed. Through polarization doping, this
naturally creates alternating p-type and n-type regions. Separate structures
are designed by varying the indium alloy profile from GaN to maximum indium
concentrations ranging from 20% to 80%, while maintaining a constant overall
structure thicknesses 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 at x=60%. Solar cell
efficiency under relaxed conditions increases to a maximum of 8.3% at 90%.
While Vegards law predicts the bandgap under relaxed conditions, a Vegard like
law is empirically determined from the output of Nextnano for varying In
compositions in order to calculate solar cell parameters under strain.
