In this work InGa0.85N p-n homojunction solar cells were grown by MOCVD on GaN/sapphire substrates and fabricated using standard techniques. When illuminated from the backside, these devices showed 65.9% improvement in JSC and 4.4% improvement in VOC as compared to identical illumination from the front. These improvements arise from removal of the losses from electrical contact shading on the front of the devices (11.7% of active area), as well as significant optical absorption by the top current spreading layer. These improvements can likely be further enhanced by utilizing double-side polished wafers, which would eliminate scattering losses on the back surface. In addition to improving electrical characteristics of single cells, backside illumination is necessary for the realization of monolithic tandem InGaN solar cells.