Demonstration and Study of Photovoltaic Performances of InGaN p-i-n Homojunction Solar Cells

We reported on the InGaN p-i-n homojunction solar cells with In contents of 0.02 and 0.12. Under the same illumination of Xe lamp, ${\hbox {In}}_{0.02}$ ${\hbox {Ga}}_{0.98}{\hbox {N}}$ cell exhibited a fill factor (FF) of 67.8%, a higher open-circuit voltage $({V}_{oc})$ of 2.15 V while ${\hbox {In}}_{0.12}{\hbox {Ga}}_{0.88}{\hbox {N}}$ cell showed a FF of 64.8% and a lower ${V}_{oc}$ of 1.35 V. The measurements of atomic force microscopy (AFM) images and leakage currents revealed that V-shaped defects, which are known to cause the increase in reverse current, were the main factor dominating the ${V}_{oc}$ of ${\hbox {In}}_{0.12}{\hbox {Ga}}_{0.88}{\hbox {N}}$ cells. Short-circuit current versus open-circuit voltage $(J _{sc} \mathchar"707B V _{oc})$ curves were consistent with the characteristics expected from the current-voltage equation. Relative external quantum efficiencies (EQEs) were also measured and showed strong dependence on V-shaped defects. These results indicate that defects in bulk InGaN has a negative impact on the photovoltaic performances of solar cells based on III-nitrides.