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, In_0.02 Ga_0.98N cell exhibited a fill factor (FF) of 67.8%, a higher open-circuit voltage (V_oc) of 2.15 V while In_0.12Ga_0.88N 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 In_0.12Ga_0.88N cells. Short-circuit current versus open-circuit voltage (J_sc - 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.