Improved Efficiency by Using Transparent Contact Layers in InGaN-Based p-i-n Solar Cells

InGaN/GaN p-i-n solar cells were fabricated either without a current spreading layer or with ITO or Ni/Au spreading layers. A 10.8% indium composition was confirmed within an i-InGaN layer using X-ray diffraction. I-V characteristics were measured at AM1.5 conditions, with solar cell parameters being obtained based on I-V curves in all cases. Current spreading layers produced strong effects on efficiency. The solar cell with the ITO current spreading layer showed the best results, i.e., a short circuit current density of 0.644 mA/cm², an open circuit voltage of 2.0 V, a fill factor of 79.5%, a peak external quantum efficiency of 74.1%, and a conversion efficiency of 1.0%.