Electroluminescence imaging of III–V multijunction solar cells

The potential of electroluminescence imaging is demonstrated for large area III-V triple junction solar cells. The cells are modeled as two dimensional diode networks and the emitted electroluminescence under forward bias is used as a measure of the local voltage. Mechanical cell defects introduce a discontinuity in this network which is shown to result in a pronounced electroluminescence signature. This makes qualitative electroluminescence imaging an ideal tool to verify the mechanical cell integrity. A quantitative evaluation of the emitted radiation from all subcells at a range of injection currents yields the local dark I-V parameters. From this, the spatial distribution of the open circuit voltage Voc as well as the current at the operating voltage Iop can be inferred. The global Voc and Iop values derived agree within ± 3 mV and ± 5 mA with the ones measured under illumination.