Absolute electroluminescence imaging of multi-junction solar cells and calibration standards

We developed absolute electroluminescence (EL) calibration standards to evaluate absolute radiative-emission rates from subcells in multi-junction (MJ) solar cells. The absolute-EL-measurement system consists of an EL imaging setup and an emission-intensity-calibrated planar light-emitting diode with a circular open aperture as an emission-intensity standard. We applied this system to the measurements of the absolute EL imaging of a monolithic satellite-use InGaP/GaAs/Ge MJ solar cell. From the observed absolute EL images, we characterized external EL quantum efficiencies and internal open-circuit voltages of InGaP and GaAs subcells.