Characterization of solar cells using electroluminescence and photoluminescence hyperspectral images

We analyze photoluminescence (PL) and electroluminescence (EL) using a hyperspectral imager that records spectrally resolved luminescence images of a GaAs solar cell. Thanks to the absolute calibration, we first investigate the reciprocity relations between Solar Cell and LED and determine the External Quantum Efficiency (EQE) from EL images for a specific range of voltage. Spatial variations are observed due to series resistance effect that we can evaluate. Second, the PL experiment allows us to plot the recombination current at a given spatial location versus the quasi Fermi level splitting at the same location. Indeed, under reasonable assumptions a link can be done with the classical plot of the short circuit current versus the open circuit voltage. We therefore can optically determine optoelectronic properties such as the saturation currents. The assumptions made in this experiment are discussed in order to correctly investigate polycrystalline solar cells in the future where strong lateral variations exist.