Quantitative Luminescence Mapping of Cu(In, Ga)Se2 Thin-Film Solar Cells

We investigate photoluminescence and electroluminescence (PL and EL) emission images from Cu(In, Ga)Se₂-based solar cells by means of a Hyperspectral Imager. Using the generalized Planck’s law, maps of the effective quasi-Fermi level splitting in absolute values are obtained. A good agreement is found between the spatially averaged splitting in PL and the global open-circuit voltage. However, from a local carrier transport discussion, we conclude that the equality does not hold locally. The spatial variations are rather attributed to local depth variations of the quasi-Fermi level splitting due to material properties spatial fluctuations. By comparing PL and EL emissions, we discuss qualitatively the local effective lifetimes and collection efficiencies.