Relation between luminescence and open-circuit voltage in Cu(In,Ga)Se2 solar cells

We report on comparative electroluminescence and photoluminescence measurements on Cu(In,Ga)Se 2 solar cells and demonstrate that the spectral peak value or the integrated luminescence spectrum may not always reflect the photovoltaic “quality” in terms of open-circuit voltage. Spectra from Cu(In,Ga)Se 2 samples may have a comparable quasi-Fermi level splitting but a different spectral width or peak height, determined by the different sub-gap absorption properties. It is suggested that a more reliable evaluation of luminescence spectra should also consider the analysis in the high-energy spectral range which reflects the quasi-Fermi level splitting and which is shown to better correlate with the open-circuit voltage.