Reducing Air- and Moisture-Induced Degradation of Cu(In,Ga)Se2 Absorber Layers for Thin Film Solar Cells by RbCl Treatment

In this contribution we are comparing the commonly used RbF post deposition treatment (PDT) of CIGS absorber layers to an alternative RbCl-PDT. The RbCl-PDT leads to similar improvements of the cell efficiency as the fluorine treatment does. While the effect of the used procedure on the open circuit voltage is not as strong as it is in case of the RbF-PDT, we could reach an even higher fill factor. Furthermore we are investigating the impact of the RbCl treatment on the degradation of already RbF-treated absorber layers. We find that the additional RbCl-PDT can decrease degradation by air-, moisture- and low temperature-exposure. A complete Na-depletion of the surface of the absorber layer is found as a possible reason for this reduced degradation. Furthermore the RbCl-PDT suppresses the formation of an additional oxide-species, which is found on the surface of degraded absorber layers.