Effects of CsF Post-deposition Treatment on Cu(In, Ga)Se 2 Thin Films and Solar Cells

Heavy alkali (such as Cs, Rb) post-deposition treatment is an indispensable process step to achieve high performing CIGS solar cells. However, there is not enough understanding of the mechanisms leading to the performance improvement by heavy alkali. Here, we report a systematic study on the effects of elemental Cs on chemical and optoelectronic properties CIGS thin films and the final solar cells. We found that main beneficial role of Cs is passivation of deep-level defects and thereby enhancing p-type conduction of the CIGS.