Post Deposition Treatments of (Ag,Cu)(In,Ga)Se2 Thin Films for Solar Cells

Different alkali alternatives for post-deposition of ACIGS were tested, both conventional fluoride salts and in the form of metals. XPS analysis of surfaces treated with K or KF as well as Rb or RbF have been performed, before (only for K and Rb) and after an ammonia etch. In addition to a strong suppression of Cu and Ag near the surface, we observe a difference in the re-distribution of Ga in the surface region after the etch depending on pdt element. Our results are consistent with the formation of K-In-Se and Rb-In-Se compounds for both metal alkalis and alkali fluorides. We find a similar beneficial effect on cell performance for the best cells with the metals as with the fluoride salts.