RbF-related post-deposition treatments on Cu(In,Ga)(S,Se)2 absorbers: The role of the chalcogen atmosphere

An intriguing area in the field of alkali fluoride post-deposition treatment (PDT) on Cu(In,Ga)(S,Se)2 (CIGSSe) absorbers is the effect of the chalcogen atmosphere on the absorber’s surface during the PDT process. In this work, we focus on RbF-PDTs and we study (i) the effect of Se and S atmosphere and (ii) the impact of In and RbF co-evaporation under S vapor on the vibrational and chemical properties of the absorber’s surface. Using micro-Raman and X-ray photoelectron spectroscopy, we examine three different PDT processes: RbF under S atmosphere (RbF(S)-PDT), In and RbF co-evaporation under S atmosphere (In + RbF(S)-PDT) and In and RbF co-evaporation under Se atmosphere (In + RbF(Se)-PDT). Our results show that under Se atmosphere the formation of a Cu-poor chalcopyrite phase is enhanced, while under S atmosphere Cu-poor chalcopyrite phases are hindered. In addition, the In + RbF(S)-PDT leads to the formation of a Rb:InxSy compound at the surface of the absorber. This almost Cu –free surface compound seems to impedes Cu inclusion during the In + RbF(S)-PDT in the indium sulfide spinelle lattice thanks to the occupation of its cationic vacancies by Rb.