This study investigates the impact of a RbF post‐deposition treatment (PDT) on the properties of Cu‐free, wide‐gap ( E G = 1.5 eV) Ag(In,Ga)Se 2 (AIGS) solar cells with either opaque Mo or transparent In 2 O 3 :W back contacts. The formation of a Rb‐In‐Se surface phase and Cd in‐diffusion from the buffer into this layer are detected. In addition, Rb is mainly located in Ag‐depleted and In‐enriched grain boundaries and at the back interface. The RbF‐PDT leads to decreased fill factor ( FF ) values, without providing any gain in open‐circuit voltage ( V OC ). This FF deterioration is more pronounced when a In 2 O 3 :W back contact is used. It is suggested that transport barriers form at the Rb‐In‐Se/AIGS front and at the AIGS/GaO x /In 2 O 3 :W back interfaces after RbF‐PDT. In addition, the GaO x thickness at the rear electrode increases. The absence of a V OC boost may be explained by the missing doping increase after the RbF‐PDT. Lastly, the AIGS solar cells from this study show slightly lower efficiencies as compared to Cu‐containing devices with the same E G but higher Ga content. However, the collection at rear illumination is marginally improved, reaching up to 72% bifaciality in short‐circuit current for the best cell with an In 2 O 3 :W back contact.
Keller et al. (Wed,) studied this question.