Thin-Film Tandem Partners based on Inline-Processed (Ag,Cu)(In,Ga)Se₂

(Ag,Cu)(In,Ga)Se-2-based solar cells can be optimized for different applications by adjusting the composition. A wide range of compositions has been explored in a production-relevant deposition line with minor adjustments to the process. The best efficiencies are achieved for the (Ag,Cu)(In,Ga)Se-2 material optimized for single-junction applications, where most optimization efforts have been directed. For tandem devices the achievable bandgap range is suitable for both top and bottom cells. In both cases, material quality must be improved and further modifications to the growth process are necessary. For the bottom cell, standard and reduced-Ga compositions could already be successfully implemented in high-efficiency two-terminal tandems with solution-processed perovskite top cells. In this contribution we review our R&D line with mostly in-line deposition steps, discuss the performance of chalcopyrite solar cells at different compositions, and present modifications which are beneficial for the development of tandem devices. Best results for completely in-house processing are over 18 % for two-terminal perovskite/(Ag,Cu)(In,Ga)Se-2 tandems and over 26.6 % for the four-terminal configuration.