Ag-alloying of CIGS absorber layers: impact of the composition, rubidium fluoride post-treatment and bandgap variations

Chalcopyrite-based solar cells have achieved remarkable efficiency, yet further advancements remain challenging. The partial substitution of copper (Cu) with silver (Ag) in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells presents a promising approach to enhance absorber properties and improving device performance. This study explores the moderately high-concentration Ag incorporation (Ag/(Ag + Cu) = 0.19) via thermal evaporation prior to co-evaporation of CIGS absorbers, combined with rubidium fluoride (RbF) post-deposition treatment. Additionally, the impact of Ag alloying is examined across absorbers with bandgaps ranging from 1.12 to 1.55 eV. Results indicate that Ag incorporation significantly influences gallium distribution, promotes larger grain growth, and enhances open-circuit voltage (V_oc). Notably, (Ag,Cu)(In,Ga)Se₂ (ACIGS) absorber with a 1.23 eV bandgap achieves a power conversion efficiency of 18.1%, while a 1.55 eV bandgap absorber reaches 7.1%.