Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se2 Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses

ABSTRACT Polycrystalline widegap Cu(In,Ga)Se 2 (CIGSe) absorbers for top cells in photovoltaic tandem devices can be synthesized via Ga/(Ga + In) (GGI) ratios of > 0.5. However, the power conversion efficiencies of such high‐GGI devices are smaller than those of the record cells with GGI 0.5, which can be attributed to low bulk lifetimes and enhanced recombination at GBs in CIGSe absorbers in this compositional range.