Optimization of alkali supply and Ga/(Ga+In) evaporation profile for thin (0.5 µm) CIGS solar cells

In this study, we investigated the performance of thin (0.5 μm) CIGS solar cells with focus on (1) the amount of alkali (NaF and KF) supplied to the CIGS layer, and (2) the Ga/(Ga+In) (GGI) evaporation profile during growth of the CIGS film. The best solar cell performance was achieved with a NaF precursor layer and a KF post-deposited layer of substantially higher doses per unit mass of CIGS compared to what is optimal for our standard 2 μm thick CIGS layer. The cells had a much weaker resulting GGI gradient in the film compared to the one obtained for standard CIGS, despite a similar deposition recipe. The best 0.5 μm solar cell achieved as a result of these optimization efforts had an efficiency of 13.8 % (without antireflection coating).