Toward low-cost large-area CIGS thin film: Compositional and structural variations in sequentially electrodeposited CIGS thin films

• CIGS film was prepared by selenizing electrodeposited Cu/In/Cu/Ga/Cu stacked layers.
• The Ga-rich phase was buried even it was electrodeposited near the surface.
• Additional heat treatment at 550 °C in Ar improved the Ga distribution.

In this study, we investigated the material growth and the local compositional homogeneity of CIGS thin films selenized from elemental Cu, In, Cu, Ga, and Cu stacked layers prepared by sequential electrodeposition, which is considered to be a promising production method for large-area thin film solar cells. It showed that the stacked layers first formed mixed metallic phases after a pre-heat treatment at 150 °C in vacuum. Several intermediate phases such as CuInSe2, CuInrichGapoorSe2, Cu2Se, InSe/In2Se3, CuGa2, and CuInpoorGarich formed in Se vapor at a lower temperature (e.g., <350 °C). Moreover, separation of the Ga-rich phase from the In-rich one was found in the film after selenization at 350 °C, which is due to relatively slow growth for the Ga-related grains that was buried by the In-rich phase growing faster in the out-of-plane orientation. All metallic phases converted to separate CuInSe2 and CuGaSe2 phases when selenized at 450 °C. Additional heat treatment at 550 °C in Ar improved the Ga distribution, which enhanced the light absorbance.

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