Microstructural study of the CdS/CuGaSe2 interfacial region in CuGaSe2 thin film solar cells

The microstructure of the CdS/CuGaSe2 interface region in Cu-rich CuGaSe2-based polycrystalline thin film solar cells with KCN-treated absorber layers are characterized. Two recipes for the chemical bath deposition (CBD) of CdS with different bath temperatures (60 and 80 °C) are compared. Coherent Cu–Se precipitates are observed in both cases in the grains of the absorber layer. This precipitation cannot be avoided and seems to be a principal limitation for the performance of Cu-rich CuGaSe2-based thin film solar cells. There is a significant difference between both recipes concerning the interaction with the absorber layer surface. For bath temperatures of 80 °C the interaction is much stronger and Cu–S inclusions are found in the buffer layer. These may be responsible for shunts across the pn junction. Owing to the reduced interaction of the CdS deposited at 60 °C there are no Cu–S inclusions. For the 80 °C recipe the CdS/CuGaSe2 interface region consists of a continuous transition zone with low defect ...

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