Crystallization of In-Se/CuInSe2 thin-film stack by sequential electrodeposition and annealing

CuInSe2 (CIS) films with large grain sizes and slightly In-rich composition ratios were realized by a sequential electrodeposition (ED) and annealing of In-Se/CIS bilayers. In general, ED-CIS films needed to be crystallized by annealing and the Cu/In ratios needed adjustment by KCN etching because they were amorphous with Cu-rich compositional ratios. KCN etchings cause pits and crevasses as defects by removal of Cu2−xSe compounds formed on the surface and in the grain boundary in the annealing process. These defects should work as shunt paths for solar cells with ED-CIS films. In this study, we attempted to fabricate In-Se/CIS bilayers by sequential ED and annealing to solve this serial issue. ED-In-Se films could be realized not on ED-CIS films but on the annealed CIS films by the difference in each oxidation potential. At the electric charges of 1.5-1.8 C for In-Se with a coulomb meter, Cu/In ratios of bilayers annealed at 600 °C for 10 min under Ar atmosphere could be adjusted to 0.9-1.0. At the same annealing condition, the complete intermixing of bilayers and the crystal grain growth were realized. As a result, the best solar cell fabricated with the film resulted in around 2% efficiency.