Mechanism of forming (2 2 0/2 0 4)-oriented CuInSe2 film on Al:ZnO substrate using a two-step selenization process

A (2 2 0/2 0 4)-preferred CuInSe2 (CIS) film formed using a two-step selenization process is reported, and the growth mechanism is explained. The CIS (2 2 0/2 0 4)-oriented film was grown on an Al:ZnO (AZO) coated glass for superstrate-type solar cell applications. The selenization temperature, Se vapor pressure, and reactive mechanisms of each selenization step were investigated. The first-step selenization at 400 °C favors the CIS (1 1 2) growth as the selenization time increases. For the second-step selenization, a high temperature (≧550 °C) and high Se vapor pressure throughout the process have a strong influence in promoting the CIS (2 2 0/2 0 4) growth. The oxygen in the self-formed In2O3 layer at the AZO interface can be replaced by selenium, and transforms to an In2Se3 (3 0 0)-preferred film, which favors the CIS (2 2 0/2 0 4) formation, in a transient and high Se vapor pressure selenization process. A Cu-rich surface, which is the usual case for selenizing precursor and which favors the CIS (1 1 2) growth, can be optimized to promote the CIS (2 2 0/2 0 4) growth by adding a thin In layer onto a slightly Cu-rich Cu/In precursor.