High-efficiency CdTe thin-film solar cell with a mono-grained CdS window layer

High-crystalline-quality CdS thin films with a mono-grained layer of submicron grain size were successfully fabricated. CdS thin films prepared by chemical bath deposition were re-crystallized under different chemical atmospheres. The microstructure of the CdS films, the hetero-junction interface CdS/CdTe, and therefore the solar cell performance were critically dependent on the film process history of the window CdS layers. Heat treatment of a CdS precursor film coated with a CdCl₂ layer and under a high CdCl₂ vapor pressure reduced over-oxidation at the grain surface and promoted in-plane grain coalescence along the CdS/FTO (F-doped SnO₂) interface. A high-crystalline-quality, mono-grain CdS layer ensured homogenous intermixing of CdS and CdTe at the junction interface. A short-circuit current as high as 25.1 mA cm⁻² was obtained for a mono-grain-CdS/CdTe solar cell. The corresponding solar cell efficiency is 14.6%.