Cu(In_1-xGa_x)S₂ Thin Films Prepared by Sulfurization of Precursors Consisting of Metallic and Gallium Sulfide Layers

Abstract

Cu(In 1- x Ga x )S 2 alloy thin films were prepared by annealing Cu/In/GaS precursors under a H 2 S atmosphere. The adhesion of the film to a Mo-coated soda-lime glass substrate was improved by introducing a GaS deposit as the first precursor layer. Optical transmission measurements revealed that the band gap of the thinner alloy film shifts from 1.42 to 2.41 eV with increasing composition ratio x . This sulfurization process, however, does not give rise to a single-phase thick Cu(In 1- x Ga x )S 2 alloy film when x is larger than 0.2. Therefore, the composition of Ga in the film should be restricted to a smaller amount. A solar cell of over 10% efficiency has been obtained using the thin film prepared from the precursor with composition ratios of Cu/(In+Ga) = 1.2 and Ga/(In+Ga) = 0.05.