Characteristics of Cu(In,Ga)Se2 (CIGS) thin films deposited by a direct solution coating process

Cu(In,Ga)Se2 (CIGS) thin films were formed by a direct non-vacuum coating and a subsequent selenization of low cost precursor solutions, and their compositional, structural and optical properties were characterized. Selenized films showed a double-layered structure with an upper layer of chalcopyrite CIGS and an amorphous bottom layer mainly composed of carbon. For the upper CIGS layer, good compositional controllability for Cu and Ga was confirmed by linear relationship between metal ratios of the precursor solution and those of the selenized films. Effects of Cu and Ga contents on structural and optical properties of the films were also characterized by X-ray diffraction (XRD), Raman and photoluminescence (PL) analyses, and the results were interpreted by defect supercluster formation (VCu–InCu) in Cu-deficient films and mass and size difference between In and Ga, respectively. Further, the bottom layer was found to be mostly composed of conductive amorphous carbon, which is the main current flow path in the completed solar cells.

► Double layered CIGS/carbon films prepared by a direct solution coating.
► Controllability of compositions of the CIGS layer.
► Effects of Cu and Ga contents on properties of the CIGS layer.
► Structure of the bottom carbon layer.