Electrodeposition methods and chemistries for deposition of CIGS precursor thin films

We studied the electroplating methods and chemistries for the deposition of several thin films including Cu-Ga, Cu-In, Cu-In-Ga, In-Se, Ga-Se and Cu-In-Ga-Se from alkaline plating solutions containing complexing agents. Our approach utilized the full potential of complexation by formulating aqueous electroplating solutions containing complexing agents in the alkaline regime instead of the commonly reported acidic regime. We found that a blend of complexing agents could be used to provide a complete chealation of all the Cu, In and Ga ions in these plating electrolytes. No appreciable complexation occurs between Se and the complexing agents. Therefore, the Se reduction potential could be independently controlled by the amount of dissolved Se in the In-Se, Ga-Se and Cu-In-Ga-Se solutions. We established that the current density applied during deposition had a pronounced effect on the composition and morphology of the films. Intentional grading of elemental species throughout the film thicknesses could be achieved in the plated layers by changing the applied current density or voltage during the electrodeposition steps. Various precursor formation techniques were developed utilizing these graded thin films for the preparation of CIGS absorber layers.