ELECTRODEPOSITION OF Cu-In-Ga FILMS FOR THE PREPARATION OF CIGS SOLAR CELLS

Electrochemical co-deposition of copper, indium and gallium was studied to obtain high-quality alloy thin films. 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. Complexing agents were employed to solubilize Cu, In and Ga ions at high pH. By optimizing the concentrations of metal salts, complexing agents, additives and the pH of the electrolytes, we were able to obtain adherent and high quality Cu-In-Ga films with controllable molar ratios of Cu/(Ga+In) and Ga/(Ga+In). We established that the current density applied during deposition had a pronounced effect on the composition and morphology of the films. At low current densities, the film was copper-rich and Ga content was minute. Ga and In content in the film increased as the current density was increased. The results indicated that desirable amounts of Ga could be incorporated into the deposit without increasing the applied current density above practical limits. In light of these results, we developed advantageous electrodeposition methods to achieve intentional grading of Cu, Ga and In within the Cu-In-Ga layer by changing the applied current density during the electroplating.