Electrochemical study of one-step electrodeposition of copper-indium-gallium alloys in acidic conditions as precursor layers for Cu(In,Ga)Se2 thin film solar cells

Highlights: → Detailed study of Cu-In-Ga electrodeposition in acidic aqueous solutions. → Deposition of CuGa2, Cu2In, In, Ga phases depending on the electrolyte. → Cu-In-Ga dendritic deposit forms dense Cu(In,Ga)Se2 absorber after selenization. → Cu(In,Ga)Se2 solar cells with conversion efficiencies up to 9.3%. - Abstract: This paper investigates one step electrodeposition of copper indium gallium metallic precursor layers for preparing CuIn1-xGaxSe2 (CIGS) absorber layers in thin film solar cells (0 ≤ x ≤ 1). Electrodeposition was carried out in acidic aqueous solutions at about pH 2. At first partial single or binary electrodeposition systems Cu, In, Ga, Cu-Ga, Cu-In were investigated by cyclic voltammetry. Then ternary Cu-In-Ga electrodeposition system was studied. The nature of the supporting electrolyte (sodium sulfate vs. sodium chloride) and the influence of sodium citrate were more specifically investigated. The applied potential, the pH and the nature of the electrolyte were optimized to obtain x values around 0.3 needed for high efficiency devices. Depositions were carried out under potentiostatic conditions in a paddle cell configuration. The electrodeposited Cu-In-Ga alloys were annealed under Se atmosphere at temperatures between 400 and 600 deg. C to produce CIGS absorbers. Films were characterized by XRF, SEM and XRD analysis. Device efficiencies up to 9.3% are achieved for optimal gallium content.