Electrophoretic deposition of Ga-Cu core-shell nanocomposites for CuGaS₂ thin films

This work reports on the syntheses of copper-gallium bimetallic nanoparticles by ultrasound-assisted chemical reduction method in alcohol solutions to prepare CuGaS₂ thin films. Gallium metal (Ga) in the form of pellet was dispersed in tetraethylene glycol by ultrasonic treatment. The chemical reduction of copper sulfate (CuSO₄) into copper metal by NaBH₄ at the surface of the Ga droplets enabled the formation of Ga-Cu core-shell structure. The Ga droplets with submicrometer size were homogenously coated with ~40-nm Cu nanoparticles. The exothermic transition of the Ga-Cu core-shell nanocomposite materials occurred at 485 °C, which corresponds to the crystalline phase formation of γ-Cu₉Ga ₄. Ga-Cu nanocomposites with a 1:1 ratio were deposited onto molybdenum substrate via electrophoretic deposition method as a precursor of CuGaS₂, a p-type semiconductor. Mechanical pressing and sulfurization provided dense CuGaS₂ thin films with good crystallinity and high phase purity.