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

• Syntheses of Cu–Ga nanoparticles by ultrasound-assisted chemical reduction.
• Liquid gallium metal droplets dispersed in tetraethylene glycol.
• Ga–Cu/Mo substrate by electrophoretic deposition as a precursor of CuGaS2.

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-Cu9Ga4. 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.