Electrodeposition of Cu-Ga Precursor Layer from Deep Eutectic Solvent for CuGaS₂Solar Energy Thin Film

Abstract

CuGaS2 solar energy thin film is fabricated with electrochemical deposition of precursor from deep eutectic solvent (DES) based on choline chloride and urea (commercially known as Reline) to eliminate the interference of hydrogen evolution reaction (HER). The process involves electrodeposition of Cu-Ga precursor on molybdenum substrate from Reline and subsequential annealing in sulfur vapor. The formation of CuGa2 alloy in precursor is observed and pure ternary chalcopyrite CuGaS2 phase in good polycrystalline structure without secondary phase is obtained after thermal treatment. The influence of applied deposition potential on the crystalline phase, morphology, compositions and carrier concentration of the films were investigated. The Cu/Ga ratio decreases with decreasing the deposition potential benefiting the formation of a pure crystallized CuGaS2 thin film. A relative positive deposition potential results in a larger crystalline size benefitting the photoelectrical conversion. Impedance spectroscopy test demonstrates the semiconductor property of the synthesized CuGaS2 polycrystalline thin film is p-type and the carrier concentration increases with negative shift of deposition potential.