Preparation of CuGaSe2 absorber layers for thin film solar cells by annealing of efficiently electrodeposited Cu–Ga precursor layers from ionic liquids

CuGaSe2 absorber layers were prepared on molybdenum substrates by electrochemical codeposition of copper and gallium and subsequential annealing in selenium vapour. The electrodeposition was made from a deep eutectic based ionic liquid consisting of choline chloride/urea (Reline) with a plating efficiency of over 85 %. The precursor film composition is controlled by the ratio of the copper to gallium fluxes under hydrodynamic conditions and by the applied deposition potential. X-ray diffraction reveals CuGa2 alloying during the electrodeposition and CuGaSe2 formation after annealing. Photoluminescence (PL) and photocurrent spectroscopy revealed the good opto-electronic properties of the CuGaSe2 absorber films. The absorber layers have been converted to full devices with the best device achieving 4.0 % solar conversion efficiency.