Electrodeposition of Cu–In alloys from a choline chloride based deep eutectic solvent for photovoltaic applications

Electrodeposition and post-annealing is a promising low-cost approach to the growth of Cu(In,Ga)Se2 for photovoltaic applications. However, In and Ga electrodeposition is not facile from aqueous electrolytes. Efficient electrodeposition can be achieved by using deep eutectic solvent (DES) based electrolytes since solvent decomposition reactions (such as hydrogen evolution reaction in water) do not occur. In this work, the electrochemical behavior of InCl3 and CuCl2–InCl3 on the DES 1:2 choline chloride:urea (ChCl:U) on a Mo rotating disk electrode is studied via cyclic voltammetry. The deposited Cu–In thin films are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) in terms of morphology and composition and X-ray diffraction (XRD) regarding crystal structure. The cyclic voltammetric studies on the ChCl:U–CuCl2–InCl3 system showed multiple cathodic and anodic responses, which were assigned to various crystalline phases. The crystalline phases, composition and morphology of the deposits were potential dependent. Cu–In intermetallics formation is studied as a function of deposition potential and electrolyte composition. Cu–In metal precursors were thermally annealed under selenium pressure to form CuInSe2