Cathodic electrochemical deposition of CuI from room temperature ionic liquid-based electrolytes

An innovative electrochemical route is proposed to obtain CuI films. The approach is based on the electrochemical reduction of I2 in a solution of copper bis(trifluoromethanesulfonyl)imide salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide room temperature ionic liquid. The mechanisms involved in the deposition process are analyzed by cyclic voltammetry, pointing out that the CuI formation occurs from the chemical reaction between the Cu2+ and I- generated from the I2 reduction. Homogenous films constituted of open-packed primary CuI nanocrystals (~100 nm) are obtained. The electrodeposition from organic solvent-based media is also investigated, finding that the solvent nature affects strongly to the nanocrystal packing density. Compact CuI thin films are electrodeposited from the isopropanol-based electrolytes. The electrodeposition of ZnO/CuI heterostructures, with high transmittance in the visible range (i.e. > 75%), is also reported. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification of ~ 2x103 at V = ± 1.5 V. This result anticipates a significant potential of the present electrochemical route to obtain CuI films with competitive optoelectronic functionalities. Keywords: CuI, Electrodeposition, Ionic liquid, Halide semiconductor