Evaluation of hydrogen evolution reaction on chemical bath deposited Cu2O thin films: Effect of copper source and triethanolamine content

Abstract

The chemical bath deposition method was used to deposit thin films of cuprous oxide. The effect of copper source and triethanolamine content on the optical, morphological, structural, electrochemical and photoelectrochemical properties of the thin films for the development of photocathodes for hydrogen production was investigated. Triethanolamine promotes the complexing of Cu+ ions independent of the copper source used, its increase promotes thicker films due to better growth control and reduction of rapid Cu2O precipitation in the bulk solution. The increase in thickness promoted a change in preferential orientation from (111) plane to (200) plane, which also influenced and reduced the conductivity because there is a decrease in disorder (Urbach energy EU). The thickness also varied due to copper source used, reaching the thickest films with copper nitrate while the thinnest films with copper acetate, this tendency is in agreement with their solubility in water. The lower solubility reduces the complexing of Cu + ions which promotes the Cu2O precipitation in the bulk solution, limiting the growth of the film. Also, electrical properties varied (measured as disorder EU) with copper source. The most conductive being the thin films deposited with copper acetate and nitrate while the most resistive being the films deposited with copper sulphate. Very little variation in optical properties was observed, estimating the band gap in the range of 2.62–2.66 eV, while high absorption coefficient (>105 cm−1) was calculated below the absorption edge (460–470 nm). All thin films showed p-type semiconducting behavior with a flat band potential in the range of −0.10 to 0.18 V (Ag/AgCl sat electrode), which confirms their ability to work as photocathodes for hydrogen production. The best photoelectrochemical performance was observed with the thinnest films, which also are the most conductive and present the highest values of absorption coefficient.