Surface modifications of chalcopyrite CuInS₂ thin films for photochatodes in photoelectrochemical water splitting under sunlight irradiation

Copper chalcopyrite semiconductors include a wide range of compounds that are of interest for photoelectrochemical water splitting which enables them to be used as photochatodes for H₂ generation. Among them, CuInS₂ is one of the most important materials due to its optimum band gap energy for sunlight absorption. In the present study, we investigated the application of CuInS₂ fabricated by electrodeposition as photochatodes for water splitting. Thin film of CuInS₂ chalcopyrite was formed on Mo-coated glass substrate by stacked electrodeposition of copper and indium followed by sulfurization under H₂S flow. The films worked as a H₂ liberation electrode under cathodic polarization from a solution containing Na₂SO₄ after loading Pt deposits on the film. Introduction of an n-type CdS layer by chemical bath deposition on the CuInS₂ surface before the Pt loading resulted appreciable improvements of H₂ liberation efficiency and a higher photocurrent onset potential. Moreover, the use of In₂S₃ layer as an alternative n-type layer to the CdS significantly improved the H₂ liberation performance: the CuInS₂ film modified with In₂S₃ and Pt deposits worked as an efficient photocathode for photoelectrochemical water splitting.