Uniform deposition of ternary chalcogenide nanoparticles onto mesoporous TiO2 film using liquid carbon dioxide-based coating

•Simultaneous deposition of two different metal precursors dissolved in l-CO2.•Uniform deposition of CuInS2 nanoparticles across mesoporous TiO2 film.•Highly crystalline CuInS2 formed on mesoporous TiO2 film.•Nearly stoichiometric ratio of Cu:In:S was obtained.

We report the simultaneous deposition of two different metal precursors dissolved in liquid carbon dioxide (l-CO2), aiming to the synthesis of ternary chalcopyrite (e.g. CuInS2) nanoparticles on a mesoporous TiO2 film. The l-CO2-based deposition of Cu and In precursors and subsequent reaction with a dilute H2S gas resulted in CuxInySz nanoparticles uniformly deposited across the entire thickness of a mesoporous TiO2 film. Further heat treatment (air annealing and sulfurization) led to the formation of more stoichiometric CuInS2 nanoparticles. The formation of CuInS2 on TiO2 was confirmed by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The crystal growth of CuInS2 was also found to be controllable by adjusting the number of coating cycles of the l-CO2-based deposition.