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

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 Cu_xIn_yS_z 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 CuInS ₂ 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-CO ₂-based deposition.