Vacancy assisted growth of copper tantalum sulfide nanocrystals

Cu-based ternary chalcogenides have received significant interest as an alternative to conventional photovoltaic materials. CuInS 2 and CuInSe 2 are the most studied copper-based ternary chalcogenides for photovoltaics. Recently, copper tantalum sulfide (CuTaS 3 ) has been proposed as a potential light absorber for photovoltaics. The synthesis conditions and growth mechanism of ternary systems control the final composition and crystal structure. However, such studies have not been explored for copper tantalum sulfides. Here, we studied the formation and growth mechanism of Cu 3 TaS 4 nanocrystals (NCs) primarily using X-ray diffraction, transmission electron microscopy, and density functional theory (DFT) calculations. The reactions proceed via the formation of cubic Cu 2− x S NCs due to soft Lewis acid - soft Lewis base interaction. The Cu 2− x S have Cu vacancies, which can be controlled by the relative concentration of the Cu precursor. Ta incorporation occurs in the Cu 2− x S NCs at Cu vacancy sites, followed by the diffusion of Ta by replacing Cu into the lattice. Low packing of atoms in Cu 3 TaS 4 provides suitable diffusion channels for Ta and Cu atoms. The diffusion barriers of Ta atoms outweigh that of Cu atoms, implying a reaction rate controlled by Ta diffusion. Thus by varying the relative Cu precursor concentration, the concentration of Cu-vacancies in Cu 2− x S can be tuned, which controls the growth rate of Cu 3 TaS 4 . Understanding of the growth mechanism obtained in this paper will significantly contribute to the rational synthesis of various Cu-based ternary chalcogenides that is not possible by direct synthesis and hence will have an impact on potential applications in photovoltaics and photocatalysis. Cu 3 TaS 4 , a ternary chalcogenide, is a promising photovoltaic material. The growth of Cu 3 TaS 4 occurs via the formation of Cu 2− x S with Cu vacancies. Ta incorporation occurs in the Cu 2− x S at Cu vacancy sites, followed by diffusion of Ta to form Cu 3 TaS 4 .