Controlled synthesis of CuInS₂, Cu₂SnS₃ and Cu₂ZnSnS₄ nano-structures: Insight into the universal phase-selectivity mechanism

Well-shaped CuInS₂ nanopyramids and nanodisks were synthesized by a wet-chemical method. The phase structure was controlled by the coordination strength between solvent and metal precursors. Zincblende CuInS₂ structure was obtained when copper iodide, indium acetate and 1-dodecanethiol were heated at 220 °C in 1-octadecene (ODE) or oleic acid (OA). When the solvent was replaced by oleylamine (OLA) or trioctylphosphine oxide (TOPO), the thermodynamically metastable wurtzite phase was obtained. Interestingly, zincblende phase can also be synthesized in OLA solvent by injecting 1-dodecanethiol into the reaction solution at 315°C. It was demonstrated that the CuInS₂ phase structure selectivity was determined at the initial formation step of a CuIn(SR)_x intermediate. An intermediate with high crystallinity will give metastable wurtzite CuInS₂ structure, while a low crystallinity intermediate transforms into zincblende CuInS₂ phase. This understanding of the crystal formation mechanism enabled us to extend the same synthetic method to another two attractive nanomaterials, Cu₂SnS₃ and Cu₂ZnSnS ₄. In this work, Cu₂SnS₃ and Cu ₂ZnSnS₄ nanocrystals with zincblende or wurtzite structures were readily synthesized using similar reaction conditions to CuInS₂ nanocrystals.