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 degrees 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 degrees 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 Cu2ZnSnS4. In this work, Cu2SnS3 and Cu2ZnSnS4 nanocrystals with zincblende or wurtzite structures were readily synthesized using similar reaction conditions to CuInS2 nanocrystals.