Synthesis of CuInS₂ nanocrystals and their structural transformation triggered by ligand exchange

Chalcopyrite-type CuInS₂ NCs was synthesized by the hot-soap method. Mixed solutions, CuI and InCl₃ dissolved in the mixture of the tri-octylphosphite and 1-octadecene and the sulfur dissolved in tri-phenylphosphite, were used as source solutions; the hexadecylamine was additionally mixed as a surfactant before the reaction. It was observed that the product CuInS₂ NCs structurally transformed from the chalcopyrite(CP)- or zincblende(ZB)- to the wurtzite(WZ)-type depending on the amount of the surfactant and a storage time after the surfactant addition. Very weak photoluminescence in the near-infrared region was observed for the CP- or ZB-type NCs. This band was attributable to the electron-hole recombination via defect levels. No photoluminescence was detected for the wurtzite-type NCs.