Formation of High-Quality I-III-VI Semiconductor Nanocrystals by Tuning Relative Reactivity of Cationic Precursors

A method for the synthesis of nearly monodisperse CuInS2 semiconductor nanocrystals (from <2 to 20 nm) was developed using generic and air-stable chemicals in a non-coordinating solvent. Such "greener" approaches also allowed the reaction temperatures to be below 200 degrees C. By introducing reactivity-controlling ligands for Cu, namely thiols, control of the Cu:In stoichiometric ratio in the nanocrystals was achieved. Amines were identified as catalytic reagents for the rapid oxidation of the CuInS2 nanocrystals, which could be prevented by the formation of CuInS2/ZnS core/shell nanocrystals by a one-pot approach. CuInS2/ZnS core/shell nanocrystals also showed greatly improved optical properties, with photoluminescence quantum yield up to about 30% and an emission peak position tunable from 500 to 950 rim. The versatility of the synthetic strategy was demonstrated by extending it to the synthesis of AgInS2 nanocrystals by simply replacing the copper salt by a silver salt.