Synthesis of CuInS₂/ZnS Nanocrystals with Thick Shell: The Effect of Temperature and Sulfur Precursor

As heavy-metal-free alternatives to Cd- and Pb-containing semiconductor nanocrystals (NCs), ternary I–III–VI₂ compounds NCs have been actively studied, especially the CuInS₂ NCs. Recently, it has been found that thick ZnS shelling can greatly improve the photochemical stability of such NCs, which undoubtedly enhances their application potential although it is still limited by the development of synthetic methods. This paper provides a facile method for preparation of thick-shell CuInS₂/ZnS NCs. The effects of reaction temperatures ($220^{\circ }$C and $300^{\circ }$C) and sulfur precursors (dodecanethiol and sulfur powder) on the shell overgrowth are discussed in detail. When low reaction temperature ($220^{\circ }$C) and inactive sulfur precursor are used, the overgrowth of ZnS shell is considerably slow and raising temperature have a limited impact on the particles’ size. On the contrary, high reaction temperature and reactive sulfur precursor can effectively improve the overgrowth rate of ZnS shell, and then thick-shell CuInS₂/ZnS NCs can be received. Furthermore, a high-speed centrifugation method is used to screen out product NCs with a relatively uniform size.