Nanocluster seed-mediated synthesis of CuInS2 quantum dots, nanodisks, nanorods, and doped Zn-CuInGaS2 quantum dots

Abstract

Recent work using seed-mediated quantum dot growth has shown that nanoparticle seeds are a useful method for providing nucleation centers in order to control the nanoparticle shape and composition. Here we present a facile nanocluster seed-mediated protocol to synthesize CuInS₂ quantum dots (q-dots) and Zn and/or Ga doped CuInS₂ (Zn-CuInGaS₂) q-dots using (NH₄)₂S as a sulfur source. Due to high reactivity of (NH₄)₂S toward metal cations, we are able to isolate a CuInS₂ nanocluster (<2 nm with low crystallinity) intermediate at low temperatures (60 °C). By varying the conditions of a “heat-up” synthesis method, these nanoclusters can be grown into CuInS₂ with different morphologies (q-dots, nanodisks, and nanorods) and different crystalline phases (chalcopyrite and wurtzite). Further, we can incorporate dopant Ga³⁺ and Zn²⁺ ions into the q-dots by introducing the dopant either during the nanocluster formation or during the crystal growth stage, resulting in CuInGaS₂ and CuInZnS q-dots. Incorporation of both Ga and Zn increases the photoluminescence intensity compared to CuInS₂; furthermore, the absorption spectra and photoluminescent emission peaks are shifted to shorter wavelengths. With this nanocluster method, we have also synthesized pentanary Zn-CuInGaS₂ for the first time. Compared to quaternary CuInGaS₂ and CuInZnS, we observe a larger blue shift in the absorption spectra when both Zn and Ga are present. The interesting optical properties of Zn-CuInGaS₂ makes it an attractive material for photovoltaic devices and light emitting diodes. The ability to isolate the intermediate CuInS₂ nanoclusters provides a strategy for synthesizing a wide variety of tailored quaternary and pentanary metal chalcogenides in the future.