Currently, CuInS2 nanocrystals enjoy a renaissance since they are non-toxic and provide exciting optical and electronic properties similar to toxic CdS or PbS nanocrystals. They find applications in numerous fields including bioimaging, photocatalysis, light emitting diodes and, in particular, solar energy conversion devices. Recently, a room temperature synthesis route for the preparation of copper indium sulfide (CuInS2) nanocrystals was developed at ICTM.
The synthesis is performed by dissolving copper and indium xanthates as precursors together with oleylamine in toluene followed by stirring for several hours at ambient temperature leading to nanocrystals, which have a size of about 3 nm and are stabilized with oleylamine ligands. The formation of the nanocrystals proceeds via a direct reaction of the amine with the metal xanthates. Thus, it is not necessary to heat up the precursors to induce a thermal decomposition of the metal xanthates as usually described in literature. Whereas the thermal pathway follows a Chugaev elimination mechanism, the performed time resolved NMR investigations disclose that the room temperature synthesis proceeds via an alternative reaction mechanism. First, the oleylamine coordinates to the metal center followed by a substitution reaction on the thiocarbonyl group of the xanthate giving the N-oleyl-thiocarbamate derivative and a metal hydrosulfide. Condensation of the metal hydrosulfide groups with concurrent elimination of hydrogen sulfide leads to copper indium sulfide nanocrystals. No compounds which would support a Chugaev mechanism were observed. The presented method can be also easily extended to the synthesis of other metal sulfide nanocrystals.For more information, see the open-access article: