A Simple Single-Pot, Heat-Up Reaction for Uniform Hexagonal CuInS ₂ Nanoplatelets and the Role of Disubstituted Thiourea Chain Length in Their Growth

Copper indium sulfide (CIS) nanocrystals are actively being investigated for a variety of applications due to their favorable optical and electronic properties. While the most popular syntheses of these materials are simple heat-up reactions that form uniform crystals, they are not very tunable, which can limit the use of the crystals in certain applications. In this work, we present a robust heat-up synthetic method for hexagonal-phase CIS nanoplatelets, which offers the potential for increased tunability by decoupling the sulfur precursor from the solvent. By using disubstituted thioureas for the sulfur precursor, the growth process of the reaction may be altered by changing the substitutions on the thiourea. Two series of thioureas were investigated: <i>N</i>-butylthiourea and <i>N</i>-isopropylthiourea, with a butyl, octyl, or dodecyl group on the opposite nitrogen. The reaction was monitored by transmission electron microscopy (TEM), and it was found that following the initial nucleation and growth, there was first a size-focusing stage and then a second ripening stage. All particles were characterized by TEM and were found to have sizes ranging from 15 to 29 nm depending on the thiourea used and the duration of growth, with the greatest reproducibility of monodisperse sizes at approximately 15 and 20 nm.