Noninjection gram-scale synthesis of monodisperse pyramidal CuInS2 nanocrystals and their size-dependent properties.

CuInS2 nanocrystals are viewed as very good candidates for solar harvesting and light emitting applications. Here we report an optimized noninjection method for the synthesis of monodisperse pyramidal CuInS2 nanocrystals with sizes ranging from 3 to 8 nm. This synthetic route is able to yield large amounts of high quality nanoparticles, usually in the gram scale for one batch experiment. The structure and surface studies showed that the resulting nanocrystals are pyramids of CuInS2 tetragonal phase with well-defined facets, while their surface is functionalized with dodecanethiol capping ligands. Spectroscopic and electrochemical measurements revealed size-dependent optical and electrical properties of CuInS2 nanocrystals, demonstrating quantum confinement effects in these systems. The size-dependent optical bandgaps of CuInS2 nanocrystals were found to be consistent with the finite-depth well effective mass approximation (EMA) calculations, which provide a convenient method to estimate the diameter of CuInS2 pyramids. Additionally we have also determined some important physical parameters, including bandgaps and energy levels, for this system, which are crucial for the integration of CuInS2 nanocrystals in potential device applications.