Superstructural Ordering in Hexagonal CuInSe2 Nanoparticles

Chalcogenide semiconducting nanoparticles are promising building blocks for solution-processed fabrication of optoelectronic devices. In this work, we report a new large-scale colloidal synthesis of metastable CuInSe2 nanoparticles with hexagonal plate-like morphology. Powder X-ray diffraction analysis of the nanoparticles showed that the structure of the nanoparticles is not simple hexagonal wurtzite-type CuInSe2 (space group P6(3)mc), indicating the formation of an ordered superstructure. Detailed insight into this structural aspect was explored by high-resolution electron microscopy, and the results evidence an unreported chemical ordering within the synthesized CuInSe2 nanoparticles. Specifically, while the Se sublattice is arranged in perfect wurtzite subcell, Cu and In are segregated over distinct framework positions, forming domains with lower symmetry. The arrangement of these domains within the hexagonal Se substructure proceeds through the formation of a number of planar defects, mainly twins and antiphase boundaries. As a semiconductor, the synthesized material exhibits a direct optical transition at 0.95 eV, which correlates well with its electronic structure assessed by density functional theory calculations. Overall, these findings may inspire the design and synthesis of other nanoparticles featuring unique chemical ordering; thus, providing an additional possibility of tuning intrinsic transport properties.