Interplay Between Morphology, Optical Properties, and Electronic Structure of Solution-Processed Bi2S3 Colloidal Nanocrystals

Bi2S3 nanocrystals with different shapes and sizes are obtained by a hot injection approach using bismuth neodecanoate and thiolamine as bismuth and sulfur precursors. The colloid morphology, from nanodots to nanorods, with sizes ranging from 3-4 nm to 40-50 nm strongly depends on the preparation conditions such as injection temperature and ratio of Bi/S precursors and ultimately impacts the optical and electrical properties of the final nanocrystals. The resulting products are analyzed using X-ray powder diffraction (XRD), transmission electron microscope (TEM), UV-vis absorption spectroscopy, and photoluminescence spectroscopy (PL). A blue shift in the band gap is observed at 1.87, 1.89, and 2.04 eV as we go from nanodots to nanorods with aspect ratios of 3, 5, and 1, respectively. These observations indicate quantum confinement effects due to the different diameters of nanocrystals. The crystallinity and morphology of nanocrystals influence significantly the PL emission, decreasing for nanodots and increasing for nanorods with the high aspect ratio. It also results in the variation in electronic structure from X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission (UPS) characterization that the valence band maximum shifts to low-energy level corresponding to the samples with aspect ratios of 3, 5, and 1, respectively.