π-SnS Colloidal Nanocrystals with Size-Dependent Band Gaps

Abstract

Colloidal quantum dot (QD) solids are materials that exploit the quantum confinement properties of the constituent nanocrystals. Significant progress in QD optoelectronic devices has been made mainly using compounds with concerning high degree of toxicity for practical applications. Sn-chalcogenides are among the possible environmentally benign alternatives the bulks of which have demonstrated intriguing properties for energy devices. Nanostructuring these Sn-chalcogenides may create variations in their crystal structures and properties. Here, we demonstrate robust quantum confinement effects in small-diameter cubic SnS colloidal nanocrystals (NCs) and their potential exploitation for high-performance optoelectronic devices. Well-controlled production of cubic SnS colloidal NCs with a 4–10 nm diameter is established by developing a one-pot synthesis procedure in an inert condition that allows Sn complexation with only a single type of ligand molecule. The analyses of the X-ray diffractogram and transmission electron micrograph revealed that the structure of NCs is the so-called π-type chiral and cubic structures. These NCs behave as quantum dots, exhibiting a quantum confinement effect with strong variations of energy band gaps by size. The photodetectors of the SnS NCs exhibit high responsivity comparable to the other established QD systems, although the channels are made only from a single or few layer(s). This new compound will open new pathways for establishing environmentally safe and high-performance QD optoelectronic and photocatalysis devices.