Highly Textured Tin(II) Sulfide Thin Films Formed from Sheetlike Nanocrystal Inks

Abstract

Highly textured tin(II) sulfide thin films are prepared from a nanocrystal ink comprised of high-aspect-ratio nanosheets. The orthorhombic nanosheets are synthesized colloidally to isolate lateral growth and minimize the presence of alternate crystal phases. The tin sulfide films deposited from the nanosheets exhibit pure elemental composition, micrometer-sized grains, and a remarkable degree of texturing. The films consist of lamellar stacking of nanosheets with some intercalation, and the average sheet thickness is ∼30 nm. The SnS films have an indirect band gap of 1.23 eV, and density functional theory calculations indicate minimal quantum confinement contributions. The anisotropic electronic properties of tin sulfide are greatly intensified in films formed by this process, yielding an in-plane mobility of 5.7 cm2/(V s) but an out-of-plane resistivity as high as 30 kΩ cm. This work represents a new strategy for nanocrystal inks in which the nanocrystal morphology is tailored to direct film orientation, grain size, and transport properties. The method provides a route for the deposition of high-quality, layered semiconductor thin films with applications in photovoltaics and two-dimensional (2-D) electronics.