Ultrathin Orthorhombic PbS Nanosheets

Colloidal lead sulfide nanosheets have attracted broad interest for a wide variety of device applications, including field-effect transistors, solar cells, and spintronic devices. Whereas confinement effects in PbS quantum dots are well studied, they are still unclear in 2-dimensional ultrathin PbS nanosheets, especially in the 1 nm thickness range. In this work, we report a synthesis of monodisperse, rectangular-shaped PbS nanosheets with a thickness of 1.2 nm, using Pb(thiocyanate)₂ as a single source precursor. These nanosheets have an orthorhombic crystal structure, a direct bandgap, and weak optical absorption properties. This is evident from the lack of both excitonic absorption features and photoluminescence, and was corroborated by density functional theory calculations. Although these properties make the PbS nanosheets unsuitable for emission based applications, the nanosheets are highly photoconductive in films, with a responsivity up to 0.1 A W^-1 and a detectivity of 1.3 × 10⁹ Jones. We detected higher photoconductivity of these films under bending stress compared to that of films of PbS quantum dots.