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.