n-Type Ultrathin Few-Layer Nanosheets of Bi-Doped SnSe: Synthesis and Thermoelectric Properties

SnSe, an environmentally friendly layered chalcogenide, has fostered immense attention in the thermoelectric community with its high thermoelectric figure of merit in single crystals. Although the stride toward developing superior p-type SnSe as a thermoelectric material is progressing rapidly, synthesis of n-type SnSe is somewhat overlooked. Here, we report the solution-phase synthesis and thermoelectric transport properties of two-dimensional (2D) ultrathin (1.2–3 nm thick) few-layer nanosheets (2–4 layers) of n-type SnSe. The n-type nature of the nanosheets initially originates from chlorination of the material during the synthesis. We could increase the carrier concentration of n-type SnSe significantly from 3.08 × 1017 to 1.97 × 1018 cm–3 via further Bi doping, which results in an increase of electrical conductivity and power factor. Furthermore, Bi-doped nanosheets exhibit ultralow lattice thermal conductivity (～0.3 W/mK) throughout the temperature range of 300–720 K, which can be ascribed to the effective phonon scattering by an interface of SnSe layers, nanoscale grain boundaries, and point defects