Facile microwave-assisted hydrothermal synthesis of SnSe: impurity removal and enhanced thermoelectric properties†
Bottom-up solution synthesis has been considered as a facile and energy-efficient approach for SnSe thermoelectric materials. Herein, we report a microwave-assisted hydrothermal method for the fast and controllable synthesis of SnSe with optimised thermoelectric properties. The NaOH concentration in solution precursors was demonstrated as a key factor influencing the phase composition, diameter, and morphology of the hydrothermal products as well as the thermoelectric properties of the corresponding sintered pellets. It is found that a NaOH : SnCl2 molar ratio of 30 leads to the formation of phase-pure SnSe microrods, and the pellet constructed from these rods obtains a maximum ZT of 1.08 and 0.78 at 773 K in parallel and perpendicular alignments to the pressing direction, respectively. These ZT values are significantly higher than the ZT value achieved by the pellet that was sintered from the hydrothermal powders prepared without NaOH and comprised the mixed phases of SnSe, SnO2, and SnSe2. This enhancement is primarily due to the improved power factor together with the lower lattice thermal conductivity owing to the significantly reduced fraction of SnO2 in the pellet. This study not only provides a microwave-assisted solution strategy for the fast, efficient, and controllable synthesis of SnSe materials, but also identifies the key synthesis parameters for securing better thermoelectric performance.