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 to the fast and controllable synthesis of SnSe with optimised thermoelectric properties. The NaOH concentration in solution precursors is demonstrated as a key factor in 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 consolidated from such rods obtains maximum ZT of 1.08 and 0.78 at 773 K along parallel and perpendicular to the pressing direction, respectively. Such ZT values are much higher than the ZT achieved by the pellet that was sintered from hydrothermal powers prepared without NaOH and consists of 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 to the fast, efficient and controllable synthesis of SnSe materials, but also identifies the key synthesis parameter in securing better thermoelectric performance.