Thermoelectric performance of n-type polycrystalline SnSe with surface depletion by pressureless sintering

[Display omitted] •Polycrystalline SnSe samples were prepared by pressureless sintering.•Depending on the sintering time, the SnSe samples show the p-n transition.•Impurities from oxidation and the deficiency of Se result in the p-n transition.•Demonstration of high n-type thermopower of SnSe by inducing Se defects. In this study, polycrystalline SnSe samples were prepared by a series of mechanical alloying (MA), uniaxial compaction, and subsequently pressureless sintering. It was found that the grains in the resultant SnSe samples grow along the (111) plane direction, resulting in forming a layered structure. Depending on the sintering time, the SnSe samples show the conversion of p-type conduction with the Seebeck coefficient value of +503 μV/K to n-type conduction with the Seebeck coefficient value of −1500 μV/K. The samples were characterized using X-ray diffraction and Raman spectroscopy to reveal that the transition of the Seebeck properties is due to the imbalanced composition of SnSe caused by impurities (SnSe2, SnSe1-x) formed during pressureless sintering. Also, the experiments and characterization results demonstrated a possibility to enhance thermoelectric properties if the pressureless sintering conditions would be well-controlled.