Excellent thermal stability and thermoelectric properties of Pnma-phase SnSe in middle temperature aerobic environment

SnSe is considered to be a promising thermoelectric material due to a high ZT value and abundant and non-toxic composition elements. However, the thermal stability is an important issue for commercial application. In particular, thermoelectric materials are in the high temperature for a long time due to the working condition. The present work investigates the thermal stability and oxidation resistance of single crystal SnSe thermoelectric materials. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the internal of SnSe crystal is not easily oxidized, while the x-ray photoelectron spectroscopy (XPS) results indicate that the surface of SnSe is slight oxidized to SnO₂. Even if the surface is oxidized, the SnSe crystal still exhibits stable thermoelectric properties. Meanwhile, the crystallization quality of SnSe samples can be improved after the appropriate heat treatment in the air, which is in favor of the carrier mobility and can improve the electrical conduction properties of SnSe. Moreover, the decrease of defect density after heat treatment can further improve the Seebeck coefficient and electrical transport properties of SnSe. The density functional theory (DFT) calculation verifies the important role of defect on the electrical conductivity and electron configuration. In summary, appropriate temperature annealing is an effective way to improve the transmission properties of SnSe single crystal thermoelectric materials.