Improvement of anisotropic thermoelectric performance in polycrystalline SnSe by metallic AgSnSe2 compositing

SnSe is an emerging star material in thermoelectric community owing to its attractive electronic band structure and ultralow intrinsic lattice thermal conductivity. By now, aliovalent doping is often employed to be a route strategy to optimize the thermoelectric properties of SnSe via improving its poor electrical conductivity. In this work, AgSnSe2, as a metallic composite, is introduced with the aim to increase the hole concentration of SnSe via metal-semiconductor contact. It is demonstrated that compositing of AgSnSe2 can effectively increase the hole concentration of polycrystalline SnSe hosts by two orders of magnitude (from 1017 to 1019 cm−3) without deteriorating the carrier mobilities. Therefore, a lager power factor of 5.72 μW cm−1 K−2 is achieved at 773 K for the SnSe + 0.020AgSnSe2 sample perpendicular to the hot-pressing direction. Combined with the intrinsic low thermal conductivity, the maximum zT value of the sample can be boosted to 0.68 at 773 K, which is increased by 124% compared to that of the uncomposited counterpart. This work proves that composite engineering should be an efficient alternative strategy in optimizing the thermoelectric performance of polycrystalline SnSe and can be synergistically used with other sophisticated approaches.