Highly Converged Valence Bands and Ultralow Lattice Thermal Conductivity for High-Performance SnTe Thermoelectrics

A two-step optimization strategy is used to improve the thermoelectric performance of SnTe via modulating the electronic structure and phonon transport. The electrical transport of self-compensated SnTe (that is, Sn_1.03 Te) was first optimized by Ag doping, which resulted in an optimized carrier concentration. Subsequently, Mn doping in Sn_1.03-x Ag_x Te resulted in highly converged valence bands, which improved the Seebeck coefficient. The energy gap between the light and heavy hole bands, i.e. ΔE_v decreases to 0.10 eV in Sn_0.83 Ag_0.03 Mn_0.17 Te compared to the value of 0.35 eV in pristine SnTe. As a result, a high power factor of ca. 24.8 μW cm^-1  K^-2 at 816 K in Sn_0.83 Ag_0.03 Mn_0.17 Te was attained. The lattice thermal conductivity of Sn_0.83 Ag_0.03 Mn_0.17 Te reached to an ultralow value (ca. 0.3 W m^-1  K^-1 ) at 865 K, owing to the formation of Ag₇ Te₄ nanoprecipitates in SnTe matrix. A high thermoelectric figure of merit (z T≈1.45 at 865 K) was obtained in Sn_0.83 Ag_0.03 Mn_0.17 Te.