Enhanced Band Convergence and Ultra-Low Thermal Conductivity Lead to High Thermoelectric Performance in SnTe.

SnTe, a structural analogue of champion thermoelectric (TE) material PbTe, has recently attracted wide attention for TE energy conversion. Herein, we demonstrate a co-doping strategy to improve the TE performance of SnTe via simultaneous modulation of electronic structure and phonon transport. The electrical transport is optimized by 3 mol % Ag doping in self-compensated SnTe (i.e., Sn1.03 Te). Further, Mg doping in SnAg0.03 Te resulted in highly converged valence bands, which enhanced the Seebeck coefficient markedly. The energy gap between two uppermost valence bands (ΔEv ) decreases to 0.10 eV in Sn0.92 Ag0.03 Mg0.08 Te compared to 0.35 eV in pristine SnTe. The optimized p-type carrier concentration and highly converged valence bands gave a high power factor of ca. 27 μW cm-1  K-2 at 865 K in Sn0.92 Ag0.03 Mg0.08 Te. The lattice thermal conductivity of Sn0.92 Ag0.03 Mg0.08 Te reached to an ultra-low value of ≈0.23 W m-1  K-1 at 865 K due to the formation of MgTe nanoprecipitates in SnTe matrix. These combined effects resulted in a high TE figure of merit, zT≈1.55 at 865 K in Sn0.92 Ag0.03 Mg0.08 Te.