Approaching Topological Insulating States Leads to High Thermoelectric Performance in n-Type PbTe

Realizing high thermoelectric performance requires high electrical transport properties and low thermal conductivity, which are essentially determined by balancing the interdependent controversy of carrier mobility, effective mass, and lattice thermal conductivity. Here, we observed an electronic band inversion (approaching topological insulating states) in Sn and Se co-alloyed PbTe, resulting in optimizing effective mass and carrier mobility. The Sn alloying in PbTe(Se) can narrow its band gap due to band inversion and induce a sharper conduction band (equals to lower carrier mass), which further facilitates high carrier mobility, similar to 251 cm(2) V-1 s(-1) in Pb0.89Sn0.11Te0.89Se0.11 at room temperature, thus leading to a high power factor. Meanwhile, we found that the lattice thermal conductivity kappa(l) can be reduced from similar to 0.77 Wm(-1) K-1 in PbTe to similar to 0.45 Wm(-1) K-1 in (Pb0.91Sn0.09)(Te0.91Se0.09) by producing point defects via Sn and Se co-alloying. Coupling reducing lattice thermal conductivity with integration of optimizing effective mass and carrier mobility by means of electronic band inversion, we obtained a maximum ZT value similar to 1.4 at 773 K in n-type (Pb0.93Sn0.07)(Te0.93Se0.07).