Giant Band Convergence and High Thermoelectric Performance in n-Type PbSe Induced by Spin-Orbit Coupling

An ideal thermoelectric material requires the multi-valley and strong dispersion band structure, for relieving the competition between thermopower and electrical conductivity, whereas the two features barely coexist in natural compounds. Here, the significantly improved thermoelectric performance in n-type PbSe-xAgSbS2 with the purposefully renormalized conduction band structure is reported. It is shown that the strong spin-orbit coupling effect splits the single valley at "L" point into three individuals delicately, as the Dirac point is shifted away from the high symmetry point by the decreasing lattice constant. Compared with the common PbSe-based compounds, the renormalized system exhibits a range of distinctive properties, such as the 2-3 times larger band gap, 5-10 times lower optimal carrier concentration, and weakly temperature-dependent Seebeck coefficient. Owing to the achieved giant band convergence and the low thermal conductivity, a high peak zT of 1.75 at 850 K and an outstanding average zT of 1.04 are obtained. Furthermore, the mechanical property and thermal stability of PbSe are considerably improved for the introduced high entropy effect and lattice shrinkage. This study reveals the remarkable impact of spin-orbit coupling on thermoelectric performance, and suggests that the optimized PbSe material holds great promise for practical applications.