Boosting the Thermoelectric Performance of PbSe from the Band Convergence Driven By Spin-Orbit Coupling

PbSe has been expected to be a competitor of the excellent thermoelectric material PbTe, whereas its performance has proved to be limited by its intrinsic electronic structure. In this work, the improved thermoelectric performance of PbSe originating in the novel spin-orbit coupling effect is reported. By alloying with NaSbSe2, valence band convergence and bandgap enlargement are achieved in PbSe, resulting in a significantly enlarged Seebeck coefficient. Theoretical calculations indicate that a modified electronic structure by spin-orbit coupling would lead to exotic thermoelectric properties and that it prefers a lower carrier concentration than the known optimal value for PbSe. When Cd-doping is introduced to decrease the carrier concentration, a high peak ZT of 1.6 at 850 K and a remarkable average ZT of 0.95 are obtained in Pb0.8Na0.1Sb0.08Cd0.02Se. Among the reported high ZT PbSe-based compounds, the sample exhibits the highest Seebeck coefficient and lowest thermal conductivity. This study provides an insight into band structure tuning of Lead chalcogenides and promotes a new strategy for the optimization of thermoelectric performance.