Simultaneous Enhancement of the Power Factor and Phonon Blocking in Nb-Doped WSe2

Transition-metal dichalcogenide WSe2 is a potentially good thermoelectric (TE) material due to its high thermopower (S). However, the low electrical conductivity (sigma), power factor (PF), and relatively large lattice thermal conductivity (kappa L) of pristine WSe2 degenerate its TE performance. Here, we show that through proper substitution of Nb for Win WSe2, its PF can be increased by similar to 10 times, reaching 5.44 mu W cm-1 K-2 (at 850 K); simultaneously, kappa L lowers from 1.70 to 0.80 W m-1 K-1. Experiments reveal that the increase of PF originates from both increased hole concentration due to the replacement of W4+ by Nb3+ and elevated thermopower (S) caused by the enhanced density of states effective mass, while the reduced kappa L comes mainly from phonon scattering at point defects NbW. As a result, a record high figure of merit max similar to 0.42 is achieved at 850 K for the doped sample W0.95Nb0.05Se2, which is similar to 13 times larger than that of pristine WSe2, demonstrating that Nb doping at the W site is an effective approach to improve the TE performance of WSe2.