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

Transition-metal dichalcogenide WSe is a potentially good thermoelectric (TE) material due to its high thermopower (). However, the low electrical conductivity (σ), power factor (PF), and relatively large lattice thermal conductivity (κ) of pristine WSe degenerate its TE performance. Here, we show that through proper substitution of Nb for W in WSe, its PF can be increased by ∼10 times, reaching 5.44 μW cm K (at 850 K); simultaneously, κ lowers from 1.70 to 0.80 W m K. Experiments reveal that the increase of PF originates from both increased hole concentration due to the replacement of W by Nb and elevated thermopower () caused by the enhanced density of states effective mass, while the reduced κ comes mainly from phonon scattering at point defects Nb. As a result, a record high figure of merit ZT ∼0.42 is achieved at 850 K for the doped sample WNbSe, which is ∼13 times larger than that of pristine WSe, demonstrating that Nb doping at the W site is an effective approach to improve the TE performance of WSe.