Simultaneous Enhancement of the Power Factor and Phonon Blocking in Nb-Doped WSe 2 .

Transition-metal dichalcogenide WSe 2 is a potentially good thermoelectric (TE) material due to its high thermopower ( S ). However, the low electrical conductivity (σ), power factor (PF), and relatively large lattice thermal conductivity (κ L ) of pristine WSe 2 degenerate its TE performance. Here, we show that through proper substitution of Nb for W in WSe 2 , its PF can be increased by ∼10 times, reaching 5.44 μW cm -1 K -2 (at 850 K); simultaneously, κ 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 W 4+ by Nb 3+ and elevated thermopower ( S ) caused by the enhanced density of states effective mass, while the reduced κ L comes mainly from phonon scattering at point defects Nb W . As a result, a record high figure of merit ZT max ∼0.42 is achieved at 850 K for the doped sample W 0.95 Nb 0.05 Se 2 , which is ∼13 times larger than that of pristine WSe 2 , demonstrating that Nb doping at the W site is an effective approach to improve the TE performance of WSe 2 .