Synergistic modulation of band structure and phonon transport for higher thermoelectric performance of WSe₂

Tungsten diselenide (WSe₂) emerges as a promising thermoelectric (TE) candidate due to its high thermopower (S), cost-effectiveness, and environmentally friendly characteristics. However, the pristine WSe₂ exhibits limited electrical conductivity (σ), a low power factor (PF), and high lattice thermal conductivity (к_L), which restrict its overall TE performance. Here, we show that via co-doping of Nb for W and Te for Se in WSe₂, its power factor (PF) undergoes 17-fold increase, reaching 8.91 μW cm⁻¹ K⁻² at 850 K. Simultaneously, its lattice thermal conductivity (к_L) decreases from 1.70 W m⁻¹ K⁻¹ to 0.48 W m⁻¹ K⁻¹. Experiments and DFT analysis demonstrate that the enhancement of the PF is linked to enhanced density of state, effective mass (m_d^∗), improved mobility (μ) and elevated electrical conductivity (σ) owing to replacing Se²⁻ with Te²⁻; while the observed 72 % reduction in κ_L results primarily from phonon scattering at defects Te_Se and Nb_W. As a result, a remarkable ZT_max ∼ 1 is obtained at 850 K for the sample W_0.95Nb_0.05Se_2-yTe_y with y = 0.3, which is ∼30-fold increase than that of WSe₂, proving that Nb and Te co-doping in WSe₂ can significantly boost its TE performance.