Strain-induced competition of thermoelectric parameters in monolayer HfS2

Band convergence strategy has been widely used to improve thermoelectric performance. However, the effect of intervalley scattering caused by band convergence on the electrical and thermal properties is usually neglected. In this work, we investigate the thermoelectric properties of monolayer HfS2 under different tensile strains. The valence band of HfS2 can realize convergence at 6% strain. In this case, the Seebeck coefficient S reaches the maximum due to the significant increase in the density of states. Furthermore, the carrier scattering channels increases due to the intervalley scattering, which makes the electrical conductivity σ drop sharply. The competition between Seebeck coefficient and electrical conductivity leads the power factor (S2σ) decreasing with strain. On the other hand, band convergence effectively reduces the lattice thermal conductivity by softening phonons and increasing the phonon scattering rate. Furthermore, it enhances phonon scattering through electron–phonon coupling. The lattice thermal conductivity leads the way in the competition between thermoelectric parameters, resulting in a significant increase in ZT following band convergence. Our work provides important insights into the modulation of thermoelectric performance through strain and band convergence strategy.