Optimizing the thermoelectric transmission of monolayer HfSe2 by strain engineering

The demand for clean energy is driving enhancements in the efficiency of conversion of thermoelectric materials. The electronic and phononic properties of thermoelectric materials can be adjusted through straining to improve their figure of merit. In this work, the authors systematically examine the effects of biaxial strain on the phononic, electronic, and thermoelectric properties of monolayer 1T-HfSe2 by using first-principles calculations combined with semi-classical Boltzmann transport theory. The results show that the monolayer HfSe2 is a good n-type thermoelectric material. The tensile strain caused the valence band to converge and increased the Seebeck coefficient to induce the transition of HfSe2 from n-type to p-type thermoelectric material. The thermal conductivity kappa(l) of the lattice decreased from 5.54 Wm(-1)kappa(-1) to 1.16 Wm(-1)kappa(-1) at 300 K owing to stronger phonon scattering and lower velocity of the phonon group as the tensile strain increased the bond distance and weakened the bonds. Due to improvements in electrical and thermal transport, ZT(max) significantly increased from 0.16 to 2.41 for the p-type material, and from 0.53 to 1.91 for the n-type material. This shows that strain engineering can improve electrical transport and reduce thermal conductivity to improve thermoelectric performance.