Twist-Angle-Dependent Phonon Transport of van der Waals MoSe₂ Thermoelectric Materials for the Recycling of Waste Heat

Transition-metal dichalcogenide MoSe 2, two-dimensional (2D) materials with a hexagonal lattice, are promising candidates for direct energy conversion due to their excellent thermoelectric properties. Twist and interlayer van der Waals (vdW) force modulation have attracted considerable attention as effective approaches to reduce thermal conductivity and hence improve thermoelectric performance. However, the underlying mechanism analysis of the twist-angle-dependent thermal conductivity remains incomprehensive, and there has been few research on the joint effects of twist and interlayer coupling strength. In this study, the heat transfer of monolayer and bilayer MoSe 2 was systematically investigated by nonequilibrium molecular dynamics and density functional theory. The results indicated that in the presence of twist angles, the calculated thermal conductivities of monolayer and bilayer MoSe 2 both exhibit “W-shaped”, achieving a maximum decrease of 56.6%. For bilayer MoSe 2, the thermal conductivities corresponding to different twist angles all decrease monotonically with increasing vdW interaction strength, and structures with twist angles larger than 5° show greater sensitivity to the variation of vdW forces. Twist induces the increase of the lattice constant of bilayer MoSe 2, leading to the reduction of the Brillouin zone and the emergence of folded phonon modes. The characteristics that dominate heat transfer, heat capacity, phonon group velocity, and phonon lifetime, display divergent tendencies, with heat capacity increasing with lattice constant while phonon group velocity and phonon lifetime do the reverse. This would provide an effective guide to further elucidate the thermal characteristics and to enhance the efficiency in thermoelectric energy conversion applications of 2D nanothermoelectric materials.