Thermoelectric properties of two-dimensional selenene and tellurene from group-VI elements

Single-layered two-dimensional (2D) materials have become very attractive due to their novel electronic behavior after the discovery of graphene. Here, we report the electronic structure and thermoelectric properties of single-layered 2D selerium (selenene) and tellurium (tellurene) by using density functional theory calculation. Both selenene and tellurene show three-phonon limited thermal conductivity. The prominent anharmonic phonon scattering process for tellurene makes it show the lowest lattice thermal conductivity among 2D single elemental materials till now. Their special square unit cells give rise to a highly anisotropic electronic structure along the zigzag and the armchair direction. The large effective mass and Seebeck coefficient along the armchair direction suggest that the thermal performance is better than that of the zigzag direction. The effect of spin-orbit coupling increases the band gap and is found to be crucial for tellurene. These studies provide a way to tune the thermoelectric properties of selenene and tellurene in the future.