Enhancing the electrical transport properties of two-dimensional semiconductors through interlayer interactions†
Thermoelectric materials attract great attention due to promising applications in refrigeration and waste heat recovery. Strategies based on band engineering have been proposed to identify new thermoelectric materials with high electrical transport performance. These approaches typically seek enhancement of the Seebeck coefficient via sharp changes in the electronic density of states near the Fermi level. Here, we emphasize a long-overlooked approach for enhancing the Seebeck coefficient through manipulation of the electronic group velocity. This can be realized through the interlayer interactions in two-dimensional materials. We construct numerous bilayers in a high-throughput manner. It is found that interlayer interactions universally introduce significant changes in the energy bands. Among the 129 isotropic systems, 34 of the bilayers exhibit higher power factors compared with the corresponding monolayers. Importantly, the improvement of the power factors and Seebeck coefficients in the As2I6, Sb2I6, and MoSe2 bilayers is due to increased electronic group velocity, contrary to the paradigm where sharper electronic densities of states favor thermoelectric performance. Our work not only illustrates the use of interlayer interactions for tuning the band structures of thermoelectric materials, but also highlights the vital importance of the group velocity for simultaneously enhancing the Seebeck coefficient and electrical conductivity.