Thermoelectric and Thermionic Transport in MoSe2

We study the thermoelectric properties of bulk MoSe₂ within relaxation time approximation including electron-phonon and ionized impurity interactions using first-principles calculations. The anisotropy of this 2D layered metal dichalcogenide is studied by calculations of electron mobility in the cross-plane and the in-plane directions. We show that the cross-plane mobility is two orders of magnitude smaller than the in-plane one. The inclusion of van der Waals interactions further lowers the carrier mobility in the cross-plane direction but minimally affects the in-plane one. The results for in-plane electrical mobility and conductivity are in close agreement with experimentally reported values indicating the accuracy of the calculations. In addition to thermoelectric transport, 2D layered heterostructures are appropriate for solid-state thermionic applications. We study electron transport across metal-MoSe₂-metal structures using first-principles calculations combined with Green’s function method. We study the effect of the number of layers, the energy barrier, and the asymmetry of the contacts on the performance of MoSe2-based thermionic converters and show that the key to high-performance thermionic diodes is to make a low-energy barrier, low-resistance metallic contacts and we identify copper as the optimum metallic contact to MoSe₂ based devices.