Anomalous behavior of the electronic transport properties in thermoelectric materials due to electron-phonon interaction

In this work we employ ab initio calculations to investigate the effects of the electron-phonon interaction on the transport properties of thermoelectric materials, focusing on the example of half-Heusler semiconductors. We calculate electron-phonon scattering rates using Wannier-Fourier interpolation of electron-phonon matrix elements and the recently developed electron-phonon averaged approximation. We find that the electron-phonon scattering can lead to anomalous behavior of the transport coefficients, namely the conductivity decreases with increasing number of charge carriers, and Seebeck coefficient changes sign, leading to an unusual peak in the power factor at high carrier concentrations. We discuss the origin and magnitude of this enhancement effect starting from the electronic band structure and identify design rules to maximize the material's performance.