Drastic Modification of Lattice Thermal Conductivity in Thermoelectrics Induced by Electron-Hole Pairs

Low lattice thermal conductivity (kappa(L)) is desirable for advancing thermoelectric (TE) materials and devices. However, kappa(L) depends on many factors such as phonon scattering sources, electron-phonon interactions, etc. It remains not fully understood how kappa(L) is influenced by excited electron-hole (e-h) pairs ubiquitously present in thermoelectrics. To address this issue, the constrained density functional theory (CDFT) simulations are performed to investigate the phonon transport properties of two typical TE materials, Mg2Si and PbTe. Surprisingly, at high e-h concentrations of similar to 10(21) cm(-3), the kappa(L) of Mg2Si is reduced significantly by similar to 30% due to the softening phonon modes. In contrast, the kappa(L) of PbTe first decreases by similar to 18% at a relatively low e-h concentration of 2.34 x 10(20) cm(-3), but it is enhanced by similar to 3.4% as the carrier concentration increases to 7.02 x 10(20) cm(-3). The different behaviors of these two materials arise from the different distributions of excess electrons and holes under eh excitation. The simulation results suggest that controlling e-h pairs may offer a promising approach to design high-performance TE devices.