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

Low lattice thermal conductivity (κL) is desirable for advancing thermoelectric (TE) materials and devices. However, κL depends on many factors such as phonon scattering sources, electron–phonon interactions, etc. It remains not fully understood how κL 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 ∼1021 cm–3, the κL of Mg2Si is reduced significantly by ∼30% due to the softening phonon modes. In contrast, the κL of PbTe first decreases by ∼18% at a relatively low e–h concentration of 2.34 × 1020 cm–3, but it is enhanced by ∼3.4% as the carrier concentration increases to 7.02 × 1020 cm–3. The different behaviors of these two materials arise from the different distributions of excess electrons and holes under e–h excitation. The simulation results suggest that controlling e–h pairs may offer a promising approach to design high-performance TE devices.