Achieving High Carrier Mobility and Low Lattice Thermal Conductivity in GeTe-based Alloys by Cationic/anionic Co-Doping

The IV–VI compound GeTe is considered as a promising alternative to the toxic PbTe for high-efficiency mid-temperature thermoelectric applications. However, pristine GeTe suffers from a high concentration of Ge vacancies, resulting in an excessively high hole concentration (> 1 × 1021 cm−3), which greatly limits its thermoelectric enhancement. To address this issue, CuBiTe2 alloying is introduced to increase the formation energy of Ge vacancies in GeTe, thereby inhibiting the high carrier concentration. The carrier scattering caused by the electronegativity difference between different elements is suppressed due to the similar electronegativity of Cu and Ge atoms. A relatively high hole mobility is obtained, which ultimately leads to a high power factor. Additionally, by introducing Se as an alloying element at the anionic site in GeTe, dense point defects with mass/strain-field fluctuations are induced. This contributes to the strengthening of phonon scattering, thereby reducing the lattice thermal conductivity from 1.44 W·m−1·K−1 for pristine GeTe to 0.28 W·m−1·K−1 for Ge0.95Cu0.05Bi0.05Te0.9Se0.15 compound at 623 K.