Interstitial Cu: An Effective Strategy for High Carrier Mobility and High Thermoelectric Performance in GeTe

Dense point defects can strengthen phonon scattering to reduce the lattice thermal conductivity and induce outstanding thermoelectric performance in GeTe-based materials. However, extra point defects inevitably enlarge carrier scattering and deteriorate carrier mobility. Herein, it is found that the interstitial Cu in GeTe can result in synergistic effects, which include: 1) strengthened phonon scattering, leading to ultralow lattice thermal conductivity of 0.48 W m⁻¹ K⁻¹ at 623 K; 2) weakened carrier scattering, contributing to high carrier mobility of 80 cm² V⁻¹ s⁻¹ at 300 K; 3) optimized carrier concentration of 1.22 × 10²⁰ cm⁻³. Correspondingly, a high figure-of-merit of ≈2.3 at 623 K can be obtained in the Ge_0.93Ti_0.01Bi_0.06Te-0.01Cu, which corresponds to a maximum energy conversion efficiency of ≈10% at a temperature difference of 423 K. This study systematically investigates the doping behavior of the interstitial Cu in GeTe-based thermoelectric materials for the first time and demonstrates that the localized interstitial Cu is a new strategy to enhance the thermoelectric performance of GeTe-based thermoelectric materials.