Synergistically Optimized Thermal Conductivity and Carrier Concentration in GeTe by Bi–Se Codoping

The GeTe compound has been revealed to be an outstanding thermoelectric compound, while its inherent high thermal conductivity restricts further improvement in its performance. Herein, we report a study on the synergistic optimization of the thermoelectric performance of GeTe by Bi–Se codoping. It is shown that the introduction of Bi decreases the carrier concentration and increases the structural parameter of the interaxial angle. With Se doping in the Te site, the lattice thermal conductivity is markedly reduced, while the carrier mobility is slightly influenced. Compared with the singly Se-doped GeTe, the Ge1–xBixTe1–ySey samples are more closed to a cubic phase, as indicated by the larger interaxial angle. On account of the reduction of carrier concentration and thermal conductivity, a ZTmax of 1.80 at 665 K and a high ZTave of 1.39 (400–800 K) are obtained in Ge0.94Bi0.06Te0.85Se0.15. This work reveals that the interaxial angle is vital to the performance optimization of rhombohedral GeTe.