Simultaneously increased carrier concentration and mobility in p-type Bi0.5Sb1.5Te3 throng Cd doping

Abstract

To improve the thermoelectric properties of a material, the carrier concentration needs to be optimized first. But the increase of carrier concentration usually results in degraded carrier mobility, which restricts the enhancement in thermoelectric performance. Herein, we report the Cd doped Bi0.5Sb1.5Te3 which overcomes such a trade-off between carrier concentration and mobility. The doping of Cd results in significantly increased hole concentration, which successfully suppresses the bipolar diffusion. Meanwhile, magnetic measurements indicate that the Hall mobility increases with the doping of Cd owing to the decrease of anti-site defects. Thus, simultaneous increase of carrier concentration and mobility is realized in p-type Bi0.5Sb1.5Te3 through Cd doping, resulting in significantly enhanced power factor. In addition, the lattice disorder induced by the substitution of Cd for Sb/Bi leads to an obvious reduction in lattice thermal conductivity. As a result, a zT value of 1.2 at 120 °C is achieved for the 2 at% Cd doped sample. The peak zT of the 4 at% Cd doped sample is shifted to 185 °C due to the effectively suppressed bipolar effect and an average zT value of ∼1.0 is obtained in the temperature range of 50–300 °C. Our achievement demonstrates that there is still a significant room to improve the thermoelectric properties of the intensively investigated BiSbTe system by simply doping a properly selected element.