Modulated doping has always been a conventional and effective way to optimize thermoelectric (TE) materials. Unfavorably, the efficiency of conventional doping is always restricted by the strong interdependence of thermoelectric parameters. Here, an unconventional grain boundary doping strategy is reported to solve the above problem using commercial p-type Bi0.5Sb1.5Te3 as matrix materials. Decoupling of the three key TE parameters and large net get of the figure of merit (ZT) could be achieved in Bi0.5Sb1.5Te3 materials by introducing the gradient Cu-doped grain boundary. A high ZT of ∼1.40 at 350 K and a superior average ZT of ∼1.24 (300-475 K) are obtained in the as-prepared samples, projecting a maximum conversion efficiency of ∼8.25% at ΔT = 200 K, which are considerably greater than those of the commercial Bi0.5Sb1.5Te3 matrix and the traditional Cu-doped Bi0.5Sb1.5Te3 sample. This study gives deep insights to understand the relationships between the microstructure and the carrier/phonon transport behaviors and promotes a new strategy for improving the thermoelectric performance of commercial p-type Bi0.5Sb1.5Te3 materials.
Keywords: Bi0.5Sb1.5Te3; commercial material; cu doping; grain boundaries; phonon scattering; thermoelectric.