Thermoelectric Performance Enhancement in Commercial Bi0.5Sb1.5Te3 Materials by Introducing Gradient Cu-Doped Grain Boundaries

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 Bi_0.5Sb_1.5Te₃ as matrix materials. Decoupling of the three key TE parameters and large net get of the figure of merit (ZT) could be achieved in Bi_0.5Sb_1.5Te₃ 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 Bi_0.5Sb_1.5Te₃ matrix and the traditional Cu-doped Bi_0.5Sb_1.5Te₃ 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 Bi_0.5Sb_1.5Te₃ materials.