Enhanced Thermoelectric Properties of p-Type Bi 0.5 Sb 1.5 Te 3 -Cu 8 GeSe 6 Composite Materials.

Bismuth-telluride-based thermoelectric materials have been applied in active room-temperature cooling, but the mediocre ZT value of ∼1.0 limits the thermoelectric (TE) device's conversion efficiency and determines its application. In this work, we show the obviously improved thermoelectric properties of p-type Bi 0.5 Sb 1.5 Te 3 by the Cu 8 GeSe 6 composite. The addition of Cu 8 GeSe 6 effectively boosts the carrier concentration and thus limits the bipolar thermal conductivity as the temperature is elevated. With the Cu 8 GeSe 6 content of 0.08 wt %, the hole concentration reaches 5.0 × 10 19 cm -3 and the corresponding carrier mobility is over 160 cm 2 V -1 s -1 , resulting in an optimized power factor of over 42 μW cm -1 K -2 at 300 K. Moreover, the Cu 8 GeSe 6 composite introduces multiple phonon-scattering centers by increasing dislocations and element and strain field inhomogeneities, which reduce the thermal conductivity consisting of a lattice contribution and a bipolar contribution to 0.51 W m -1 K -1 at 350 K. As a consequence, the peak ZT of the Bi 0.5 Sb 1.5 Te 3 -0.08 wt % Cu 8 GeSe 6 composite reaches 1.30 at 375 K and the average ZT between 300 and 500 K is improved to 1.13. A thermoelectric module comprised of this composite and commercial Bi 2 Te 2.5 Se 0.5 exhibits a conversion efficiency of 5.3% with a temperature difference of 250 K, demonstrating the promising applications in low-grade energy recovery.