Achieving High Thermoelectric Performance in p-Type BST/PbSe Nanocomposites through the Scattering Engineering Strategy.

To achieve high thermoelectric conversion efficiency in Bi0.4Sb1.6Te3 (BST) alloy is vital for its applications in low-grade energy harvesting. Here, we show that 56% increase in the power factor (PF) (from 16 to 25 μW cm-1 K-2) and 32% reduction of lattice thermal conductivity κL (from 0.56 to 0.38 W m-1 K-1) as well as an approximately four-fold decrease in bipolar-effect contribution κb (from 0.48 to 0.12 W m-1 K-1) can be achieved at 512 K through the incorporation of 0.2 vol % PbSe nanoparticles in the BST matrix. Analyses indicate that the remarkable increase in PF for the composite samples can be mainly attributed to strong electron scattering at the large interface barriers, inhibiting effectively the electron contribution to the total thermopower at elevated temperatures, while the large drop of κL and κb originates from enhanced phonon scattering by PbSe nanoinclusions as well as phase boundaries (among BST and PbSe nanophase) and suppression of electron transport, respectively. As a result, a maximum figure of merit (ZT) of 1.56 (at 400 K) and an average ZT (ZTave) of 1.44 in the temperature range of 300-512 K are reached. Correspondingly, a record projected conversion efficiency η = 11% is achieved at the cold side 300 K and hot side 512 K in the BST-based composite incorporated with 0.2 vol % PbSe nanoinclusions.