High density lath twins lead to high thermoelectric conversion efficiency in Bi2Te3 modules.

Abstract

Thermoelectric (TE) generators based on bismuth telluride (Bi2Te3) are recognized as a credible solution for low-grade heat harvesting. In this study, an combinative doping strategy of both the donor (Ag) and the acceptor (Ga) in Ag9GaTe6 as dopants is developed to modulate the microstructure and improve the ZT value of p-type Bi0.4Sb1.6Te3. Specifically, the distribution of Ag and Ga in the matrix synergistically introduces multiple phonon scattering centers including lath twins, triple junction boundaries, and Sb-rich nanoprecipitates, leading to an obviously suppressed lattice thermal conductivity of 0.50 W m-1 K-1 at 300 K. At the same time, such unique microstructures of lath twins synergistically enhance the room-temperature power factor to 48.8 μW cm-1 K-2 and improve the Vickers hardness to 0.90 GPa. Consequently, a high ZT of 1.40 at 350 K and ZTave of 1.24 (300-500 K) are achieved in the Bi0.4Sb1.6Te3 + 0.03 wt% Ag9GaTe6 sample. Based on that, a competitive conversion efficiency of 6.5% at ΔT = 200 K is obtained in the constructed 17-couple TE module, which exhibits no significant change in the output property after 30 thermal cycle tests benefiting from the stable microstructure.