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

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 Bi_0.4Sb_1.6Te₃. 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 ZT_ave of 1.24 (300-500 K) are achieved in the Bi_0.4Sb_1.6Te₃ + 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.