Regulation of exciton for high thermoelectric performance in (Bi, Sb)2Te3 alloys via doping with Pb and multi-scale microstructure

Abstract

Herein, we report a reproducible improvement of the thermoelectric performance in BiSbTe alloy via kinetically and dynamically regulating excitation behavior in the intrinsic excitation regime. Doping with Pb increases the carrier concentration to the optimal value, kinetically pushing the onset temperature for the intrinsic excitation from 350 K for Bi0.46Sb1.54Te3 sample to 450 K for Pb0.01(Bi0.46Sb1.54)0.995Te3 sample. Moreover, the refined grains, nanostructures as well as dense dislocations induced by the melt-spinning process not only lower the lattice thermal conductivity via intensifying the interfacial phonon scattering but also selectively block the migration of minority carrier, modifying the dynamic process of the charge carrier and resulting in a smaller ratio of (μe/μh). This improves the power factor in the measured temperature range and suppresses the bipolar thermal conductivity in the intrinsic excitation regime. Thus, a maximum power factor of 4.44 mW m−1 K−2 and the lowest thermal conductivity of 1.06 W m−1 K−1 are attained for the sample with refined grains and nanostructures. All these contribute to the highest ZT value of 1.31 at 380 K and the highest average ZT value of 1.17 from 300 K to 500 K for Pb0.002(Bi0.46Sb1.54)0.999Te3 sample. This improved thermoelectric property was further verified in a thermoelectric module with the conversion efficiency of 4.38 % under a temperature gradient of 175 K, which is 20 % higher than that of the commercial ZM-based module under the same temperature gradient.