Improvement in the thermoelectric performance of highly reproducible n-type (Bi,Sb)2Se3 alloys by Cl-doping

Abstract

(Bi,Sb)₂Se₃ alloys are promising alternatives to commercial n-type Bi₂(Te,Se)₃ ingots for low-mid temperature thermoelectric power generation due to their high thermoelectric conversion efficiency at elevated temperatures. Herein, we report the enhanced high-temperature thermoelectric performance of the polycrystalline Cl-doped Bi_2−xSb_xSe₃ (x = 0.8, 1.0) bulks and their sustainable thermal stability. Significant role of Cl substitution, characterized to enhance the power factor and reduce the thermal conductivity synergetically, is clearly elucidated. Cl-doping at Se-site of both Bi_1.2Sb_0.8Se₃ and BiSbSe₃ results in a high power factor by carrier generation and Hall mobility improvement while maintaining converged electronic band valleys. Furthermore, point defect phonon scattering originated from mass fluctuations formed at Cl-substituted Se-sites reduces the lattice thermal conductivity. Most importantly, spark plasma sintered Cl-doped Bi_2−xSb_xSe₃ bulks are thermally stable up to 700 K, and show a reproducible maximum thermoelectric figure of merit, zT, of 0.68 at 700 K.