Synergistic band gap expansion and grain refinement toward high thermoelectric efficiency and robust mechanics in p-type (Bi,Sb)2Te3

Abstract

Bismuth telluride-based thermoelectric materials remain the benchmark candidates for near-room temperature applications. However, their widespread utilization is hindered by moderate thermoelectric efficiency and insufficient mechanical robustness. In this work, we report Ag₉GaSe₆-doped p-type Bi_0.3Sb_1.7Te₃ prepared via high-energy ball milling followed by hot pressing. The incorporation of Ag₉GaSe₆ increases carrier concentration, expands the band gap, refines grains, and introduces abundant defects. These synergistic effects lead to a simultaneous enhancement of electronic and phononic transport, manifested by an improved power factor across the entire temperature range, effective suppression of bipolar conduction, and strengthened phonon scattering. Consequently, the optimized Bi_0.3Sb_1.7Te₃ + 0.15 wt% Ag₉GaSe₆ achieves a peak zT of ∼1.4 at 375 K, an average zT of ∼1.25 between 300–500 K, and a Vickers hardness of ∼0.92 GPa. Moreover, a fabricated 7-pair thermoelectric device delivers a maximum conversion efficiency of ∼6.4% under a temperature difference of 200 K. This work demonstrates a viable strategy to concurrently boost thermoelectric performance and mechanical reliability in bismuth telluride-based materials, paving the way for their practical deployment in energy conversion devices.