Improving near-room-temperature thermoelectrics: the role of Ag2Se doping and Bi/Sb ratio in (Bi,Sb)2Te3†

Abstract

(Bi,Sb)₂(Te,Se)₃ remains the only commercially viable thermoelectric (TE) material for near-room-temperature applications. However, its TE performance is significantly impaired by intrinsic excitation at high temperatures, limiting its potential in power generation applications. We employ a two-step optimization strategy involving Ag₂Se doping and Bi/Sb ratio adjustment to enhance the carrier concentration and regulate the intrinsic defects, ultimately achieving progressively higher μ_w/κ_lat and optimized quality factor B. The diffusion of Ag atoms plays a pivotal role in optimizing the carrier concentration, suppressing high-temperature bipolar diffusion, and enhancing the power factor across the entire temperature range. Simultaneously, grain refinement and increased microporosity introduce abundant phonon scattering centers, markedly reducing the lattice thermal conductivity. Fine-tuning the Bi/Sb ratio further modifies the intrinsic defects, leading to a peak zT of ∼1.3 at 403 K and an average zT of ∼1.17 at 303–503 K. Furthermore, a 7-pair integrated TE module achieves a conversion efficiency of ∼4.6% at a temperature difference of 208 K. This work offers a novel perspective on enhancing bismuth telluride materials’ and device performance by mitigating the electron–phonon coupling via the μ_w/κ_lat framework.