n‑Bi_2–xSb_xTe₃: A Promising Alternative to Mainstream Thermoelectric Material n‑Bi₂Te_3–xSe_x near Room Temperature

For decades, the V₂VI₃ compounds, specifically p-type Bi_2–xSb_xTe₃ and n-type Bi₂Te_3–xSe_x, have remained the cornerstone of commercial thermoelectric solid-state cooling and power generation near room temperature. However, a long-standing problem in V₂VI₃ thermoelectrics is that n-type Bi₂Te_3–xSe_x is inferior in performance to p-type Bi_2–xSb_xTe₃ near room temperature, restricting the device efficiency. In this work, we developed high-performance n-type Bi_2–xSb_xTe₃, a composition long thought to only make good p-type thermoelectrics, to replace the mainstream n-type Bi₂Te_3–xSe_x. The success arises from the synergy of the following mechanisms: (i) the donorlike effect, which produces excessive conduction electrons in Bi₂Te₃, is compensated by the antisite defects regulated by Sb alloying; (ii) the conduction band degeneracy increases from 2 for Bi₂Te₃ and Bi₂Te_3–xSe_x to 6 for Bi_2–xSb_xTe₃, favoring high Seebeck coefficients; and (iii) the larger mass fluctuation yet smaller electronegativity difference and smaller atomic radius difference between Bi and Sb effectively suppresses the lattice thermal conductivity and retains decent carrier mobility. A state-of-the-art zT of 1.0 near room temperature was attained in hot deformed Bi_1.5Sb_0.5Te₃, which is higher than those for most known n-type thermoelectric materials, including commercial Bi₂Te_3–xSe_x ingots and the popular Mg₃Sb₂. Technically, building both the n-leg and p-leg of a thermoelectric module using similar chemical compositions has key advantages in the mechanical strength and the durability of devices. These results attested to the promise of n-type Bi_2–xSb_xTe₃ as a replacement of the mainstream n-type Bi₂Te_3–xSe_x near room temperature.