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 Bi2–xSbxTe3 and n-type Bi2Te3–xSex, 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 Bi2Te3–xSex is inferior in performance to p-type Bi2–xSbxTe3 near room temperature, restricting the device efficiency. In this work, we developed high-performance n-type Bi2–xSbxTe3, a composition long thought to only make good p-type thermoelectrics, to replace the mainstream n-type Bi2Te3–xSex. 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 Bi2Te3–xSex to 6 for Bi2–xSbxTe3, 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 Bi1.5Sb0.5Te3, which is higher than those for most known n-type thermoelectric materials, including commercial Bi2Te3–xSex 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 Bi2–xSbxTe3 as a replacement of the mainstream n-type Bi2Te3–xSex near room temperature.