Development of Nanostructured Bi₂Te₃ with High Thermoelectric Performance by Scalable Synthesis and Microstructure Manipulations

Nanostructuring of thermoelectric (TE) materials leads to improved energy conversion performance; however, it requires a perfect fit between the nanoprecipitates' chemistry and crystal structure and those of the matrix. We synthesize bulk Bi₂Te₃ from molecular precursors and characterize their structure and chemistry using electron microscopy and analyze their TE transport properties in the range of 300-500 K. We find that synthesis from Bi₂O₃ + Na₂TeO₃ precursors results in n-type Bi₂Te₃ containing a high number density (N_v ∼ 2.45 × 10²³ m^-3) of Te-nanoprecipitates decorating the Bi₂Te₃ grain boundaries (GBs), which yield enhanced TE performance with a power factor (PF) of ∼19 μW cm^-1 K^-2 at 300 K. First-principles calculations validate the role of Te/Bi₂Te₃ interfaces in increasing the charge carrier concentration, density of states, and electrical conductivity. These optimized TE coefficients yield a promising TE figure of merit (zT) peak value of 1.30 at 450 K and an average zT of 1.14 from 300 to 500 K. This is one of the cutting-edge zT values recorded for n-type Bi₂Te₃ produced by chemical routes. We believe that this chemical synthesis strategy will be beneficial for future development of scalable n-type Bi₂Te₃ based devices.