Hierarchical Low-Temperature n-Type Bi₂Te₃ with High Thermoelectric Performances

The high performance of a multistage thermoelectric cooler (multi-TEC) used in a wide low-temperature range depends on the optimized thermoelectric (TE) performance of materials during the corresponding working temperature range for each stage. Despite decades of research on the commercial TE materials of Bi₂Te₃, the main research is still focused on temperatures above 300 K, lacking suitable hierarchical low-temperature n-Bi₂Te₃ for multistage TEC. In this work, we systematically investigated the influence of doping concentration and matrix material compositions on the TE performance of n-Bi₂Te₃ below room temperature by the high-energy ball milling and hot deformation. Consequently, two hierarchical n-Bi₂Te₃ materials with excellent mechanical properties working below 248 and around 298 K, respectively, have been screened out. The Bi₂Te_2.7Se_0.3 + 0.03 wt % TeI₄ can be adopted in a low-temperature range that exhibits the high average figure of merit (zT_ave) of 0.61 within 173-248 K. Meanwhile, the Bi₂Te_2.7Se_0.3 + 0.05 wt % TeI₄ sample displays a competitive zT_ave of 0.85 within 248-298 K, which can be applied above 248 K. The research of hierarchical TE materials provides valuable insights into the high-performance design of multistage TE cooling devices.