Currently, the application of thermoelectric power generators based on Bi2Te3-based alloys for the recovery of low-quality waste heat is still limited because of the aggravated intrinsic excitation of the material at elevated temperatures. In this study, excessive Te and dopant I are introduced to the n-type Bi2Te2.4Se0.6 material with the purpose of suppressing its intrinsic excitation and improving the thermoelectric performance at elevated temperatures. These Te and I atoms act as electron donors to effectively reduce the density of minority carriers (holes) and weaken their negative contribution to the Seebeck coefficient. Likewise, the initial band structure and the carrier scattering mechanism are scarcely altered. Similar to the p-type Bi2Te3-based alloys, we found the "conductivity-limiting" mechanism is also well obeyed in the present n-type Bi2Te2.4Se0.6-based materials. The reduced minority carrier partial electrical conductivity in these Te-excessive and I-doped Bi2Te2.4Se0.6 samples significantly decreases the bipolar thermal conductivity, leading to lowered total thermal conductivity at elevated temperatures. Finally, the peak zT is successfully shifted up to higher temperatures for these Te-excessive and I-doped Bi2Te2.4Se0.6 samples. A maximum zT of 1.0 at 400 K and an average zT of 0.8 at 300-600 K have been realized in Te-excessive Bi2Te2.41Se0.6.
Keywords: bismuth telluride; intrinsic excitation; minority carrier; power generation; thermoelectric.