Synergistic Improvement of BiI₃ and In on Thermoelectric Properties of Zone-Melted n-Type Bi₂Te_2.7Se_0.3

Bismuth telluride (Bi 2 Te 3 ) is the only commercial thermoelectric material so far, and it is also the best thermoelectric material with the best performance at room temperature. However, up to now, the zT value of n -type materials used on a large scale is only about 1.0; this makes the thermoelectric conversion efficiency of thermoelectric devices and thermoelectric applications stagnant. Therefore, under the synergistic action of BiI 3 and In, the properties of n -type Bi 2 Te 2.7 Se 0.3 material are improved. The experiments show that BiI 3, which is nontoxic and non-absorbent, can effectively improve the power factor of the material and inhibit the bipolar effect and is an effective dopant. After the inclusion of In, due to the low bond energy of the In–Te bond, it is easy to form the InTe phase in the matrix material and then introduce the second phase, and the presence of the second phase in the material will scatter phonons and reduce the lattice thermal conductivity so that it can reach 0.31 W m –1 K –1 at 350 K. Ultimately, a high maximum zT of 1.20 at 325 K and a remarkable average zT of 1.04 (300–500 K) are attained in the In 0.005 Bi 1.995 Te 2.7 Se 0.3 + 0.13 wt % BiI 3 sample.