Mechanism of Property Difference between n-Type and p-Type Bi ₂ Te ₃ -Based Thermoelectric Materials

The thermoelectric performance of the n-type Bi 2 Te 3 -based material is generally poorer than that of the p-type material, whereas there is a lack of an in-depth understanding of the performance-difference mechanism behind. Thus, by combining density functional theory calculations with experimental characterization, the intrinsic physical mechanisms of the performance difference between n-type Bi 2 Te 2.85 Se 0.15 and p-type Bi 0.4 Sb 1.6 Te 3 hot-extruded thermoelectric materials were clarified in this work. One of the primary reasons for the poorer thermoelectric performance of the n-type material is associated with its high intrinsic carrier concentration due to higher carrier effective mass, which results in lower Seebeck coefficient and higher carrier thermal conductivity. Another important reason is that the p-type material has more twin boundaries, which could increase its intrinsic carrier concentration and improve the thermoelectric performance through selectively transporting carriers and scattering phonons. Based on the above theoretical findings, a twining-induced strategy of decoupling thermal and electrical transport was proposed for improving thermoelectric performance.