Enhancement of Thermoelectric Properties of n-Type Bi₂Te_3–xSe_x by Energy Filtering Effect

A pair of n-type Bi2Te3–xSex and p-type (Bi,Sb)2Te3 is known as a promising candidate for assembling a high thermoelectric efficiency module operating at near room temperature. While the dimensionless figure of merit (zT) of p-type (Bi,Sb)2Te3 is commonly larger than 1.0, n-type Bi2Te3–xSex has a lower zT value of ∼0.8 at room temperature. Here, we aim to enhance the zT of n-type Bi2Te3–xSex through the energy filtering effect that can improve the Seebeck coefficient by adding Au. In the Bi2Te2.8Se0.2 + 5 at % Au composite, the Seebeck coefficient is significantly improved, and the electrical resistivity does not change significantly, leading to an approximately twice as high power factor as that of the non-Au-added one at near room temperature. Also, the addition of Au suppresses the thermal conductivity. These advantages result in a maximum zT of over 1.0 at room temperature and average zT value of 1.05 at T = 300–400 K, an ∼75% improvement, which is comparable to those of the reported n-type Bi2Te3-based materials. Also, Au addition shows no negative effect on the mechanical properties as well as high-temperature stability of Bi2Te3–xSex. These results indicate that Au addition is a promising method to improve the thermoelectric properties of n-type Bi2Te3–xSex used for assembling a practical thermoelectric module operating at near room temperature.