Nanostructuring and band engineering boosting thermoelectric performance of Bi-Sb-Te alloys via CsBr doping

Bismuth telluride has become a widely commercially utilized thermoelectric material due to its exceptional properties. However, there remains space for further improvement in the properties of p-type Bi-Sb-Te thermoelectric materials obtained through the melting method. In this work, CsBr was employed to enhance the thermoelectric properties of Bi0.42Sb1.58Te3 (BST) materials. The bulk materials of BST + x wt% CsBr (x = 0, 0.10, 0.20, 0.30) were fabricated using a combination of melting method and spark plasma sintering. Cs and Br co-doping could significantly increase the electrical conductivity of BST alloy, while reducing thermal conductivity, resulting in a maximum figure of merit (ZT) value of 1.2 at 323 K and an average ZT value of 1.1 below 400 K for x = 0.20 sample. Density functional theory and transmission electron microscopy analyses reveal that Cs doping effectively reduces the band gap, increases the density of states near the Fermi level, and flattens the energy band, resulting in the great enhancement of electrical transport properties (with a maximum power factor of approximately 3500 mu W m(-1) K-2). Furthermore, Cs doping causes Sb to dissociate from the lattice and combine with free oxygen to form nanoscale Sb2O3, which efficiently scatters mid-frequency phonons and reduces thermal conductivity while maintaining a high Seebeck coefficient. This study presents a novel approach to resolving the trade-off between electrical and thermal conductivity in thermoelectric materials by solely utilizing CsBr doping.