High thermoelectric performance of Bi-Te alloy: Defect engineering strategy

Waste-to-energy conversion generally means incineration, and the combustion of organic waste material for energy recovery involves generation of carbon dioxide. In contrast, thermoelectric energy conversion from waste heat is another way of green energy harvesting without generating pollution. Heat sources around room temperature are omnipresent in portable electronics and home appliances. The Bi-Te alloy system has been known to produce relatively high thermoelectric performance around room temperature. Here, we review the current state-of-the-art defect engineering strategies for Bi-Te alloy systems used to achieve high thermoelectric figure of merit performance. These include alloying effects, grain refinement, and nanocomposites; when used together they are commonly referred to as an all-scale hierarchical architecture. The alloying effect generates point impurities in the host matrix, grain refinement creates a large density of grain boundaries, while nanocomposites create a large amount of new interfaces. Inclusion of such effects significantly reduces the lattice thermal conductivity by enhanced phonon scattering at point defects, interfaces, and grain boundaries. Nonetheless, these types of defects scatter only low or high frequency phonons. Research on scattering of mid-range frequency phonons has rarely been reported. We propose an approach of plastic deformation that generates dislocations, which scatters mid-range frequency phonons. A material engineered using an all-scale hierarchical architecture with plastic deformation is able to scatter full spectrum phonons.