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Considering only about one third of the world's energy consumption is effectively utilized for functional uses, and the remaining is dissipated as waste heat, thermoelectric (TE) materials, which offer a direct and clean thermal-to-electric conversion pathway, have generated a tremendous worldwide interest. The last two decades have witnessed a remarkable development in TE materials. This Review summarizes the efforts devoted to the study of non-equilibrium synthesis of TE materials with multi-scale structures, their transport behavior, and areas of applications. Studies that work towards the ultimate goal of developing highly efficient TE materials possessing multi-scale architectures are highlighted, encompassing the optimization of TE performance via engineering the structures with different dimensional aspects spanning from the atomic and molecular scales, to nanometer sizes, and to the mesoscale. In consideration of the practical applications of high-performance TE materials, the non-equilibrium approaches offer a fast and controllable fabrication of multi-scale microstructures, and their scale up to industrial-size manufacturing is emphasized here. Finally, the design of two integrated power generating TE systems are described-a solar thermoelectric-photovoltaic hybrid system and a vehicle waste heat harvesting system-that represent perhaps the most important applications of thermoelectricity in the energy conversion area.

from automobile exhausts, in powering the deep space probes, as well as managing spot-size distributed cooling of electronic devices and household appliances. [3] To date, TE conversion is mainly driven by the development of higher performing, practically stable, and environmentally friendly TE materials. The major scientific and technological challenge is to compete successfully with the established energy conversion technologies and broaden the range of industrial applications of thermoelectricity. The efficiency of a TE material is gauged by its dimensionless figure of merit ZT, defined as ZT = α 2 σT/(κ L +κ e), where α, σ, κ L , κ e , and T are the Seebeck coefficient, electrical conductivity, lattice thermal conductivity, electronic thermal conductivity, and the absolute temperature, respectively. [1] Among various classes of TE materials, mixed ionic-electronic conductors, such as Cu

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