The bottleneck of thermoelectrics is their low efficiency, focusing on the fundmental physics and chemistry of thermoelectrics, the team devotes the efforts on the design and development of high-efficiency thermoelectric materials and devices. Based on our previous knowledge, we will continue our work on the topics including: 1. Advanced synthesis technology; 2. Comprehensive characteriazation of electrical, thermal, optical, magnetic properties and microstructures; 3. Underlying physics and chemistry of energy materials; 4. Design and development of novel energy materials under the guidance of theory; 5. New semiconductor materials for other applications.
Utilizing the equilibrium phase diagram and precipitation kinetics, we developed a controllable technique for making thermoelectric nanocomposites. We directly observed a significant reduction in lattice thermal conductivity due to the well controlled nanostructures. It is also demonstrated that the critical parameter for phonon scattering is the interface spacing but not the size of the inclusions as normally emphasized. Most importantly, it is found that many nanostructured thermoelectrics have their lattice thermal conductivity approaching the theoretical minimum, which limits the further enhancement in
into a narrow space by reducing the lattice thermal conductivity only. This guides us to increase thermoelectric performance through other strategies such as band structure engineering for electronic property enhancement.
Surprisingly, both n- and p-type PbSe can achieve zT above 1, making PbSe a competitive and less expensive alternative to PbTe. High zT In p-type is due to the convergence of bands. In n-type PbSe, with much smaller band degeneracy, high zT achieved is due to a weak scattering strength (deformation potential—the degree of interaction between charge carriers and lattice vibrations), which leads to higher mobility of electrons compared to that of holes. We demonstrated the importance of scattering strength in selecting and engineering optimum band structures for thermoelectrics.
Optimal carrier concentration strongly depends on temperature