Thermoelectric conversion technology uses the carrier transport inside the semiconductor to realize the direct conversion between thermal energy and electrical energy. Thermoelectric devices have the advantages of small size, no moving parts, no noise, high reliability and long service life. They have wide and important applications in the fields of special power supplies, waste heat power generation, and portable precision refrigeration. Focusing on layered structure thermoelectric materials such as bismuth telluride and new IV-VI group compounds, the optoelectronic functional materials and device team of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences has closely combined theory and experiment to carry out a series of Research work on characteristics and effectiveness.
The research team added Ge0.5Mn0.5Te with high hardness to bismuth telluride, and combined the two processes of zone melting and hot pressing. The obtained composite material has good mechanical properties and thermoelectric properties, which makes it more Conducive to the application of micro thermoelectric devices (J. Mater. Chem. A 2019, 7: 9241). In terms of layered Mg-based Zintl phase thermoelectric materials, the research team first elaborated from the theoretical perspective the common localized formation characteristics of such materials and the multi-energy valley control mechanism (J. Mater. Chem. A 2019, 7: 8922), And cooperated with the team of Professor Ren Zhifeng of the University of Houston in the United States to achieve the performance optimization of SmMg2Bi2 high-entropy thermoelectric materials (J. Mater. Chem. A 2020, doi: 10.1039 / c9ta13224d). In terms of new IV-VI compounds, the research team systematically elaborated the coordinated regulation of doped cation orbital energy levels and structural factors on the light and heavy valence bands, and cooperated with the team of Professor Mori of the National Institute of Materials Science and Technology in Japan to achieve a significant improvement of the GeTe thermoelectric figure (Mater. Today Phys. 2019, 9, 100094).
Recently, for SnSe thermoelectric materials with a layered structure, the research team prepared PbBr2 doped SnSe0.95 single crystal, combined with test characterization and first-principles calculations, revealed the evolution of the Fermi surface caused by the increase of the lattice constant. Regulation of thermoelectric performance. Experimental research found that with the increase of PbBr2 content, the lattice constant a gradually increased, the material's electrical transport performance was significantly improved; when the concentration of PbBr2 reached 3%, the carrier mobility and conductivity decreased sharply. Fermi surface dynamics research shows that as the lattice constant a increases, the low Fermi surface of the conduction band gradually decreases, and the overlap of electron clouds also decreases. When the overlap of electron clouds decreases to a certain degree, it will cause mobility A sudden drop; on the other hand, the Fermi surface at the Γ point gradually increases, and the enhanced inter-valley scattering also causes a decrease in mobility. To demonstrate the mechanism of Fermi surface kinetic regulation, the researchers further designed a Ge doping experiment based on the 3% PbBr2 doped sample, showing that a proper reduction of the lattice constant a can increase the carrier mobility and increase the optimized ZT value from 0.6 To 1.7. The work was published in Energy Environ. Sci. 2020, 13: 616 with the title of "Fermi-surface dynamics and high thermoelectric performance along the out-of-plane direction in n-type SnSe crystals".