Thermoelectric material is a kind of "green" energy material that can convert "thermal energy" and "electric energy" without any external force. It can use waste heat in life and production to generate electricity, or achieve accurate heat transfer under the condition of applying bias. , Is widely used in temperature difference battery-powered, micro-system chip temperature control refrigeration and other fields. Traditional thermoelectric materials are inorganic covalent / ionic bond crystals. For example, bismuth telluride (Bi2Te3) is the most widely used thermoelectric material. Its periodic layered structure is covalent / ionic bond connection, and the interlayer is Weak Van der Waals force connection, therefore, has intrinsic brittleness and cannot be deformed flexibly. Traditional thermoelectric materials cannot closely fit heat source surfaces with complex curvature changes (such as heat source pipes, human body surfaces, etc.) in practical applications. Such poor thermal contact results in heat loss and lower thermoelectric conversion efficiency; it is also difficult to adapt to thermoelectricity. Devices are increasingly miniaturized and highly integrated. Therefore, the research and development of high-performance flexible thermoelectric materials has become the focus and difficulty of research in this field.
Recently, the research group of Kaiping Ping, the research group of Liu Chang and the collaborators of the Institute of Metal Research of the Chinese Academy of Sciences have developed a high-performance bismuth telluride / single-wall carbon nanotube (Bi2Te3 / SWCNT) flexible thermoelectric material. Researchers use an independently designed and improved magnetron sputtering deposition system, using a three-dimensional network of self-supporting carbon nanotubes with excellent mechanical and electrical properties as the skeleton, and using sub-nanometer-scale carbon tube bundle grooves to limit diffusion and induce ordered nucleation and The temperature-selective crystal plane growth mechanism of thin film materials, the first preparation of Bi2Te3 / SWCNT composite self-supporting thermoelectric thin film materials with highly ordered microscopic characteristics. The composite material has a nanopore structure. The deposited Bi2Te3 nanocrystals are closely attached to the surface of the carbon nanotube bundle and have a high (000l) surface texture. The crystal orientation of Bi2Te3 is parallel to the axis of the carbon nanotube bundle. The interval between adjacent Bi2Te3 nanocrystals is Small angle orientation tilts grain boundaries. Bi2Te3 (000l) surface texture is conducive to improving the in-plane conduction of carriers. Small-angle grain boundaries can further reduce its scattering effect on conducting carriers. Nanopore structure and Bi2Te3 / SWCNT interface defects reduce scattering phonons. The role of thermal conductivity. Studies have shown that in this (000l) surface texture, -Te1-Te1-atomic planes connected by weak van der Waals forces are parallel to the free surface of the composite film, and the relative motion between van der Waals force layers is manifested when the composite film is deformed out of plane The important mechanism of good flexibility is that the adjacent Bi2Te3 crystal orientations are highly oriented and are easy to slip on the (000l) van der Waals crystal plane, which facilitates the transfer of van der Waals interlayer displacements between adjacent grains. In addition, the nano-porous structure is also beneficial to accommodate the relative displacement of the material during flexible deformation, which further improves the ability of flexible deformation. The unique microstructure gives the composite a thermoelectric figure of merit (ZT) of up to ~ 0.9 in the (000l) in-plane direction in the range of room temperature to 100 degrees Celsius, which is equivalent to the ZT performance of commercial bulk brittle thermoelectric materials, and has very good performance. Flexural mechanical properties. Further research shows that the composite material has good bending flexibility and self-supporting structure, so it can be cut into arbitrary geometries and transferred to various types of substrates using micro-nano processing methods such as ion beam and femtosecond laser. It is convenient for flexible and convenient preparation of thermoelectric devices with various structures, and the composite thermoelectric material can even be manipulated by non-contact methods such as electrostatic force. At the same time, research shows that the preparation principle and technology of the composite material can also be applied to other layered structure semiconductor material systems with weak van der Waals force connection, and has broad application prospects in the field of flexible semiconductor materials and devices.