Developing renewable energy is a well-established national policy of our country and the key to ensuring economic stability and sustainable development. About 80% of the global power plants use thermal power to generate electricity. However, the average efficiency of these plants is only ~ 30%, and ~ 15 TWT Heat loss to the environment, if this part of the energy recycling, can effectively alleviate the current outstanding energy and environmental issues. Thermoelectric materials as the core of the thermoelectric conversion technology can not rely on any external force 'hot' and 'electricity' are two different The direct conversion of energy in form has drawn much attention from the scientific and industrial fields.Especially in recent years, a new generation of smart micro-nano electronic systems, such as wearable and implantable devices, is in urgent need of developing micro-watt-milliwatt self-powered Technology to replace the traditional rechargeable batteries to meet its technology to miniaturization, high density, high stability and reliability of the development of the thermoelectric materials, the human body temperature and ambient temperature difference between the power generation, it has become a portable intelligent electronic devices since Power supply technology and effective solutions.
On the one hand, compared with other kinds of energy conversion forms, the conversion efficiency of the thermoelectric technology is not high, only ~ 10%, seriously restricting the development of the thermoelectric technology industry. The performance of the thermoelectric material can be measured by zT:
zT = S 2σT / (κe + κL)
Where S is the Seebeck coefficient of the material, σ is the electrical conductivity, T is the operating temperature, κe and κL are the thermal conductivities of electrons and phonons, respectively. Due to the limitation of the intrinsic physical properties, the various parameters that determine the zT value are related to each other, So that the coefficient of merit of thermoelectric materials is difficult to significantly improve.
On the other hand, in order to maintain the temperature difference and make full use of thermal power generation, the thermoelectric materials / devices need to be closely attached to the surface of the heat source, however, in practical applications, both the body surface and the heat source pipe have complex geometric changes in curvature. Inorganic thermoelectric materials, due to their intrinsic brittleness, can not meet the requirements of closely conforming curvature changing heat source surface, so that the heat energy loss between the heat source and the thermoelectric material / device is in a higher range. In addition to the pyroelectric material itself, The thermal energy loss caused by the poor contact between the heat source and the thermoelectric material has become one of the key factors restricting the development of the existing thermoelectric technology.
Therefore, it is proposed to increase the Seebeck coefficient by means of scaling effect, alloying and interfacial energy barrier control, and to design strategies for scattering phonon using multi-scale defects and suppressing thermal conductivity to improve the thermoelectric conversion performance, and to develop new high performance flexible thermoelectric materials and Device preparation technology, research on the mechanism of improving intrinsic brittleness of inorganic thermoelectric materials have become the global difficulties and hot issues in the field at present.
Institute of Metal Research, Chinese Academy of Sciences, Shenyang, State Key Laboratory of Materials Science 邰 Kaiping project team is committed to the atomic scale design and preparation of highly ordered microstructure of thermoelectric thin film materials and devices. The use of physical vapor deposition technology to control the adjacent grains For small angle tilt grain boundaries, for the first time to achieve a large area preparation of in-plane and out-of-plane orientation are highly textured Bi 2Te 3The results show that the small angle of tilting grain boundaries can inhibit the scattering of carriers to enhance the in-plane conductivity, while maintaining the scattering of phonons to reduce the thermal conductivity, significantly improve the thermoelectric conversion performance, is the preparation of high-performance Bi 2Te 3An effective method of thermoelectric thin film material.
Figure 1. Non-equilibrium magnetron deposition for the preparation of small-angle tilted grain boundaries 2Te 3SEM (a), TEM (b) Microstructure Analysis and Thermoelectric Thin Film Cooler Optical Microanalysis (c), Three-Dimensional Topography (d) and Schematic Diagram of Cooler Structure (e) - (f)
Based on the above technology, combined with the research team designed and constructed high-precision micro-beam laser processing platform, developed Bi 2Te 3Alloy thin film micro-cooler, the thickness of the thermoelectric pair is ~ 25μm, the minimum in-plane size is ~ 200 × 200μm, and the micro-zone cooling flux can reach ~ 40W / cm 2The device has a wide range of applications in the field of micro-system thermal management, such as CPU chip fixed-point heat, micro-laser diode temperature control, etc. This work achieved a breakthrough in the field of preparation and processing of thermoelectric thin film microcomputers in China, won the 2017 China Materials Conference 'Thermoelectric Materials and Devices Branch Wall Outstanding Award', an application for invention patents, authorized two.
For the first time, the team used unbalanced magnetron sputtering technology to prepare a bismuth telluride composite thermoelectric thin film material with multi-scale pore structure from micron to nanometer based on cellulose paper, as shown in the following figure.
Figure 2. Multi-scale pore structure design schematic and cellulose /
Bi 2Te 3SEM Characterization of Composite Flexible Thermoelectric Materials
The results show that due to the unbalanced magnetron sputtering technology, the bismuth telluride film and the cellulose interface are tightly bonded, the nominal thickness of the deposit can reach tens of micrometers, which can effectively reduce the internal resistance of the thin film device and improve the output efficiency of the thermoelectric conversion; Cellulose / Bi 2Te 3Unique network structure, multi-scale pore structure and Bi 2Te 3Film scale effect gives cellulose / Bi 2Te 3The composites show good bending flexibility. The multi-scale pore structure in the composite thermoelectric thin film can effectively scatter the phonon to reduce the thermal conductivity value to be close to the theoretical minimum thermal conductivity of Bi2Te3. Bi 2Te 3An intrinsic oxide layer exists on the surface of the film, and when the carriers are transported between two adjacent thin films of Bi2Te3, the oxide layer at the interface can diffuse and filter the low-energy carriers and improve the Seebeck coefficient. 2Te 3The ZT value of the composite at room temperature up to 473K can reach 0.24-0.38 and is expected to be further enhanced by carrier concentration optimization. The composite flexible thermoelectric material is tailored and integrated with the demonstration device by using a high precision microbeam laser platform Based on this flexible composite thermoelectric 'generator', this work provides new ideas and solutions for exploring new high performance flexible thermoelectric materials and opens up a new direction for the practical development of flexible thermoelectric devices.
The research work has been supported by the National Natural Science Youth Fund, the Funds on the Surface and the "Hundred Talents Program" of the Chinese Academy of Sciences.
Figure 3. Cellulose /
Bi 2Te 3Thermoelectric Properties (a-d) and Flexural Bending Properties of Composites
Figure 4. XPS analysis of multi-scale pore bismuth telluride composites and 3D nanoscale X-ray image analysis of composite thin film materials and interface barrier filtration low-energy carrier effect diagram
Figure 5. Composite flexible thermoelectric materials in situ bending electrical properties of the test and the use of human body temperature and the temperature difference between the formation of thermal voltage
Figure 6. Schematic design of flexible thermoelectric generator 'device structure and demonstration of demonstration of recovery of waste heat power generation
