Shanghai Institute of Ceramics and others opened up a new research direction of inorganic flexible thermoelectric materials
The flexible thermoelectric energy conversion technology can convert the ubiquitous temperature difference in the environment into electrical energy output, and has broad application prospects in the fields of flexible electronics and the like. However, the current high-performance inorganic thermoelectric materials are brittle materials and do not have a flexible function. Miniaturization and integration of them on a flexible substrate can achieve a certain degree of bending performance, but they are very susceptible to fracture under large bending or deformation; and Although organic thermoelectric materials have good flexibility and bending properties, the carrier mobility is much lower than inorganic materials, and it is difficult to achieve efficient energy conversion and electrical energy output. Recently, Shi Xun, Chen Lidong, Sun Yiyang, Associate Researcher Qiu Pengfei, researchers at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, etc., and He Jian, a professor at Clemson University, developed a new high-performance inorganic flexible thermoelectric material and device based on Ag2S flexible semiconductor . This research opens up a new direction of research on inorganic flexible thermoelectric materials, and solves the initial and most critical difficulty for the development of new technologies for fully flexible thermoelectric conversion based on high-performance inorganic materials. Related research results were published in Energy & Environmental Science (2019, DOI: 10.1039 / C9EE01777A) under the title of Flexible thermoelectrics: from silver chalcogenides to full-inorganic devices New high-performance inorganic flexible thermoelectric materials must take into account both good plasticity and thermoelectric properties. The team previously reported that Ag2S (Nature Mateials., 2018, 17, 421-426), the first inorganic flexible semiconductor material at room temperature, is unbreakable and freely bendable, with excellent flexibility and bending properties. However, the energy band gap of Ag2S is about 1.0 eV, its conductivity and thermoelectric performance at room temperature are extremely low, and the optimization effect of its intrinsic defects (such as interstitial Ag atoms, etc.) is very weak. Therefore, Ag2S matrix is ​​not an ideal thermoelectric material. Doping and modifying it is expected to greatly improve its thermoelectric performance, but whether the material can continue to maintain good flexibility and plasticity has become an unknown and critical issue. In this work, the research team synthesized a series of Se or Te solid solution Ag2S materials, and found that the solid solution of Se and Te can significantly reduce the defect formation energy of Ag interstitial ions, resulting in an increase in the concentration of Ag interstitial ions, thus the electrical transport performance Obviously, the power factor can be up to about 5 μW · cm-1 · K-2. At the same time, the solid solution Se / Te greatly reduces the energy band gap of the material, so that the peak value of the thermoelectric optimal value moves to the low temperature direction, and the maximum value of the thermoelectric optimal value is 0.44 at room temperature. Both Ag2Se and Ag2Te are brittle at room temperature and do not possess plasticity and flexibility. Therefore, solid solution Se or Te will also have a huge impact on the mechanical properties of Ag2S. Mechanical test results such as compression test and three-point bending test show that when the content of Se is less than 60% or the content of Te is less than 70%, the plasticity and flexibility of the material are maintained. Therefore, when the composition of Se or Te is in the range of 20% -60%, the material has good plasticity and thermoelectric properties. The research team selected a bending radius of 3 mm for testing, and found that the Ag2S0.5Se0.5 sheet had almost no change in conductivity and Seebeck coefficient after 1,000 repeated bendings, indicating that the performance of the material is less affected by stress and can be flexible and wearable. Power requirements. On the basis of obtaining high-performance inorganic flexible thermoelectric materials, the research team prepared an in-plane thermoelectric power generation device composed of 6 pairs of n-type Ag2S0.5Se0.5 thermoelectric arms and p-type Pt-Rh wires. At a temperature difference of 20 K, the maximum normalized power density reaches 0.08 W · m-2, which is 1-2 orders of magnitude higher than the best pure organic thermoelectric devices currently available. The new high-performance inorganic flexible thermoelectric materials and devices based on Ag2S flexible semiconductors developed by the institute can provide excellent flexibility and thermoelectric conversion performance at the same time, and have the advantages of environmental friendliness, stability and reliability, and long life. The new generation of intelligent micro-nano electronic systems represented by wearable and implantable types are widely used. The research work was supported and supported by the National Key R & D Project, the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the Shanghai Youth Science and Technology Star Project.
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