The Shanghai Institute of Ceramics has made new progress in the research of organic thermoelectric materials.
Shenjia Hydraulics
Release time:
2020-10-20
Organic polymer thermoelectric materials are an emerging class of clean-energy materials that can directly convert heat into electricity. These materials are solution-processable, lightweight, inexpensive, and exhibit excellent flexibility, making them promising for applications in wearable electronic devices. Compared to inorganic thermoelectric materials, polymer thermoelectric materials suffer from a limited variety and low thermoelectric conversion efficiency, primarily due to the lack of a deep understanding of the relationship between molecular structure and thermoelectric performance.
Organic polymer thermoelectric materials are an emerging class of clean-energy materials that can directly convert heat into electricity. These materials are solution-processable, lightweight, inexpensive, and exhibit excellent flexibility, making them promising for applications in wearable electronic devices. Compared with inorganic thermoelectric materials, polymer thermoelectric materials suffer from a limited variety and low thermoelectric conversion efficiency, primarily due to the lack of a deep understanding of the relationship between molecular structure and thermoelectric performance. Chemical doping is a key approach for enhancing the conductivity of polymers and tuning their thermoelectric properties. However, current doping techniques for polymer semiconductor materials suffer from low doping efficiency, and high-concentration doping can easily disrupt the polymer's own molecular packing, significantly reducing carrier mobility. As a result, not only is high electrical conductivity unattainable, but the Seebeck coefficient is also severely compromised, seriously limiting the improvement of thermoelectric device performance.
Recently, Associate Researcher Li Hui and Researcher Chen Lidong from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, employed a functional unit random copolymerization strategy to co-polymerize donor-acceptor building blocks with bithiophene units via the Stille coupling reaction, thereby obtaining a series of novel conductive polymers. This approach achieved synergistic optimization of doping efficiency and carrier mobility, providing a new design strategy for high-performance polymer thermoelectric materials. The related research findings, titled “Synergistically Improved Molecular Doping and Carrier Mobility by Copolymerization of Donor-Acceptor and Donor-Donor Building Blocks for Thermoelectric Application,” were published in the prestigious international academic journal Advanced Functional Materials (article link: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202070270) and were selected as the back cover of the current issue.
The chemical structure of this new material features the following characteristics: (1) Electrostatic interactions between donor-acceptor units enhance the close packing of polymer chains; (2) Alkoxy-modified bithiophene donor units improve the doping efficiency of the polymer; (3) A random copolymerization approach introduces irregularity into the polymer backbone, which helps to increase the Seebeck coefficient. Compared with conventional polythiophene-based semiconductors, which suffer from low intrinsic carrier mobility and tend to become brittle at high doping concentrations, as well as alternating donor-acceptor polymers that are more difficult to dope and exhibit a significant drop in mobility at high doping levels, the functional-unit copolymerization strategy allows us to combine the advantages of different polymer units. This approach ensures good crystallinity of the polymer while achieving high doping efficiency, enabling the novel polymer semiconductor to maintain a carrier mobility above 1 cm² V⁻¹ s⁻¹ even at relatively high doping concentrations, with carrier concentrations reaching 10²⁰ to 10²¹ cm⁻³, ultimately resulting in flexible thin films with high electrical conductivity. Moreover, since random copolymerization reduces the regularity of the polymer backbone, the novel polymer exhibits a higher Seebeck coefficient than all-thiophene polymers, leading to a power factor exceeding 110 μW K⁻² m⁻¹. This demonstrates that random copolymerization of functional units is an effective strategy for preparing new high-performance thermoelectric materials.
The research was funded and supported by projects including the National Key Research Program, the National Natural Science Foundation of China, and the Shanghai Yangfan Program. Associate Researcher Li Hui is the first author and corresponding author, while Researcher Chen Lidong is a co-corresponding author.
The relationship between chemical doping characteristics and thermoelectric parameters of classic polythiophene-based materials (top), alternating donor-acceptor polymers (middle), and the novel polymer designed in this work (bottom)
Trends in Hall Mobility and Carrier Concentration as a Function of Doping Concentration, and Thermoelectric Properties of Polymers
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