Chinese Researchers Set World Record with New Flexible Thermoelectric Polymer Film

In the future, wearable devices such as smart watches and health monitoring patches may no longer suffer from frequent charging troubles. On 6 March Beijing time, a research team from the Institute of Chemistry, Chinese Academy of Sciences, in collaboration with domestic partners, published the latest research results on organic thermoelectric materials in the international academic journal Science. The team proposed a new strategy of "creating order from disorder" and developed a new type of thermoelectric polymer film with an irregular hierarchical pore structure (IHP-TEP), whose key performance indicator, the thermoelectric figure of merit (zT value), reached 1.64 at 343K, setting a world record for flexible thermoelectric materials in the same temperature range.

With the popularization of wearable devices, frequent charging has become a common pain point. Harnessing body temperature and various environmental temperature differences to generate electricity is expected to realize "permanent power supply" for electronic devices. Thermoelectric materials, which can directly convert thermal energy into electrical energy and vice versa, are the key to this goal. When there is a temperature difference between the two ends of the material, it can directly convert thermal energy into electrical energy (the Seebeck effect); conversely, one end of the material becomes hot and the other cold when energized (the Peltier effect). This characteristic endows high-performance thermoelectric materials with broad application prospects in waste heat recovery and solid-state refrigeration, especially suitable for the self-power supply needs of new electronic products such as wearable devices and IoT sensors, and has long been regarded as a major scientific challenge and disruptive research direction internationally.

Organic thermoelectric materials, featuring intrinsic flexibility and solution processability, can be attached to different curved surfaces and continuously convert human body heat or environmental "waste heat" into electrical energy. Compared with traditional inorganic thermoelectric materials, polymer materials have obvious advantages such as light weight, good flexibility and large-area printability. However, the performance of polymer thermoelectric materials has long lagged behind that of inorganic materials — currently, the zT value of flexible inorganic materials can reach 1.0-1.4, while that of organic ones is mostly below 0.5. In 2024, the team raised the zT value of polymer thermoelectric materials to 1.28, but it still could not match high-performance flexible inorganic materials, and the complex preparation process restricted its practical application.

The key challenge in improving polymer thermoelectric performance lies in the mutual coupling and restriction of various performance parameters, which are difficult to regulate independently. An ideal thermoelectric material conforms to the "phonon glass-electron crystal" model: for heat transfer, the material should have a disordered structure like glass to block phonons; for charge transport, it should have ordered molecular packing like a crystal to allow unimpeded charge flow. This "synergistic regulation of electrical-thermal transport" is extremely difficult, becoming a long-standing bottleneck restricting the improvement of polymer thermoelectric performance.

The newly developed IHP-TEP film establishes a new synergistic regulation mechanism of "disordered pores enhancing phonon scattering" and "confinement enhancing ordered molecular assembly". The material is filled with irregular nano-to-micron pores of varying sizes and shapes, which can effectively enhance multiple phonon scattering to significantly inhibit heat conduction; meanwhile, the confinement effect of nanochannels promotes the highly ordered arrangement of polymer molecules, greatly improving charge transport performance. Figuratively, this structure is like building an expressway in a rugged mountain area: disordered pores force heat to "climb mountains and cross ridges" while ordered molecular channels ensure charge "travels at high speed", realizing the decoupling and synergistic regulation of electrical and thermal transport.

The team constructed the structure using a "polymer phase separation" method: mixing PDPPSe-12 (polymer semiconductor) and PS (polystyrene, a common plastic) solutions uniformly, and phase separation occurs as the solvent evaporates. By precisely controlling parameters such as blending ratio, the size, quantity and distribution of pores can be adjusted. The IHP-TEP structure can synergistically regulate phonon-boundary scattering, phonon-phonon interaction and size effect, reducing thermal conductivity by 72% and increasing carrier mobility by up to 52%. Its zT value of 1.64 at 343K surpasses that of flexible inorganic thermoelectric materials in the same temperature range, and its compatibility with spray technology endows it with great potential in large-area flexible power generation.

This research breaks the traditional limitation of difficult synergistic optimization of charge transport and phonon scattering in polymer thermoelectric materials, providing a new development path for the field of flexible thermoelectric materials. In the future, with the continuous development of related technologies, ordinary plastic products around us may become micro power stations and personal air conditioners, turning waste heat into valuable resources and making green energy ubiquitous and accessible.