Imagine a future where wearable devices no longer rely on bulky batteries but are powered by your body heat alone. This vision is no longer science fiction but an emerging reality, thanks to a groundbreaking development in thermoelectric materials.
An international research team led by scientists from China has developed a novel polymer-based thermoelectric material that achieves unprecedented performance, potentially revolutionizing flexible electronics and wearable technology. The findings were published on July 24, 2024, in the prestigious journal Nature .
The "Phonon Glass-Electron Crystal" Paradigm
High-performance thermoelectric materials have long pursued what scientists call the "phonon glass-electron crystal" ideal. This means the material should block heat transfer (phonons) like glass while allowing electrons to flow freely like crystals. While plastic materials naturally exhibit low thermal conductivity (phonon glass properties), their ordered molecular structures often compromise this advantage, limiting their thermoelectric performance.
Despite decades of research in molecular design and doping, polymer-based thermoelectric materials had plateaued at a figure of merit (ZT) around 0.5—far below commercial inorganic materials. This performance gap has severely hindered practical applications of organic thermoelectrics.
The PMHJ Breakthrough
The research team, led by Prof. Zhong'an Di from the Chinese Academy of Sciences and Prof. Lidong Zhao from Beihang University, developed a revolutionary polymer multi-period heterojunction (PMHJ) structure. This innovative design alternates layers of two different polymers with precise thickness control, creating periodic interfaces that effectively scatter phonons while maintaining good electrical conductivity.
By carefully selecting PDPPSe-12 and PBTTT polymers and using a 4Bx crosslinker, the team created PMHJ films with optimized layer thicknesses: 6.3±0.5 nm for PDPPSe-12, 4.2±0.4 nm for PBTTT, and 3.9±0.4 nm for the interface layer. This precise engineering resulted in a remarkable ZT value of 1.28 at 368 K (about 95°C), the first time any plastic-based thermoelectric material has surpassed the critical ZT>1.0 threshold.
Interface Engineering and Thermal Transport Control
The key to this breakthrough lies in the material's sophisticated interface design. By adjusting crosslinker content, researchers achieved a transition from bulk heterojunction to hierarchical heterojunction structures. Advanced characterization techniques, including in-situ depth-dependent optical absorption spectroscopy and nano-infrared AFM, confirmed the formation of well-defined periodic interfaces when crosslinker content reached 2 wt%.
These rough interfaces enhance phonon scattering, dramatically reducing thermal conductivity. Systematic experiments and theoretical collaborations revealed that when individual layer thickness approaches the phonon mean free path (below 10 nm), lattice thermal conductivity drops sharply—by over 70% in the optimized (6,4,4) PMHJ structure.
Versatility and Practical Applications
The PMHJ approach proved universally effective across different high-mobility polymers (PDPP3T, PDPP4T, and P3HT), reducing their thermal conductivity by 36%-76%. The resulting devices demonstrate exceptional flexibility, with curvature radii below 100 μm, enabling conformal attachment to irregular surfaces like human skin.
Notably, the team successfully scaled up production using solution processing, with uniform large-area films confirmed by TOF-SIMS characterization. Integrated devices achieved a normalized power density of 1.12 μW cm -2 K -2 , showcasing comprehensive advantages in both performance and manufacturability.
A New Chapter for Flexible Electronics
This breakthrough overcomes the fundamental limitation in polymer thermoelectrics by demonstrating effective thermal transport control. The PMHJ architecture provides a new pathway for further performance improvements in plastic-based thermoelectric materials.
The development opens exciting possibilities for self-powered flexible electronics, wearable devices, and biosensors. With performance now matching commercial inorganic materials at room temperature, PMHJ-based devices could soon power the next generation of portable and wearable technologies, bringing us closer to the vision of battery-free wearable electronics.