An emerging liquid-crystalline conducting polymer thermoelectrics: Opportunities and challenges

As wearable electronics and IoT sensors proliferate, the demand for flexible, melt-processable thermoelectric (TE) materials that convert body heat into electricity is soaring. Now, researchers from Shenzhen University, led by Prof. Guangming Chen, comprehensively review the latest leaps in poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT)—a liquid-crystalline conjugated polymer whose figure of merit has catapulted from <0.1 to a record 1.28 at 368 K through asymmetric doping, multi-heterojunction architectures and phonon-blocking strategies.

Why PBTTT Matters

• Highest Organic ZT: 1.28 rivals inorganic Bi₂Te₃ yet retains mechanical flexibility and solution/melt processability.
• Scalable Processing: Compatible with roll-to-roll blade coating, floating-film transfer and high-T rubbing; 35 × 21 cm² uniform films demonstrated.
• Melt Advantage: 140–180 °C smectic phase enables solvent-free alignment, cutting fabrication cost and environmental impact.

Innovative Design & Features

• Multi-Heterojunction Architecture: Alternating PBTTT/PDPPSe-12 nanolayers suppress out-of-plane κ to 0.06 W m^-1 K^-1 (55 % reduction) while preserving σ = 196 S cm^-1, yielding an exceptional power factor of 628 μW m^-1 K^-2.
• PCET & NEII Doping: Proton-coupled electron-transfer tunes Fermi level within ±25 meV precision; nanoconfined electrochemical ion implantation achieves 100 nm spatial resolution for independent crystalline/amorphous domain control.
• Anion-Exchange Doping: Ionic-liquid mediators push conductivity to 1,120 S cm^-1 without disrupting π–π stacking, maintaining high Seebeck coefficient.

Applications & Outlook

• Flexible TEGs: 522 nW output under 38 K gradient, 95 % retention after 100,000 bending cycles; 3.3 mV on human skin.
• Energy Filtering: Low-energy carrier filtering and tie-chain blending decouple σ–S trade-off, opening routes to >2 mW m^-1 K^-2 power factors.
• Next Steps: Integration with melt-spinning fibers and jointless p–n legs for watt-level wearable modules; AI-guided side-chain design to push ZT > 2.

This review bridges fundamental insights and scalable manufacturing, positioning PBTTT as a front-runner for eco-friendly, mass-produced organic thermoelectrics. Stay tuned for more advances from Prof. Chen’s group!