Engineering Molecular Assembly for High Performance Plastic Thermoelectrics.

Area of Science:

• Materials Science
• Energy Science
• Polymer Science

Background:

• The global energy crisis necessitates sustainable energy solutions, driving interest in converting low-grade heat to electricity using polymeric thermoelectrics.
• Flexible, solution-processable polymers offer potential for wearable and portable power systems, but performance has been limited by molecular design.
• Recent advances focus on molecular assembly engineering to improve microstructural order and hierarchical morphology for enhanced charge transport.

Purpose of the Study:

• To optimize both charge and thermal transport in polymeric thermoelectrics beyond molecular design limitations.
• To develop strategies for overcoming the trade-off between Seebeck coefficient and electrical conductivity.
• To explore novel architectures for reducing thermal conductivity and enhancing the overall thermoelectric figure of merit (ZT).

Main Methods:

• Developed a mixed-orientation strategy with bimodal molecular orientation to enhance doping, ordering, and density of states.
• Introduced heterogeneous assembly with porous architectures to induce phonon scattering and lower thermal conductivity.
• Created a polymeric multi-heterojunction (PMHJ) architecture via cross-linking-assisted assembly for significant thermal conductivity reduction.

Main Results:

• The mixed-orientation strategy achieved a peak figure of merit (ZT) more than four times higher than single-orientation films.
• Heterogeneous assembly with porous architectures raised ZT to 0.52 by lowering lattice thermal conductivity.
• The PMHJ architecture yielded a record-high ZT of 1.28, comparable to commercial bismuth telluride, with a thermal conductivity of 0.10 W·m⁻¹·K⁻¹.
• Anomalously large Nernst coefficients were observed in doped polymers, suggesting potential for advanced lateral organic thermoelectric devices.

Conclusions:

• Advanced molecular assembly and heterogeneous structuring are effective strategies for significantly enhancing polymeric thermoelectric performance.
• The developed PMHJ architecture offers a pathway to high-performance, flexible thermoelectric materials competitive with inorganic counterparts.
• The discovery of large Nernst coefficients opens new avenues for designing novel organic thermoelectric devices.