Engineering Molecular Assembly for High Performance Plastic Thermoelectrics

ConspectusThe escalating global energy crisis, coupled with the environmental impact of conventional energy consumption, has intensified the pursuit of green and sustainable energy solutions. Converting low-grade heat into electricity using flexible, lightweight, and solution-processable polymeric thermoelectrics offers unique opportunities for next-generation wearable and portable power systems. Early studies in this field predominantly emphasized molecular design, optimizing conjugated backbones and side chains to enhance the charge transport and Seebeck coefficients. These efforts yielded valuable insights into the relationships among molecular structure, electronic states, and thermoelectric performance. More recently, molecular assembly engineering has attracted growing interest driven by recognition of how microstructural order and hierarchical morphology affect carrier mobility and energy filtering. Strategies such as controlled self-assembly, directional alignment, and interface engineering have proven highly effective, enabling property enhancement beyond the limits of molecular design alone. This shift has not only produced high-performance polymeric thermoelectric materials but also broadened their functional scope, opening opportunities for integration into flexible and versatile energy systems.The "phonon-glass, electron-crystal" (PGEC) concept envisions an ideal assembly that combines the intrinsically low thermal conductivity of amorphous glasses with the exceptional charge transport of crystalline solids. Guided by these design principles, our recent work has addressed the coupled optimization of charge and thermal transport while exploring novel functional capabilities in polymeric thermoelectrics. To mitigate the persistent trade-off between the Seebeck coefficient (S) and electrical conductivity (σ), we developed a mixed-orientation strategy in which bimodal molecular orientation generates interfacial weak hydrogen bonds, promoting efficient chemical doping, improved molecular ordering, and increased density of states. This synergistic effect yielded simultaneous enhancements in S and σ, achieving a peak figure of merit (ZT) more than four times higher than that of single-orientation films. In addition, we tackled the underestimated role of thermal conductivity (κ) by introducing a heterogeneous assembly approach for high-mobility polymers. Incorporating porous architectures induced localized vibrational scattering, lowering lattice κ and raising ZT to 0.52. Building further, we introduced a polymeric multi-heterojunction (PMHJ) architecture via cross-linking-assisted assembly, where pronounced size effects and interfacial diffuse scattering reduced κ to 0.10 W·m^-1·K^-1, delivering a record-high ZT of 1.28, comparable to that of commercial Bi₂Te₃ materials in the near-room-temperature region. Extending beyond performance metrics, we revealed anomalously large Nernst coefficients in doped polymers, 2-3 orders of magnitude above classical Fermi-liquid predictions─paving the way for advanced lateral organic thermoelectric devices.