Intrinsically Stretchable and Printable Thermoelectric Materials for Highly Sustainable Thermal Energy Harvesting

Thermoelectric (TE) materials have the potential to capture and convert waste heat from low-grade thermal sources into electricity for solid-state energy harvesting. Despite the significant advances in TE energy conversion efficiency through material-level discoveries, diversification of heat sources presents a barrier to sustainable thermal energy harvesting from arbitrarily shaped and deformable targets, such as the human body. To address such challenge, the TE materials are expected to flawlessly accommodate the applied strains and deformation through improved intrinsic stretchability without undermining the TE properties. However, efforts to enhance the stretchability of high-zT inorganic TE materials or inherently flexible TE polymers often result in compromised TE properties due to the introduction of plasticizing agents. Stretchable TE generator designs can only partially complement the intrinsically insufficient material stretchability, at the clear expense of limited material selection and manufacturing processes. Likewise, the empirical trade-off between the material mechanical reliability and TE efficiency presents a formidable hurdle towards flawless thermal energy conversion with high mechanical reliability under harsh operating environments.<br/><br/>In this study, we introduce an innovative approach to restructure and hybridize single-walled carbon nanotube (SWCNT) networks to achieve simultaneous facilitation of mechanical reliability and TE efficiency. Low-molecular-weight polymeric dopants can allocate greater free volume within the SWCNT network, while concurrently promoting its electrical conductivity, and the resulting restructured film can be stretched up to 100% with more homogeneously size-controlled microcracks. Moreover, incorporation of ionic liquids with high dielectric constants alleviates the aggregation of <i>π</i>-<i>π</i> interacting SWCNT bundles to further improve the film stretchability to ≥170%. As a consequence of SWCNT debundling and SWCNT-polymer heterointerfaces, phonon scattering is further intensified to considerably suppress the lattice thermal conductivity for enhanced TE figure of merit (<i>zT</i> &gt;0.1). Such exceptional deformability and programmable viscoelasticity allow for our restructured SWCNT to be directly printed into three-dimensional structures at micrometer-scale resolution to achieve soft TE generators with an unprecedented pair of exceptional mechanical reliability and TE harvesting efficiency. Our ingenious strategy promises to spark innovations in leveraging thermal energy for a broad range of practical applications encompassing wearable electronics and Peltier thermoregulation.