Selenium‐Incorporated Polymerized Nonfullerene Acceptors/SWCNT Composites with Polymer‐Assisted n‐Doping for High‐Performance Organic Thermoelectrics

ABSTRACT Selenium‐incorporated polymerized nonfullerene acceptors (PNFAs) were developed to modulate interfacial interactions with single‐walled carbon nanotubes (SWCNTs) for high‐performance organic thermoelectric composites. The selenium‐incorporated PCB2Se with curved backbone exhibited the strongest π–π interactions with SWCNTs, enabling excellent CNT dispersion, reduced bundle size, and optimized molecular packing. These structural advantages delivered a high electrical conductivity of 609.7 S cm ‒1 , an elevated Seebeck coefficient of 65.1 µV K − 1 , and a low thermal conductivity of 0.32 W m ‒1 K ‒1 , resulting in a state‐of‐the‐art zT of 0.29 for conjugated‐polymer/SWCNT composites. Sequential N‐DMBI doping further converted PCB2Se/SWCNT into an efficient n‐type material with a power factor of 92.5 µW m ‒1 K − 2 . Spectroscopic and electronic analyses revealed a polymer‐assisted n‐doping mechanism in which PCB2Se first accepts electrons from N‐DMBI and subsequently transfers them to the CNT network, enabling effective carrier modulation. Utilizing the bipolar processability of PCB2Se/CNT, a flexible thermoelectric generator (TEG) containing five p–n junction pairs was fabricated, delivering an output voltage of 20.8 mV. The TEG maintained stable operation after 1000 bending cycles at a radius of 4 cm, demonstrating excellent mechanical robustness. This work highlights selenium‐based molecular engineering as an effective strategy for achieving high‐ zT organic thermoelectrics and durable flexible energy‐harvesting devices.