Brønsted Acid Doping Enhances Thermoelectric Performance of Polymer‐Carbon Nanotube Composites for Flexible Energy Harvesting

ABSTRACT Organic thermoelectric materials are promising for flexible waste‐heat recovery, yet their inherently low electrical conductivity restricts practical use. Here, we demonstrate significant performance enhancement via chemical doping of PJ71 conjugated polymer‐wrapped single‐walled carbon nanotubes (SWCNTs). The donor‐acceptor polymer PJ71 effectively disperses SWCNTs while preserving their intrinsic electrical characteristics, achieving optimal performance at 50 wt.% SWCNT loading with conductivity (σ ) = 386 S cm −1 and Seebeck coefficient ( S ) = 33 µV K −1 . Chemical doping with tris(pentafluorophenyl)borane (BCF) through a Brønsted acid mechanism boosts σ to 1196 S cm −1 while retaining S = 26 ± 2 µV K −1 . The optimized composite exhibits a peak power factor of 125 µW m −1 K −2 at 434 K, approximately twice that of the undoped film. Flexible thermoelectric generators fabricated from these materials deliver 20 mV open‐circuit voltage at ΔT = 100 K and maintain stable output over 500 bending cycles. These results establish an efficient molecular‐doping strategy for scalable, high‐performance organic thermoelectrics suitable for flexible energy harvesting.