High Conductivity and Electron‐Transfer Validation in an n‐Type Fluoride‐Anion‐Doped Polymer for Thermoelectrics in Air

Air‐stable and soluble tetrabutylammonium fluoride (TBAF) is demonstrated as an efficient n‐type dopant for the conjugated polymer ClBDPPV. Electron transfer from F− anions to the π‐electron‐deficient ClBDPPV through anion–π electronic interactions is strongly corroborated by the combined results of electron spin resonance, UV–vis–NIR, and ultraviolet photoelectron spectroscopy. Doping of ClBDPPV with 25 mol% TBAF boosts electrical conductivity to up to 0.62 S cm−1, among the highest conductivities that have been reported for solution‐processed n‐type conjugated polymers, with a thermoelectric power factor of 0.63 µW m−1 K−2 in air. Importantly, the Seebeck coefficient agrees with recently published correlations to conductivity. Moreover, the F−‐doped ClBDPPV shows significant air stability, maintaining the conductivity of over 0.1 S cm−1 in a thick film after exposure to air for one week, to the best of our knowledge the first report of an air‐stable solution‐processable n‐doped conductive polymer with this level of conductivity. The result shows that using solution‐processable small‐anion salts such as TBAF as an n‐dopant of organic conjugated polymers possessing lower LUMO (lowest unoccupied molecular orbital), less than −4.2 eV) can open new opportunities toward high‐performance air‐stable solution‐processable n‐type thermoelectric (TE) conjugated polymers. Simple, air‐stable, solution‐processable tetrabutylammonium fluoride (TBAF) doping of an electron‐deficient polymer can boost the electrical conductivity to 0.62 S cm−1 and maintain it at >0.1 S cm−1 in a thick film after exposure to air for one week, the first report of an air‐stable solution‐processable n‐doped conductive polymer with this conductivity level. Electron transfer is verified using multiple techniques.