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

Xingang Zhao; Deepa Madan; Yan Cheng; Jiawang Zhou; Hui Li; Susanna M Thon; Arthur E Bragg; Mallory E DeCoster; Patrick E Hopkins; Howard E Katz

doi:10.1002/adma.201606928

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

Adv Mater. 2017 Sep;29(34). doi: 10.1002/adma.201606928. Epub 2017 Jul 14.

Authors

Xingang Zhao¹, Deepa Madan^{1

2}, Yan Cheng³, Jiawang Zhou⁴, Hui Li¹, Susanna M Thon³, Arthur E Bragg⁴, Mallory E DeCoster⁵, Patrick E Hopkins⁵, Howard E Katz^{1

4}

Affiliations

¹ Department of Materials Science and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
² Department of Mechanical Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD, 21250, USA.
³ Department of Electrical and Computer Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
⁴ Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
⁵ Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer's Way, Charlottesville, VA, 22904, USA.

PMID: 28707300
DOI: 10.1002/adma.201606928

Abstract

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.

Keywords: chemical doping; fluoride salts; n-type conjugated polymers; organic semiconductors; thermoelectrics.