Combination of Counterion Size and Doping Concentration Determines the Electronic and Thermoelectric Properties of Semiconducting Polymers

Kyle N. Baustert, Joel H. Bombile, Md Tawabur Rahman, Augustine O. Yusuf, Ruipeng Li, Aron J. Huckaba, Chad Risko, Kenneth Graham

Research output: Contribution to journalArticlepeer-review

Abstract

In both chemical and electrochemical doping of organic semiconductors (OSCs), a counterion, either from the electrolyte or ionized dopant, balances the charge introduced to the OSC. Despite the large influence of this counterion on OSC optical and electronic response, there remains substantial debate on how a fundamental parameter, ion size, impacts these properties. This work resolves much of this debate by accounting for two doping regimes. In the low-doping regime, the Coulomb binding energies between charge carriers on the OSC and the counterions are significant, and larger counterions lead to decreased Coulomb interactions, more delocalized charge carriers, and higher electrical conductivities. In the high-doping regime, the Coulomb binding energies become negligible due to the increased dielectric constant of the films and a smoothing of the energy landscape; thereby, the electrical conductivities depend primarily on the extent of morphological disorder in the OSC. Moreover, in regioregular poly(3-hexylthiophene), rr-P3HT, smaller counterions lead to greater bipolaron concentrations in the low-doping regime due to the increased Coulomb interactions. Emphasizing the impact of the counterion size, it is shown that larger counterions can lead to increased thermoelectric power factors for rr-P3HT.

Original languageEnglish
JournalAdvanced Materials
DOIs
StateAccepted/In press - 2024

Bibliographical note

Publisher Copyright:
© 2024 Wiley-VCH GmbH.

Keywords

  • conjugated polymers
  • counterion size
  • electrochemical doping
  • organic semiconductors
  • thermoelectrics

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering

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