Electrically Programmed Doping Gradients Optimize the Thermoelectric Power Factor of a Conjugated Polymer

Jian Liu, Mariavittoria Craighero, Vandna K. Gupta, Dorothea Scheunemann, Sri Harish Kumar Paleti, Emmy Järsvall, Youngseok Kim, Kai Xu, Juan Sebastián Reparaz, L. Jan Anton Koster, Mariano Campoy-Quiles, Martijn Kemerink, Anna Martinelli, Christian Müller*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)
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Abstract

Functionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in-plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6-tetrafluoro-tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight-fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll-off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices.

Original languageEnglish
Article number2312549
Number of pages10
JournalAdvanced Functional Materials
Volume34
Issue number18
Early online date24-Jan-2024
DOIs
Publication statusPublished - 2-May-2024

Keywords

  • chemical doping
  • conjugated polymer
  • counterion drift
  • functionally graded materials
  • organic thermoelectrics

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