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In-situ studies of the swelling by electrolyte in the electrochemical doping of an ethylene glycol substituted polythiophene



Lee J. Richter, Lucas Flagg, Lauren Asselta, Nicholas D'Antona, Natalie Stingelin, Tommaso Nicolini, Jonathan Onorato, Christine Luscombe, Ruipeng Li


Organic mixed ionic electronic conductors (OMIECs) have the potential to enable diverse new technologies, ranging from biosensors to flexible energy storage devices and neuromorphic computing platforms. However, study of these materials in their operating state, which convolves both passive and potential driven solvent, cation, and anion ingress is extremely difficult, inhibiting rational materials design. In this report, we present a novel approach to the in-situ study, via grazing-incidence X-Ray scattering, of the electrochemical switching of a prototypical OMIEC, based on oligo(ethylene glycol), oEG, substitution of a semi-crystalline regio-regular polythiophene. By studying the crystal lattice both dry and in contact with electrolyte while maintaining potential control, we can directly observe the evolution of the crystalline domains and their relationship to film performance in an electrochemically gated transistor. Despite the oEG side chain enabling bulk electrolyte uptake, we find the crystalline regions are relatively hydrophobic, exhibiting little (less than one water per thiophene) swelling of the undoped polymer suggesting that the amorphous regions dominate the reported passive swelling behavior. With applied potential, we observe that the - separation in the crystals contracts while the lamella spacing increases in a balanced fashion, resulting in negligible change in the crystal volume. The potential induced changes in the crystal structure do not clearly correlate to electrical performance of the film as an organic electrochemical transistor, suggesting that the transistor performance is strongly influenced by the amorphous regions of the film. However, the carrier mobilities are not degraded in comparison to doped, alkylated polythiophenes.
ACS Applied Materials and Interfaces


organic electrochemical transistor, OMIEC, X-ray diffraction, in-situ


Richter, L. , Flagg, L. , Asselta, L. , D'Antona, N. , Stingelin, N. , Nicolini, T. , Onorato, J. , Luscombe, C. and Li, R. (2022), In-situ studies of the swelling by electrolyte in the electrochemical doping of an ethylene glycol substituted polythiophene, ACS Applied Materials and Interfaces, [online],, (Accessed May 22, 2024)


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Created June 13, 2022, Updated January 30, 2023