The Role of Side Chains and Hydration on Mixed Charge Transport in n-Type Polymer Films

Jokūbas Surgailis, Lucas Q. Flagg, Lee J. Richter, Victor Druet, Sophie Griggs, Xiaocui Wu, Stefania Moro, David Ohayon, Christina J. Kousseff, Adam Marks, Iuliana P. Maria, Hu Chen, Maximilian Moser, Giovanni Costantini, Iain McCulloch, Sahika Inal

Research output: Contribution to journalArticlepeer-review


Introducing ethylene glycol (EG) side chains to a conjugated polymer backbone is a well-established synthetic strategy for designing organic mixed ion-electron conductors (OMIECs). However, the impact that film swelling has on mixed conduction properties has yet to be scoped, particularly for electron-transporting (n-type) OMIECs. Here, the authors investigate the effect of the length of branched EG chains on mixed charge transport of n-type OMIECs based on a naphthalene-1,4,5,8-tetracarboxylic-diimide-bithiophene backbone. Atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and scanning tunneling microscopy (STM) are used to establish the similarities between the common-backbone films in dry conditions. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and in situ GIWAXS measurements reveal stark changes in film swelling properties and microstructure during electrochemical doping, depending on the side chain length. It is found that even in the loss of the crystallite content upon contact with the aqueous electrolyte, the films can effectively transport charges and that it is rather the high water content that harms the electronic interconnectivity within the OMIEC films. These results highlight the importance of controlling water uptake in the films to impede charge transport in n-type electrochemical devices.

Original languageEnglish (US)
JournalAdvanced Materials
StateAccepted/In press - 2024
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering


  • electrochemical transistors
  • in operando
  • organic mixed conductors
  • quartz crystal microbalance
  • swelling


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