Enhancing the Backbone Coplanarity of n-Type Copolymers for Higher Electron Mobility and Stability in Organic Electrochemical Transistors

Iuliana P. Maria*, Sophie Griggs, Reem B. Rashid, Bryan D. Paulsen, Jokubas Surgailis, Karl Thorley, Vianna N. Le, George T. Harrison, Craig Combe, Rawad Hallani, Alexander Giovannitti, Alexandra F. Paterson, Sahika Inal, Jonathan Rivnay*, Iain McCulloch

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Electron-transporting (n-type) conjugated polymers have recently been applied in numerous electrochemical applications, where both ion and electron transport are required. Despite continuous efforts to improve their performance and stability, n-type conjugated polymers with mixed conduction still lag behind their hole-transporting (p-type) counterparts, limiting the functions of electrochemical devices. In this work, we investigate the effect of enhanced backbone coplanarity on the electrochemical activity and mixed ionic-electronic conduction properties of n-type polymers during operation in aqueous media. Through substitution of the widely employed electron-deficient naphthalene diimide (NDI) unit for the core-extended naphthodithiophene diimide (NDTI) units, the resulting polymer shows a more planar backbone with closer packing, leading to an increase in the electron mobility in organic electrochemical transistors (OECTs) by more than two orders of magnitude. The NDTI-based polymer shows a deep-lying lowest unoccupied molecular orbital level, enabling operation of the OECT closer to 0 V vs Ag/AgCl, where fewer parasitic reactions with molecular oxygen occur. Enhancing the backbone coplanarity also leads to a lower affinity toward water uptake during cycling, resulting in improved stability during continuous electrochemical charging and ON-OFF switching relative to the NDI derivative. Furthermore, the NDTI-based polymer also demonstrates near-perfect shelf-life stability over a month-long test, exhibiting a negligible decrease in both the maximum on-current and transconductance. Our results highlight the importance of polymer backbone design for developing stable, high-performing n-type materials with mixed ionic-electronic conduction in aqueous media.

Original languageEnglish (US)
Pages (from-to)8593-8602
Number of pages10
JournalChemistry of Materials
Issue number19
StatePublished - Oct 11 2022

Bibliographical note

Funding Information:
This research was funded in part, by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 952911, project BOOSTER, grant agreement no. 862474, project RoLA-FLEX, and grant agreement no. 101007084 CITYSOLAR, as well as EPSRC Project EP/T026219/1 and EP/W017091/1. The authors acknowledge financial support from KAUST Office of Sponsored Research (OSR) award no. OSR-2019-CRG8-4086. A.G. acknowledges funding from the TomKat Center for Sustainable Energy at Stanford University. In addition, B.D.P. and J.R. gratefully acknowledge support from the National Science Foundation grant no. NSF DMR-1751308. Special thanks to Joseph Strzalka and Qingteng Zhang for beam line assistance. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work utilized Keck-II facility of Northwestern University’s NUANCE Center and Northwestern University Micro/Nano Fabrication Facility (NUFAB), which are both partially supported by Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the Materials Research Science and Engineering Center (NSF DMR-1720139), the State of Illinois, and Northwestern University. Additionally, the Keck-II facility is partially supported by the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Finally, VL and AFP acknowledge support from Kentucky EPSCoR.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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