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.
|Number of pages
|Chemistry of Materials
|Published - Oct 11 2022
Bibliographical noteFunding 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.
© 2022 American Chemical Society. All rights reserved.
ASJC Scopus subject areas
- Chemistry (all)
- Chemical Engineering (all)
- Materials Chemistry