Hole-limited electrochemical doping in conjugated polymers
Simultaneous transport and coupling of ionic and electronic charges is fundamental to electrochemical devices used in energy storage and conversion, neuromorphic computing and bioelectronics. While the mixed conductors enabling these technologies are widely used, the dynamic relationship between ionic and electronic transport is generally poorly understood, hindering the rational design of new materials. In semiconducting electrodes, electrochemical doping is assumed to be limited by motion of ions due to their large mass compared to electrons and/or holes. Here, we show that this basic assumption does not hold for conjugated polymer electrodes. Using operando optical microscopy, we reveal that electrochemical doping speeds in a state-of-the-art polythiophene can be limited by poor hole transport at low doping levels, leading to substantially slower switching speeds than expected. We show that the timescale of hole-limited doping can be controlled by the degree of microstructural heterogeneity, enabling the design of conjugated polymers with improved electrochemical performance.
Acknowledgements: S.T.K. gratefully acknowledges funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement no. 101022365. S.T.K. also acknowledges a graphics processing unit donation from the Nvidia Academic Hardware Grant Program. J.E.M.L. acknowledges funding from the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Award no. EP/R513180/1. R.P. acknowledges funding from an EPSRC Doctoral Prize Fellowship and Clare College, University of Cambridge. C.S. acknowledges financial support from the Royal Commission for the Exhibition of 1851. P.A.M. acknowledges financial support from the EPSRC, UK (grant no. EP/R008779/1), and funding from the European Union’s Horizon 2020 Research and Innovation Programme (grant no. 823717, project ‘ESTEEM3’). 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 grant nos. EP/T026219/1 and EP/W017091/1. A.R. acknowledges funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (grant agreement no. 758826). I.M., A.R. and G.G.M. acknowledge support from the Engineering and Physical Sciences Research Council (UK) (grant no. EP/W017091/1). This work was funded by the UKRI. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.
Funder: University of Cambridge | Clare College, University of Cambridge; doi: https://doi.org/501100001625
Funder: Royal Commission for the Exhibition of 1851; doi: https://doi.org/501100000700
EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council) (101022365, 823717, 952911, 862474, 101007084, 758826)