Developing material design guidelines for organic mixed ionic–electronic conductors (OMIECs) is critical to enable high efficacy mixed transport within bioelectronics. One important feature which has yet to be thoroughly explored is the role of molecular weight on OMIEC performance. In this work, we examined a series of prototypical glycolated polythiophene materials (P3MEEET) with systematically increasing molecular weights within organic electrochemical transistors (OECTs)─a common testbed for investigating mixed transport. We find that there is improved performance beyond an intermediate molecular weight; however, this relationship is electrolyte dependent. Operando analysis suggests that the enhanced mobility at higher molecular weights may be negated by significant swelling when operated in NaCl due to disruption of intercrystallite charge percolation. The role of molecular weight is revealed through operation in KTFSI, as doping occurs through cation expulsion, preventing detrimental swelling and maintaining percolative pathways. These findings demonstrate the importance of both molecular weight and electrolyte composition to enhance the performance of OMIECs.
Bibliographical noteKAUST Repository Item: Exported on 2023-04-10
Acknowledged KAUST grant number(s): OSR-2019-CRG8-4086
Acknowledgements: J.R. gratefully acknowledges funding support from Sloan under award no. FG-2019-12046. R.W., B.D.P., and J.R. acknowledge support from the National Science Foundation grant no. NSF DMR-1751308. R.W., D.M., and J.R. acknowledge funding from King Abdullah University of Science and Technology Office of Sponsored Research (OSR) under award no. OSR-2019-CRG8-4086. J.T. was primarily supported by an Office of Naval Research (ONR) Young Investigator Program (YIP) award no. N00014-20-1-2777. This work utilized the Keck-II facility of Northwestern University’s NUANCE Center and Northwestern University Micro/Nano Fabrication Facility (NUFAB), which are both partially supported by the 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 KeckII facility is partially supported by the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. We acknowledge the generous support from Christopher J. Takacs for his assistance with scattering experiments and data analysis.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.