The Effect of a Polymer Electrolyte on N-Type Bioelectronic Device Performance

Oligo ethylene glycol (OEG) side chain modification has granted well-known semiconducting polymers, such as pBTTT and N2200, the ability to transport ions within the bulk of their films. Through this approach, a wide variety of polymer semiconductors have been produced for bioelectronic applications, where ion transport is the native speech.¹ Another way to facilitate ionic charge transport by omitting the synthetic work is through polyelectrolyte/polymer electrolyte blending. For efficient mixed conduction in such blends, the separation of the electron conducting phase, which is envisaged to be rigid and packed, and the ion conducting phase, which allows for water uptake and ion motion, must be carefully optimized. Polymer electrolytes, such as poly(ethylene oxide) (PEO), have been blended hydrophobic polymers to grant ion access to the bulk.^2,3<br/>To this end, we investigate the mixtures of PEO with an electron transporting (n-type) polymer, namely poly(benzimidazobenzophenanthroline) (BBL).⁶ Using PEO of various molecular weights, we modulate the phase separation between the two components that allow for the most optimized charge transport. We find that, by solution blending with PEO, we can enhance volumetric capacitance (C*) and not deteriorate electronic mobility (µ), both of which go into the figure of merit of organic electrochemical transistors (OECT), µC*. This study shows that the film microstructure, hence, mixed conduction at the electrolyte interface, can be controlled through simple solution blending of ion conducting phase, presenting a route to develop high performance devices.<br/>1. Moser, M., Ponder, J. F., Wadsworth, A., Giovannitti, A. & McCulloch, I. Materials in Organic Electrochemical Transistors for Bioelectronic Applications: Past, Present, and Future. <i>Adv. Funct. Mater.</i> <b>29</b>, 1807033 (2019).<br/>2. Frankenstein, H. <i>et al.</i> Blends of polymer semiconductor and polymer electrolyte for mixed ionic and electronic conductivity. <i>J. Mater. Chem. C</i> <b>9</b>, 7765–7777 (2021).<br/>3. Cao, Y., Yu, G., Heeger, A. J. & Yang, C. Y. Efficient, fast response light-emitting electrochemical cells: Electroluminescent and solid electrolyte polymers with interpenetrating network morphology. <i>Appl. Phys. Lett.</i> <b>68</b>, 3218–3220 (1996).<br/>4. Ghosh, S. Networks of Electron-Conducting Polymer in Matrices of Ion-Conducting Polymers Applications to Fast Electrodes. <i>Electrochem. Solid-State Lett.</i> <b>3</b>, 213 (1999).<br/>5. Parr, Z. S. <i>et al.</i> Semiconducting Small Molecules as Active Materials for p-Type Accumulation Mode Organic Electrochemical Transistors. <i>Adv. Electron. Mater.</i> <b>6</b>, 2000215 (2020).<br/>6. Surgailis, J. <i>et al.</i> Mixed Conduction in an N-Type Organic Semiconductor in the Absence of Hydrophilic Side-Chains. <i>Adv. Funct. Mater.</i> <b>31</b>, 2010165 (2021).