Dissipative Charge Transport in Organic Mixed Ionic-Electronic Conductor Channels

Understanding charge transport in organic mixed ionic-electronic conductors (OMIECs) is crucial for optimizing material properties in bioelectronic and neuromorphic devices. Recent experimental and theoretical findings show how the low-impedance properties of OMIECs are related to the chemical (or volumetric) capacitance <i>c_v</i> of such materials. Of interest for signal amplification in organic electrochemical transistors is the transconductance that was demonstrated to be proportional to the product of <i>c_v</i> and the charge carrier mobility<i> μ_e</i>. A less considered quantity is the velocity of signal transmission through OMIEC channels and the related energy dissipation.<br/>To achieve a quantitative description, we conduct experimental measurements of the phase velocity in microstructured PEDOT:PSS channels of different length at different frequencies. We compare data obtained from direct electrical measurements with local measurements of ionic displacements done with modulated electrochemical force microscopy [1]. Our findings are in excellent agreement to a simplified transmission line model describing charge transport through a mixed ionic electronic conductor channel. By combining the experimental data with the transmission line model, we resolve the dispersion relation for transport in OMIECs. We demonstrate that at relevant frequencies, the phase velocity is fully dominated by the ratio of <i>μ_e</i>/<i>c_v</i>. The results allow us to describe some principal limits in OMIECs based circuits and to compare their efficiency to neuronal signal transmission.<br/><br/>[1] F. Bonafe et al. Adv. Sci. 2024, https://doi.org/10.1002/advs.202308746