Ion diffusion overestimates figures of merit in polymeric mixed conductors

In this work, we investigate why the commonly used figure of merit for OMIECs—the µC* product—can be incorrectly estimated when extracted from organic electrochemical transistors (OECTs). We identify the source of the current “kink” that leads to this error, showing that it originates from a change in the ion diffusion rate within the OMIEC channel. Our study also demonstrates that OECT channel geometry plays a much larger role than previously recognized, significantly affecting how ions distribute throughout the material. Finally, we reveal a sequential transport mechanism in which electronic carriers must first enter and drift through the OMIEC before ions can follow from the electrolyte.