Tailoring Organic Mixed Ionic-Electronic Conductors for Neuromorphic Devices

Organic mixed ionic-electronic conductors (OMIECs) have emerged as a key material for the development of biohybrid neuromorphic devices due to their soft mechanical properties, biocompatibility, and modulation of conductance through reversible electrochemical doping. While OMIECs are widely used for bioelectronics, there are many challenges that remain to understand mixed ionic-electronic transport in these materials as well as to optimize them for use in biohybrid neuromorphic systems. In my talk, I will discuss microscopic characterization, stability, and processing of OMIECs. First, I will discuss how we can use microscopy to characterize mixed ionic-electronic transport in real time by acquiring spatial, temporal, and spectral information during doping and dedoping. We find that the ionic transport process is diffusion-like resulting from the large gradient in the chemical potential of electronic carriers. During doping of intrinsic semiconductors, we find that electrochemical doping speeds can be limited by poor electronic transport at low doping levels, leading to substantially slower speeds than expected. Next, I will discuss how the stability of OMIEC devices operated in aqueous environments depend on the operating voltage ranges. We find that the maximum stability for OMIEC devices is achieved when they are either operated in the saturation regime to maximize current gain (transconductance) or in the subthreshold regime to maximize the on/off ratio. Last, I will discuss how water-stable PEDOT:PSS can be prepared without the use of a chemical crosslinker with a simple thermal treatment. The heat-treated PEDOT:PSS films are as stable as their chemically-crosslinked counterparts, with performance maintained for more than 20 days both in vitro and in vivo, while yielding a higher electrical performance by eliminating electrically insulating crosslinkers.