Tuning transport properties of organic mixed ionic electronic conductors with deep eutectic solvent additives

Organic mixed ionic-electronic conductors (OMIECs) are key materials for bioelectronic interfaces, where effective transduction of ionic fluxes from biological environments into electrical signals is required. This thesis presents a systematic study on how various deep eutectic solvent (DES) additives, composed of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) can impact on transport properties and microstructural organization of PEDOT:PSS. Nine different DES additives containing as HBA either choline chloride (ChCl), acetylcholine chloride (AcChCl) or betaine-choline chloride (BeChCl) and as HBD either ethylene glycol (EG), glycerol (GLY), or 1,3-propanediol (1.3P) were investigated. To study ionic and electronic transport properties in such materials, microstructured OMIEC channel devices of varying lengths were achieved with photolithography. Transport properties of electrolyte-gated microchannel devices were studied through OECT measurements and AC signal propagation analysis, extracting figures of merit including threshold voltage, mobility, volumetric capacitance, ionic conductivity, reduced propagation constant. Nanoscale morphology and PEDOT domain organization was studied with AFM imaging in tapping mode. The results reveal that the choice of DES additive impacts on the doping state of OMIECs, ion permeability, phase separation of PEDOT-rich and PSS-rich domains, their connectivity and organization. Observed impacts are linked to the hydrogen bonding strength of HBAs and number of polar groups in HBDs. Overall, this work demonstrates that deep eutectic solvents act as versatile additives modulating both ionic and electronic transport in PEDOT:PSS, for specific bioelectronic applications.