Impact of Fluorinated Anions on Organic Mixed Conductors

The performance of organic mixed ionic-electronic conductors (OMIECs) for applications ranging from bioelectronics to neuromorphic computing depends on numerous factors including polymer chemistry, polymer microstructure, and electrolyte properties. Notably, the use of fluorinated ions often enhances OMIEC performance when used as the active layer in organic electrochemical transistors (OECTs), yet whether this effect is universal remains unclear. In this work, we investigate the impact of fluorinated anions on the electrochemical doping of the conjugated polymer poly(2-(3,3′-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-[2,2′-bithiophen]-5-yl)thieno[3,2-b]thiophene) (p(g2T-TT)) by comparing fluorinated and nonfluorinated anions with the same chemical structure. By using electrochemical quartz crystal microbalance (EQCM) and operando grazing incidence wide-angle X-ray scattering (GIWAXS) as a function of voltage, we find that fluorinated anions significantly alter the amorphous regions of p(g2T-TT), leading to water and/or cation expulsion. While fluorinated anions do not universally enhance OECT performance, they generally increase charge carrier mobility (μ) compared to their nonfluorinated counterparts. These findings underscore the complexity of electrolyte selection in OMIEC-based devices, highlighting that fluorination alone does not guarantee improved OECT performance.