Impact of the Degree of Sulfonation on the Mixed Ionic-Electronic Properties of PEDOT:PSS-co-PS

• Brian Harrity, , University of Delaware

• Laure Kayser, Materials Science & Chemistry and Biochemistry, University of Delaware

Brian Harrity, Kelsey P. Koutsoukos, Chun-Yuan Lo, Laure V. Kayser* 

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been extensively studied for its mixed ionic-electronic conductivity, which is crucial for applications including sensors, energy storage devices, and flexible electronics. Despite extensive research, the influence the degree of sulfonation has on the mixed transport properties within PEDOT:PSS remains poorly understood. This study aims to explore and quantify how different degrees of sulfonation affect the ionic and electronic conductivity of PEDOT:PSS, allowing for further examination of structure-property relationships to inform molecular design. Polystyrene was sulfonated to create PSS-co-PS with varying degrees of sulfonation (38%, 55%, 82%, and 92%). PSS-co-PS was then used to oxidatively polymerize EDOT to make PEDOT:PSS-co-PS. Thin films were spin-coated onto interdigitated electrodes for electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and organic electrochemical transistor (OECT) testing. Our findings reveal that the degree of sulfonation significantly impacts the conductivity of the films. Electronic conductivity increased significantly with higher sulfonation, attributed to enhanced hole hopping facilitated by the larger degree of doping of PEDOT. Ionic conductivity also improved with higher degrees of sulfonation. A higher number of sulfonate groups provided more sites for cation interactions, facilitating greater ion penetration into the PEDOT:PSS-co-PS film thereby enhancing ionic transport. This improvement was reflected in the volumetric capacitance, a measure of ionic conductivity. This study indicates that higher sulfonation levels lead to a significant improvement in both ionic and electronic conductivity, and higher degrees of sulfonation are necessary for optimal device performance.