Impact of molecular weight and size distribution on the performance of PEDOT:PSS in organic electrochemical transistors

Organic electrochemical transistors (OECTs) are gaining momentum in biosensing applications for their ability to effectively transduce ionic signals from biological processes to electronic signals readable using conventional electronics. OECT devices rely on the use of organic mixed ionic-electronic conductors (OMIECs) as channel materials exposed to an aqueous electrolyte. The most commonly used OMIEC for OECT is the commercially available polyelectrolyte complex PEDOT:PSS, previously extensively used as an organic conductor and anti-static coating in “dry” conditions. Yet, key molecular features, such as molecular weight and size distribution, in this complex material are kept a trade secret by the manufacturer, preventing the establishment of important structure-property relationships. In this presentation, I will share how we used controlled radical polymerization to synthesize PSS with precise molecular weights and dispersity to establish their effect on the performance of PEDOT:PSS in OECTs [Lo et al. Polym. Chem., 2022, 13, 2707]. In particular, we found that the conductivity of PEDOT:PSS under “dry” conditions is correlated to the molecular weight of PSS, but independent of the dispersity. In the presence of an electrolyte, however, the molecular weight has little effect on the capacitance and OECT transconductance, but dispersity does. A broad dispersity (1.7 vs 1.1) leads to a four time increase in OECT performance. We correlated these findings to differences in film morphology.