Evaluation of Ion Penetration Dynamics in Conjugated Polymers Using Bilayer OECTs

Recently, conjugated polymer based organic mixed semiconductors have attracted increase interests due to their simultaneous ionic-electronic transport properties, enabling unique operations in electrochemical devices. Accurate determination and control of ion penetration is vital to design and screen promising mixed semiconductors. Here, we demonstrate a simple method to electrically evaluate ion penetration dynamics in various conjugated polymers using a bilayer organic electrochemical transistor (OECT) structure, where the top poly (3, 4-propylenedioxythiophene) (PProDOT) and buried PEDOT:PSS layers serve as the ionic buffer and electronic transport layer, respectively. The specific separation of these two conducting pathways allows precise measurements of ion penetration timescales. Upon increasing the hydrophilicity of the top buffer layer, significant accelerate of response timescales was observed for high hydrate anions (Cl^-), which only changed slightly for low hydrate alternatives (TFSI^-). These results are consistent with the calculated diffusion constants using cyclic voltammetry. Our findings offer a simple and direct method to evaluate ion penetration dynamics in a wide range of polymers and can also serve as a general tool for re-establishing OECT operating models.