Beyond Capacitance Ratio: Electrolyte Voltage Division and a New Impedance Model for Organic Electrochemical...

Organic electrochemical transistors (OECTs) can be optimized by tuning the gate-channel capacitance ratio via geometry or materials. However, electrolyte properties also critically influence performance, which is a phenomenon unexplained by capacitive models alone. This study demonstrates that varying electrolyte concentration modulates the on-state current (Ion), the off-state current (Ioff), the on-off ratio (Ion/Ioff), and the threshold voltage (VT). We propose a new impedance-based model incorporating both capacitive coupling and resistive voltage division across the electrolyte to explain these effects. This model successfully predicts and verifies a frequency-dependent VT shift under high-frequency signals. Leveraging this insight, we demonstrate that appropriately increasing the gate DC bias compensates for this shift, thereby enhancing transconductance in high-frequency applications.