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

High Resolution Image Download MS PowerPoint Slide 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 ( I on ), the off-state current ( I off ), the on–off ratio ( I on / I off ), and the threshold voltage ( V T ). 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 V T 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.