Polymerization‐Charge Controlled Threshold Voltage Tunability in Organic Electrochemical Transistors

Abstract Threshold voltage (V th ) is an important parameter in organic electrochemical transistors (OECTs), which are widely used in bio‐sensing and neuromorphic applications. In bio‐sensors, low V th , consequently near zero gate voltage at transconductance maximum, is appreciated in device/cell interfaces, while in neuromorphic devices, the threshold voltage determines the switching behaviour and energy efficiency of artificial synapses and neurons. In this work, electropolymerization is used to fine‐tune the V th of azidomethyl‐PEDOT based OECTs, a clickable analogue of PEDOT. The tuning is achieved through the control of the deposited charge density in a chronoamperometry mode. Azidomethyl‐PEDOT based OECTs yield similarly high transconductance as PEDOT based ones, while reaching maximum transconductance near zero gate voltage. Comprehensive comparisons with PEDOT based OECTs in terms of morphologies, ion transport and capacitance show that Azidomethyl‐PEDOT forms a thinner and flatter morphology under the same electropolymerization conditions, a contributing factor for its low ion mobility, and in turn the strong dependence of switching speed on the film thickness, revealing the underlying mechanisms for V th tuneability. This approach provides a simple and effective strategy for V th modulation in OECTs in certain organic mixed ionic electronic conductors of particular interest.