Gate-voltage-dependent ionic diffusion and transient dynamics in organic electrochemical transistors

Organic electrochemical transistors (OECTs) exhibit transient current responses governed by the interplay between ionic motion and electronic transport in the polymer channel. In this work, transient behaviours of PEDOT:PSS OECTs are investigated under a step change in gate voltage. The gate current consistently decays exponentially across different drain biases, allowing extraction of the ionic diffusion time constant τ d via comparison with an analytical model. In contrast, drain current transients show bias- and polarity-dependent temporal profiles, reflecting the modulation of lateral transit of electronic carriers by the drain-source potential. Despite these variations, the extracted decay constants remain consistent with those from gate-current analysis. These results demonstrate that vertical ionic diffusion predominantly determines the device's intrinsic temporal response and lateral electronic transport shapes the transient characteristics, providing a clear physical basis for interpreting time-dependent behaviours in mixed ionic–electronic conductors.