Publication date: 21st July 2025
Ion transport governs the transient response of mixed ionic–electronic conductors (MIECs). In this work, we provide complementary insights into PEDOT:PSS through two device platforms. First, in vertical two-terminal structures, we demonstrate for the first time that time-domain (chronoamperometry) and frequency-domain (impedance spectroscopy) measurements yield quantitatively consistent descriptions of anomalous ion diffusion. This establishes a direct correspondence between domains, a critical step toward a unified transport mechanism in MIECs.
Building on this foundation, we investigated organic electrochemical transistors (OECTs) and experimentally validated the diffusion–transport model proposed by Bisquert and Tessler. For the first time, all four classes of transient responses predicted by the model—positive/negative spikes and monotonic decays—are observed and mapped across bias conditions. Drain- and gate-current analyses consistently yield the ionic diffusion time τd, confirming the model’s predictive power in real devices.
Finally, we clarify the origin of τd and its interplay with the electronic transit time τe. The intrinsic τd is primarily set by the gate-voltage step ΔVg and channel thickness, while τe shapes the transient waveform without altering τd. Gate currents provide the most direct probe of τd, while drain currents highlight the competition between τd and τe.
Together, these results (i) establish time–frequency correspondence in vertical PEDOT:PSS devices, (ii) provide the first full experimental validation of the four-class diffusion–transport framework in OECTs, and (iii) identify the respective roles of τd and τe. This unified picture advances the mechanistic understanding of ionic dynamics and informs the design of MIEC-based bioelectronic and neuromorphic devices.
The work was funded by the European Research Council (ERC) via Horizon Europe Advanced Grant, grant agreement n° 101097688 (“PeroSpiker”).
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