Yuhang Wu

Electrochemically polymerized PEDOT–MA was investigated as an OECT channel material, exhibiting a porous nanofibrillar morphology, tunable thickness, fast and stable operation, and thiol–maleimide “click chemistry” post-functionalizability.

This roadmap presents key advances and future directions in the field of the conducting polymer polyethylene dioxythiophene (PEDOT), with a focus on its role as multifunctional material in emerging electronic applications. It covers a broad spectrum of topics, including self-healing materials, plant bioelectronics, energy harvesting and storage, and neural interfaces. The roadmap also addresses recent progress in the synthesis and functionalization of PEDOT derivatives, as well as insights from molecular dynamics simulations and transport physics. Emphasis is placed on a range of processing techniques, such as electropolymerization, vapor phase polymerization, and 3D printing, and their implications for device performance. Specific applications explored include thermoelectrics, biosensors, organic electrochemical transistors, and advanced bioelectronic platforms for neuromodulation, stretchable electronics, and neuromorphic computing. This collective effort aims to serve as a comprehensive resource outlining the current state of PEDOT research and identifying challenges and opportunities for its integration across diverse electronic technologies.

Organic electrochemical transistors (OECTs) prepared from poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) have been widely investigated, typically with films prepared by spin-casting and drying from aqueous commercially available suspensions. Electrochemical deposition of PEDOT makes it possible to more precisely control film thickness and counterion composition. Here, we examined the influence of channel thickness and counterion composition on the properties of OECTs fabricated using electrochemically polymerized PEDOT with p-toluene sulfonate (pTS) and PSS on interdigitated gold electrodes. While PEDOT:PSS films deposited with a particular charge density were somewhat thicker (with more PSS in the film), PEDOT:pTS films showed higher volumetric capacitances consistent with their more rough, irregular surface morphologies. The maximum transconductance (gm,max) (∼70 mS) and on-current levels barely changed over the examined range of channel thicknesses (100–800 nm) with both counterions. The device stability (current retention in ON/OFF cycling) and transient response times (∼10 ms) were enhanced with larger counterions, thinner channel films (∼100 nm), and lower applied drain voltages (under −0.1 V). These design insights were used to create channel-functionalized OECT-based label-free glucose sensors with high stability. These results demonstrate the ability to optimize and enhance the performance and stability of electrochemically deposited PEDOT-based interdigitated OECT devices.

Modifying the surface chemistry of poly-(3,4-ethylenedioxythiophene) (PEDOT) with biological moieties is of interest for optimizing interactions in biointerfacing applications. Here, we demonstrate the attachment of cholesterol, a lipid prevalent in animal blood and cell membranes, and cysteine, an amino acid prevalent in proteins, onto PEDOT surfaces through efficient thiol-maleimide click-chemistry between maleimide-functionalized PEDOT (PEDOT-MA) and corresponding thiol derivatives. The reaction process of cholesterol post-treatment was actively monitored by electrochemical impedance spectroscopy (EIS) taken at different incubation times. An equivalent circuit model was used to deconvolute the impedance data. It was found that the charge transfer capability, as well as the ion diffusion within the PEDOT film, decreased systematically with incubation time. However, the film resistance remained unchanged in this process, indicating the relatively unaffected bulk properties. This finding was supported by scanning electron microscopy (SEM) results where no significant morphological changes were observed after the post-treatment. In addition, the charge storage capability also decreased, with only 23% of the original capacitance remaining after the post-treatment. The water contact angle increased from 23 to 115° after the cholesterol binding, confirming the formation of a hydrophobic film that correlates with the decreased charge transport behavior. In contrast, the attachment of cysteine showed almost no effect on the charge transport behavior and charge storage capability of PEDOT-MA. Contact angle measurements confirmed the high hydrophilicity of the cysteine-treated film. Again, SEM experiments showed there were no significant changes in the surface morphology. X-ray photoelectron spectroscopy (XPS) confirmed the presence of cholesterol and cysteine on the sample surface. Our results demonstrate that thiol-maleimide click-chemistry provides an efficient and effective route for the surface functionalization of PEDOT with biomolecules.

Electrochemical deposition of maleimide-functionalized 3,4-ethylenedioxythiophene (EDOT+) monomers and their conducting polymer derivatives (PEDOT+). PEDOT+ can be created by depositing EDOT-MA, or by exposing PEDOT-MA to the functionalized thiol.

Electronically conductive hydrogels have gained popularity in bioelectronic interfaces because their mechanical properties are similar to biological tissues, potentially preventing scaring in implanted electronics. Hydrogels have low elastic moduli, due to their high water content, which facilitates their integration with biological tissues. To achieve electronically conductive hydrogels, however, requires the integration of conducting polymers or nanoparticles. These “hard” components increase the elastic modulus of the hydrogel, removing their desirable compatibility with biological tissues, or lead to the heterogeneous distribution of the conductive material in the hydrogel scaffold. A general strategy to transform hydrogels into electronically conductive hydrogels without affecting the mechanical properties of the parent hydrogel is still lacking. Herein, a two‐step method is reported for imparting conductivity to a range of different hydrogels by in‐situ polymerization of a water‐soluble and neutral conducting polymer precursor: 3,4–ethylenedioxythiophene diethylene glycol (EDOT‐DEG). The resulting conductive hydrogels are homogenous, have conductivities around 0.3 S m⁻¹, low impedance, and maintain an elastic modulus of 5–15 kPa, which is similar to the preformed hydrogel. The simple preparation and desirable properties of the conductive hydrogels are likely to lead to new materials and applications in tissue engineering, neural interfaces, biosensors, and electrostimulation.

The commercially available polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is ubiquitous in organic and hybrid electronics. As such, it has often been used as a benchmark material for fundamental studies and the development of new electronic devices. Yet, most studies on PEDOT:PSS have focused on its electronic conductivity in dry environments, with less consideration given to its ion transport, coupled ionic-electronic transport, and charge storage properties in aqueous environments. These properties are essential for applications in bioelectronics (sensors, actuators), charge storage devices, and electrochromic displays. Importantly, past studies on mixed ionic-electronic transport in PEDOT:PSS neglected to consider how the molecular structure of PSS affects mixed ionic-electronic transport. Herein, we therefore investigated the effect of the molecular weight and size distribution of PSS on the electronic properties and morphology of PEDOT:PSS both in dry and aqueous environments, and overall performance in organic electrochemical transistors (OECTs). Using reversible addition–fragmentation chain transfer (RAFT) polymerization with two different chain transfer agents, six PSS samples with monomodal, narrow (Đ = 1.1) and broad (Đ = 1.7) size distributions and varying molecular weights were synthesized and used as matrices for PEDOT. We found that using higher molecular weight of PSS (M_n = 145 kg mol⁻¹) and broad dispersity led to OECTs with the highest transconductance (up to 16 mS) and [μC*] values (∼140 F cm⁻¹ V⁻¹ s⁻¹) in PEDOT:PSS, despite having a lower volumetric capacitance (C* = 35 ± 4 F cm⁻³). The differences were best explained by studying the microstructure of the films by atomic force microscopy (AFM). We found that heterogeneities in the PEDOT:PSS films (interconnected and large PEDOT- and PSS-rich domains) obtained from high molecular weight and high dispersity PSS led to higher charge mobility (μ_OECT ∼ 4 cm² V⁻¹ s⁻¹) and hence transconductance. These studies highlight the importance of considering molecular weight and size distribution in organic mixed ionic-electronic conductor, and could pave the way to designing high performance organic electronics for biological interfaces.

Here we examined the capacitive behavior of electrodeposited poly(2′-maleimideomethyl-3,4-ethylenedioxythiophene) (PEDOT-maleimide) and compared it to poly(3,4-ethylenedioxythiophene) (PEDOT). According to results of linear cyclic voltammetry (linear CV) and galvanostatic charging/discharging (GCD) in 0.1 M KCl aqueous solution, PEDOT-maleimide presented higher areal specific capacitance, 5.8 × 10⁻³ F cm⁻² at 25 mV s⁻¹ and 7.0 × 10⁻³ F cm⁻² at 1.6 × 10⁻⁴ A cm⁻², while PEDOT exhibited 5.4 × 10⁻³ F cm⁻² at 25 mV s⁻¹ and 6.3 × 10⁻³ F cm⁻² at 1.6 × 10⁻⁴ A cm⁻². Improved cyclic stability of the PEDOT-maleimide was also achieved which correlated with better mechanical properties as revealed by nanoindentation. The effective Young's modulus for PEDOT-maleimide was 4.5 GPa, while it was 1.8 GPa for PEDOT. Roughness studies on surface topographies, determined by atomic force microscopy (AFM) and analyzed by power spectral density (PSD) and root-mean-square (RMS) roughness, revealed that PEDOT-maleimide was rougher than PEDOT at small length scales (below ∼1 μm) but smoother at large length scales (above ∼1 μm), which was also consistent with complementary observations by scanning electron microscopy (SEM). PEDOT-maleimide showed decreased scattering from the side-to-side (lamellar stacking) ∼1.21 nm and ∼0.34 nm face-to-face (π–π stacking) signals as confirmed by grazing-incidence wide-angle X-ray scattering (GIWAXS). This change directly made PEDOT-maleimide less conductive than PEDOT, 0.58 vs. 3.34 S cm⁻¹. However, the impedance performance across a broad range of frequencies (10⁻¹ to 10⁵ Hz) was similar for both PEDOT and PEDOT-maleimide, indicating that both materials remained effective at charge transport. Those results indicate that PEDOT-maleimide is a promising alternative to PEDOT for charge storage applications.