Organic mixed ion-electron conductors (OMIECs), such as PEDOT:PSS, are key materials for organic electrochemical transistors (OECTs) owing to their combined ionic and electronic transport properties. The functionalization of OMIEC films is critical for enabling sensing capabilities in applications ranging from biomolecular detection to monitoring environmental stimuli such as temperature and light. In this presentation, we introduce two distinct strategies for constructing functional OECT interfaces: (1) spontaneous formation of functionalized surface ("skin") layers and (2) surface-initiated polymerization of organic and hybrid organic–inorganic materials.

The first approach utilizes phase-separated blend films of PEDOT:PSS and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM). Through X-ray photoelectron spectroscopy (XPS) and high-resolution scanning probe microscopy (SPM), we reveal a vertical compositional gradient with PNIPAM-rich domains emerging at the film surface, forming a functional skin layer. This architecture enables dynamic response to temperature changes without compromising electrical performance.

The second approach involves the in situ polymerization of polydopamine (PDA) on PEDOT:PSS films. We investigate the adhesion properties of PDA with various inorganic nanoparticles and enzymes, demonstrating its potential as a versatile interfacial layer for biofunctionalization. The hybrid films show promising mechanical robustness and functional stability.

These interfacial design strategies provide valuable insights into the development of multi-responsive and bio-interfaced OECTs, paving the way for future applications in neuromorphic computing, biosensing, and soft bioelectronics.

Doping of organic semiconductor films enhances their conductivity for applications in organic electronics, thermoelectrics and bioelectronics. However, much remains to be learnt about the properties of the conductive charges in order to optimize the design of the materials. Electrochemical doping is important for organic electrochemical transistors (OECTs) used in neuromorphic systems. Benefits of doping via electrochemistry include controllable doping levels, reversibility and high achievable carrier densities. We introduce a new technique, applying in-situ terahertz (THz) spectroscopy directly to electrochemically doped polymers in combination with time-resolved spectro-electrochemistry, chronoamperometry and OECT device measurements. We evaluate the intrinsic short-range transport properties of the polymers (without the effects of long-range disorder, grain boundaries and contacts), while precisely tuning the doping level, and thus the density and nature of charges species, via the applied oxidation voltage. Results will be shown for a variety of polymers, including polythiophene backbones with different sidechains and n-type BBL materials.

Mixed conducting redox polymers have garnered significant attention in recent years for their potential usage as active layers in opto-electronic devices, bioelectronics and organic electrochemical transistors (OECTs).

Our contribution will show the electropolymerization of 3,4-ethylenedioxythiophene (EDOT) and how this method is particularly suitable for creating active layers on OECTs. The electrochemical mechanism behind electropolymerization will be explored [1] and perspectives towards applications will be discussed with the focus being the electropolymerization on OECTs directly [2] and the ways in which the material can be modified and optimized for this purpose.

Our contribution will also showcase the electrochemical study of two polymer systems, one of which focuses on carbazole-based redox polymers and the other focusing on triphenylamine-based redox polymers [3]. In-situ spectroelectrochemistry is employed to monitor the crosslinking of both the carbazole and the triphenylamine units and identify the redox active species. This crosslinking reaction significantly expands the conjugated system of both polymers which results in lower onset potentials and increased conductivities. Additionally, it becomes possible to reach higher oxidation states for these systems, from neutral to radical cation to dication. In line with these higher oxidation states are additional functionalities like an electrochromic reaction during the doping process. In our carbazole system, this colour change is from light green to dark green to black but the colour range can be adapted by chemically modifying the redox active unit. This not only has an impact on its oxidation potentials but also the colour range accessible for these systems.

The multiple advantages of these systems are combined with a wide range of possible processing methods. This includes printing or solution processing and subsequent crosslinking which leads to the growing of our redox system even in post-processing. All of this combined makes these mixed conductors particularly suitable for usage as OECT materials.

In line with the principles of Safe and Sustainable by Design (SSbD) framework, the development of organic semiconductors must consider not only performance, but also factors such as human and environmental safety, resource efficiency, and circularity. Typically, organic semiconductors are processed from harmful solvents while substrates such as glass, plastic, and more recently natural materials such as cellulose are used as mechanical support, which has implication for how these materials are designed regarding processability and recoverability. Ideally, organic semiconductors are designed to be water-processable to enable benign fabrication methods and form intimate mixtures or composites with cellulosic materials. Additionally, these materials must maintain mechanical integrity and resist degradation or delamination under aqueous conditions during use. Furthermore, to separate the various device components at end-of-life, ideally the design of the organic semiconductor allows for chemical recycling that enables recovering of the separate components.

We have demonstrated that incorporating physical crosslinking moieties into polar polythiophenes enhances their structural robustness while retaining their processability.(1) Our more recent work focuses on the functionalization of these polymers with carboxylate groups(2) that offer water-processability and improved compatibility with cellulose derivatives, supports the creation of stable hybrid materials, and enables recovery of individual components at end-of-life.  In this talk, we will present several aspects of these carboxylate-functionalized polythiophenes, such as their stability, use in electroactive cellulose composites, recoverability and their interaction with molecular oxygen under aqueous conditions.   

Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons (electron-phonon coupling), significantly affecting charge transport properties. Understanding the formation/ deformation and localization/ delocalization of polarons induced by ions is critical for development of organic electrochemical devices such as organic electrochemical transistors (OECTs) and organic synaptic transistors (OSTs). However, there have been only few studies reported in this area, lacking direct evidence on in situ polaron formation/ deformation and associated structural changes. In this talk, I will show our recent work in this area. First, how a minor modification of side chains (nature and density) in conjugated polymers affects the polaron formation /deformation via electrochemical doping, changing the polymers electrical properties. Second, how glycol sidechain length of conjugated polymers impact polaron formation, with the optimal length enabling a balance between ionic and electronic charge transport. Finally, I will show molecular structure dependent ion retention by tracking polaron-induced structural changes during OST operation. These results provide key experimental evidence and fundamental understanding of the strong electron-phonon coupling in molecular semiconductors and its impact on organic electrochemical devices.

Mixed conducting polymers have become attractive for their potential application as active materials in electrochemical devices such as organic electrochemical transistors (OECTs).

This contribution will highlight our ongoing research on electrochemical doping behavior of n-type polymers, namely the donor-acceptor copolymer poly[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)[P(NDI2OD-T2)] [1], [2], [3] and its derivatives modified with oligo(ethylene glycol) side chains and selenophene-vinylene-selenophene as donor units [4]. We used an in situ spectroelectrochemical approach to investigate their absorption characteristics with different doping degrees and to identify their redox states during electrochemical doping. We further employed in situ technique to determine the reduction onset potentials through spectral evolution mapping from the neutral in the first reduced state. Compared to conventional cyclic voltammetry, this approach improves the certainty in the onset potential determination of conducting polymers, enabling more accurate estimation of the lowest unoccupied molecular orbital (LUMO) energy levels for their device applications. The glycolated and fluorinated P(NDIEG7-FSVS) exhibited a LUMO energy level of -4.63 eV [4], significantly lower than that of P(NDI2OD-T2) around -4.0 eV [1], [2], [3].

Furthermore, UV-vis-NIR absorption spectroscopy confirms that the redox states of electrochemically doped polymer films can be retained in the solid state [3]. Four-line probe measurements of P(NDI2OD-T2) films with different doping levels showed a characteristic bell-shaped conductivity profile, indicating mixed valence charge transport in the conjugated redox polymer system [3]. For aligned films prepared by blade-coating, conductivity measurements after electrochemical doping reveal anisotropic charge transport behavior, with higher conductivity achieved along the polymer chain direction [2], [3]. This offers a morphology-control strategy for designing high-performance organic electronics.

The explosion of internet usage, the Internet of things (IoT), and the artificial intelligence (AI) is generating a vast amount of data daily that traditional computing systems are not able to handle efficiently. Neuromorphic computing is emerging as a new computing paradigm that can overcome the limitations of silicon-based computing by emulating the functioning of the most efficient computing system known, the human brain.[1] Organic electrochemical memtransistors (OECmTs) are potential candidates to be used as the artificial synapses that the neuromorphic hardware needs.[2] However, OECmTs fabricated with n-type organic mixed ionic-electronic conductors (OMIECs) have not been successfully employed in organic artificial synapses because they usually show instability in ambient conditions.[3] In this work, we prove the potential of the recently developed n-doped poly-[benzodifurandione] (n-PBDF) polymer to fabricate high-performance n-type OECmTs, using protons as the principal migrating ions.[4] The devices exhibit resistive switching and synaptic plasticity leading to high-quality long-term potentiation (LTP)/depression (LTD) functions at low gate voltages and short pulses. The applicability of n-PBDF OECTs in neuromorphic computing is validated by performing simulations with a deep neural network (DNN) model for handwritten digit recognition with different Gaussian noise levels.[5] This work opens new avenues for the future development of n-PBDF-based (bio)electronic circuits for diverse applications such as (bio)sensing and neuromorphic computing.

Organic electrochemical transistors (OECTs), which rely on organic mixed ionic–electronic conductors (OMIECs) to modulate bulk conductivity through ion exchange with an electrolyte, are increasingly used in bioelectronics, energy storage, actuation, and sensing. We recently introduced a new design paradigm based on blending p-type and n-type OMIECs to achieve enhanced device performance and multifunctionality. By tuning the blend composition and applying thermal treatments, we precisely control microstructural features such as phase separation, crystallinity, and domain morphology—optimizing both ionic and electronic transport and their coupling. This strategy enabled the realization of fully balanced ambipolar OECTs capable of modulating both cations and anions in a single device. Moreover, we extended this approach to create dual-mode transistors that combine OMIECs and organic semiconductors, allowing operation as both an Electrolyte-Gated Organic Field-Effect Transistor (EGOFET) and an OECT. Controlled phase separation facilitates seamless switching between these modes. Our results offer a new materials framework for designing tunable, multifunctional organic transistors with improved ionic–electronic coupling—advancing the development of next-generation bioelectronic interfaces and sensing technologies.

Organic electrochemical transistors (OECTs) rely on the use of organic mixed ionic-electronic conductors (OMIECs) as active channel materials [1]. These materials must simultaneously support electronic and ionic transport throughout the bulk of the film, enabling dynamic modulation of their redox states and conductivity via interactions with electrolyte ions and solvent molecules. Conjugated polymers have emerged as promising OMIEC platforms: their π-conjugated backbones facilitate electronic conduction, while their bulk structure allows for ion penetration and transport. In this context, poly(benzimidazobenzophenanthroline) (BBL), a ladder-type conjugated polymer with a rigid, planar backbone and high density of redox-active sites, provides a compelling model system [2]. Despite extensive experimental investigations, the atomistic-level understanding of ion and solvent interactions within BBL remains limited.
A combined classical molecular dynamics and quantum chemical (DFT) approach was employed to investigate the interaction mechanisms between BBL and two electrolytes (NaCl and NH₄Cl) in order to rationalize extensive experimental studies (including operando GIWAXS and 2H-NMR, E-QCMD, IR, CV and THz conductivity measurements) performed on various BBL:cation systems.
Our DFT calculations reveal distinct interaction modes between NH₄⁺ and BBL, ranging from hydrogen bonding to proton transfer, depending on the redox state and specific binding site within the polymer. To further mimic the OECT working environment, we performed molecular dynamics simulations of BBL crystallites immersed in electrolyte solutions at different doping levels. These simulations allowed us to quantify the swelling of the crystallites upon doping and to characterize the nature and spatial distribution of intercalated species. Notably, we observed differences in the behavior of cations based on their ability to form hydrogen bonds.
Altogether, this multi-scale approach sheds light on the fundamental ion-polymer interactions in BBL systems, and more broadly contributes to the molecular-level understanding of OMIEC operation, offering guidelines for the design of future materials with optimized mixed conduction properties.

Conjugated polymers bearing polar side chains are capable of supporting mixed electronic and ionic conduction, including in aqueous electrolytes, and as such are attractive candidates for electrodes in electrochemical devices such as sensors and energy storage devices [1]. Performance of devices is controlled by the rate of charging and discharging, the sensitivity of conduction to applied bias, the depth of charging and the stability of the materials under electrochemical cycling. These properties depend, in turn, on the chemical structure of the polymer backbone and side chains and the choice of electrolyte. We will report on studies using operando measurements and simulations to demonstrate how polymer chemical structure, electrolyte and charging conditions control these functional properties of the electrode. We show how side chain design can assist cycling stability, how electrolyte composition influences ion dynamics during charging and how polymer backbone structure controls specific capacity [2,3]. The findings can help to develop chemical designs for improved conjugated polymer electrodes for aqueous environments.

The identification of novel physiological biomarkers in sweat requires real-time sampling and analysis. Wearable microfluidic devices have emerged to address this need, utilizing soft, flexible, and hypoallergenic materials like PDMS and polyurethane to facilitate sample handling in sweat-sensing patches. However, the inherent limitations of sweat—namely low sample volumes easily subject to contamination and evaporation—pose current obstaclesfor for its adoption in remote health monitoring. I will present our latest work on the microfabrication of epidermal microfluidics within textiles via stereolithography (SLA) 3D printing [1]. Flexible SLA resin defines impermeable fluid-guiding microstructures in textile microfluidic modules. Their vertical stacking reduces device footprint and required sample volume, and facilitates on-body fluid collection, storage, and transport. Embedded internal modules act as a reservoir and injection valve, releasing a defined volume of sweat to the sensing unit. The pressure gradient across the modules provides a vertically distributed, capillary-driven sweat flow, guided by the wicking power of the textile structure. Their full integration into apparels offers non-cumulative flow through an extended air-liquid interface, ensuring continuous sweat transfer and evaporation. For real-time sweat analysis, we use a remotely screen-printed potassium (K⁺) ion detector based on organic electrocemical transistors. Its combination with ion-selective membranes offers a robust system when tested with more complex artificial sweat solutions by eliminating the need for a pseudo-reference electrode. The sensor demonstrated high sensitivity and selectivity, which are key for monitoring dehydration, electrolyte balance, and cardiovascular health. This modular approach provides fabric-integrated, mechanically ergonomic microfluidics with multi-parameter detection through rapid additive manufacturing for advanced point-of-care diagnostics.

By virtue of their giant gate capacitance, organic electrochemical transistors (OECTs) are a powerful platform for fundamental investigations of hole and electron transport in organic semiconductors as a function of continuously tunable charge up to 0.1-1 carrier per molecule. At these charge densities essentially all organic semiconductors examined so far exhibit a strong peak in conductivity versus charge density (or drain current vs. gate voltage). We have observed similar peak behavior in OECTs based on p- and n-type single crystals (rubrene and C₆₀)^1,2 and p- and n-type polymers, including polythiophenes^3,4 and BBL. The conductivity peak appears to be due to filling of a sub-band (or even a full band) in the density of states. In some cases, the shape or height of the peak, and the reverse scan hysteresis, depend on the size of the ions in the electrolyte, suggesting that ion-carrier interactions can be important. The high carrier densities obtained offer exciting opportunities to examine insulator-metal transitions and carrier correlation effects in organic systems. In poly(3-hexylthiophene) (P3HT) we approach the insulator-metal transition as gate voltage is increased toward the conductivity maximum, but do not quite reach it.³ However, we observe a large Coulomb gap, which decreases with carrier density as the carriers become more delocalized. Recent work on polymer EGTs by Sirringhaus, et al. also demonstrates a Coulomb gap and striking band filling effects in polythiophenes.⁵ In C₆₀ devices, we have good evidence for Mott-Hubbard band splitting at carrier densities of 1 e/molecule and above, Figure 2.² The Mott-Hubbard picture is modified by ion-size dependence of the transport behavior. Carrier-carrier as well as ion-carrier correlations are abundant in organic conductors with ample opportunity for molecular design to manipulate these interactions and profoundly affect the transport.

Organic mixed ionic-electronic conductors (OMIECs) are π-conjugated materials designed for reversible electrochemical (de)doping. Processed as thin films, they serve as the active channel in organic electrochemical transistors (OECTs)—the core of bioelectronic devices such as biosensors and neuromorphic systems. Understanding the fundamental processes governing OMIEC doping is therefore crucial to guide molecular engineering and advance the OECT technology.

Cavassin et al. demonstrated how the ratio of ordered to disordered domains in thin films directly influences both the extent and kinetics of OMIEC doping.^[1] Specifically, we find that (i) more ordered domains undergo faster doping, and (ii) more disordered domains promote ion uptake and the formation of more delocalized doped states.

Building on these insights, we introduce in this oral contribution PBTTT-⁸O, a novel PBTTT derivative featuring single-ether side chains with a single oxygen atom in the 8^th position. We showcase the potential of single-ether side chains as a promising alternative to conventional alkyl chains and oligo(ethylene glycol) side chains for high-performance OMIECs. These single-ether side chains are not only simple to synthesize but also offer a trade-off between crystallinity and polarity to promote dopant insertion while preserving molecular order. Notably, by combining single-ether side chain engineering with uniaxial polymer chain alignment, we present an effective strategy to precisely control the channel morphology, resulting in unprecedented signal amplification performance in p-type accumulation-mode OECTs (geometry-normalized gm over 2500 S cm-1).^[2]

To further rationalize these enhancements, we systematically investigated five PBTTT-xO polymers with single-ether side chains, varying the oxygen position (x = 3, 5, 8, 11), and compared them to the benchmark PBTTT-C12.^[3] Our findings reveal a clear dependence of ether position on the thermo-structural behavior and crystallinity index of PBTTT-xO, highlighting how fine-tuning side chain polarity and polymer organization can optimize OMIEC doping properties and OECT performance. Preliminary results achieved on anisotropic OECTs made of the next generation of PBTTT polymers may be presented.

Organic electrochemical transistors operate via electrochemical doping, where an applied gate potential in an electrolyte modulates the channel conductivity through counterion injection into and expulsion from the semiconducting polymer. This process, and the resulting current in devices, affects and is affected by the structure of the underlying organic mixed ionic-electronic conductor (OMIEC) and the polymer-electrolyte interface, ultimately impacting a range of properties including doping/dedoping kinetics, polymer mechanics, charge transport, and doping efficiency. Given the nanostructured nature of OMIECs, scanning probe microscopy techniques can reveal important information about the underlying process, particularly as these methods can be performed operando in aqueous electrolytes. Here we discuss microscopy-driven investigations using optical and atomic force microscopy methods to probe the OMIECs before, during, and after the electrochemical doping process. We use these methods to explore tradeoffs between sidechain chemistry and uptake, as well as how elastic modulus and adhesion change upon oxidation. Beyond mechanics, we discuss how materials can exhibit vastly different levels of doping efficiency, using a combination of Kelvin probe force microscopy and spectroelectrochemistry to provide insight into charge transport models and delocalized carrier density. Together, these methods link real-space operando measurements with device level performance and can provide a rational basis for optimizing materials.