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The development of devices based on organic electrochemical transistors (OECTs) relies on the rational design of high‐performing organic mixed ionic‐electronic conductors (OMIECs). Here, a series of solution‐processable copolymers composed of unsubstituted 2,2′‐bis‐(3,4‐ethylenedioxy)thiophene (biEDOT) and 3,4‐propylenedioxythiophene (ProDOT) substituted with linear or branched oligo(ethylene oxy) (OE) side chains are reported. By varying the size of the linear and branched side chains, it is found that the highest OECT performance is achieved with a near equivalent molar mass of the side chain and electroactive conjugated polymer repeat unit. With four OE units (PE2‐OE4, electroactive content of 49%), OECTs with state‐of‐the‐art normalized transconductance (453 ± 70 S cm−1) and µC* (830 ± 37 F cm−1 V−1 s−1), rapid dedoping kinetics, and a pulsing stability of 99% IDS retention over 200 ON/OFF cycles are achieved. A consistent improvement in OECT stability with decreasing side‐chain size is also observed. The origin of the enhanced stability is rationalized by correlating IDS losses to changes in channel absorbance cycle after cycle during operation. This work encourages the calculation of the electroactive polymer content of an OMIEC when designing the side chains. It also shows that the PE2 backbone with short OE side chains is a promising structure for (bio)electrochemical devices. [ABSTRACT FROM AUTHOR]

Solid‐state lithium‐metal batteries are considered as one of the most promising candidates for next‐generation energy storage devices with high energy density and enhanced safety. Great efforts have been made to design solid‐state electrolytes with enhanced ionic conductivity and to protect the electrochemical interface of the lithium anode. However, the obstruction of ionic‐electronic transport within the cathode remains as another key challenge that needs to be addressed for the practical application of solid‐state batteries. Here, we prepared organic mixed ionic‐electronic conductors (OMIECs) by in‐situ co‐polymerization of three organic monomers (boron‐type crosslinker, ionic liquid, and sulfolene) in the network of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate). The as‐prepared OMIECs show an electronic conductivity up to 33.6 S cm−1 and ionic conductivity of 1.7×10−4 S cm−1 at 30 °C, and also binder functionality, providing a combined path for Li+/e− transport in cathodes and maintaining mechanical/(electro−)chemical stability. As a result, solid‐state cathodes composed of 90.0 wt % active materials and only 10.0 wt % OMIECs display exceptional electrochemical characteristics at 30 °C, including high C‐rate capabilities and prolonged cycle life. This novel design of all‐in‐one OMIECs for carbon‐free cathodes demonstrates a promising strategy for developing multifunctional additives for high‐performance solid‐state batteries. [ABSTRACT FROM AUTHOR]

The conversion of electrochemical processes into mechanical deformation in organic mixed ionic‐electronic conductors (OMIECs) enables artificial muscle‐like actuators but is also critical for degradation processes affecting OMIEC‐based devices. To provide a microscopic understanding of electroactuation, the modulated electrochemical atomic force microscopy (mEC‐AFM) is introduced here as a novel in‐operando characterization method for electroactive materials. The technique enables multidimensional spectroscopic investigations of local electroactuation and charge uptake giving access to the electroactuation transfer function. For poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based microelectrodes, the spectroscopic measurements are combined with multichannel mEC‐AFM imaging, providing maps of local electroactuation amplitude and phase as well as surface morphology. The results demonstrate that the amplitude and timescales of electroactuation are governed by the drift motion of hydrated ions. Accordingly, slower water diffusion processes are not limiting, and the results illustrate how OMIEC microactuators can operate at sub‐millisecond timescales. [ABSTRACT FROM AUTHOR]

Organic mixed ionic‐electronic conductors (OMIECs) are organic materials capable of transporting both ionic species and electronic charges, facilitating ionic‐electronic coupling and enhancing electrical conductivity. PEO‐PEDOT/KOTf composite films synthesized in this study demonstrate significant electrical conductivity enhancement due to the ionic‐electronic coupling. The electrical conductivity of PEO‐PEDOT is 7.05 S.cm−1, predominantly arising from the electronic transport of PEDOT polarons with a minor contribution from ionic transport in PEO. However, introducing KOTf into the PEO‐PEDOT matrix at varying concentrations gradually increases electrical conductivity. At a KOTf concentration of 16 wt.%, the electrical conductivity reaches 51.06 S.cm−1. This pronounced enhancement can be primarily due to the ionic‐electronic coupling occurring at the interface between phase‐separated regions within the polymer matrix. The incorporation of KOTf into PEO‐PEDOT was characterized using FTIR spectroscopy. Moreover, our investigation involved X‐ray diffraction and differential scanning calorimetry analysis, which unveiled a notable trend. As the KOTf concentrations increased, the degree of crystallinity in the PEO‐PEDOT/KOTf composite films declined. This observation provides valuable insights into the structural changes occurring within the films as KOTf is integrated. The potential implications of this discovery span across numerous fields, opening exciting possibilities for advancing electronic and energy‐related technologies. [ABSTRACT FROM AUTHOR]

Abstract The conversion of electrochemical processes into mechanical deformation in organic mixed ionic‐electronic conductors (OMIECs) enables artificial muscle‐like actuators but is also critical for degradation processes affecting OMIEC‐based devices. To provide a microscopic understanding of electroactuation, the modulated electrochemical atomic force microscopy (mEC‐AFM) is introduced here as a novel in‐operando characterization method for electroactive materials. The technique enables multidimensional spectroscopic investigations of local electroactuation and charge uptake giving access to the electroactuation transfer function. For poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based microelectrodes, the spectroscopic measurements are combined with multichannel mEC‐AFM imaging, providing maps of local electroactuation amplitude and phase as well as surface morphology. The results demonstrate that the amplitude and timescales of electroactuation are governed by the drift motion of hydrated ions. Accordingly, slower water diffusion processes are not limiting, and the results illustrate how OMIEC microactuators can operate at sub‐millisecond timescales.

Polythiophenes, built on head‐to‐head (HH) linked 3,3′‐oligomer ethylene glycol‐2,2′‐bithiophene (gT2), have simple chemical structure, good backbone planarity, and relatively high‐lying the lowest unoccupied molecular orbital (LUMO) energy levels, hence showing excellent p‐type performance in organic electrochemical transistors (OECTs) with µC* of several hundred F cm−1 V−1 s−1. In this study, sequential cyano substitution is utilized to enable transformation of charge carrier polarity from p‐type to n‐type in OECTs, based on the parent polythiophene g4T2‐T2. With the increase of cyano group number, the polythiophenes exhibit gradually lowered LUMO levels from −2.55 to −3.90 eV. As a result, from g4T2‐T2 to CNg4T2‐CNT2, the p‐type performance dramatically diminishes accomplished by the enhancement of n‐type one when applied in OECTs. To the authors' delight, polymer CNg4T2‐CNT2 with the highest content of cyano groups exhibits a remarkable n‐type µC* of 27.01 F cm−1 V−1 s−1 and high gm,norm of 6.75 S cm−1 with negligible p‐type character. This study demonstrates that sequential cyano substitution provides a powerful approach for developing high‐performance n‐type polymers for OECT applications. [ABSTRACT FROM AUTHOR]

Water‐resistant poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are valuable in biomedical applications; however, they typically require crosslinkers to stabilize the films, which can introduce undesired aggregation or phase separation reactions. Herein, a dipping‐based process to prepare PEDOT:PSS films on nonplanar surfaces without crosslinker is developed. Sequential soaking of a dip‐coated PEDOT:PSS film in ethanol and water imparts water resistance to the film. Microscopic and spectroscopic techniques are used to monitor the process and confirm that the ethanol soaking elutes the excess PSS from the film bulk, which stabilizes the film prior to the water‐soaking process. The obtained films act as conductors and semiconductors on curved surfaces, including 3D‐printed objects. A film deposited on a curved surface is successfully applied as the channel layer in a neuromorphic organic electrochemical transistor. This approach can enable integrated bioelectronic and neuromorphic applications that can be readily deployed for facile prototyping. [ABSTRACT FROM AUTHOR]

Organic mixed ionic–electronic conductors (OMIECs) have varied performance requirements across a diverse application space. Chemically doping the OMIEC can be a simple, low‐cost approach for adapting performance metrics. However, complex challenges, such as identifying new dopant materials and elucidating design rules, inhibit its realization. Here, these challenges are approached by introducing a new n‐dopant, tetrabutylammonium hydroxide (TBA‐OH), and identifying a new design consideration underpinning its success. TBA‐OH behaves as both a chemical n‐dopant and morphology additive in donor acceptor co‐polymer naphthodithiophene diimide‐based polymer, which serves as an electron transporting material in organic electrochemical transistors (OECTs). The combined effects enhance OECT transconductance, charge carrier mobility, and volumetric capacitance, representative of the key metrics underpinning all OMIEC applications. Additionally, when the TBA+ counterion adopts an "edge‐on" location relative to the polymer backbone, Coulombic interaction between the counterion and polaron is reduced, and polaron delocalization increases. This is the first time such mechanisms are identified in doped‐OECTs and doped‐OMIECs. The work herein therefore takes the first steps toward developing the design guidelines needed to realize chemical doping as a generic strategy for tailoring performance metrics in OECTs and OMIECs. [ABSTRACT FROM AUTHOR]

Abstract Polythiophenes, built on head‐to‐head (HH) linked 3,3′‐oligomer ethylene glycol‐2,2′‐bithiophene (gT2), have simple chemical structure, good backbone planarity, and relatively high‐lying the lowest unoccupied molecular orbital (LUMO) energy levels, hence showing excellent p‐type performance in organic electrochemical transistors (OECTs) with µC* of several hundred F cm−1 V−1 s−1. In this study, sequential cyano substitution is utilized to enable transformation of charge carrier polarity from p‐type to n‐type in OECTs, based on the parent polythiophene g4T2‐T2. With the increase of cyano group number, the polythiophenes exhibit gradually lowered LUMO levels from −2.55 to −3.90 eV. As a result, from g4T2‐T2 to CNg4T2‐CNT2, the p‐type performance dramatically diminishes accomplished by the enhancement of n‐type one when applied in OECTs. To the authors' delight, polymer CNg4T2‐CNT2 with the highest content of cyano groups exhibits a remarkable n‐type µC* of 27.01 F cm−1 V−1 s−1 and high gm,norm of 6.75 S cm−1 with negligible p‐type character. This study demonstrates that sequential cyano substitution provides a powerful approach for developing high‐performance n‐type polymers for OECT applications.

Abstract Water‐resistant poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are valuable in biomedical applications; however, they typically require crosslinkers to stabilize the films, which can introduce undesired aggregation or phase separation reactions. Herein, a dipping‐based process to prepare PEDOT:PSS films on nonplanar surfaces without crosslinker is developed. Sequential soaking of a dip‐coated PEDOT:PSS film in ethanol and water imparts water resistance to the film. Microscopic and spectroscopic techniques are used to monitor the process and confirm that the ethanol soaking elutes the excess PSS from the film bulk, which stabilizes the film prior to the water‐soaking process. The obtained films act as conductors and semiconductors on curved surfaces, including 3D‐printed objects. A film deposited on a curved surface is successfully applied as the channel layer in a neuromorphic organic electrochemical transistor. This approach can enable integrated bioelectronic and neuromorphic applications that can be readily deployed for facile prototyping.

Eutectogels are an emerging family of soft ionic materials alternative to ionic liquid gels and organogels, offering fresh perspectives for designing functional dynamic platforms in water‐free environments. Herein, the first example of mixed ionic and electronic conducting supramolecular eutectogel composites is reported. A fluorescent glutamic acid‐derived low‐molecular‐weight gelator (LMWG) was found to self‐assemble into nanofibrillar networks in deep eutectic solvents (DES)/poly(3,4‐ethylenedioxythiophene) (PEDOT): chondroitin sulfate dispersions. These dynamic materials displayed excellent injectability and self‐healing properties, high ionic conductivity (up to 10−2 S cm−1), good biocompatibility, and fluorescence imaging ability. This set of features turns the mixed conducting supramolecular eutectogels into promising adaptive materials for bioimaging and electrostimulation applications. [ABSTRACT FROM AUTHOR]

Neuromorphic systems that display synaptic conditioning based on biochemical signaling activity have recently been introduced in the form of artificial synapses that are model devices to develop tissue‐interfaced platforms. In this regard, biohybrid synapses promise adaptive neuron‐integrated functions. However, these systems suffer from both molecular cross‐talk as biological neural circuits signal transmission typically involves more than one neuromodulator, and unstable electronics wirings as complex architectures are required to interface the tissues. Moreover, whilst novel spiking circuits can work as artificial neurons, they only recreate the biological electrical signaling pathway while electrochemical signal transduction is required for inter‐neuron communication. As such, artificial chemically‐mediated synapses are essential to perform memory/learning computing functions. Herein, an electrochemical neuromorphic organic device (ENODe) working as an artificial synapse that overcomes electrochemical and readout interferences while it emulates two neurotransmitters synaptic weight modulation and their recycling machinery at the synaptic cleft is shown. Neuronal short‐ and long‐term plasticity are replicated by transducing two separate neurotransmitter‐mediated chemical signals into reversible and nonreversible variations of PEDOT:PSS conductance. By exploiting the electrochromic properties of PEDOT:PSS, an alternative optical monitoring strategy is introduced which promises stable multidevice readout from complex bio‐hybrid interfaces. The platform emulates high‐order biological processes such as intrinsic forgetting, memory consolidation, and neurotransmitter co‐modulation. These brain‐inspired functionalities herald the development of tissue‐integrated neuromorphic systems that combine spiking (electrical neurons) and nonspiking (electrochemical synapses) elements, thus envisioning prosthetic bridges for neural engineering and regenerative medicine. [ABSTRACT FROM AUTHOR]

The ability to bridge ionic and electronic transport coupled with large volumetric capacitance renders organic electrochemical transistors (OECTs) ideal candidates for bioelectronic applications. Adopting ionic-liquid-based solid electrolytes extends their applicability and facilitates large-area printable productions. However, OETCs employing solid electrolytes tend to show a pronounced hysteresis in the transfer curve. A detailed understanding of the hysteresis is crucial for their accurate characterizations and reliable applications. Here, we demonstrated fully photopatternable poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos)- based OECTs incorporating the ionic liquid [EMIM][EtSO4] in a solid electrolyte (SE). The PEDOT:Tos films deposited through vapor phase polymerization (VPP) were annealed for different durations after the polymerization step. Upon rinsing with ethanol and the deposition of the SE, the OECTs made of these films showed impressive bias stress stability under prolonged operation cycles, a high switching ratio, a low threshold voltage, and a high transconductance. Furthermore, by taking transfer measurements with different sweep rates, we revealed two distinct regimes of hysteresis: kinetic hysteresis and non-kinetic hysteresis. We observed pronounced changes in these regimes after annealing. Finally, impedance spectroscopy exhibited that the PEDOT:Tos turned from a Faradaic to a non-Faradaic response through annealing, explaining the observed hysteresis changes in both regimes. [ABSTRACT FROM AUTHOR]

Internal ion‐gated organic electrochemical transistor (IGT) demonstrates volume‐dependent transconductance with the unprecedented advantages of high speed and self‐(de)doping capability among ion‐based transistors. The novel characteristics have albeit rendered IGT a promising platform for integrated bioelectronics, its potential in high‐frequency applications has yet been fully harnessed. Moreover, a study from a material's point of view is especially needed for this recently emerged platform as the necessity of maintaining the internal ion reservoir has posed difficulties in processing hydrated poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulphonate) (PEDOT:PSS) with electronically favorable morphologies. Herein, a comprehensive investigation of the structural and functional properties of ion‐embedded PEDOT:PSS modified by different annealing temperatures is performed and correlated to the IGT performance. A short‐time high‐temperature annealing treatment is found effective in facilitating the formation of compact microstructures without significantly influencing film hydration. The structural improvement enhances the film's conductivity and hole mobility, with the corresponding IGTs exhibiting higher gain, higher conductance, and high cut‐off frequency consistently in a batch. This study also successfully demonstrates the first use of electrochemical transistors like IGTs in high‐frequency applications through proof‐of‐concept experiments simulating fluid estimation in 50 kHz bioimpedance analysis. This work contributes to the development of high‐performance IGTs for extensive biological applications. [ABSTRACT FROM AUTHOR]

The ability to bridge ionic and electronic transport coupled with large volumetric capacitance renders organic electrochemical transistors (OECTs) ideal candidates for bioelectronic applications. Adopting ionic-liquid-based solid electrolytes extends their applicability and facilitates large-area printable productions. However, OETCs employing solid electrolytes tend to show a pronounced hysteresis in the transfer curve. A detailed understanding of the hysteresis is crucial for their accurate characterizations and reliable applications. Here, we demonstrated fully photopatternable poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos)- based OECTs incorporating the ionic liquid [EMIM][EtSO4] in a solid electrolyte (SE). The PEDOT:Tos films deposited through vapor phase polymerization (VPP) were annealed for different durations after the polymerization step. Upon rinsing with ethanol and the deposition of the SE, the OECTs made of these films showed impressive bias stress stability under prolonged operation cycles, a high switching ratio, a low threshold voltage, and a high transconductance. Furthermore, by taking transfer measurements with different sweep rates, we revealed two distinct regimes of hysteresis: kinetic hysteresis and non-kinetic hysteresis. We observed pronounced changes in these regimes after annealing. Finally, impedance spectroscopy exhibited that the PEDOT:Tos turned from a Faradaic to a non-Faradaic response through annealing, explaining the observed hysteresis changes in both regimes.

Understanding the dynamics of ion migration and volume change is crucial to studying the functionality and long-term stability of soft polymeric materials operating at liquid interfaces, but the subsurface characterization of swelling processes in these systems remains elusive. In this work, we address the issue using modulated electrochemical atomic force microscopy as a depth-sensitive technique to study electroswelling effects in the high-performance actuator material polypyrrole doped with dodecylbenzenesulfonate (Ppy:DBS). We perform multidimensional measurements combining local electroswelling and electrochemical impedance spectroscopies on microstructured Ppy:DBS actuators. We interpret charge accumulation in the polymeric matrix with a quantitative model, giving access to both the spatiotemporal dynamics of ion migration and the distribution of electroswelling in the electroactive polymer layer. The findings demonstrate a nonuniform distribution of the effective ionic volume in the Ppy:DBS layer depending on the film morphology and redox state. Our findings indicate that the highly efficient actuation performance of Ppy:DBS is caused by rearrangements of the polymer microstructure induced by charge accumulation in the soft polymeric matrix, increasing the effective ionic volume in the bulk of the electroactive film for up to two times the value measured in free water.

Organic mixed ionic–electronic conductors (OMIECs) combine electronic semiconductor functionality with ionic conductivity, biocompatibility, and electrochemical stability in water and are currently investigated as the active material in devices for bioelectronics, neuromorphic computing, as well as energy conversion and storage. Operation speed of such devices depends on fast electronic transport in OMIECs. However, due to contact resistance problems, reliable measurements of electronic mobility are difficult to achieve in this class of materials. To address the problem, the electrolyte‐gated van der Pauw (EgVDP) method is introduced for the simple and accurate determination of the electrical characteristics of OMIEC thin films, independent of contact effects. The technique is applied to the most widespread OMIEC blend, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS). By comparing with organic electrochemical transistor (OECT) measurements, it is found that gate voltage dependent contact resistance effects lead to systematic errors in OECT based transport characterization. These observations confirm that a contact‐independent technique is crucial for the proper characterization of OMIECs, and the EgVDP method reveals to be a simple, elegant, but effective technique for this scope. [ABSTRACT FROM AUTHOR]

Electrochemically induced volume changes in organic mixed ionic‐electronic conductors (OMIECs) are particularly important for their use in dynamic microfiltration systems, biomedical machinery, and electronic devices. Although significant advances have been made to maximize the dimensional changes that can be accomplished by OMIECs, there is currently limited understanding of how changes in their molecular structures impact their underpinning fundamental processes and their performance in electronic devices. Herein, a series of ethylene glycol functionalized conjugated polymers is synthesized, and their electromechanical properties are evaluated through a combined approach of experimental measurements and molecular dynamics simulations. As demonstrated, alterations in the molecular structure of OMIECs impact numerous processes occurring during their electrochemical swelling, with sidechain length shortening decreasing the number of incorporated water molecules, reducing the generated void volumes and promoting the OMIECs to undergo different phase transitions. Ultimately, the impact of these combined molecular processes is assessed in organic electrochemical transistors, revealing that careful balancing of these phenomena is required to maximize device performance. [ABSTRACT FROM AUTHOR]

In alignment with widespread interest in carbon neutralization and sustainable practices, we disclose that conjugated polyelectrolyte (CPE) hydrogels are a type of recyclable, electrochemically stable, and environmentally friendly pseudocapacitive material for energy storage applications. By leveraging ionic-electronic coupling in a relatively fluid medium, one finds that hydrogels prepared using a fresh batch of an anionic CPE, namely, Pris-CPE-K, exhibit a specific capacitance of 32.6 ± 6.6 F g -1 in 2 M NaCl and are capable of 80% (26.1 ± 6.5 F g -1 ) capacitance retention after 100,000 galvanostatic charge-discharge (GCD) cycles at a current density ( J ) of 10 A g -1 . We note that equilibration under a constant potential prior to GCD analysis leads to the K + counterions in the CPE exchanging with Na + and, thus, the relevant active material Pris-CPE-Na. It is possible to remove the CPE material from the electrochemical cell via extraction with water and to carry out a simple purification through dialysis to produce a recycled material, namely Re-CPE-Na. The recycling workup has no significant detrimental impact on the electrochemical performance. Specifically, Re-CPE-Na hydrogels display an initial specific capacitance of 26.3 ± 1.2 F g -1 (at 10 A g -1 ) and retain 77% of the capacitance after a subsequent 100,000 GCD cycles. Characterization by NMR, FTIR, and Raman spectroscopies, together with XPS and GPC measurements, revealed no change in the structure of the backbone or side chains. However, rheological measurements gave evidence of a slight loss in G ' and G ''. Overall, that CPE hydrogels display recyclability argues in favor of considering them as a novel materials platform for energy storage applications within an economically viable circular recycling strategy.

Conjugated polymers are increasingly used as organic mixed ionic-electronic conductors in electrochemical applications for neuromorphic computing, bioelectronics, and energy harvesting. The design of efficient electrochemical devices relies on large modulations of the polymer conductivity, fast doping/dedoping kinetics, and high ionic uptake. In this work, structure-property relations are established and control of these parameters by the co-existence of order and disorder in the phase morphology is demonstrated. Using in situ time-resolved spectroelectrochemistry, resonant Raman, and terahertz (THz) conductivity measurements, the electrochemical doping in the different morphological domains of poly(3-hexylthiophene) (P3HT) is investigated. The main finding is that bipolarons are found preferentially in disordered polymer regions, where they are formed faster and are thermodynamically more favored. On the other hand, polarons show a preference for ordered domains, leading to drastically different bipolaron/polaron ratios and doping/dedoping dynamics in the distinct regions. A significant enhancement of the electronic conductivity is evident when bipolarons start forming in the disordered regions, while the presence of bipolarons in the ordered regions is detrimental for transport. This study provides significant advances in the understanding of the impact of morphology on the electrochemical doping of conjugated polymers and the induced increase in conductivity., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Understanding the ionic composition and distribution in organic mixed ionic-electronic conductors (OMIECs) is crucial for understanding their structure-property relationships. Despite this, direct measurements of OMIEC ionic composition and distribution are not common. In this work, we investigated the ionic composition and mesoscopic structure of three typical p-type OMIEC materials: an ethylene glycol-treated crosslinked OMIEC with a large excess fixed anionic charge (EG/GOPS-PEDOT:PSS), an acid-treated OMIEC with a tunable fixed anionic charge (crys-PEDOT:PSS), and a single-component OMIEC without any fixed anionic charge (pg2T-TT). A combination of X-ray fluorescence (XRF) and X-ray photoelectron spectroscopies, gravimetry, coulometry, and grazing incidence small-angle X-ray scattering (GISAXS) techniques was employed to characterize these OMIECs following electrolyte exposure and electrochemical cycling. In particular, XRF provided quantitative ion-to-monomer compositions for these OMIECs from passive ion uptake following aqueous electrolyte exposure and potential-driven ion uptake/expulsion following electrochemical doping and dedoping. Single-ion (cation) transport in EG/GOPS-PEDOT:PSS due to Donnan exclusion was directly confirmed, while significant fixed anion concentrations in crys-PEDOT:PSS doping and dedoping were shown to occur through mixed anion and cation transport. Controlling the fixed anionic (PSS - ) charge density in crys-PEDOT:PSS mapped the strength of Donnan exclusion in OMIEC systems following a Donnan-Gibbs model. Anion transport dominated pg2T-TT doping and dedoping, but a surprising degree of anionic charge trapping (∼10 20 cm -3 ) was observed. GISAXS revealed minimal ion segregation both between PEDOT- and PSS-rich domains in EG/GOPS-PEDOT:PSS and between amorphous and semicrystalline domains in pg2T-TT but showed significant ion segregation in crys-PEDOT:PSS at length scales of tens of nm, ascribed to inter-nanofibril void space. These results bring new clarity to the ionic composition and distribution of OMIECs which are crucial for accurately connecting the structure and properties of these materials.

Conjugated polymers with oligoether side chains are promising mixed ionic-electronic conductors, but they tend to feature a low glass transition temperature and hence a low elastic modulus, which prevents their use if mechanical robust materials are required. Carboxymethylated cellulose nanofibrils (CNF) are found to be a suitable reinforcing agent for a soft polythiophene with tetraethylene glycol side chains. Dry nanocomposites feature a Young's modulus of more than 400 MPa, which reversibly decreases to 10 MPa or less upon passive swelling through water uptake. The presence of CNF results in a slight decrease in electronic mobility but enhances the ionic mobility and volumetric capacitance, with the latter increasing from 164 to 197 F cm -3 upon the addition of 20 vol % CNF. Overall, organic electrochemical transistors (OECTs) feature a higher switching speed and a transconductance that is independent of the CNF content up to at least 20 vol % CNF. Hence, CNF-reinforced conjugated polymers with oligoether side chains facilitate the design of mechanically adaptive mixed ionic-electronic conductors for wearable electronics and bioelectronics.

Exchanging hydrophobic alkyl-based side chains to hydrophilic glycol-based side chains is a widely adopted method for improving mixed-transport device performance, despite the impact on solid-state packing and polymer-electrolyte interactions being poorly understood. Presented here is a molecular dynamics (MD) force field for modeling alkoxylated and glycolated polythiophenes. The force field is validated against known packing motifs for their monomer crystals. MD simulations, coupled with X-ray diffraction (XRD), show that alkoxylated polythiophenes will pack with a "tilted stack" and straight interdigitating side chains, whilst their glycolated counterpart will pack with a "deflected stack" and an s-bend side-chain configuration. MD simulations reveal water penetration pathways into the alkoxylated and glycolated crystals-through the π-stack and through the lamellar stack respectively. Finally, the two distinct ways triethylene glycol polymers can bind to cations are revealed, showing the formation of a metastable single bound state, or an energetically deep double bound state, both with a strong side-chain length dependence. The minimum energy pathways for the formation of the chelates are identified, showing the physical process through which cations can bind to one or two side chains of a glycolated polythiophene, with consequences for ion transport in bithiophene semiconductors., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

n-Type organic mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop. As a result, the figure-of-merit (µC*) of n-type organic electrochemical transistors (OECTs) lags far behind the p-type analogs, restraining the development of OECT-based low-power complementary circuits and biosensors. Here, two n-type donor-acceptor (D-A) polymers based on fused bithiophene imide dimer f-BTI2 as the acceptor unit and thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. The cyanation of TVT enables polymer f-BTI2g-TVTCN with simultaneously enhanced ion-uptake ability, film structural order, and charge-transport property. As a result, it is able to obtain a high volumetric capacitance (C*) of 170 ± 22 F cm -3 and a record OECT electron mobility (μ e,OECT ) of 0.24 cm 2 V -1 s -1 for f-BTI2g-TVTCN, subsequently achieving a state-of-the-art µC* of 41.3 F cm -1 V -1 s -1 and geometry-normalized transconductance (g m,norm ) of 12.8 S cm -1 in n-type accumulation-mode OECTs. In contrast, only a moderate µC* of 1.50 F cm -1 V -1 s -1 is measured for the non-cyanated polymer f-BTI2g-TVT. These remarkable results demonstrate the great power of cyano functionalization of polymer semiconductors in developing n-type OMIECs with substantial electron mobility in aqueous environment for high-performance n-type OECTs., (© 2022 Wiley-VCH GmbH.)

Organic mixed ionic-electronic conductors (OMIECs) are central to bioelectronic applications such as biosensors, health-monitoring devices, and neural interfaces, and have facilitated efficient next-generation brain-inspired computing and biohybrid systems. Despite these examples, smart and adaptive circuits that can locally process and optimize biosignals have not yet been realized. Here, a tunable sensing circuit is shown that can locally modulate biologically relevant signals like electromyograms (EMGs) and electrocardiograms (ECGs), that is based on a complementary logic inverter combined with a neuromorphic memory element, and that is constructed from a single polymer mixed conductor. It is demonstrated that a small neuromorphic array based on this material effects high classification accuracy in heartbeat anomaly detection. This high-performance material allows for straightforward monolithic integration, which reduces fabrication complexity while also achieving high on/off ratios with excellent ambient p- and n-type stability in transistor performance. This material opens a route toward simple and straightforward fabrication and integration of more sophisticated adaptive circuits for future smart bioelectronics., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Organic electrochemical transistors (OECTs) hold promise for developing a variety of high-performance (bio-)electronic devices/circuits. While OECTs based on p-type semiconductors have achieved tremendous progress in recent years, n-type OECTs still suffer from low performance, hampering the development of power-efficient electronics. Here, it is demonstrated that fine-tuning the molecular weight of the rigid, ladder-type n-type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n-type OECTs with record-high geometry-normalized transconductance (g m,norm  ≈ 11 S cm -1 ) and electron mobility × volumetric capacitance (µC* ≈ 26 F cm -1  V -1 s -1 ), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermolecular charge transport in high-molecular-weight BBL than in the low-molecular-weight counterpart. OECT-based complementary inverters are also demonstrated with record-high voltage gains of up to 100 V V -1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub-1 V complementary inverters reported to date. These findings demonstrate the importance of molecular weight in optimizing the OECT performance of rigid organic mixed ionic-electronic conductors and open for a new generation of power-efficient organic (bio-)electronic devices., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Electroactive polymer thin films undergo repeated reversible structural change during operation in electrochemical applications. While synchrotron X-ray scattering is powerful for the characterization of stand-alone and ex situ organic thin films, in situ/operando structural characterization has been underutilized-in large part due to complications arising from supporting electrolyte scattering. This has greatly hampered the development of application relevant structure property relationships. Therefore, a new methodology for in situ/operando X-ray characterization that separates the incident and scattered X-ray beam path from the electrolyte is developed. As a proof of concept, the operando structural characterization of weakly-scattering, organic mixed conducting thin films in an aqueous electrolyte environment is demonstrated, accessing previously unexplored changes in the π-π peak and diffuse scatter, while capturing the solvent swollen thin film structure which is inaccessible in previous ex situ studies. These in situ/operando measurements improve the sensitivity to structural changes, capturing minute changes not possible ex situ, and have multimodal potential such as combined Raman measurements that also serve to validate the true in situ/operando conditions of the cell. Finally, new directions enabled by this in situ/operando cell design are examined and state of the art measurements are compared., (© 2021 Wiley-VCH GmbH.)