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Neuromorphic computing devices offer promising solutions for next‐generation computing hardware, addressing the high throughput data processing demands of artificial intelligence applications through brain‐mimicking non‐von Neumann architecture. Herein, PEDOT:Tos/PTHF‐based organic electrochemical transistors (OECTs) with dual‐modal memory functions—both short‐term and long‐term—are demonstrated. By characterizing memory levels and relaxation times, the device has been efficiently manipulated and switched between the two modes through coupled control of pulse voltage and duration. Both short‐term and long‐term memory functions are integrated within the same device, enabling its use as artificial neurons for the reservoir unit and synapses in the readout layer to build up a reservoir computing (RC) system. The performance of the dynamic neuron and synaptic weight update are benchmarked with classification tasks on hand‐written digit images, respectively, both attaining accuracies above 90%. Furthermore, by modulating the device as both reservoir mode and synaptic mode, a full‐OECT RC system capable of distinguishing electromyography signals of hand gestures is demonstrated. These results highlight the potential of simplified, homogeneous integration of dual‐modal OECTs to form brain‐like computing hardware systems for efficient biological signal processing across a broad range of applications. [ABSTRACT FROM AUTHOR]

In bioelectronics, organic electrochemical transistors (OECTs) are pivotal in bridging electronic devices and biological systems, especially in sensing, neuromorphic interfacing, and biological monitoring. Current OECT fabrication methods face challenges due to conductive polymers incompatibility with photoresist solvents and the complexity of multi‐step parylene‐C coatings. This work introduces a scalable photolithographic fabrication process for high‐performance OECTs using the prototypical conductive polymer poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS). The method employs a two‐layer photoresist approach with controlled cross‐linking, incorporating (3‐glycidyloxypropyl)trimethoxysilane to pattern polymeric channel and encapsulate electrodes. This process yields high‐performance OECTs with highly reproducible characteristics, typical ON/OFF current modulation of 5 103, and transconductance normalized to channel thickness > 200 S cm−1. To avoid cytotoxic Ag/AgCl pellets, the impact of scaling polarizable gates is analyzed on device performance, including bare Au, protein‐functionalized, and PEDOT:PSS gates. The analysis provides design rules to tailor OECT performance for diverse applications. The effectiveness of the approach is demonstrated by integrating OECTs with polarizable gates in current‐driven circuit configuration, allowing ion detection at a supply voltage as low as 0.4 V with a sensitivity of up to 2620 mV dec−1, the highest ever reported. These advancements open opportunities for next‐generation integrated bioelectronics and neuromorphic biosensing. [ABSTRACT FROM AUTHOR]

The existing device models for organic electrochemical transistors (OECTs) fail to provide any device design guidelines for optimized performance parameters such as transconductance that are pivotal for the applications OECTs in sensing. Moreover, the current models are based on the questionable assumption of a homogenous organic semiconductor layer, and all predict a linear behavior of the resistance with the OECT channel length. Consequently, the experimentally observed nonlinear resistance behavior in OECTs has been overlooked thus far. Here, an OECT device model is developed that accurately describes the nonlinear behavior of the OECT channel resistance and offers the first guidelines for maximizing transconductance. The model is inherently nonlinear and the nonlinearity stem from the non‐monolithic capacitance of the organic semiconductor layer. Moreover, the model provides a consistent and reliable estimations for the contact resistance in OECTs. The success of the model in accurately describing and providing predictions of the OECT operation by relating the device's geometrical parameters with electrochemical parameters of the semiconductor layer paves the way toward unlocking OECT potentials in diverse applications, from biosensing to neuromorphic computing and flexible electronics. [ABSTRACT FROM AUTHOR]

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The development of n‐type polymers for organic electrochemical transistors (OECTs) has lagged significantly behind their p‐type counterparts. Moreover, these polymers are often synthesized via Stille polycondensation. Herein, three polymers with thiazole‐flanked diketopyrrolopyrrole is synthesized as the monomer through C─H/C─H oxidative direct arylation polycondensation (Oxi‐DArP). This protocol employs unfunctionalized (C─H terminated) monomers, and the generated byproducts are environmentally benign. The electron‐deficient polymer backbone confers these polymers with LUMO energy levels below −4.20 eV, enabling all of them to exhibit n‐type behavior in OECTs. Additionally, the resulting polymers are soluble in the green solvent anisole. With an optimized alkyl spacer between oligo(ethylene glycol) side chain and conjugated backbone, the polymer gTzDPP‐C8 showed the best device performance with geometry normalized transconductance (gm,norm) up to 6.31 S cm−1 and µC* up to 23.1 F V−1 cm−1 s−1. This work has successfully proved that C─H/C─H Oxi‐DArP is a promising method for synthesizing n‐type OMIECs to fulfill high‐performance OECTs. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) represent a promising approach for flexible, wearable, biomedical electronics, and sensors integrated with diverse substrates. Their ability to operate at low voltages and interact effectively with biological systems makes them particularly suitable for neuromorphic applications. For neuromorphic devices, OECTs must enhance electrical performance, biocompatibility, and signal storage/erasure capabilities. While UV cross‐linking methods with various side effects on organic semiconductors are predominant in improving mobility and current retention time, thermal cross‐linking based on the solution process has not been extensively explored. Additionally, despite significant research on the modification of electrolyte property, the ionic charge compensation mechanisms between multiple electrolytes are still unclear. This study employs a cross‐linking strategy involving the chemical reaction of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with di‐tert‐butyl‐peroxide (DTBP) to create a cross‐linked P3HT active layer. Furthermore, a dual ion gel structure combining a conventional ion gel with a chitosan‐based ion gel is investigated for increased ionic transport to enhance OECT performance. Using the above two methods, the enhanced electrical performance showing the mobility of 25 F cm−1 V−1 s−1 and synaptic properties showing long‐term plasticity of cross‐linked OECTs with a dual ion gel structure are demonstrated, suggesting their potential application as high‐performance neuromorphic devices. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) are promising for neuromorphic architectures as they can generate multiple electrical states through the control of ion transport. However, conventional OECTs face limitations in mimicking a fully functional biological synapse due to their inability to achieve long‐term plasticity. In this study, a metal‐organic framework (MOF)‐enhanced OECT (MOECT) is fabricated by introducing MOF into the ion‐organic semiconductor (OSC) layer. MOFs are synthesized using the layer‐by‐layer (LBL) method, and additional cross‐linked OSC is introduced to prevent damage to the semiconductor layers during synthesis. The synthesized MOF layers hinder the rediffusion of ions in OECT, allowing ions to remain in the OSC for an extended period. In this study, the MOECT showed a change in current depending on the doping level, recording a current state 4.4 × 107 times higher than that of pristine OECT. Ultimately, the developed MOECTs are applied as synaptic transistors. MOECTs show 14% higher excitatory postsynaptic current (EPSC) after 130 s compared to pristine OECT, thereby strengthening the long‐term plasticity characteristics of neuromorphic devices. This method enhances the performance of synaptic transistors by introducing MOF, offering various possibilities through the selection of different MOF structures and ions, indicating it is a methodological approach with high potential. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) are of great interest owing to their potential applications in bioelectronics and neuromorphic systems. However, n‐type OECTs suffer from poor stability and facile degradation, mainly due to the oxygen reduction reactions in organic mixed ionic‐electronic conductors during device operation. In this study, a small‐molecule passivation strategy is introduced to greatly improve the stability of poly(benzobisimidazobenzophenanthroline) (BBL)‐based n‐type OECTs. 6,6‐Phenyl‐C61‐butyric acid methyl ester (PCBM) is spin‐coated onto the BBL layer to form a smooth and hydrophobic passivation layer, which effectively inhibits the oxygen reduction reactions while enabling ion permeation in aqueous electrolytes. Consequently, the OECTs employing the PCBM/BBL bilayers with an optimized PCBM thickness exhibit significantly improved operational stability at various electrolyte conditions (0.1 m NaCl or NaOH) and over a wide gate‐voltage sweep range (from −0.7 to 0.7 V). Owing to the high electron mobility of PCBM, the carrier mobility and switching speed of the PCBM/BBL OECTs are also improved compared with those of the pristine BBL OECTs. This study demonstrates the beneficial effects of simple surface passivation in organic mixed ionic‐electronic conductors and provides valuable insights for the design of high‐performance and stable OECTs for more specialized and advanced applications. [ABSTRACT FROM AUTHOR]

Achieving low threshold voltage (Vth) in organic electrochemical transistors (OECTs) is essential for minimizing power consumption and enhancing sensitivity in bioelectronic devices. However, obtaining OECT materials with ultra‐low Vth, close to 0 V for n‐type conjugated polymers remains challenging. Here, a conjugated polymer FBDOPV‐CNTVT is introduced, which features a rigid backbone structure and high electron deficiency, leading to an exceptionally low lowest unoccupied molecular orbital (LUMO) energy level of −4.67 eV, achieved through dual electron‐withdrawing substitutions. With its ultra‐low LUMO energy level, FBDOPV‐CNTVT exhibits high susceptibility to electrochemical doping, even demonstrating efficient doping near 0 V. Consequently, the OECT device employing FBDOPV‐CNTVT as the active material shows an ultra‐low Vth of 7.5 mV, setting a new record for the Vth of n‐type OECT devices. Furthermore, FBDOPV‐CNTVT exhibits a µC* value of 6.13 F cm−1 V−1 s−1 and retains ≈85% of its current after 2000 s cycling. This study highlights the potential of conjugated polymers with dual electron‐withdrawing substitutions to achieve ultra‐low LUMO energy levels, effectively reducing the Vth of n‐type OECT devices and promising advancements in bioelectronics. [ABSTRACT FROM AUTHOR]

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]

GaAs thin‐film solar cells have high efficiency, reliability, and operational stability, making them a promising solution for self‐powered skin‐conformal biosensors. However, inherent device thickness limits suitability for such applications, making them uncomfortable and unreliable in flexural environments. Therefore, reducing the flexural rigidity becomes crucial for integration with skin‐compatible electronic devices. Herein, this study demonstrated a novel one‐step surface modification bonding methodology, allowing a streamlined transfer process of ultra‐thin (2.3 µm thick) GaAs solar cells on flexible polymer substrates. This reproducible technique enables strong bonding between dissimilar materials (GaAs‐polydimethylsiloxane, PDMS) without high external pressures and temperatures. The fabricated solar cell showed exceptional performance with an open‐circuit voltage of 1.018 V, short‐circuit current density of 20.641 mA cm−2, fill factor of 79.83%, and power conversion efficiency of 16.77%. To prove the concept, the solar cell is integrated with a skin‐compatible organic electrochemical transistor (OECT). Competitive electrical outputs of GaAs solar cells enabled high current levels of OECT under subtle light intensities lower than 50 mW cm−2, which demonstrates a self‐powered electrocardiogram sensor with low noise (signal‐to‐noise ratio of 32.68 dB). Overall, this study presents a promising solution for the development of free‐form and comfortable device structures that can continuously power wearable devices and biosensors. [ABSTRACT FROM AUTHOR]

Ion‐selective transistor‐based sensors play a pivotal role in quantifying ion concentrations in aqueous media. Existing solutions rely on direct coupling between ion‐selective membrane and channel, requiring bulky electrolyte reservoirs or complex technological approaches and material interfaces. This work introduces a transformative paradigm with ion‐selective floating‐gate organic electrochemical transistors (ISFG‐OECTs) and their integration in sensing circuits. ISFG‐OECTs feature spatial separation between ion‐selective gating and ionic‐electronic current modulation. Leveraging volumetric capacitance and solid‐state ionic liquid, efficient ionic coupling with the channel is obtained. These distinctive features make them an ideal solution for streamlined materials integration, eliminating the need for liquid reservoirs. Theoretical foundations and design guidelines for efficient ISFG‐OECT implementation are elucidated. Experimental results demonstrate the effectiveness of ISFG‐OECTs in both transistor‐sensors and current‐driven circuit configurations, revealing highly selective detection of K+ ions with a limit of detection as low as 11 × 10−6 m, even in the presence of interfering Na+ ions at concentrations two orders of magnitude higher. The proposed approach is simple, reliable, and scalable, offering opportunities for a broad range of fields, such as medical diagnostics, precision agriculture, and environmental monitoring. [ABSTRACT FROM AUTHOR]

Highlights Transient response plays a crucial role as a performance indicator for organic electrochemical transistors (OECTs), particularly in their application in high-speed logic circuits and neuromorphic computing systems. This review presents a systematic overview on the fundamental principles underlying OECT transient responses, emphasizing the essential roles of transient electron and ion dynamics, as well as structural evolution, in both volatile and non-volatile behaviors. We also discuss the materials, morphology, device structure strategies on optimizing transient responses.

We present a series of newly developed donor‐acceptor (D‐A) polymers designed specifically for organic electrochemical transistors (OECTs) synthesized by a straightforward route. All polymers exhibited accumulation mode behavior in OECT devices, and tuning of the donor comonomer resulted in a three‐order‐of‐magnitude increase in transconductance. The best polymer gFBT‐g2T, exhibited normalized peak transconductance (gm,norm) of 298±10.4 S cm−1 with a corresponding product of charge‐carrier mobility and volumetric capacitance, μC*, of 847 F V−1 cm−1 s−1 and a μ of 5.76 cm2 V−1 s−1, amongst the highest reported to date. Furthermore, gFBT‐g2T exhibited exceptional temperature stability, maintaining the outstanding electrochemical performance even after undergoing a standard (autoclave) high pressure steam sterilization procedure. Steam treatment was also found to promote film porosity, with the formation of circular 200–400 nm voids. These results demonstrate the potential of gFBT‐g2T in p‐type accumulation mode OECTs, and pave the way for the use in implantable bioelectronics for medical applications. [ABSTRACT FROM AUTHOR]

Faradaic‐mode organic electrochemical transistors (OECT) are promising but usually need hundreds of millivolts to sustain redox reactions. Decrease or even removal of the voltage penalty is highly desirable. Herein, the Faradic regime of the OECT is broadened toward zero bias by integrating a p‐n heterojunction of Cu2S‐diethylenetriamine (DETA)‐CdS for efficient photogating of poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) channel. Upon light illumination, it is found that an obvious Faradaic process is evolved at the gate/electrolyte interface under zero gate bias, suggesting the potential of sensitive amperometric biodetection with enhanced signal resolution. At the Cu2S‐DETA‐CdS/liquid interface, a biosensing process is introduced, combining with a DNA walker and enzymatic biocatalytic precipitation to produce a target‐dependent diffusion barrier, modulating the amperometric output with enhanced signal variations under light irradiation compared to that in the dark. The proposed system achieves the desired analytical performance for representative target miRNA‐10b with a low detection limit of 0.21 fM. This work features a light‐mediated OECT device with enhanced signal resolution and provides new operational paradigms and insights for novel optoelectronics interfacing with biological systems. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) are of great interest in low‐power bioelectronics and neuromorphic computing, as they utilize organic mixed ionic‐electronic conductors (OMIECs) to transduce ionic signals into electrical signals. However, the poor environmental stability of OMIEC materials significantly restricts the practical application of OECTs. Therefore, the non‐fused planar naphthalenediimide (NDI)‐dialkoxybithiazole (2Tz) copolymers are fine‐tuned through varying ethylene glycol (EG) side chain lengths from tri(ethylene glycol) to hexa(ethylene glycol) (namely P‐XO, X = 3–6) to achieve OECTs with high‐stability and low threshold voltage. As a result, the NDI‐2Tz copolymers exhibit ambipolarity, rapid response (<10 ms), and ultra‐high n‐type stability. Notably, the P‐6O copolymers display a threshold voltage as low as 0.27 V. They can operate in n‐type mode in an aqueous solution for over 60 h, maintaining an on‐off ratio of over 105. This work sheds light on the design of exceptional n‐type/ambipolar materials for OECTs. It demonstrates the potential of incorporating these ambipolar polymers into water‐operational integrated circuits for long‐term biosensing systems and energy‐efficient brain‐inspired computing. [ABSTRACT FROM AUTHOR]

Thin films of organic mixed ionic electronic conductors (OMIECs) constitute the functional layer in organic electrochemical transistors (OECTs), organic bioelectronic transducers and other ionic‐electronic devices. The thin‐film configuration constrains devices to be fabricated on impermeable substrates in the form of 2D microstructures with lateral electrodes to drive an electronic current through the thin film. In order to alleviate such constraints, novel OMIEC deposition methods are needed that produce alternatives to thin‐film devices and that are compatible with permeable substrates and electronic transport in the vertical direction. Here OMIECs filled nanoporous membranes are introduced as functional layer in devices with mixed ionic electronic transport. Electropolymerization of ethylenedioxythiophene (EDOT) monomers is used to fabricate OMIEC filled nanochannels. Electronic and ionic transport through such nanochannels are investigated and modulation of electronic as well as ionic carrier density by action of a third gate electrode is demonstrated. The novel OMIEC nanochannels enable the fabrication of vertical OECTs with high transconductance and organic ionic transistors using only additive fabrication methods. [ABSTRACT FROM AUTHOR]

Organic mixed ionic‐electronic conductors (OMIECs) have emerged as promising materials for biological sensing, owing to their electrochemical activity, stability in an aqueous environment, and biocompatibility. Yet, OMIEC‐based sensors rely predominantly on the use of composite matrices to enable stimuli‐responsive functionality, which can exhibit issues with intercomponent interfacing. In this study, an approach is presented for non‐enzymatic glucose detection by harnessing a newly synthesized functionalized monomer, EDOT‐PBA. This monomer integrates electrically conducting and receptor moieties within a single organic component, obviating the need for complex composite preparation. By engineering the conditions for electrodeposition, two distinct polymer film architectures are developed: pristine PEDOT‐PBA and molecularly imprinted PEDOT‐PBA. Both architectures demonstrated proficient glucose binding and signal transduction capabilities. Notably, the molecularly imprinted polymer (MIP) architecture demonstrated faster stabilization upon glucose uptake while it also enabled a lower limit of detection, lower standard deviation, and a broader linear range in the sensor output signal compared to its non‐imprinted counterpart. This material design not only provides a robust and efficient platform for glucose detection but also offers a blueprint for developing selective sensors for a diverse array of target molecules, by tuning the receptor units correspondingly. [ABSTRACT FROM AUTHOR]

The improvement of living standards and the advancement of medical technology have led to an increased focus on health among individuals. Detections of biomarkers are feasible approaches to obtaining information about health status, disease progression, and response to treatment of an individual. In recent years, organic electrochemical transistors (OECTs) have demonstrated high electrical performances and effectiveness in detecting various types of biomarkers. This review provides an overview of the working principles of OECTs and their performance in detecting multiple types of biomarkers, with a focus on the recent advances and representative applications of OECTs in wearable and implantable biomarker detections, and provides a perspective for the future development of OECT‐based biomarker sensors. [ABSTRACT FROM AUTHOR]

An ultra-high sensitivity pH sensor based on vertical organic electrochemical transistors (vOECT) with extended gate was proposed. The vOECT, which exhibited high transconductance (gm), was for the first time used in the preparation of a pH sensor. The extended gate was modified by electrochemical deposition of polyaniline (PANI) using the cyclic voltammetry (CV) technique. Open circuit potential (OCP) measurements were used to optimize the scan rate, showing a super-Nernstian sensitivity at all scan rates. The pH sensor based on vOECT with extended gate was investigated at different pH levels, and it exhibited an ultra-high sensitivity of 3363.6 µA/pH in the pH range 5–9, which was about 36 times greater than the maximum current sensitivity (91 µA/pH) of other transistor-based pH sensors, to the best of our knowledge. This pH sensor performed excellently in terms of reversibility, long-term stability, and selectivity. To confirm the reliability of the pH sensor, we conducted measurements on real samples using this pH sensor and compared the results with those obtained from a standard pH meter. The ultra-high sensitivity pH sensor based on vOECT with extended gate offers a sensitive and promising alternative in environmental monitoring, food safety, chemistry, clinical diagnostics, and bio-sensing applications. [ABSTRACT FROM AUTHOR]

The continued advancement of organic electronic technology will establish organic electrochemical transistors as pivotal instruments in the field of biological detection. Here, we present a comprehensive review of the state-of-the-art technology and advancements in the use of organic electrochemical transistors as biosensors. This review provides an in-depth analysis of the diverse modification materials, methods, and mechanisms utilized in organic electrochemical transistor-structured biosensors (OETBs) for the selective detection of a wide range of target analyte encompassing electroactive species, electro-inactive species, and cancer cells. Recent advances in OETBs for use in sensing systems and wearable and implantable applications are also briefly introduced. Finally, challenges and opportunities in the field are discussed. [ABSTRACT FROM AUTHOR]

Highlights: Transient response plays a crucial role as a performance indicator for organic electrochemical transistors (OECTs), particularly in their application in high-speed logic circuits and neuromorphic computing systems. This review presents a systematic overview on the fundamental principles underlying OECT transient responses, emphasizing the essential roles of transient electron and ion dynamics, as well as structural evolution, in both volatile and non-volatile behaviors. We also discuss the materials, morphology, device structure strategies on optimizing transient responses. The rapid development of organic electrochemical transistors (OECTs) has ushered in a new era in organic electronics, distinguishing itself through its application in a variety of domains, from high-speed logic circuits to sensitive biosensors, and neuromorphic devices like artificial synapses and organic electrochemical random-access memories. Despite recent strides in enhancing OECT performance, driven by the demand for superior transient response capabilities, a comprehensive understanding of the complex interplay between charge and ion transport, alongside electron–ion interactions, as well as the optimization strategies, remains elusive. This review aims to bridge this gap by providing a systematic overview on the fundamental working principles of OECT transient responses, emphasizing advancements in device physics and optimization approaches. We review the critical aspect of transient ion dynamics in both volatile and non-volatile applications, as well as the impact of materials, morphology, device structure strategies on optimizing transient responses. This paper not only offers a detailed overview of the current state of the art, but also identifies promising avenues for future research, aiming to drive future performance advancements in diversified applications. [ABSTRACT FROM AUTHOR]

We present the construction of an organic electrochemical transistor (OECT) based on poly(3,4-ethylendioxythiophene, PEDOT) and polyallylamine (PAH) and its evaluation as a bioelectronic platform for urease integration and urea sensing. The OECT channel was fabricated in a one-step procedure using chemical polymerization. Then, urease was immobilized on the surface by electrostatic interaction of the negatively charged enzyme at neutral pH with the positively charged surface of PEDOH-PAH channels. The real-time monitoring of the urease adsorption process was achieved by registering the changes on the drain–source current of the OECT upon continuous scan of the gate potential during enzyme deposition with high sensitivity. On the other hand, integrating urease enabled urea sensing through the transistor response changes resulting from local pH variation as a consequence of enzymatic catalysis. The response of direct enzyme adsorption is compared with layer-by-layer integration using polyethylenimine. Integrating a polyelectrolyte over the adsorbed enzyme resulted in a more stable response, allowing for the sensing of urine even from diluted urine samples. These results demonstrate the potential of integrating enzymes into the active channels of OECTs for the development of biosensors based on local pH changes. [ABSTRACT FROM AUTHOR]

Abstract The existing device models for organic electrochemical transistors (OECTs) fail to provide any device design guidelines for optimized performance parameters such as transconductance that are pivotal for the applications OECTs in sensing. Moreover, the current models are based on the questionable assumption of a homogenous organic semiconductor layer, and all predict a linear behavior of the resistance with the OECT channel length. Consequently, the experimentally observed nonlinear resistance behavior in OECTs has been overlooked thus far. Here, an OECT device model is developed that accurately describes the nonlinear behavior of the OECT channel resistance and offers the first guidelines for maximizing transconductance. The model is inherently nonlinear and the nonlinearity stem from the non‐monolithic capacitance of the organic semiconductor layer. Moreover, the model provides a consistent and reliable estimations for the contact resistance in OECTs. The success of the model in accurately describing and providing predictions of the OECT operation by relating the device's geometrical parameters with electrochemical parameters of the semiconductor layer paves the way toward unlocking OECT potentials in diverse applications, from biosensing to neuromorphic computing and flexible electronics.

The effect of the electrolyte's counter‐ion in organic electrochemical transistors is often neglected. the influence of anions (i.e., counter ions) is investigated on organic electrochemical transistors (OECTs) with a PEDOT:PSS‐like semiconductor through device simulations. The study examined the effects of mobile anions on OECT performance under two scenarios: when anions are blocked by the semiconductor and when they can penetrate it. In each case, the OECT's ON and OFF states are analyzed. The findings show that when anions can penetrate the semiconductor, the ON/OFF ratio of the OECT remains unchanged while the transconductance significantly increases. In the ON state, the case of blocked anions is observed that the current is predominantly surface‐current, whereas it becomes volumetric only when anions can penetrate the semiconductor. Furthermore, the extreme case is explored in which anions remain stationary within the electrolyte. In this scenario, achieving a reasonable ON/OFF ratio necessitates an ion density within the electrolyte that is two orders of magnitude higher than the dopant density of the semiconductor. This work underscores the substantial influence of counter anions on OECT performance, highlighting their critical role in shaping device behavior. [ABSTRACT FROM AUTHOR]

The high transconductance gm of organic electrochemical transistors (OECTs) has received widespread attention and made OECTs a valid candidate for wearable sensor systems. However, the large transconductance is often accompanied by large switching time constants, τ, making the transconductance an imperfect benchmark. For a fair assessment, the ratio of transconductance to switching time constant gmτ$\frac{g_m}{\tau }$ has to be considered instead of any single parameter in isolation. One approach put forward to optimize OECTs is a vertical design, in which the channel length can be scaled into the sub‐micrometer regime. Here, a new vertical device geometry is proposed, in which the active volume of the mixed conductor is confined to a small cavity between source and drain, yielding excellent performance and reproducibility. It is shown that this approach yields optimized gmτ$\frac{g_m}{\tau }$ ratios instead of maximized transconductance only. However, this scaling is effective only in a small range of device dimensions and requires careful optimization of the device to not be limited by parasitic effects such as excess volume of the mixed conductor or parasitic series resistances. Overall, the design considerations discussed here provide new guidelines to optimize OECTs, not only for high transconductance but for operation at high frequencies as well. [ABSTRACT FROM AUTHOR]

n‐Type organic electrochemical transistors (OECTs) are fundamental building blocks of biosensors and complementary circuits along with p‐type. Yet, their development has been lagging behind their p‐type counterparts since first emergence in 2016. The key component of an OECT is the channel material, which is an organic mixed ionic‐electronic conductor (OMIEC), that dictates the function and performance of the OECT via interactions with electrolyte ions. OMIECs of OECTs are benchmarked by the product of charge‐carrier mobility (μ) and volumetric capacitance (C*), μC*. Significant progress is made for the development of novel n‐type OMIECs, with best μC* now reaching 180 F cm−1 V−1 s−1. This review elucidates such material development progress of n‐type OMIECs with emphases on the underlying molecular design strategies and structure‐property relationships. Furthermore, the operational stability of channel materials and the applications of n‐type OECTs are also discussed to offer readers a comprehensive view of the field. Finally, current limitations are discussed along with outlook. [ABSTRACT FROM AUTHOR]

Neuromorphic computing offers the opportunity to curtail the huge energy demands of modern artificial intelligence (AI) applications by implementing computations into new, brain‐inspired computing architectures. However, the lack of fabrication processes able to integrate several computing units into monolithic systems and the need for new, hardware‐tailored training algorithms still limit the scope of application and performance of neuromorphic hardware. Recent advancements in the field of organic transistors present new opportunities for neuromorphic systems and smart sensing applications, thanks to their unique properties such as neuromorphic behavior, low‐voltage operation, and mixed ionic‐electronic conductivity. Organic neuromorphic transistors push the boundaries of energy efficient brain‐inspired hardware AI, facilitating decentralized on‐chip learning and serving as a foundation for the advancement of closed‐loop intelligent systems in the next generation. The biocompatibility and dual ionic‐electronic conductivity of organic materials introduce new prospects for biointegration and bioelectronics. Their ability to sense and regulate biosystems, as well as their neuro‐inspired functions can be combined with neuromorphic computing to create the next‐generation of bioelectronics. These systems will be able to seamlessly interact with biological systems and locally compute biosignals in a relevant matter. [ABSTRACT FROM AUTHOR]

The organic electrochemical transistor (OECT) is one of the most versatile building blocks within the bioelectronics device toolbox. While p‐type organic semiconductors have progressed as OECT channel materials, only a few n‐type semiconductors have been reported, precluding the development of advanced sensor‐integrated OECT‐based complementary circuits. Herein, green aldol polymerization is uses to synthesize lactone‐based n‐type conjugated polymers. Fluorination of the lactone‐based acceptor endows a fully locked backbone with a low‐lying lowest unoccupied molecular orbital, facilitating efficient ionic‐to‐electronic charge coupling. The resulting polymer has a record‐high n‐type OECT performance with a high product of mobility and capacitance (µC* = 108 F cm−1 V−1 s−1), excellent mobility (0.912 cm2 V−1 s−1), low threshold voltage (0.02 V), and fast switching speed (τON, τOFF = 336 µs,108 µs). This work demonstrates two types of device architectures and applications enabled by the high performance of this n‐type OECT, i.e., an artificial synapse and a complementary amplifier for detecting α‐synuclein, a potential biomarker of Parkinson's disease. This study shows that materials that enable high gain and fast speed n‐type OECTs can be developed via a green polymerization route, and the diverse form factors that these devices take promise for exploration of other application areas. [ABSTRACT FROM AUTHOR]

In this paper, we study the drift behavior of organic electrochemical transistor (OECT) biosensors in a phosphate-buffered saline (PBS) buffer solution and human serum. Theoretical and experimental methods are illustrated in this paper to understand the origin of the drift phenomenon and the mechanism of ion diffusion in the sensing layer. The drift phenomenon is explained using a first-order kinetic model of ion adsorption into the gate material and shows very good agreement with experimental data on drift in OECTs. We show that the temporal current drift can be largely mitigated using a dual-gate OECT architecture and that dual-gate-based biosensors can increase the accuracy and sensitivity of immuno-biosensors compared to a standard single-gate design. Specific binding can be detected at a relatively low limit of detection, even in human serum. [ABSTRACT FROM AUTHOR]

Four glycolated polythiophene‐based organic mixed ionic‐electronic conductors (OMIECs), PE2gTT, PE2gT, PT2gTT, and PT2gT are prepared by atom‐efficient direct arylation polymerization, avoiding the need for toxic organometallic precursors. PE2gT, PT2gTT, and PT2gT are operable in p‐type accumulation mode organic electrochemical transistors (OECTs), with PT2gT displaying the best device performance with a µC* product figure‐of‐merit of 290 F cm−1 V−1 s−1. A record volumetric capacitance among p‐type glycolated polythiophene OMIECs of 313 F cm−3 is observed for PE2gT, ascribed to the high proportionality of polar components in its materials design. The good OECT performance of PE2gT with µC* = 84.2 F cm−1 V−1 s−1, comparable with state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) devices, coupled with its synthetic accessibility and favorable accumulation mode operation makes PE2gT an ideal glycolated alternative to PEDOT:PSS in bioelectronics. PE2gT with the least negative threshold voltage also displays the best OECT operational cycling stability, linked to better resistance of its oxidized state against parasitic redox side reactions. Shelf life stability of OECTs stored (without bias) is observed to be better for materials with a more negative threshold voltage and higher average molecular weight (PT2gT), that are less susceptible to ambient auto‐oxidation and film delamination. [ABSTRACT FROM AUTHOR]

Abstract Thin films of organic mixed ionic electronic conductors (OMIECs) constitute the functional layer in organic electrochemical transistors (OECTs), organic bioelectronic transducers and other ionic‐electronic devices. The thin‐film configuration constrains devices to be fabricated on impermeable substrates in the form of 2D microstructures with lateral electrodes to drive an electronic current through the thin film. In order to alleviate such constraints, novel OMIEC deposition methods are needed that produce alternatives to thin‐film devices and that are compatible with permeable substrates and electronic transport in the vertical direction. Here OMIECs filled nanoporous membranes are introduced as functional layer in devices with mixed ionic electronic transport. Electropolymerization of ethylenedioxythiophene (EDOT) monomers is used to fabricate OMIEC filled nanochannels. Electronic and ionic transport through such nanochannels are investigated and modulation of electronic as well as ionic carrier density by action of a third gate electrode is demonstrated. The novel OMIEC nanochannels enable the fabrication of vertical OECTs with high transconductance and organic ionic transistors using only additive fabrication methods.

Organic electrochemical transistors (OECT) have shown great potential in diverse applications; however, in many OECTs, their slow transient response has thus far limited their practical use. One reason for the slow response is the complex interplay between lateral and vertical ion transport that has so far been poorly understood. In this work, we study the impact of lateral ion transport on OECT transient response, introduce a robust pre-charging method to manipulate the slow lateral ion transport. This approach leads to quicker ion redistribution and improved switching speeds. We show the general utility of pre-charging method in enhancing the switching speeds across various material systems, characterized by both low and high ion mobilities, and across different device architectures, achieving nearly symmetric speeds for both on-switching and off-switching. Moreover, we showcase the efficacy of the pre-charging method in enabling slow OECTs to capture rapid signals in real-world applications. Our findings present a groundbreaking strategy for enhancing the response times of OECT devices and deepening our understanding of the transient mechanisms in OECT device.

Abstract The high transconductance gm of organic electrochemical transistors (OECTs) has received widespread attention and made OECTs a valid candidate for wearable sensor systems. However, the large transconductance is often accompanied by large switching time constants, τ, making the transconductance an imperfect benchmark. For a fair assessment, the ratio of transconductance to switching time constant gmτ has to be considered instead of any single parameter in isolation. One approach put forward to optimize OECTs is a vertical design, in which the channel length can be scaled into the sub‐micrometer regime. Here, a new vertical device geometry is proposed, in which the active volume of the mixed conductor is confined to a small cavity between source and drain, yielding excellent performance and reproducibility. It is shown that this approach yields optimized gmτ ratios instead of maximized transconductance only. However, this scaling is effective only in a small range of device dimensions and requires careful optimization of the device to not be limited by parasitic effects such as excess volume of the mixed conductor or parasitic series resistances. Overall, the design considerations discussed here provide new guidelines to optimize OECTs, not only for high transconductance but for operation at high frequencies as well.

Abstract The effect of the electrolyte's counter‐ion in organic electrochemical transistors is often neglected. the influence of anions (i.e., counter ions) is investigated on organic electrochemical transistors (OECTs) with a PEDOT:PSS‐like semiconductor through device simulations. The study examined the effects of mobile anions on OECT performance under two scenarios: when anions are blocked by the semiconductor and when they can penetrate it. In each case, the OECT's ON and OFF states are analyzed. The findings show that when anions can penetrate the semiconductor, the ON/OFF ratio of the OECT remains unchanged while the transconductance significantly increases. In the ON state, the case of blocked anions is observed that the current is predominantly surface‐current, whereas it becomes volumetric only when anions can penetrate the semiconductor. Furthermore, the extreme case is explored in which anions remain stationary within the electrolyte. In this scenario, achieving a reasonable ON/OFF ratio necessitates an ion density within the electrolyte that is two orders of magnitude higher than the dopant density of the semiconductor. This work underscores the substantial influence of counter anions on OECT performance, highlighting their critical role in shaping device behavior.

Abstract Four glycolated polythiophene‐based organic mixed ionic‐electronic conductors (OMIECs), PE2gTT, PE2gT, PT2gTT, and PT2gT are prepared by atom‐efficient direct arylation polymerization, avoiding the need for toxic organometallic precursors. PE2gT, PT2gTT, and PT2gT are operable in p‐type accumulation mode organic electrochemical transistors (OECTs), with PT2gT displaying the best device performance with a µC* product figure‐of‐merit of 290 F cm−1 V−1 s−1. A record volumetric capacitance among p‐type glycolated polythiophene OMIECs of 313 F cm−3 is observed for PE2gT, ascribed to the high proportionality of polar components in its materials design. The good OECT performance of PE2gT with µC* = 84.2 F cm−1 V−1 s−1, comparable with state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) devices, coupled with its synthetic accessibility and favorable accumulation mode operation makes PE2gT an ideal glycolated alternative to PEDOT:PSS in bioelectronics. PE2gT with the least negative threshold voltage also displays the best OECT operational cycling stability, linked to better resistance of its oxidized state against parasitic redox side reactions . Shelf life stability of OECTs stored (without bias) is observed to be better for materials with a more negative threshold voltage and higher average molecular weight (PT2gT), that are less susceptible to ambient auto‐oxidation and film delamination.

Organic electrochemical transistors (OECTs) are recognized for their ability to combine electronic and ionic transport in the channel, resulting in improved transconductance and reduced operation voltage compared to organic field‐effect transistors (OFETs). Nevertheless, the hydrophobic nature of conjugated polymers remains a hindrance to ion drift, thereby causing slow switching speed and limiting their practical application. This study introduces the ionic liquid 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) adsorbed in a metal–organic framework (MOF‐525) as an ion reservoir within a conjugated polymer, for the first time, to serve as the active channel in OECTs. Due to shortened ionic drift time, in the poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT‐C14) system, the original polymer membrane without MOF‐525/[EMIM][TFSI] exhibits a characteristic ON time (τON) of 28.75 s, whereas the PBTTT‐C14/MOF‐525/[EMIM][TFSI] composite film significantly reduces the τON to 2.56 s with ON/OFF current ratio of 102. Enhancing response speed through facile physical blending of MOF‐525/[EMIM][TFSI] in conjugated polymer film can also be realized on flexible substrate and in poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) system which provide a general strategy to broaden the selection of conjugated polymers in accumulation mode OECTs. [ABSTRACT FROM AUTHOR]

Organic thin‐film transistors (OTFTs) as a vital component among transistors have shown great potential in smart sensing, flexible displays, and bionics due to their flexibility, biocompatibility and customizable chemical structures. Even though linear conjugated polymer semiconductors are common for constructing channel materials of OTFTs, advanced materials with high charge carrier mobility, tunable band structure, robust stability, and clear structure‐property relationship are indispensable for propelling the evolution of OTFTs. Two‐dimensional conjugated polymers (2DCPs), featured with conjugated lattice, tailorable skeletons, and functional porous structures, match aforementioned criteria closely. In this review, we firstly introduce the synthesis of 2DCP thin films, focusing on their characteristics compatible with the channels of OTFTs. Subsequently, the physics and operating mechanisms of OTFTs and the applications of 2DCPs in OTFTs are summarized in detail. Finally, the outlook and perspective in the field of OTFTs using 2DCPs are provided as well. [ABSTRACT FROM AUTHOR]

The gradual channel approximation forms the foundation for the analysis of field‐effect transistors. It has been used to discuss transistors that are not necessarily based on the field‐effect as well, such as the organic electrochemical transistor (OECT). Here, the applicability of the gradual channel approximation for OECTs is studied by a 2D drift‐diffusion model. It is found that OECT switching can be described by two separate effects—a doping/dedoping mechanism and the formation of an electrostatic double layer at the interface between the mixed conductor and the electrolyte. The balance between these two mechanisms is determined by the morphology of the mixed conductor, in particular the question if ions move in the same phase and electric potential as the holes, or if separate ion and hole phases are formed. It is argued that the gradual channel approximation can only be used to describe electrostatic switching at the mixed conductor/electrolyte interface (the two‐phase model), but cannot be employed to analyze devices operating on a doping/de‐doping mechanism (the one‐phase model). [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) have gained considerable attention due to their potential applications in emerging biosensor platforms. The use of conjugated polyelectrolytes (CPEs) as active materials in OECTs is particularly advantageous owing to their functional, water‐processable, and biocompatible nature, as well as their tunable electronic and ionic transport properties. However, there exists a lack of systematic studies of the structure‐property relationships of these materials with respect to OECT performance. This study shows how by tuning the molecular weight of self‐doped CPE (CPE‐K) it is possible to fabricate OECTs with a µC* value of 14.7 F cm−1 V−1 s−1, one order of magnitude higher than previously reported CPE‐based devices. Furthermore, OECTs with a transconductance of 120 mS are demonstrated via device engineering. While CPE‐K batches with different molecular weights show good doping behavior and high volumetric capacitance, as confirmed by spectroelectrochemistry and electrochemical impedance spectroscopy, the medium molecular weight possesses the highest carrier mobility of ≈0.1 cm2 V−1 s−1 leading to the highest transconductance. The enhanced charge transport is due to a favorable charge percolation pathway, as revealed by the combination of X‐ray analysis and conductive atomic force microscope. These insights provide guidelines for further improving the performance of CPE‐based OECTs. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) based complementary inverters have been considered as promising candidates in electrophysiological amplification, owing to their low power consumption, and high gain. To create complementary inverters, it is important to use highly stable p‐type and n‐type polymers with well‐balanced current. In this study, the electrochemical stability of p‐type ladder‐conjugated polymer‐based OECT is improved through an annealing process that maintains its doped‐state drain current from 76% to 105% after 4,500 cycles in ambient environment. Next an OECT‐based complementary inverter made from p‐type and n‐type ladder‐conjugated polymers (PBBTL and BBL) that possess ultra‐low power consumption (≈170 nW), high gain (67 V/V), and high noise margin (92%) with full rail‐to‐rail swing, is presented. Furthermore, its potential for amplifying the envelope of surface electromyography (EMG) for robotic hand control is demonstrated. The high variation in the output (0.35 V) allows the amplified EMG signals to be directly captured by a commercial analog‐to‐digital converter, which in turn controls the robot hand to grasp different objects with low delay and low noise. These results demonstrate the capability of OECT inverter‐based amplifier in future signal processing‐free human‐machine interface, particularly useful for prosthetic control and gesture control applications. [ABSTRACT FROM AUTHOR]

The continued advancement of organic electronic technology will establish organic electrochemical transistors as pivotal instruments in the field of biological detection. Here, we present a comprehensive review of the state-of-the-art technology and advancements in the use of organic electrochemical transistors as biosensors. This review provides an in-depth analysis of the diverse modification materials, methods, and mechanisms utilized in organic electrochemical transistor-structured biosensors (OETBs) for the selective detection of a wide range of target analyte encompassing electroactive species, electro-inactive species, and cancer cells. Recent advances in OETBs for use in sensing systems and wearable and implantable applications are also briefly introduced. Finally, challenges and opportunities in the field are discussed.