The use of organic electrochemical transistors (OECTs) for various applications ranging from neuromorphic devices [1] to transducers for biological sensing, including detection of ions, [2,3] metabolites (such as glucose [4,5] ), DNA, [6] antibodyantigen interaction, [7] and cancer cells [8] has received significant attention in recent years. An OECT consists of a conjugated polymer channel in direct contact with an electrolyte, where the operation involves doping and dedoping of the conjugated polymer by reversible exchange of ions present in an electrolyte under the application of a very low gate voltage (V G < 1 V). The measured drain current (I D ) of the polymer channel between the source and drain contacts is therefore modulated through accumulation or depletion of charges throughout the bulk of the polymer. The corresponding transconductance (g m = ∂I D /∂V G ) is typically large (up to 2.0 mS for micrometer-scale devices [9] ), making OECTs an efficient ionto-electron transducers, capable of amplifying small chemical signals and with high signal-to-noise ratios. One important advantage of OECTs is that they can be fabricated from biocompatible organic materials, enabling an amiable interface with cells and tissues in aqueous environments (water-based electrolytes). [10] Also, their simple structure allows the potential for large-area and low-cost electronics through their facile fabrication processes such as printing and easy integration with microfluidic lab-on-a-chip applications. [11,12] The OECT transconductance, g m , is defined as follows: [13] µ ( )where d, W, and L are the thickness, width, and length of the channel respectively, µ is the carrier mobility, C* is the volumetric capacitance, and V th is the threshold voltage of the channel. In particular, the µC* figure of merit dictates the carrier and ionic transport and therefore affects the g m parameter. [14] In general, a good OECT channel material needs to have good electronic transport properties (high µ) and allows effective ion penetration from the electrolyte into active channel (high C*). The ability to have mixed ionic and electronic Organic electrochemical transistors (OECTs) are highly attractive for applications ranging from circuit elements and neuromorphic devices to transducers for biological sensing, and the archetypal channel material is poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS. The operation of OECTs involves the doping and dedoping of a conjugated polymer due to ion intercalation under the application of a gate voltage. However, the challenge is the trade-off in morphology for mixed conduction since good electronic charge transport requires a high degree of ordering among PEDOT chains, while efficient ion uptake and volumetric doping necessitates open and loose packing of the polymer chains. Ionic-liquid-doped PEDOT:PSS that overcomes this limitation is demonstrated. Ionic-liquid-doped OECTs show high transconductance, fast transient response, and high device stability over 3600 switching cycles. The ...

A stretchable and self‐healable conductive material with high conductivity is critical to high‐performance wearable electronics and integrated devices for applications where large mechanical deformation is involved. While there has been great progress in developing stretchable and self‐healable conducting materials, it remains challenging to concurrently maintain and recover such functionalities before and after healing. Here, a highly stretchable and autonomic self‐healable conducting film consisting of a conducting polymer (poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) and a soft‐polymer (poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid), PAAMPSA) is reported. The optimal film exhibits outstanding stretchability as high as 630% and high electrical conductivity of 320 S cm−1, while possessing the ability to repair both mechanical and electrical breakdowns when undergoing severe damage at ambient conditions. This polymer composite film is further utilized in a tactile sensor, which exhibits good pressure sensitivity of 164.5 kPa−1, near hysteresis‐free, an ultrafast response time of 19 ms, and excellent endurance over 1500 consecutive presses. Additionally, an integrated 5 × 4 stretchable and self‐healable organic electrochemical transistor (OECT) array with great device performance is successfully demonstrated. The developed stretchable and autonomic self‐healable conducting film significantly increases the practicality and shelf life of wearable electronics, which in turn, reduces maintenance costs and build‐up of electronic waste.

The major challenges in developing self-healable conjugated polymers for organic electrochemical transistors (OECTs) lie in maintaining good mixed electronic/ionic transport and the need for fast restoration to the original electronic and structural properties after the selfhealing process. Herein, we provide the first report of an all solid state OECT that is selfhealable and possess good electrical performance, by utilizing a matrix of poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and non-ionic surfactant, Triton X-100 as channel, and ion conducting poly(vinyl alcohol) hydrogel as a quasi-solid-state polymer electrolyte. The fabricated OECT exhibits high transconductance (maximum 54 mS), on/off current ratio of ~1.5×10 3 , fast response time of 6.8 ms and good operational stability after 68 days of storage. Simultaneously, the OECT showed remarkable self-healing and ion-sensing behaviors and recovered ~95% of its ion sensitivity after healing. These findings will contribute to the development of high performing and robust OECTs for wearable bioelectronic devices.

Organic electrochemical transistors (OECTs) with high transconductance and good operating stability in an aqueous environment are receiving substantial attention as promising ion-toelectron transducers for bioelectronics. However, to date, in most of the reported OECTs, the fabrication procedures have been devoted to the spin coating processes which may nullify the advantages of large-area and scalable manufacturing. In addition, conventional microfabrication and photolithography techniques are complicated or incompatible with various nonplanar flexible and curved substrates. Herein, we demonstrate a facile patterning method via spray-deposition to fabricate ionic liquid doped poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based OECTs, with a high peak transconductance of 12.9 mS and high device stability over 4000 switching cycles.More importantly, this facile technique makes it possible to fabricate high-performance OECTs on versatile substrates with different textures and form factors such as thin permeable membranes, flexible plastic sheets, hydrophobic elastomers and rough textiles. Overall, the results highlight the spray-deposition technique as a convenient route to prepare high performing OECTs and will contribute to the translation of OECTs into real-world applications.

The ability to operate in aqueous environments makes poly(3,4-ethylenedioxyt hiophene):poly(styrenesulfonate), PEDOT:PSS, based organic electrochemical transistors (OECTs) excellent candidates for a variety of biological applications. Current research in PEDOT:PSS based OECTs is primarily focused on improving the conductivity of PEDOT:PSS film to achieve high transconductance (g m ). The improved conductivity and electronic transport are attributed to the formation of enlarged PEDOT-rich domains and shorter PEDOT stacking, but such a change in morphology sacrifices the ionic transport and, therefore, the doping/de-doping process. Additionally, little is known about the effect of such morphology changes on the gate bias that makes the maximum g m ( P Pe ea ak k V G G ), threshold voltage (V T ), and transient behavior of PEDOT:PSS based OECTs. Here, the molecular packing and nanostructure of PEDOT:PSS films are tuned using ionic liquids as additives, namely, 1-Ethyl-3-methylimidazolium (EMIM) as cation and anions of chloride (Cl), trifluoromethanesulfonate (OTF), bis(trifluoromethylsulfonyl)imide (TFSI), and tricyanomethanide (TCM). It is demonstrated that an optimal morphology is realized using EMIM OTF ionic liquids that generate smaller fibril-like PEDOT-rich domains with relatively loose structures. Such optimal morphology improves ion accessibility, lowering the gate bias required to completely de-dope the channel, and thus enabling to achieve high transconductance, fast transient response, and at lower gate bias window simultaneously.

Ionic‐electronic coupling across the entire volume of conjugated polymer films endows organic electrochemical transistors (OECTs) with high transconductance (gm) and low operating voltage. However, OECTs utilize liquid electrolytes, which limit their long‐term operation, reproducibility, and integration while solid electrolytes typically result in inefficient ion transport. Here, a solid polymer electrolyte is shown that can facilitate good electrochemical response in conjugated polymers and yield high OECT performance. This allows for the OECT‐based pressure sensors, modulated through a pressure sensitive ionic doping process. The pressure sensor exhibits the highest sensitivity ever measured (≈10 000 kPa−1) and excellent stability. Flexible sensor arrays achieve static capture of spatial pressure distribution and enable monitoring of dynamic pressure stimuli. The findings here demonstrate that all‐solid‐state OECTs are good candidates for providing rich tactile information, enabling applications for soft robotics, health monitoring, and human‐machine interfaces.

The classical organic semiconducting material used for OECTs is an ionomer mixture called poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), comprising of a conjugated PEDOT phase and a deprotonated PSS phase. Holes in the PEDOT phase is compensated by the negatively charged sulfonate ions in the PSS phase, making the PEDOT phase conducting. In the absence of a gate bias (V GS = 0 V), the flow of mobile holes within the polymer maintains a hole current when a drain voltage (V DS) is applied (ON state). By applying a positive gate voltage (V GS > 0 V), cations from the electrolyte are injected into the channel and PSS anions are charge compensated, initiating the dedoping of PEDOT, reducing the hole density and thus lowering the drain current (OFF state). Such mode of operation is known as depletion mode; the OECT is ON in the absence of a gate bias. It is also possible to operate the OECT in accumulation mode if the conjugated polymer does not consist of any native dopants. Accumulatedmode OECT is typically in the OFF state and application of a negative gate voltage leads to injection of anions into the semiconducting polymer, initiating an electrochemically driven hole accumulation in the channel, leading to the ON state. Recently, naphthalene diimides (NDIs)-based polymers, [15] ladder-type polymers such as poly(benzimidazobenzophenanthro-line) (BBL), [16] fullerene derivatives with glycolated side chains, [17] and random copolymer with glycol side chain such as P-90 [9,18] were reported to be promising n-type materials to develop accumulation mode OECTs with stable operation in aqueous environments. Another class of promising p-type materials for accumulation mode OECTs is semiconducting polymers based on benzodithiophene or bithiophene core with glycol side chains, [19,20] glycolated thiophene (g2T-T) polymers, [21] poly(3hexylthiophene) (P3HT), [22,23] conjugated polyelectrolytes based on poly(6-(thiophene-3-yl)hexane-1-sulfonate) tetrabutylammonium (PTHS), [24] polythiophene derivative with ethylene glycolbased side chains (P3MEEMT), [12] and poly(6-(thiophen-3-yl) hexane-1-sulfonate) tetrabutylammonium (PTHS:TEA). [25] Generally, the material must have simultaneously an aggregated, interconnected structure that supports efficient hole transport, and an amorphous phase to hydrate, and thus enable the transport of ions. The in-depth introduction on active materials for OECTs can be found in several review papers. [26-30] The key feature of OECT is that the transition of doping/ dedoping states occurs over the entire channel volume, as Organic electrochemical transistors (OECTs), where conjugated polymers undergo doping/dedoping from an electrolyte, are widely studied for applications ranging from switching elements, artificial synapses to transducers for biological sensing. The concurrent transport of electronic and ionic charges within the channel provide OECTs with excellent amplification capability and efficient ion-to-electron transduction at low operating voltages (<1 V). Herein, the la...

The increasing interest in organic electrochemical transistors (OECTs) for next‐generation bioelectronic applications motivates the design of novel conjugated polymers with good electronic and ionic transport. Many conjugated polymers developed for organic field‐effect transistors (OFETs) exhibit high charge carrier mobilities but they are not suitable for OECTs due to poor ion‐uptake arising from the non polar alkyl chain substituted on the conjugated backbone. They are also sensitive to moisture, resulting in poor performance in aqueous electrolytes. Herein, the widely used conjugated building block diketopyrrolopyrrole (DPP) is used and functionalized it with polar triethylene glycol side chains (PTDPP‐DT) to promote ion penetration. The electrical performance of PTDPP‐DT based OECT in two types of aqueous electrolytes is studied and the electrochemical doping response is investivated. It is found that the tetrafluoroborate (BF4−) anion with large crystallographic radius allows high‐efficiency electrochemical doping of the PTDPP‐DT polymer, and thus gives rise to the high transconductance of 21.4 ± 4.8 mS with good device stability, where it maintained over 91 % of its doped‐state drain current after over 500 cycles of pulse measurement.