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 ...

Emulation of biological synapses is necessary for future brain-inspired neuromorphic computational systems that could look beyond the standard von Neuman architecture. Here, artificial synapses based on ionic-electronic hybrid oxide-based transistors on rigid and flexible substrates are demonstrated. The flexible transistors reported here depict a high field-effect mobility of ≈9 cm V s with good mechanical performance. Comprehensive learning abilities/synaptic rules like paired-pulse facilitation, excitatory and inhibitory postsynaptic currents, spike-time-dependent plasticity, consolidation, superlinear amplification, and dynamic logic are successfully established depicting concurrent processing and memory functionalities with spatiotemporal correlation. The results present a fully solution processable approach to fabricate artificial synapses for next-generation transparent neural circuits.

Biomaterials have been attracting attention as a useful building block for biocompatible and bioresorbable electronics due to their nontoxic property and solution processability. In this work, we report the integration of biocompatible keratin from human hair as dielectric layer for organic thin-film transistors (TFTs), with high performance, flexibility, and transient property. The keratin dielectric layer exhibited a high capacitance value of above 1.27 μF/cm at 20 Hz due to the formation of electrical double layer. Fully solution-processable TFTs based on p-channel poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b]dithiophen-2-yl)-alt[1,2,5]thiadiazolo[3,4-c]-pyridine] (PCDTPT) and keratin dielectric exhibited high electrical property with a saturation field-effect mobility of 0.35 cm/(Vs) at a low gate bias of -2 V. We also successfully demonstrate flexible TFTs, which exhibited good mechanical flexibility and electrical stability under bending strain. An artificial electronic synaptic PCDTPT/keratin transistor was also realized and exhibited high-performance synaptic memory effects via simple operation of proton conduction in keratin. An added functionality of using keratin as a substrate was also presented, where similar PCDTPT TFTs with keratin dielectric were built on top of keratin substrate. Finally, we observed that our prepared devices can be degraded in ammonium hydroxide solution, establishing the feasibility of keratin layer as various components of transient electrical devices, including as a substrate and dielectric layer.

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.

4689www.MaterialsViews.com wileyonlinelibrary.com key in switching components for next generation displays such as smart windows, transparent mobile displays, and electronic papers. [1][2][3][4][5][6][7][8][9] Recently, high-quality OS fi lms on plastic substrates have been successfully fabricated by developing lowtemperature and solution-based processes (e.g., combustion process, [ 3 ] 'sol-gel on chip' process, [ 4 ] and photochemical activation methods [ 5 ] ). These methods can accelerate the adoption of fl exible OS TFTs to practical applications.While the novel OS fi lm-fabricating techniques are important, raising drive currents in low-operating voltages is also critical for low-power consuming and high-performance OS TFTs. [10][11][12][13] One of the conventional strategies to increase the drain current ( I D ) for transistors is to increase the gate-insulator capacitances ( C i ) based on the relationship of I D ∝ C i from the metal-oxide-semiconductor fi eldeffect transistors (MOSFETs) theory. [ 14 ] Empirically, such strategies has been applied to solution-processed OS TFTs. However, the enhanced behaviors of I D in the OS TFTs are quite different to that in MOSFETs, [ 3,5,[10][11][12][13] since disordered metal ions or dense grain boundaries in the solution-processed OSs make the fi eld-effect mobility ( μ FE ) of the OS TFTs depend on the total number of accumulated charge carriers in the channel. [ 15,16 ] Therfore, μ FE depends on C i , and I D is not in a linear relationship to C i . The relationship between C i and μ FE is important for low-voltage and high-performance solutionprocessed OS TFTs. Futhermore, theoretical predictions for the device performances can be essential guidelines for designing and optimizing integrated TFT circuits.The solution-processed OS disordering states can be categorized with nanocrystalline and amorphous states, which is determined by the number of metal elements that compose the OS fi lms. Binary oxide systems (number of metal elements = 1) such as ZnO, InO 2 , and SnO 2 , have nanocrystalline states, [ 6,7,12,13 ] while the ternary or quaternary oxide systems (number of metal elements > 1) like ZnSnO, InZnO, and InGaZnO have the amorhpous phases. [ 3,5,8 ] In the experiment, both nanocrystalline and amorhpous OS TFTs by engineering C i differ in electron-transporting mechanisms, but follow two Solution-processed oxide semiconductors (OSs) used as channel layer have been presented as a solution to the demand for fl exible, cheap, and transparent thin-fi lm transistors (TFTs). In order to produce high-performance and longsustainable portable devices with the solution-processed OS TFTs, the lowoperational voltage driving current is a key issue. Experimentally, increasing the gate-insulator capacitances by high-k dielectrics in the OS TFTs has signifi cantly improved the fi eld-effect mobility of the OS TFTs. But, methodical examinations of how the fi eld-effect mobility depends on gate capacitance have not been presented yet. Here, a systematic analysis of the fi eld...

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P-doping of conjugated polymers requires electron transfer from the conjugated polymer to the p-dopant. This implies that the highest occupied molecular orbital (HOMO) of the conjugated polymer has to be higher than the lowest unoccupied molecular orbital (LUMO) of the p-dopant. Although commonly used p-dopants such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) have a low LUMO of −5.24 eV, most conjugated polymers used in high-performance field-effect transistors are donor–acceptor-type polymers with deep HOMO values, making them difficult to be effectively doped by F4TCNQ. Here, we utilized the proquinoidal 2,6-dialkyl-benzo­[1,2-d;4,5-d′]­bistriazole (BBTa26) moiety in conjugated polymers to destabilize HOMO, allowing effective p-doping using very dilute F4TCNQ solutions. The extent of the quinoidal character and hence their intrinsic conductivities and the ability to be doped are dependent on the dihedral angles and aromaticity of the aryl spacer groups along the polymer backbone. Intrinsic conductivities as high as 10–2 S cm–1 were achieved. Upon doping using F4TCNQ, highly delocalized polarons were observed. As such, electrical conductivities of over 100 S cm–1 and an enhancement of the Seebeck coefficient from carrier-induced softening can be achieved. A maximum power factor of 11.8 μW m–1 K–2 was achieved in thin-film thermoelectric devices. These results are among the highest for solution-phase p-doping using F4TCNQ without additional processing.

4 V-operated all solid symmetrical supercapacitors that employ mixtures of various weight compositions with c-P4VPh and EMITFSI electrolytes have been demonstrated and characterized.