Transient Response and Ionic Dynamics in Organic Electrochemical Transistors

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.

Device design principles and bioelectronic applications for flexible organic electrochemical transistors

Organic electrochemical transistors(OECTs) exhibit significant potential for applications in healthcare and human-machine interfaces, due to their tunable synthesis, facile deposition, and excellent biocompatibility. Expanding OECTs to the fexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work,we summarize the device physics of fexible OECTs, aiming to offer a foundational understanding and guidelines for material selection and device architecture. Particular attention is paid to the advanced manufacturing approaches, including photolithography and printing techniques, which establish a robust foundation for the commercialization and large-scale fabrication. And abundantly demonstrated examples ranging from biosensors, artificial synapses/neurons, to bioinspired nervous systems are summarized to highlight the considerable prospects of smart healthcare. In the end, the challenges and opportunities are proposed for fexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of fexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Organic Electrochemical Transistor based on Polypyrrole/ Crosslinked Chitosan/Nylon Fibers

Glutaraldehyde(GA)crosslinked chitosan(CHIT)was modified on nylon fibers.Afterwards,pyrrole was in-situ polymerized on the surface of the CHIT/Nylon fiber.The SEM and FT-IR results show that the functional fiber is successfully prepared,and the obtained polypyrrole(PPy)presents nanorods morphology on the fiber surface.The mechanical properties of the fibers were studied by Instron.The organic electrochemical transistors based on PPy/Nylon fiber,PPy/CHIT/Nylon fiber,and PPy/GA-CHIT/Nylon fiber as channels were prepared and their transistors performance was compared.It is found that PPy/GA-CHIT/Nylon fiber-based transistor has great output,transfer,transient curves,and excellent transconductance of 6.8 mS,providing a new platform for the field of wearable devices.Furthermore,the study introduces chitosan material with excellent biocompatibility,which makes prepared transistors also have potential applications in the field of biosensing.

Non-invasive Healthcare Analytical Platform Based on Organic Electrochemical Transistors

Non-invasive bioelectronics,especially organic electrochemical transistors(OECTs),have drawn extensive attentions of academical and medical communities by virtue of their efficient bio-electronic interfacing,water-involved ionic transport,excellent ionic-electronic coupling,ultralow power consumption,wide detectable range,and outstanding detection sensitivity.Designable structure diversity,low-temperature solution processability,facile bio/chemical functionalization,and excellent biocompatibility of organic mixed ionic-electronic conductors(OMIECs)render OECTs particularly suitable for non-invasive or minimally invasive healthcare analytical platform.Here,we comprehensively review recent advances of the non-invasive analytical healthcare applications based on OECTs,especially on the detection of biomarkers or metabolites in the excretory biofluids,as well as the recording of electrophysiological signals.A brief introduction of OECT and its comparison with other organic thin-film transistors upon device configuration and working mechanism are firstly discussed.State-of-the-art non-invasive OECT-based biosensors are summarized on their detection of ionic and molecular biomarkers,following with circuit design strategies of OECTs for real-time and in-situ electrophysiological recording from skin surface.In conclusion,remaining barriers and future challenges of non-invasive OECT-based bioelectronics towards lower detection limit,more accurate quantitative relationship between analyte concentrations and measured parameters,more intimate device-tissue interface,and long-term operation stability are deeply analyzed with a critical outlook.

Artificial synapses based on organic electrochemical transistors with self-healing dielectric layers

Organic electrochemical transistors(OECTs)have emerged as one type of promising building block for neuromorphic systems owing to their capability of mimicking the morphology and functions of biological neurons and synapses.Currently,numerous kinds of OECTs have been developed,while self-healing performance has been neglected in most reported OECTs.In this work,the OECTs using self-healing polymer electrolytes as dielectric layers are proposed.Several important synaptic behaviors are simulated in the OECTs by doping the channel layers with ions from the electrolytes.Benefitting from the dynamic hydrogen bonds in the self-healing polymer electrolytes,the OECTs can successfully maintain their electrical performance and the ability of emulating synaptic behaviors after self-healing compared with the initial state.More significantly,the sublinear spatial summation function is demonstrated in the OECTs and their potential in flexible electronics is also validated.These results suggest that our devices are expected to be a vital component in the development of future wearable and bioimplantable neuromorphic systems.

Stretchable organic electrochemical transistors via threedimensional porous elastic semiconducting films for artificial synaptic applications

Neuromorphic computing targets realizing biomimetic or intelligence systems capable of processing abundant tasks in parallel analogously to our brain,and organic electrochemical transistors(OECTs)that rely on the mixed ionic-electronic synergistic couple possess significant similarity to biological systems for implementing synaptic functions.However,the lack of reliable stretchability for synaptic OECTs,where mechanical deformation occurs,leads to consequent degradation of electrical performance.Herein,we demonstrate stretchable synaptic OECTs by adopting a three-dimensional poly(3-hexylthiophene)(P3HT)/styrene-ethylene-butylene-styrene(SEBS)blend porous elastic film for neuromorphic computing.Such architecture shows the full capability to emulate biological synaptic behaviors.Adjusting the accumulated layer numbers of porous film enables tunable OECT output and hysteresis,resulting in transition in plasticity.Especially,with a trilayer porous film,large-scale conductance and hysteresis are endorsed for efficient mimicking of memory-dependent synapse behavior.Benefitted from the interconnected three-dimensional porous structures,corresponding stretchable synaptic OECTs exhibit excellent mechanical robustness when stretched at a 30%strain,and maintain reliable electrical characteristics after 500 stretching cycles.Furthermore,near-ideal weight updates with near-zero nonlinearities,symmetricity in long-term potentiation(LTP)and depression,and applications for image simulation are validated.This work paves a universal design strategy toward highperformance stretchable neuromorphic computing architecture and could be extended to other flexible/stretchable electronics.

Layer by Layer Self-assembly Fiber-based Flexible Electrochemical Transistor

Poly(3,4-ethylenedioxyethiophene)-polystyrene sulfonic acid(PEDOT:PSS)/polyallyl dimethyl ammonium chloride modified reduced graphene oxide(PDDA-rGO)was layer by layer self-assembled on the cotton fiber.The surface morphology and electric property was investigated.The results confirmed the dense membrane of PEDOT:PSS and the lamellar structure of PDDA-rGO on the fibers.It has excellent electrical conductivity and mechanical properties.The fiber based electrochemical transistor(FECTs)prepared by the composite conductive fiber has a maximum output current of 8.7 mA,a transconductance peak of 10 mS,an on time of 1.37 s,an off time of 1.6 s and excellent switching stability.Most importantly,the devices by layer by layer self-assembly technology opens a path for the true integration of organic electronics with traditional textile technologies and materials,laying the foundation for their later widespread application.

Coaxial fiber organic electrochemical transistor with high transconductance

Fiber organic electrochemical transistors(OECTs)have received extensive attention in wearable and implantable biosensors because of their high flexibility and low working voltage.However,the transconductance of fiber OECTs is much lower compared with the planar counterparts,leading to low sensitivity.Here,we developed fiber OECTs in a coaxial configuration with microscale channel length to achieve the highest transconductance of 135 mS,which is one to two orders of magnitude higher than that of the state-of-the-art fiber OECTs.Coaxial fiber OECT based sensors showed high sensitivities of 12.78,20.53 and 3.78 mA/decade to ascorbic acid,hydrogen peroxide and glucose,respectively.These fiber OECTs were woven into a fabric to monitor the glucose in sweat during exercise and implanted in mouse brain to detect ascorbic acid.This coaxial architectural design offers an effective way to promote the performance of fiber OECTs and realize highly sensitive detection of biochemicals.

Plasmonic organic electrochemical transistors for enhanced sensing

Organic electrochemical transistors(OECTs)have been hailed as highly sensitive biomolecular sensors among organic electronic devices due to their superior stability in an aqueous environment and high transconductance.At the same time,plasmon based sensors are known to provide high sensitivity for biosensing due to the highly localized plasmonic field.Here we report a plasmonic OECT(POET)device that synchronizes the advantages of OECTs and plasmonic sensors on a single platform.The platform is fabricated by a simple,cost-effective,and high-throughput nanoimprinting process,which allows plasmonic resonance peak tuning to a given visible wavelength of interest for versatile biosensing.With glucose sensing as proof,a five-times sensitivity enhancement is obtained for POET compared to a regular(non-plasmonic)OECT.Thus,the POET paves the way to a new paradigm of optoelectronic sensors that combines the inherent high sensitivity of OECTs and localized plasmonic field to sense a vast realm of biomolecules.

High-performance organic electrochemical transistors gated with 3D-printed graphene oxide electrodes

Organic electrochemical transistors(OECTs)have garnered significant interest due to their ability to facilitate both ionic and electronic transport.A large proportion of research efforts thus far have focused on investigating high-performance materials that can serve as mixed ion doping and charge transport layers.However,relatively less attention has been given to the gateelectrode materials,which play a critical role in controlling operational voltage,redox processes,and stability,especially in the context of semiconductor-based OECTs working in accumulation mode.Moreover,the demand for planarity and flexibility in modern bioelectronic devices presents significant challenges for the commonly used Ag/AgCl electrodes in OECTs.Herein,we report the construction of high-performance accumulation-mode OECTs by utilizing a gate electrode made of three-dimensional(3D)-printed graphene oxide.The 3D-printed graphene oxide electrode incorporating one-dimensional(1D)carbon nanotubes,is directly printed using an aqueous-based ink and showcases exceptional mechanical flexibility and porosity properties,enabling high-throughput preparation for both top gates and integrated planar architecture,as well as fast ion/charge transport.OECTs with high performance comparable to that of Ag/AgCl-gated OECTs are thus achieved and present promising feasibility for electrocardiograph(ECG)signal recording.This provides a promising choice for the application of flexible bioelectronics in medical care and neurological recording.

Fiber-shaped organic electrochemical transistors for biochemical detections with high sensitivity and stability

Precise and continuous monitoring of biochemicals by biosensors assists to understand physiological functions for various diagnostics and therapeutic applications.For implanted biosensors,small size and flexibility are essential for minimizing tissue damage and achieving accurate detection.However,the active surface area of sensor decreases as the sensor becomes smaller,which will increase the impedance and decrease the signal to noise ratio,resulting in a poor detection limit.Taking advantages of local amplification effect,organic electrochemical transistors(OECTs)constitute promising candidates for high-sensitive monitoring.However,their detections in deep tissues are rarely reported.Herein,we report a family of implantable,fiber-shaped all-in-one OECTs based on carbon nanotube fibers for versatile biochemical detection including H2O2,glucose,dopamine and glutamate.These fiber-shaped OECTs demonstrated high sensitivity,dynamical stability in physiological environment and antiinterference capability.After implantation in mouse brain,7-day dopamine monitoring in vivo was realized for the first time.These fiber-shaped OECTs could be great additions to the"life science"tool box and represent promising avenue for biomedical monitoring.

Flexible organic electrochemical transistors for chemical and biological sensing

Chemical and biological sensing play important roles in healthcare,environmental science,food-safety tests,and medical applications.Flexible organic electrochemical transistors(OECTs)have shown great promise in the field of chemical and biological sensing,owing to their superior sensitivity,high biocompatibility,low cost,and light weight.Herein,we summarize recent progress in the fabrication of flexible OECTs and their applications in chemical and biological sensing.We start with a brief introduction to the working principle,configuration,and sensing mechanism of the flexible OECT-based sensors.Then,we focus on the fabrication of flexible OECT-based sensors,including material selection and structural engineering of the components in OECTs:the substrate,electrodes,electrolyte,and channel.Particularly,the gate modification is discussed extensively.Then,the applications of OECT-based sensors in chemical and biological sensing are reviewed in detail.Especially,the array-based and integrated OECT sensors are also introduced.Finally,we present the conclusions and remaining challenges in the field of flexible OECT-based sensing.Our timely review will deepen the understanding of the flexible OECT-based sensors and promote the further development of the fast-growing field of flexible sensing.

High-Transconductance,Highly Elastic,Durable and Recyclable All-Polymer Electrochemical Transistors with 3D Micro-Engineered Interfaces

Organic electrochemical transistors(OECTs)have emerged as versatile platforms for broad applications spanning from flexible and wearable integrated circuits to biomedical monitoring to neuromorphic computing.A variety of materials and tailored micro/nanostructures have recently been developed to realized stretchable OECTs,however,a solid-state OECT with high elasticity has not been demonstrated to date.Herein,we present a general platform developed for the facile generation of highly elastic all-polymer OECTs with high transconductance(up to 12.7 mS),long-term mechanical and environmental durability,and sustainability.Rapid prototyping of these devices was achieved simply by transfer printing lithium bis(trifluoromethane)sulfonimide doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS/LiTFSI)microstructures onto a resilient gelatin-based gel electrolyte,in which both depletion-mode and enhancement-mode OECTs were produced using various active channels.Remarkably,the elaborate 3D architectures of the PEDOT:PSS were engineered,and an imprinted 3D-microstructured channel/electrolyte interface combined with wrinkled electrodes provided performance that was retained(>70%)through biaxial stretching of 100%strain and after 1000 repeated cycles of 80%strain.Furthermore,the anti-drying and degradable gelatin and the self-crosslinked PEDOT:PSS/LiTFSI jointly enabled stability during>4 months of storage and on-demand disposal and recycling.This work thus represents a straightforward approach towards high-performance stretchable organic electronics for wearable/implantable/neuromorphic/sustainable applications.

High-gain signal-on PEDOT:PSS organic photoelectrochemical transistor biosensing modulated by a MXene/MOFs/NiO Schottky heterojunction

Herein we report a high-gain signal-on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)organic electrochemical transistor(OECT)biosensing using an accumulation-mode PEDOT:PSS OECT modulated by a light-fueled MXene/MOFs/Ni O Schottky heterojunction.In such a system,the MXene/MOFs/Ni O Schottky heterojunction exhibited superior gating effect,as it not only enabled the fast-directional charge transfer but also guaranteed the maximal accessibility of the electrolyte to topped 2D MXene with large surface area.In linkage with a bi-enzyme cascade system,the quinone derivatives produced by the cascade reaction of alkaline phosphatase(ALP)and tyrosinase(TYR)could serve as effective electron acceptors for the representative Ti_(3)C_(2)/PCN-224/Ni O heterojunction,underpinning an innovative method for sensitive detection of ALP activity with a low detection limit of 0.001 U L^(-1).Remarkably,the as-developed system demonstrated a remarkable current gain as high as near 10^(4),which to our knowledge is the highest one among existing OECT biosensory devices.This work represents a generic protocol to develop the novel signal-on PEDOT:PSS OECT platform towards biochemical detection and beyond.

Stretchable,skin-conformable neuromorphic system for tactile sensory recognizing and encoding

Expanding wearable technologies to artificial tactile perception will be of significance for intelligent human-machine interface,as neuromorphic sensing devices are promising candidates due to their low energy consumption and highly effective operating properties.Skin-compatible and conformable features are required for the purpose of realizing wearable artificial tactile perception.Here,we report an intrinsically stretchable,skin-integrated neuromorphic system with triboelectric nanogenerators as tactile sensing and organic electrochemical transistors as information processing.The integrated system provides desired sensing,synaptic,and mechanical characteristics,such as sensitive response(~0.04 kPa^(-1))to low-pressure,short-and long-term synaptic plasticity,great switching endurance(>10000 pulses),symmetric weight update,together with high stretchability of 100%strain.With neural encoding,demonstrations are capable of recognizing,extracting,and encoding features of tactile information.This work provides a feasible approach to wearable,skin-conformable neuromorphic sensing system with great application prospects in intelligent robotics and replacement prosthetics.