Recent Progress of Fiber Shaped Lighting Devices for Smart Display Applications-A Fibertronic Perspective

Low Driving Voltage Electroluminescence Device for Integrated Visual Strain Sensing

As a pivotal component in human-machine interactions, display devices have undergone rapid development in modern life. Displays such as alternative current electroluminescence|alternative current electroluminescent (ACEL) devices with high flexibility and long operational lifetimes are essential for wearable electronics. However, ACEL devices are constrained by their inherent high driving voltage and complex fabrication processes. Our work presents an easy blade-coating method for fabricating flexible ACEL display devices based on an all-solution process. By dispersing BaTiO3 and ZnS/Cu powder into waterborne polyurethane, we successfully combined dielectric and fluorescence functionalities within a single layer, significantly reducing the device's driving voltage. Additionally, the ionic conducting hydrogel was chosen as a transparent electrode to achieve good electrical contact and strong interfacial adhesion through in situ polymerization. Owing to the unique method, our ACEL device exhibits high flexibility, low driving voltage (20-100 V), high brightness (300+ cd/m2 at 60 V), and environmental friendliness. Furthermore, by repurposing the hydrogel electrode, we integrated strain visualization capabilities within a single device, highlighting its potential for applications such as wearable healthcare monitoring.

Structural design of light-emitting fibers and fabrics for wearable and smart devices

Flexible light-emitting fibers and fabrics serve to bridge human-machine interactions. The desire for practical applications and the commercialization of flexible light-emitting fibers has accelerated structural progress and improvements. This review focuses on the structural design of light-emitting fibers and fabrics, starting with a summary of design principles, emission mechanisms, and structural evolution of coaxial structured light-emitting fibers. Subsequently, we explore recent advances in the helical structure design strategies that boost the mechanical sensitivity of light-emitting fibers. Following that, we analyze continuous preparation processes and the development of large-area intelligent light-emitting fabrics based on interwoven structures. Examples based on stiff and rigid inorganic-based light-emitting diodes integrated into flexible systems are also presented. Finally, we discuss the current challenges and future opportunities for light-emitting applications in the field of wearable and smart devices.

Porous Conductive Textiles for Wearable Electronics

Over the years, researchers have made significant strides in the development of novel flexible/stretchable and conductive materials, enabling the creation of cutting-edge electronic devices for wearable applications. Among these, porous conductive textiles (PCTs) have emerged as an ideal material platform for wearable electronics, owing to their light weight, flexibility, permeability, and wearing comfort. This Review aims to present a comprehensive overview of the progress and state of the art of utilizing PCTs for the design and fabrication of a wide variety of wearable electronic devices and their integrated wearable systems. To begin with, we elucidate how PCTs revolutionize the form factors of wearable electronics. We then discuss the preparation strategies of PCTs, in terms of the raw materials, fabrication processes, and key properties. Afterward, we provide detailed illustrations of how PCTs are used as basic building blocks to design and fabricate a wide variety of intrinsically flexible or stretchable devices, including sensors, actuators, therapeutic devices, energy-harvesting and storage devices, and displays. We further describe the techniques and strategies for wearable electronic systems either by hybridizing conventional off-the-shelf rigid electronic components with PCTs or by integrating multiple fibrous devices made of PCTs. Subsequently, we highlight some important wearable application scenarios in healthcare, sports and training, converging technologies, and professional specialists. At the end of the Review, we discuss the challenges and perspectives on future research directions and give overall conclusions. As the demand for more personalized and interconnected devices continues to grow, PCT-based wearables hold immense potential to redefine the landscape of wearable technology and reshape the way we live, work, and play.

Machine embroidery of light-emitting textiles with multicolor electroluminescent threads

Advances in electroluminescent threads, suitable for weaving or knitting, have opened doors for the development of light-emitting textiles, driving growth in the market for flexible and wearable displays. Although direct embroidery of these textiles with custom designs and patterns could offer substantial benefits, the rigorous demands of machine embroidery challenge the integrity of these threads. Here, we present embroiderable multicolor electroluminescent threads-in blue, green, and yellow-that are compatible with standard embroidery machines. These threads can be used to stitch decorative designs onto various consumer fabrics without compromising their wear resistance or light-emitting capabilities. Demonstrations include illuminating specific messages or designs on consumer products and delivering emergency alerts on helmet liners for physical hazards. Our research delivers a comprehensive toolkit for integrating light-emitting textiles into trendy, customized crafts tailored to the unique requirements of diverse flexible and wearable displays.

Wearable and Wavelength-Tunable Near-Infrared Organic Light-Emitting Diodes for Biomedical Applications

Near-infrared organic light-emitting diodes (NIR OLEDs) have significant potential for wearable phototherapeutic applications because of the unique properties of the OLEDs, including their free-form electronics and the excellent biomedical effects of NIR emission. In spite of their tremendous promise, given that the majority of NIR OLEDs in previous research have relied on the utilization of an intrinsically brittle indium tin oxide (ITO) electrode, their practicality in the field of wearable electronics is inherently constrained. Here, we report wearable and wavelength-tunable NIR OLEDs that employ a high-performance NIR emitter and an innovative architecture by replacing the ITO with a silver (Ag) electrode. The NIR OLEDs permit wavelength tuning of emissions from 700 to 800 nm and afford stable operation even under repeated bending conditions. The NIR OLEDs provide a lowered device temperature of 37.5 °C even during continuous operation under several emission intensities. In vitro experiments were performed with freshly fabricated NIR OLEDs. The outcomes were evaluated against experimental results performed using the same procedure utilizing blue, green, and red OLEDs. When exposed to NIR light irradiation, the promoting effect of cell proliferation surpassed the proliferative responses observed under the influence of visible light irradiation. The proliferation effect of human hair follicle dermal papilla cells is clearly related to the irradiation wavelength and time, thus underscoring the potential of wavelength-tunable NIR OLEDs for efficacious phototherapy. This work will open novel avenues for wearable NIR OLEDs in the field of biomedical application.

Fiber Crossbars: An Emerging Architecture of Smart Electronic Textiles

Smart wearables have a significant impact on people's daily lives, enabling personalized motion monitoring, realizing the Internet of Things, and even reshaping the next generation of telemedicine systems. Fiber crossbars (FCs), constructed by crossing two fibers, have become an emerging architecture among the accessible structures of state-of-the-art smart electronic textiles. The mechanical, chemical, and electrical interactions between crossing fibers result in extensive functionalities, leading to the significant development of innovative electronic textiles employing FCs as their basic units. This review provides a timely and comprehensive overview of the structure designs, material selections, and assembly techniques of FC-based devices. The recent advances in FC-based devices are summarized, including multipurpose sensing, multiple-mode computing, high-resolution display, high-efficient power supply, and large-scale textile systems. Finally, current challenges, potential solutions, and future perspectives for FC-based systems are discussed for their further development in scale-up production and commercial applications.

Room-temperature phosphorescent materials derived from natural resources

Room-temperature phosphorescent (RTP) materials have enormous potential in many different areas. Additionally, the conversion of natural resources to RTP materials has attracted considerable attention. Owing to their inherent luminescent properties, natural materials can be efficiently converted into sustainable RTP materials. However, to date, only a few reviews have focused on this area of endeavour. Motivated by this lack of coverage, in this Review, we address this shortcoming and introduce the types of natural resource available for the preparation of RTP materials. We mainly focus on the inherent advantages of natural resources for RTP materials, strategies for activating and enhancing the RTP properties of the natural resources as well as the potential applications of these RTP materials. In addition, we discuss future challenges and opportunities in this area of research.

A Review of Structure Engineering of Strain-Tolerant Architectures for Stretchable Electronics

Stretchable electronics possess significant advantages over their conventional rigid counterparts and boost game-changing applications such as bioelectronics, flexible displays, wearable health monitors, etc. It is, nevertheless, a formidable task to impart stretchability to brittle electronic materials such as silicon. This review provides a concise but critical discussion of the prevailing structural engineering strategies for achieving strain-tolerant electronic devices. Not only the more commonly discussed lateral designs of structures such as island-bridge, wavy structures, fractals, and kirigami, but also the less discussed vertical architectures such as strain isolation and elastoplastic principle are reviewed. Future opportunities are envisaged at the end of the paper.

LEGO-like Assembly of Fibrous Modules for Display Textiles

Due to their promising advantages over classical rigid devices, the development of display textiles has exciting potential for various fields, including sensor technology, healthcare, and communication. To realize display textiles, it is necessary to prepare light-emitting building blocks at the fiber level and then weave or knit them to form the desired textile structures. However, from a practical viewpoint, it is difficult to continuously weave functional fibers containing light-emitting devices using conventional textile technologies. To address this issue, we introduced fibrous modules that can be assembled like LEGO blocks to realize textile displays. A unique feature of this work is that the light-emitting pixels are generated through a simple contact between modular electrochemiluminescent (ECL) fibers. Each fiber is composed of a single metallic wire coated with a gel-type ECL electrolyte that is formed by using a simple dip-coating method in ambient air. The sticky nature of the gel electrolyte enables the construction of light-emitting pixels through the simple physical contact of two or more fiber modules without the need for external pressure or heating. The diversity of this technology offers in terms of fibrous module arrangements and assembly can provide various options for designing the geometries of light-emitting pixels. We have implemented this technique to demonstrate not only a 1 × 1 pixel but also 3 × 3 pixels with an irregular shape. These results demonstrate that the unique strategy for display devices developed in this work provides a feasible approach for various electronic and optical textile applications.

Stretchable and Self-Healable Fiber-Shaped Conductors Suitable for Harsh Environments

Fiber-shaped conductors with high electrical conductivity, stretchability, and durability have attracted increasing attention due to their potential for integration into arbitrary wearable forms. However, these fiber conductors still suffer from low reliability and short life span, particularly in harsh environments. Herein, a conductive, environment-tolerant, stretchable, and healable fiber conductor (CESH), which consists of a self-healable and stretchable organohydrogel fiber core, a conductive and buckled silver nanowire coating, and a self-healable and waterproof protective sheath, is reported. Such a multilayer core-sheath design not only offers high stretchability (≈2400%), high electrical conductivity (1.0 × 106 S m-1 ), outstanding self-healing ability and durability, but also possesses unprecedented tolerance in harsh environments including wide working temperature (-60-20 °C), arid (≈10 % RH (RH: room humidity)), and underwater conditions. As proof-of-concept demonstrations, CESHs are integrated into various wearable formats as interconnectors to steadily perform the electric function under different mechanical deformations and harsh conditions. Such a new type of multifunctional fiber conductors can bridge the gap in stretchable and self-healing fiber technologies by providing ultrastable electrical conductance and excellent environmental tolerance, which can greatly expand the range of applications for fiber conductors.

Optimizing the luminescence efficiency of an europium (Eu3+) doped SrY2O4 phosphor for flexible display and lighting applications

This research paper reports the synthesis and luminescence study of an Eu³⁺ activated SrY₂O₄ phosphor prepared by a modified solid-state reaction method with varying concentrations of Eu³⁺ ions (0.1-2.5 mol%). X-ray diffraction (XRD) revealed the orthorhombic structure and Fourier transform infrared spectroscopy (FTIR) methods were used to analyse the produced phosphors. Photoluminescence emission and excitation spectra were recorded for varying concentrations of Eu³⁺ ions, and an optimum concentration of 2.0 mol% was found to produce the highest intensity. Under 254 nm excitation the emission peaks were found to be at 580 nm, 590 nm, 611 nm and 619 nm, corresponding to transitions at ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, and ⁵D₀ → ⁷F₂ respectively. Because of Eu³⁺ inherent luminosity, these emission peaks indicate radiative transitions between excited states of ions, making them useful for developing white light-emitting phosphors for optoelectronic and flexible display applications. The 1931 CIE (x, y) chromaticity coordinates were calculated from the photoluminescence emission spectra and found to be near white light emission, indicating the potential application of the prepared phosphor for light emitting diodes (white component). TL glow curve analysis was also performed for various concentrations of doping ions and UV exposure times, and a single broad peak was observed at 187 °C. Using the computerised glow curve deconvolution (CGCD) method, kinetic parameters were computed.

Highly Air-Stable, Flexible, and Water-Resistive 2D Titanium Carbide MXene-Based RGB Organic Light-Emitting Diode Displays for Transparent Free-Form Electronics

Flexible see-through displays are considered to be the next generation smart display, providing improved information flow, safety, situational awareness, and overall user experience in smart windows, automotive displays, glass-form biomedical displays, and augmented reality systems. 2D titanium carbides (MXenes) are promising material as electrodes of the transparent and flexible displays due to their high transparency, metallic conductivity, and flexibility. However, current MXene-based devices have insufficient air stability and lack engineering schemes to develop matrix-addressable display forms with sufficient pixels to display information. Here, we develop an ultraflexible and environmentally stable MXene-based organic light-emitting diode (OLED) display by combining high performance MXene electrodes, flexible OLEDs, and ultrathin and functional encapsulation systems. The MXene material was synthesized and used to fabricate a highly reliable MXene-based OLED that can stably operate in air condition for over 2000 h, endure repetitive bending deformation of 1.5 mm radius, and maintain environmental stability for 6 h when exposed to wet surroundings. The RGB MXene-based OLEDs were fabricated, (1691 cd m^-2 at 40.4 mA cm^-2 for red, 1377 cd m^-2 at 4.26 mA cm^-2 for green, and 1475 cd m^-2 at 18.6 mA cm^-2 for blue) and a matrix-addressable transparent OLED display was demonstrated that could display letters and shapes.

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

Emerging Electrochromic Materials and Devices for Future Displays

With the rapid development of optoelectronic fields, electrochromic (EC) materials and devices have received remarkable attention and have shown attractive potential for use in emerging wearable and portable electronics, electronic papers/billboards, see-through displays, and other new-generation displays, due to the advantages of low power consumption, easy viewing, flexibility, stretchability, etc. Despite continuous progress in related fields, determining how to make electrochromics truly meet the requirements of mature displays (e.g., ideal overall performance) has been a long-term problem. Therefore, the commercialization of relevant high-quality products is still in its infancy. In this review, we will focus on the progress in emerging EC materials and devices for potential displays, including two mainstream EC display prototypes (segmented displays and pixel displays) and their commercial applications. Among these topics, the related materials/devices, EC performance, construction approaches, and processing techniques are comprehensively disscussed and reviewed. We also outline the current barriers with possible solutions and discuss the future of this field.

Structures and Materials in Stretchable Electroluminescent Devices

Stretchable electroluminescent (EL) devices are obtained by partitioning a large emission area into areas specifically for stretching and light-emission (island-bridge structure). Buckled and textile structures are also shown effective to combine the conventional light emitting diode fabrication with elastic substrates for structure-enabled stretchable EL devices. Meanwhile, intrinsically stretchable EL devices which are characterized with uniform stretchability down to microscopic scale are relatively less developed but promise simpler device structure and higher impact resistance. The challenges in fabricating intrinsically stretchable EL devices with high and robust performance are in many facets, including stretchable conductors, emissive materials, and compatible processes. For the stretchable transparent electrode, ionically conductive gel, conductive polymer coating, and conductor network in surface of elastomer are all proven useful. The stretchable EL materials are currently limited to conjugated polymers, conjugated polymers with surfactants and ionic conductors added to boost stretchability, and phosphor particles embedded in elastomer matrices. These emissive materials operate under different mechanisms, require different electrode materials and fabrication processes, and the corresponding EL devices face distinctive challenges. This review aims to provide a basic understanding of the materials meeting both the mechanical and electronic requirements and important techniques to fabricate the stretchable EL devices.

Advances in High-Performance Autonomous Energy and Self-Powered Sensing Textiles with Novel 3D Fabric Structures

The seamless integration of emerging triboelectric nanogenerator (TENG) technology with traditional wearable textile materials has given birth to the next-generation smart textiles, i.e., textile TENGs, which will play a vital role in the era of Internet of Things and artificial intelligences. However, low output power and inferior sensing ability have largely limited the development of textile TENGs. Among various approaches to improve the output and sensing performance, such as material modification, structural design, and environmental management, a 3D fabric structural scheme is a facile, efficient, controllable, and scalable strategy to increase the effective contact area for contact electrification of textile TENGs without cumbersome material processing and service area restrictions. Herein, the recent advances of the current reported textile TENGs with 3D fabric structures are comprehensively summarized and systematically analyzed in order to clarify their superiorities over 1D fiber and 2D fabric structures in terms of power output and pressure sensing. The forward-looking integration abilities of the 3D fabrics are also discussed at the end. It is believed that the overview and analysis of textile TENGs with distinctive 3D fabric structures will contribute to the development and realization of high-power output micro/nanowearable power sources and high-quality self-powered wearable sensors.

Water Washable and Flexible Light-Emitting Fibers Based on Electrochemiluminescent Gels

Herein, a new concept of device architecture to fabricate fibrous light-emitting devices is demonstrated based on an electrochemiluminescence (ECL) material for an electronic textile system. A unique feature of this work is that instead of conventional semiconductor materials, such as organics, perovskites, and quantum dots for fibrous light emitting devices, a solid-state ECL electrolyte gel is employed as a light-emitting layer. The solid-state ECL gel is prepared from a precursor solution composed of matrix polymer, ionic liquid, and ECL luminophore. From this, we successfully realize light-emitting fibers through a simple and cost-effective single-step dip-coating method in ambient air, without complicated multistep vacuum processes. The resulting fiber devices reliably operated under applied AC bias of ±2.5 V and showed luminance of 47 cd m^-2. More importantly, the light-emitting fibers exhibited outstanding water resistance without any passivation layers, owing to the water immiscible and hydrophobic nature of the ECL gel. In addition, because of their simple structure, the fiber devices can be easily deformed and woven together with commercial knitwear by hand. Therefore, these results suggest a promising strategy for the development of practical fiber displays and contribute to progress in electronic textile technology.

Electro-Thermochromic Luminescent Fibers Controlled by Self-Crystallinity Phase Change for Advanced Smart Textiles

Smart textiles with tunable luminescence have received special attention due to their great potential in various advanced photonic applications. Particularly, the development of one-dimensional, on-demand, responsive fluorescence fibers with excellent adaptability is of great significance. Herein, we propose electro-thermochromic fluorescence fibers regulated by a self-crystallinity phase change; that is, their tunable luminescence properties are derived from the reversible conversion of the dispersion state and fluorescence emission of fluorophore molecules during the crystallization/melting processes of phase-change materials. First results obtained with an alginate wet-spinning system demonstrate that the self-crystallinity phase change can produce polymeric fibers with thermochromic fluorescence behavior, which are prepared using microemulsion particles containing a phase-change fatty acid and coumarin fluorescent dyes. These thermochromic fluorescence fibers possess a fast response speed, high emission contrast, and good reversibility (>100 cycles). Particularly, the thermochromic fluorescent fibers can gain an electrotriggered capability by means of electric heating materials, and their great potential in precision operation applications is demonstrated. It is easy to adjust the switching point of the electro-thermochromic fluorescence fibers, highlighting their potential use in a diverse range of applications, the designs of which can be personalized. This work offers a simple yet versatile strategy for constructing electro-thermochromic fluorescence fibers for advanced smart textiles.

Mechanoluminescence Rebrightening the Prospects of Stress Sensing: A Review

The emergence of new applications, such as in artificial intelligence, the internet of things, and biotechnology, has driven the evolution of stress sensing technology. For these emerging applications, stretchability, remoteness, stress distribution, a multimodal nature, and biocompatibility are important performance characteristics of stress sensors. Mechanoluminescence (ML)-based stress sensing has attracted widespread attention because of its characteristics of remoteness and having a distributed response to mechanical stimuli as well as its great potential for stretchability, biocompatibility, and self-powering. In the past few decades, great progress has been made in the discovery of ML materials, analysis of mechanisms, design of devices, and exploration of applications. One can find that with this progress, the focus of ML research has shifted from the phenomenon in the earliest stage to materials and recently toward devices. At the present stage, while showing great prospects for advanced stress sensing applications, ML-based sensing still faces major challenges in material optimization, device design, and system integration.

An O-Carborane Derivative of Perylene Bisimide-Based Thin Film Displaying both Electrochromic and Electrofluorochromic Properties

The widespread application in displays, information encryption, and sensors has boosted studies of electrochromic (EC) systems combining large contrast, fast response, high robustness, and low-cost properties. Herein, we report a film-type new EC system with a non-planar perylene bisimide-carborane derivative (PBI-CB) as the electroactive materials. It was revealed that the film demonstrated outstanding EC properties with response times of 1.18 and 0.94 s for the coloration and bleaching processes, respectively, large transmittance variation around 630 nm (45.7%), and superior stability for more than 200 coloration-bleaching cycles. Moreover, the film also showed precious electrofluorochromic (EFC) properties. The emission around 650 nm at the "on" state could be more than 24.5 times than that at the "off" state, and the response times of the off and on processes could reach 2.2 s and 4.3 s, respectively. Considering the facts that the film was fabricated via simple drop-coating, the EC/EFC operation was performed via a routine three-electrode system and the voltage applied is only -1.3 V, we believe that the EC/EFC system as developed would find applications in smart windows, information encryption, optoelectrical sensing, etc. In addition, the work could also pave the way for developing combined EC/EFC systems via employing known organic fluorophores as the electrochemical active materials, which are not only abundant in numbers but also solution-processable.

Fiber‐Shaped Electronic Devices

Textile electronics embedded in clothing represent an exciting new frontier for modern healthcare and communication systems. Fundamental to the development of these textile electronics is the development of the fibers forming the cloths into electronic devices. An electronic fiber must undergo diverse scrutiny for its selection for a multifunctional textile, viz., from the material selection to the device architecture, from the wearability to mechanical stresses, and from the environmental compatibility to the end‐use management. Herein, the performance requirements of fiber‐shaped electronics are reviewed considering the characteristics of single electronic fibers and their assemblies in smart clothing. Broadly, this article includes i) processing strategies of electronic fibers with required properties from precursor to material, ii) the state‐of‐art of current fiber‐shaped electronics emphasizing light‐emitting devices, solar cells, sensors, nanogenerators, supercapacitors storage, and chromatic devices, iii) mechanisms involved in the operation of the above devices, iv) limitations of the current materials and device manufacturing techniques to achieve the target performance, and v) the knowledge gap that must be minimized prior to their deployment. Lessons learned from this review with regard to the challenges and prospects for developing fiber‐shaped electronic components are presented as directions for future research on wearable electronics.

Dendritic Network Implementable Organic Neurofiber Transistors with Enhanced Memory Cyclic Endurance for Spatiotemporal Iterative Learning

Dendritic network implementable organic neurofiber transistors with enhanced memory cyclic endurance for spatiotemporal iterative learning are proposed. The architecture of the fibrous organic electrochemical transistors consisting of a double-stranded assembly of electrode microfibers and an iongel gate insulator enables the highly sensitive multiple implementation of synaptic junctions via simple physical contact of gate-electrode microfibers, similar to the dendritic connections of a biological neuron fiber. In particular, carboxylic-acid-functionalized polythiophene as a semiconductor channel material provides stable gate-field-dependent multilevel memory characteristics with long-term stability and cyclic endurance, unlike the conventional poly(alkylthiophene)-based neuromorphic electrochemical transistors, which exhibit short retention and unstable endurance. The dissociation of the carboxylic acid of the polythiophene enables reversible doping and dedoping of the polythiophene channel by effectively stabilizing the ions that penetrate the channel during potentiation and depression cycles, leading to the reliable cyclic endurance of the device. The synaptic weight of the neurofiber transistors with a dendritic network maintains the state levels stably and is independently updated with each synapse connected with the presynaptic neuron to a specific state level. Finally, the neurofiber transistor demonstrates successful speech recognition based on iterative spiking neural network learning in the time domain, showing a substantial recognition accuracy of 88.9%.

Electronic fibers and textiles: Recent progress and perspective

Wearable electronics are receiving increasing attention with the advances of human society and technologies. Among various types of wearable electronics, electronic fibers/textiles, which integrate the comfort and appearance of conventional fibers/textiles with the functions of electronic devices, are expected to play important roles in remote health monitoring, disease diagnosis/treatment, and human-machine interface. This article aims to review the recent advances in electronic fibers/textiles, thus providing a comprehensive guiding reference for future work. First, we review the selection of functional materials and fabrication strategies of fiber-shaped electronic devices with emphasis on the newly developed functional materials and technologies. Their applications in sensing, light emitting, energy harvest, and energy storage are discussed. Then, the fabrication strategies and applications of electronic textiles are summarized. Furthermore, the integration of multifunctional electronic textiles and their applications are summarized. Finally, we discuss the existing challenges and propose the future development of electronic fibers/textiles.

Scalable fluid-spinning nanowire-based inorganic semiconductor yarns for electrochromic actuators

Semiconductor yarns with unique functional characteristics have great potential applications in next-generation electronic devices. However, scalable inorganic semiconductor yarns with excellent mechanical and electrical properties, and environmental stability have not been discovered. In this study, we explored a unique fluid-spinning strategy to obtain a series of scalable inorganic semiconductor yarns including neat and hybrid semiconductor yarns. Different from the conventional yarn spinning strategy through a mechanical motor, we utilized the fluid force from the triple-phase interface to assemble and twist inorganic nanofiber building blocks simultaneously, and eventually obtained highly oriented inorganic nanowire-based semiconductor yarns. The obtained semiconductor yarns showed an excellent flexibility (curvature exceeding 2 cm^-1) and mechanical strength (tensile strength of 443 MPa) because of their highly oriented hierarchical nanostructures, which make them coiling able with highly twisted insertion. Additionally, coiled yarns were obtained by combining the host core material and functional guest sheath in a fluid-spinning process, which are flexible in deep cryogenic temperature owing to the pure inorganic building blocks (26.28% tensile strain in liquid nitrogen). In particular, inorganic yarn-based electrochromic actuators can obtain as high as 15.3% tensile stroke and 0.82 J g^-1 work capacity by electrochemical charge injection-associated multicolor switching.

Functional Fibers and Fabrics for Soft Robotics, Wearables, and Human-Robot Interface

Soft robotics inspired by the movement of living organisms, with excellent adaptability and accuracy for accomplishing tasks, are highly desirable for efficient operations and safe interactions with human. With the emerging wearable electronics, higher tactility and skin affinity are pursued for safe and user-friendly human-robot interactions. Fabrics interlocked by fibers perform traditional static functions such as warming, protection, and fashion. Recently, dynamic fibers and fabrics are favorable to deliver active stimulus responses such as sensing and actuating abilities for soft-robots and wearables. First, the responsive mechanisms of fiber/fabric actuators and their performances under various external stimuli are reviewed. Fiber/yarn-based artificial muscles for soft-robots manipulation and assistance in human motion are discussed, as well as smart clothes for improving human perception. Second, the geometric designs, fabrications, mechanisms, and functions of fibers/fabrics for sensing and energy harvesting from the human body and environments are summarized. Effective integration between the electronic components with garments, human skin, and living organisms is illustrated, presenting multifunctional platforms with self-powered potential for human-robot interactions and biomedicine. Lastly, the relationships between robotic/wearable fibers/fabrics and the external stimuli, together with the challenges and possible routes for revolutionizing the robotic fibers/fabrics and wearables in this new era are proposed.

Spirally Wrapped Carbon Nanotube Microelectrodes for Fiber Optoelectronic Devices beyond Geometrical Limitations toward Smart Wearable E-Textile Applications

Fiber optoelectronics technology has recently attracted attention as enabling various form factors of wearable electronics, and the issue of how to control and optimize the configuration and physical properties of the electrode micropatterns in the microfiber devices has become important. Here, spirally wrapped carbon nanotube (CNT) microelectrodes with a controlled dimension are demonstrated for high-performance fiber optoelectronic devices. Inkjet-printed CNT microelectrodes with the desired dimension on an agarose hydrogel template are rolling-transferred onto a microfiber surface with an efficient electrical interface. A fiber organic field-effect transistor with spirally wrapped CNT microelectrodes verifies the feasibility of this strategy, where the transferred microelectrodes intimately contact the organic semiconductor active layer and the output current characteristics are simply controlled, resulting in characteristics that exceed the previous structural limitations. Furthermore, a fiber organic photodiode with spirally wrapped CNT microelectrodes, when used as a transparent electrode, exhibits a high I_light/I_dark ratio and good durability of bending. This fiber photodiode can be successfully incorporated into a textile photoplethysmography bandage for the real-time monitoring of human vital signals. This work offers a promising and efficient strategy to overcome the geometric factors limiting the performance of fiber-optic optoelectronic devices.

Noncovalent π-stacked robust topological organic framework

Organic frameworks (OFs) offer a novel strategy for assembling organic semiconductors into robust networks that facilitate transport, especially the covalent organic frameworks (COFs). However, poor electrical conductivity through covalent bonds and insolubility of COFs limit their practical applications in organic electronics. It is known that the two-dimensional intralayer π∙∙∙π transfer dominates transport in organic semiconductors. However, because of extremely labile inherent features of noncovalent π∙∙∙π interaction, direct construction of robust frameworks via noncovalent π∙∙∙π interaction is a difficult task. Toward this goal, we report a robust noncovalent π∙∙∙π interaction-stacked organic framework, namely πOF, consisting of a permanent three-dimensional porous structure that is held together by pure intralayer noncovalent π∙∙∙π interactions. The elaborate porous structure, with a 1.69-nm supramaximal micropore, is composed of fully conjugated rigid aromatic tetragonal-disphenoid-shaped molecules with four identical platforms. πOF shows excellent thermostability and high recyclability and exhibits self-healing properties by which the parent porosity is recovered upon solvent annealing at room temperature. Taking advantage of the long-range π∙∙∙π interaction, we demonstrate remarkable transport properties of πOF in an organic-field-effect transistor, and the mobility displays relative superiority over the traditional COFs. These promising results position πOF in a direction toward porous and yet conductive materials for high-performance organic electronics.

Optical Waveguides and Integrated Optical Devices for Medical Diagnosis, Health Monitoring and Light Therapies

Optical waveguides and integrated optical devices are promising solutions for many applications, such as medical diagnosis, health monitoring and light therapies. Despite the many existing reviews focusing on the materials that these devices are made from, a systematic review that relates these devices to the various materials, fabrication processes, sensing methods and medical applications is still seldom seen. This work is intended to link these multidisciplinary fields, and to provide a comprehensive review of the recent advances of these devices. Firstly, the optical and mechanical properties of optical waveguides based on glass, polymers and heterogeneous materials and fabricated via various processes are thoroughly discussed, together with their applications for medical purposes. Then, the fabrication processes and medical implementations of integrated passive and active optical devices with sensing modules are introduced, which can be used in many medical fields such as drug delivery and cardiovascular healthcare. Thirdly, wearable optical sensing devices based on light sensing methods such as colorimetry, fluorescence and luminescence are discussed. Additionally, the wearable optical devices for light therapies are introduced. The review concludes with a comprehensive summary of these optical devices, in terms of their forms, materials, light sources and applications.

Two-Dimensionally Stretchable Organic Light-Emitting Diode with Elastic Pillar Arrays for Stress Relief

Recent advanced studies on flexible and stretchable electronic devices and optoelectronics have made possible a variety of soft and more functional electronic devices. With consumer demand for highly functional or free-form displays, high flexibility and stretchability in light-emitting devices are needed. Herein, we developed a unique structure of stretchable substrates with pillar arrays to reduce the stress on the active area of devices when strain is applied. We confirmed the advantages of the produced structures using mechanical simulation tools and determined that the structures effectively lessen the applied stress of interconnection as well as the active area in a stretched state. With this stress-relief stretchable substrate, we realized stretchable OLEDs that are compliant and maintain their performance under high strain deformation. Also, devices can be stretched in the biaxis, which is superior to only one-directional stretchable electronics; as such, devices can be used in practical applications like wearable electronics and health monitoring systems. We propose, for the first time, stretchable OLEDs patterned by the thermal evaporation fabrication process onto stress-relief substrates. These OLEDs can mitigate certain problems in previous studies of stretchable OLEDs without need to find new materials or to use a prestrained fabrication process.

Fibertronic Organic Light-Emitting Diodes toward Fully Addressable, Environmentally Robust, Wearable Displays

Significant potential of electronic textiles for wearable applications has triggered active studies of luminescent fibers toward smart textile displays. In spite of notable breakthroughs in the lighting fiber technology, a class of information displays with a luminescent fiber network is still underdeveloped due to several formidable challenges such as limited electroluminescence fiber performance, acute vulnerability to chemical and mechanical factors, and lack of decent engineering schemes to form fibers with robust interconnectable pixels for two-dimensional matrix addressing. Here, we present a highly feasible strategy for organic light-emitting diode (OLED) fiber-based textile displays that can overcome these issues by implementing prominent solution options including compatible fabrication method of OLED pixel arrays on adapted fiber configurations and chemically/mechanically sturdy but electrically conductive passivation system. To create solid interconnectable OLED fibers without compromising the high electroluminescence performance, phosphorescence OLED materials are deposited onto process-friendly fibers of rectangular stripes, where periodically patterned OLED pixels are selectively passivated with robust polymer and circumventing metal pads by a stamp-assisted printing method. A woven textile of interlaced interconnectable OLED fibers with perpendicularly arranged conductive fibers serves as a matrix-addressable two-dimensional network that can be operated by the passive matrix scheme. Successful demonstrations of stably working woven OLED textile in the water, as well as under the applied tensile force, support feasibility of the present approach to reify fully addressable, environmentally durable, fiber-based textile displays.

Sandwich-structure transferable free-form OLEDs for wearable and disposable skin wound photomedicine

Free-form optoelectronic devices can provide hyper-connectivity over space and time. However, most conformable optoelectronic devices can only be fabricated on flat polymeric materials using low-temperature processes, limiting their application and forms. This paper presents free-form optoelectronic devices that are not dependent on the shape or material. For medical applications, the transferable OLED (10 μm) is formed in a sandwich structure with an ultra-thin transferable barrier (4.8 μm). The results showed that the fabricated sandwich-structure transferable OLED (STOLED) exhibit the same high-efficiency performance on cylindrical-shaped materials and on materials such as textile and paper. Because the neutral axis is freely adjustable using the sandwich structure, the textile-based OLED achieved both folding reliability and washing reliability, as well as a long operating life (>150 h). When keratinocytes were irradiated with red STOLED light, cell proliferation and cell migration increased by 26 and 32%, respectively. In the skin equivalent model, the epidermis thickness was increased by 39%; additionally, in organ culture, not only was the skin area increased by 14%, but also, re-epithelialization was highly induced. Based on the results, the STOLED is expected to be applicable in various wearable and disposable photomedical devices.