An Environment‑Tolerant Ion‑Conducting Double‑Network Composite Hydrogel for High‑Performance Flexible Electronic Devices

High-performance ion-conducting hydrogels(ICHs)are vital for developing flexible electronic devices.However,the robustness and ion-conducting behavior of ICHs deteriorate at extreme tempera-tures,hampering their use in soft electronics.To resolve these issues,a method involving freeze–thawing and ionizing radiation technology is reported herein for synthesizing a novel double-network(DN)ICH based on a poly(ionic liquid)/MXene/poly(vinyl alcohol)(PMP DN ICH)system.The well-designed ICH exhibits outstanding ionic conductivity(63.89 mS cm^(-1) at 25℃),excellent temperature resistance(-60–80℃),prolonged stability(30 d at ambient temperature),high oxidation resist-ance,remarkable antibacterial activity,decent mechanical performance,and adhesion.Additionally,the ICH performs effectively in a flexible wireless strain sensor,thermal sensor,all-solid-state supercapacitor,and single-electrode triboelectric nanogenerator,thereby highlighting its viability in constructing soft electronic devices.The highly integrated gel structure endows these flexible electronic devices with stable,reliable signal output performance.In particular,the all-solid-state supercapacitor containing the PMP DN ICH electrolyte exhibits a high areal specific capacitance of 253.38 mF cm^(-2)(current density,1 mA cm^(-2))and excellent environmental adaptability.This study paves the way for the design and fabrication of high-performance mul-tifunctional/flexible ICHs for wearable sensing,energy-storage,and energy-harvesting applications.

Flexible perovskite light-emitting diodes for display applications and beyond

The flexible perovskite light-emitting diodes(FPeLEDs),which can be expediently integrated to portable and wearable devices,have shown great potential in various applications.The FPeLEDs inherit the unique optical properties of metal halide perovskites,such as tunable bandgap,narrow emission linewidth,high photoluminescence quantum yield,and particularly,the soft nature of lattice.At present,substantial efforts have been made for FPeLEDs with encouraging external quantum efficiency(EQE)of 24.5%.Herein,we summarize the recent progress in FPeLEDs,focusing on the strategy developed for perovskite emission layers and flexible electrodes to facilitate the optoelectrical and mechanical performance.In addition,we present relevant applications of FPeLEDs in displays and beyond.Finally,perspective toward the future development and applications of flexible PeLEDs are also discussed.

Viologen-based flexible electrochromic devices

Electrochromic technology has gained significant attention in various fields such as displays,smart windows,biomedical monitoring,military camouflage,human-machine interaction,and electronic skin due to its ability to provide reversible and fast color changes under applied voltage.With the rapid development and increasing demand for flexible electronics,flexible electrochromic devices(FECDs)that offer smarter and more controllable light modulation hold great promise for practical applications.The electrochromic material(ECM)undergoing color changes during the electrochemical reactions is one of the key components in electrochromic devices.Among the ECMs,viologens,a family of organic small molecules with 1,1'-disubstituted-4,4'-dipyridinium salts,have garnered extensive research interest,due to their well-reversible redox reactions,excellent electron acceptance ability,and the ability to produce multiple colors.Notably,viologen-based FECDs demonstrate color changes in the liquid or semisolid electrolyte layer,eliminating the need for two solid electrodes and thus simplifying the device structure.Consequently,viologens offer significant potential for the development of FECDs with high optical contrast,fast response speed,and excellent stability.This review aims to provide a comprehensive overview of the progress and perspectives of viologen-based FECDs.It begins by summarizing the typical structure and recent exciting developments in viologen-based FECDs,along with their advantages and disadvantages.Furthermore,the review discusses recent advancements in FECDs with additional functionalities such as sensing,photochromism,and energy storage.Finally,the remaining challenges and potential research directions for the future of viologen-based FECDs are addressed.

Light-emitting devices based on atomically thin MoSe_(2)

Atomically thin MoSe_(2) layers,as a core member of the transition metal dichalcogenides(TMDs)family,benefit from their appealing properties,including tunable band gaps,high exciton binding energies,and giant oscillator strengths,thus pro-viding an intriguing platform for optoelectronic applications of light-emitting diodes(LEDs),field-effect transistors(FETs),sin-gle-photon emitters(SPEs),and coherent light sources(CLSs).Moreover,these MoSe_(2) layers can realize strong excitonic emis-sion in the near-infrared wavelengths,which can be combined with the silicon-based integration technologies and further encourage the development of the new generation technologies of on-chip optical interconnection,quantum computing,and quantum information processing.Herein,we overview the state-of-the-art applications of light-emitting devices based on two-dimensional MoSe_(2) layers.Firstly,we introduce recent developments in excitonic emission features from atomically thin MoSe_(2) and their dependences on typical physical fields.Next,we focus on the exciton-polaritons and plasmon-exciton polaritons in MoSe_(2) coupled to the diverse forms of optical microcavities.Then,we highlight the promising applications of LEDs,SPEs,and CLSs based on MoSe_(2) and their heterostructures.Finally,we summarize the challenges and opportunities for high-quality emis-sion of MoSe_(2) and high-performance light-emitting devices.

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.

Research on the Application of Flexible Electronics Technology in Wearable Devices

This study employs theoretical analysis to explore the application prospects of flexible electronics technology in wearable devices. The research first reviews the development history and theoretical foundations of flexible electronics technology, including materials science, electronic engineering, and human-computer interaction theory. Through systematic analysis, the study evaluates the theoretical potential of flexible displays, flexible sensors, and flexible energy storage devices in wearable technology. The research finds that flexible electronics technology can significantly improve the comfort, functionality, and durability of wearable devices. Theoretical analysis indicates that flexible sensors have unique advantages in physiological monitoring and human-computer interaction, while flexible displays and batteries may revolutionize the form and usage patterns of wearable devices. However, the study also points out theoretical challenges faced by flexible electronics technology, such as material stability and feasibility of large-scale manufacturing. To address these challenges, the research proposes an interdisciplinary research framework, emphasizing the synergistic innovation of materials science, electronic engineering, and ergonomics. Finally, the study envisions the theoretical prospects of integrating flexible electronics with other emerging technologies, providing directions for future research.

Improving Efficiency by Doping PtOEP into Spiro Light-Emitting Devices

To investigate effective means of improving the efficiency of organic light-emitting devices （OLEDs） by making full use of ,triplet emission, a phosphorescent material Pt （II） Octaethylporphine （PtOEP） is doped into polymer host polyspirobifluorene （Spiro） to allow radiative recombination of triplet excitons. The current and brightness characteristics of the devices are tested and the electroluminescent spectra are described. Both fluorescence and phosphorescence are ob- served,and an obvious increase in external quantum efficiency is realized compared to undoped devices when different phosphorescent dopant concentrations are tried. Thus,the phosphorescent emission from triplet excited states might be an effective way to increase the efficiency of OLEDs when the concentration of the phosphorescent dopant is properiy controlled.

Flexible Strain Sensors with Ultra‑High Sensitivity and Wide Range Enabled by Crack‑Modulated Electrical Pathways

This study presents a breakthrough in flexible strain sensor technology with the development of an ultrahigh sensitivity and wide-range sensor,addressing the critical challenge of reconciling sensitivity with measurement range.Inspired by the structure of bamboo slips,we introduce a novel approach that utilises liquid metal to modulate the electrical pathways within a cracked platinum fabric electrode.The resulting sensor demonstrates a gauge factor greater than 108 and a strain measurement capability exceeding 100%.The integration of patterned liquid metal enables customisable tuning of the sensor’s response,while the porous fabric structure ensures superior comfort and air permeability for the wearer.Our design not only optimises the sensor’s performance but also enhances the electrical stability that is essential for practical applications.Through systematic investigation,we reveal the intrinsic mechanisms governing the sensor’s response,offering valuable insights for the design of wearable strain sensors.The sensor’s exceptional performance across a spectrum of applications,from micro-strain to large-strain detection,highlights its potential for a wide range of real-world uses,demonstrating a significant advancement in the field of flexible electronics.

Ultra‑Transparent and Multifunctional IZVO Mesh Electrodes for Next‑Generation Flexible Optoelectronics

Mechanically durable transparent electrodes are essential for achieving long-term stability in flexible optoelectronic devices.Furthermore,they are crucial for applications in the fields of energy,display,healthcare,and soft robotics.Conducting meshes represent a promising alternative to traditional,brittle,metal oxide conductors due to their high electrical conductivity,optical transparency,and enhanced mechanical flexibility.In this paper,we present a simple method for fabricating an ultra-transparent conducting metal oxide mesh electrode using selfcracking-assisted templates.Using this method,we produced an electrode with ultra-transparency(97.39%),high conductance(Rs=21.24Ωsq^(−1)),elevated work function(5.16 eV),and good mechanical stability.We also evaluated the effectiveness of the fabricated electrodes by integrating them into organic photovoltaics,organic light-emitting diodes,and flexible transparent memristor devices for neuromorphic computing,resulting in exceptional device performance.In addition,the unique porous structure of the vanadium-doped indium zinc oxide mesh electrodes provided excellent flexibility,rendering them a promising option for application in flexible optoelectronics.

Design strategies and insights of flexible infrared optoelectronic sensors

Infrared optoelectronic sensing is the core of many critical applications such as night vision,health and medication,military,space exploration,etc.Further including mechanical flexibility as a new dimension enables novel features of adaptability and conformability,promising for developing next-generation optoelectronic sensory applications toward reduced size,weight,price,power consumption,and enhanced performance(SWaP^(3)).However,in this emerging research frontier,challenges persist in simultaneously achieving high infrared response and good mechanical deformability in devices and integrated systems.Therefore,we perform a comprehensive review of the design strategies and insights of flexible infrared optoelectronic sensors,including the fundamentals of infrared photodetectors,selection of materials and device architectures,fabrication techniques and design strategies,and the discussion of architectural and functional integration towards applications in wearable optoelectronics and advanced image sensing.Finally,this article offers insights into future directions to practically realize the ultra-high performance and smart sensors enabled by infrared-sensitive materials,covering challenges in materials development and device micro-/nanofabrication.Benchmarks for scaling these techniques across fabrication,performance,and integration are presented,alongside perspectives on potential applications in medication and health,biomimetic vision,and neuromorphic sensory systems,etc.

Emerging CoMn-LDH@MnO2 electrode materials assembled using nanosheets for flexible and foldable energy storage devices

CoMn layered double hydroxides(CoMn-LDH)are promising electrode materials for supercapacitors because of their excellent cyclic stability.However,they possess relatively low capacitances.In this work,hybrid CoMn-LDH@MnO2 products grown on Ni foams were obtained through a facile hydrothermal method.The as-synthesized samples employed as electrodes deliver a specific capacitance of 2325.01 F g^-1 at 1 A g^-1.An assembled asymmetric supercapacitor using these products as positive electrodes shows a maximum energy density of 59.73 W h kg^-1 at 1000.09 W kg^-1.The prominent electrochemical performance of the as-prepared electrodes could be attributes to hierarchical structures.These findings suggest that hybrid structures might be potential alternatives for future flexible energy storage devices.

Air-Stable Ultrabright Inverted Organic Light-Emitting Devices with Metal Ion-Chelated Polymer Injection Layer

Here,this work presents an air-stable ultrabright inverted organic lightemitting device(OLED)by using zinc ionchelated polyethylenimine(PEI)as electron injection layer.The zinc chelation is demonstrated to increase the conductivity of the PEI by three orders of magnitude and passivate the polar amine groups.With these physicochemical properties,the inverted OLED shows a record-high external quantum efficiency of 10.0% at a high brightness of 45,610 cd m^(-2) and can deliver a maximum brightness of 121,865 cd m^(-2).Besides,the inverted OLED is also demonstrated to possess an excellent air stability(humidity,35%)with a half-brightness operating time of 541 h@1000 cd m^(-2) without any protection nor encapsulation.

Graphene-based materials for flexible energy storage devices

The booming developments in portable and wearable electronics promote the design of flexible energy storage systems. Flexible supercapacitors and batteries as promising energy storage devices have attracted tremendous attention. As the key component of both supercapacitors and batteries, electrode materials with excellent flexibility should be considered to match with highly flexible energy storage devices. Owing to large surface area, good thermal and chemical stability, high conductivity and mechanical flexibility,graphene-based materials have been widely employed to serve as promising electrodes of flexible energy storage devices. Considerable efforts have been devoted to the fabrication of flexible graphene-based electrodes through a variety of strategies. Moreover, different configurations of energy storage devices based on these active materials are designed. This review highlights flexible graphene-based two-dimensional film and one-dimensional fiber supercapacitors and various batteries including lithium-ion, lithium–sulfur and other batteries. The challenges and promising perspectives of the graphene-based materials for flexible energy storage devices are also discussed.

Polymer nanocomposite dielectrics with high electrocaloric effect for flexible solid-state cooling devices

Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices （OLEDs） based on N,N＇-bis（1-naphthyl）-N,N＇-diphenyl-N,1＇- biphenyl-4,4＇-diamine （NPB） （the hole transport layer） and tris（8-hydroxyquinoline） aluminum （Alq3） （both emission and electron transport layers） is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm2, which is about 86% higher than that of an ordinary device （without a LiF interlayer, 3.2 cd/A）. An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.

Bifunctional flexible electrochromic energy storage devices based on silver nanowire flexible transparent electrodes

Flexible electrochromic energy storage devices(FECESDs)for powering flexible electronics have attracted considerable attention.Silver nanowires(AgNWs)are one kind of the most promising flexible transparent electrodes(FTEs)materials for the emerging flexible devices.Currently,fabricating FECESD based on AgNWs FTEs is still hindered by their intrinsic poor electrochemical stability.To address this issue,a hybrid AgNWs/Co(OH)_(2)/PEDOT:PSS electrode is proposed.The PEDOT:PSS could not only improve the resistance against electrochemical corrosion of AgNWs,but also work as functional layer to realize the color-changing and energy storage properties.Moreover,the Co(OH)_(2)interlayer further improved the color-changing and energy storage performance.Based on the improvement,we assembled the symmetrical FECESDs.Under the same condition,the areal capacitance(0.8 mF cm^(−2))and coloration efficiency(269.80 cm^(2)C−1)of AgNWs/Co(OH)_(2)/PEDOT:PSS FECESDs were obviously higher than AgNWs/PEDOT:PSS FECESDs.Furthermore,the obtained FECESDs exhibited excellent stability against the mechanical deformation.The areal capacitance remained stable during 1000 times cyclic bending with a 25 mm curvature radius.These results demonstrated the broad application potential of the AgNWs/Co(OH)_(2)/PEDOT:PSS FECESD for the emerging portable and multifunctional electronics.

Flexible energy storage devices for wearable bioelectronics

With the growing market of wearable devices for smart sensing and personalized healthcare applications,energy storage devices that ensure stable power supply and can be constructed in flexible platforms have attracted tremendous research interests.A variety of active materials and fabrication strategies of flexible energy storage devices have been intensively studied in recent years,especially for integrated self-powered systems and biosensing.A series of materials and applications for flexible energy storage devices have been studied in recent years.In this review,the commonly adopted fabrication methods of flexible energy storage devices are introduced.Besides,recent advances in integrating these energy devices into flexible self-powered systems are presented.Furthermore,the applications of flexible energy storage devices for biosensing are summarized.Finally,the prospects and challenges of the self-powered sensing system for wearable electronics are discussed.

Layered double hydroxides as electrode materials for flexible energy storage devices

To prevent and mitigate environmental degradation,high-performance and cost-effective electrochemical flexible energy storage systems need to be urgently developed.This demand has led to an increase in research on electrode materials for high-capacity flexible supercapacitors and secondary batteries,which have greatly aided the development of contemporary digital communications and electric vehicles.The use of layered double hydroxides(LDHs)as electrode materials has shown productive results over the last decade,owing to their easy production,versatile composition,low cost,and excellent physicochemical features.This review highlights the distinctive 2D sheet-like structures and electrochemical characteristics of LDH materials,as well as current developments in their fabrication strategies for expanding the application scope of LDHs as electrode materials for flexible supercapacitors and alkali metal(Li,Na,K)ion batteries.

Dependence of Performance of Organic Light-emitting Devices on Sheet Resistance of Indium-tin-oxide Anodes

The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

Highly efficient polymer phosphorescent light-emitting devices based on a new polyfluorene derivative as host

Several highly efficient iridium-complex polymer light-emitting devices （PLEDs） are fabricated, with a newly synthesized blue conjugated polymer, poly[（9,9-bis（4-（2-ethylhexyloxy）phenyl）-fluorene）-co-（3,7-dibenziothiene-S,S- dioxide15）] （PPF-3,TSO15）, chosen as host. High luminous efficiencies of 7.4 cd.A-1 and 27.4 cd.A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis（1- phenylisoquinoline） （acetylacetonate） （Ir（piq）） and green phosphorescent dye iridium tris（2-（4-tolyl）pyridinato-N, C2＇） （Ir（mppy）3）.Furthermore, highly efficient white PLEDs （WPLEDs） with the Commission Internationale de l＇Eclairage （CIE） coordinates of （0.35, 0.38） are successfully produced by carefully controlling the doping concentration of the irid- ium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd.A-1 and 10.1 lm.W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd.m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.