Applications In Flexible Devices Research Articles

Polypyrrole in-situ polymerized MXene/TPU fiber electrode for flexible supercapacitors

Ti3C2Tx-based flexible fibers have great potential and wide applications in the energy storage field of wearable electronic textiles and portable electronic devices. This work reports a Ti3C2Tx-MXene/TPU/polypyrrole(PPy) fiber in which PPy is grown on the surface of Ti3C2Tx/TPU fiber by in-situ polymerization. Through efficient wet spinning and in-situ polymerization, Ti3C2Tx/TPU/PPy fiber exhibit pore structure and abundant active sites, which significantly enhance charge transfer rate and conductivity. The fiber exhibits a capacitance of 41.2 F g−1(5 mV S−1) and excellent rate performance in 1 M H2SO4 electrolyte. Its symmetrical fiber-based flexible supercapacitors(SCs) can provide an energy density of 2.36 mW h g−1. At the same time, the fiber has good flexibility and can be woven into a fabric SCs as a wearable energy storage device to realize power supply applications such as electronic watches and LEDs, which provides a potential strategy for the application of flexible wearable energy storage devices.

Flexible and stretchable implantable devices for peripheral neuromuscular electrophysiology.

The peripheral nervous and muscular system, a cornerstone of human physiology, plays a pivotal role in ensuring the seamless functioning of the human body. This intricate network, comprising nerves and muscles extending throughout the body, is essential for motor control, sensory feedback, and the regulation of autonomic bodily functions. The qualified implantable peripheral interface can accurately monitor the biopotential of the target tissue and conduct treatment with stimulation, enhancing the human-machine interaction and new achievements in disease cure. Implantable electrodes have revolutionized the field of neuromuscular interfaces, offering precise bidirectional communication between the neuromuscular system and external devices. They enable natural control for individuals with limb loss, bridging the gap between mind and machine and aiding neuromuscular rehabilitation. In research and medical diagnostics, implantable electrodes provide invaluable tools for studying neuromuscular function and the development of therapies. However, traditional rigid electrodes face challenges due to the dynamic nature of the peripheral neuromuscular system. Flexible and stretchable devices show immense promise in accommodating dynamic alterations, offering adaptability, and accurate monitoring of electrophysiological signals. This review delves into the challenges associated with the peripheral interface, primarily focusing on monitoring and stimulation. It then provides a summary of common materials and structural design optimizations, discusses technologies for enhancing interface adhesion and surface functionalization, and explores encapsulation methods for implanted devices. Recent advancements in energy supply and the applications of implantable, flexible, and stretchable devices are also comprehensively reviewed, with due consideration given to ethical concerns and signal analysis. The promising directions are finally presented to provide enlightenment for high-performance sensor-tissue interfaces in the future, which will promote profound progress in clinical and human-machine interaction research. Flexible and stretchable devices are at the forefront of healthcare, with the potential to transform the treatment of neuromuscular disorders and enhance human augmentation, blurring the lines between natural and artificial limbs. They represent a promising avenue for the future, with exciting applications in healthcare, science, and technology, promising to bring us closer to the seamless integration of human and machine in the realm of neuromuscular interfaces.

Li-ion intercalation-driven control of two-dimensional magnetism in van der Waals FePS3 bilayers.

Manipulating two-dimensional (2D) magnetism in layered van der Waals (vdW) materials like FePS3 (FPS), with its wide-ranging applications in flexible spintronic devices, poses a persistent challenge. Through first-principles calculations, we have achieved reversible ferrimagnetic (FiM, FePS3 bilayer) ↔ antiferromagnetic (AFM, 1Li-intercalated FePS3 bilayer) ↔ ferromagnetic (FM, 2Li-intercalated FePS3 bilayer) phase transitions by using a Li-ion intercalation method. Intercalated Li ions significantly enhance the Fe-3d and S-3p hybridization and reduce the Fe-Fe, Li-Fe, Li-S, and Li-P bond lengths. The manipulation of 2D magnetism in Li-intercalated FPS bilayers can be attributed to the charge transfer between two FPS monolayers mediated by Li ions. Moreover, this study offers insights into the underlying physical mechanisms that govern the variations of electronic structures, 2D magnetism, magnetic anisotropy energy, and exchange couplings. Our reversible Li-ion intercalation permits straightforward de-intercalation using a two-step route, thereby reinstating the initial magnetic order of the FPS bilayer. Our purpose-designed FPS bilayer with different Li concentrations and robust exchange coupling not only enriches the Li-intercalation physics in the FPS system but also offers a general pathway for manipulating 2D magnetism in Fe-based vdW trisulfides.

Constructing ultra-stable, high-energy, and flexible aqueous zinc-ion batteries using environment-friendly organic cathodes.

Due to their sustainability, environmental friendliness, high specific capacity, and rapid reaction kinetics, quinone cathodes have broad application prospects in aqueous zinc-ion batteries (AZIBs). However, conventional small-molecule quinone cathodes usually suffer from unavoidable dissolution, resulting in terrible cycling stability. Herein, based on a strategy of molecular structure optimization, calix[8]quinone (C8Q) is for the first time used as a cathode in AZIBs. By extending the structure of the classical small-molecule quinone cathode calix[4]quinone (C4Q), C8Q further adds four p-benzoquinone structural units, which significantly suppresses the dissolution of its discharge products and greatly improves the cycle stability of the cathode. Specifically, the C8Q cathode displays a discharge specific capacity of 207.2 mA h g-1 at 1 A g-1 and a long-life cycle stability (93 mA h g-1/10 A g-1/10000th). Even with a high active material loading of 11 mg cm-2, the Zn‖C8Q battery also exhibits high redox reversibility and remarkable electrochemical stability. Furthermore, the belt-shaped Zn‖C8Q battery has high stability and outstanding flexibility, indicating its promising application in flexible wearable electronic devices.

Multifunctional aqueous polyurethanes with high strength and self-healing efficiency based on silver nanowires for flexible strain sensors.

Advanced sensor technology is widely applied in human motion monitoring and research. However, it often encounters problems such as scratches, fractures, and aging, which affect its lifespan and reliability. To address these challenges, we draw inspiration from the inherent self-healing properties of organic biological entities in nature to endow our sensors with self-healing capability. In this work, we constructed a reversible multi-hydrogen-bonded physical crosslinking network and introduced aromatic disulfide bonds into the polyurethane backbone. This design not only achieves a very high mechanical strength of the material, but also efficient self-healing properties. At 80 °C, the tensile strength of the WPU-U2D1 material reached 28.88 MPa, with a fracture elongation of 748.64%, and a self-healing efficiency as high as 99.24%. Based on this material, we successfully prepared a flexible conductive composite film (WPU@AgNW) and applied it to flexible strain sensors. The sensor demonstrated excellent sensitivity and reliability in human motion monitoring (electrical conductivity of 2.66 S cm-1), which provides a new idea for realising the breakthrough of high-performance flexible sensors. These outstanding properties makes it have great potential for application in flexible wearable devices, human-computer interaction, bionic electronic devices and other fields.

Metal nanowire-based transparent electrode for flexible and stretchable optoelectronic devices.

High-quality transparent electrodes are indispensable components of flexible optoelectronic devices as they guarantee sufficient light transparency and electrical conductivity. Compared to commercial indium tin oxide, metal nanowires are considered ideal candidates as flexible transparent electrodes (FTEs) owing to their superior optoelectronic properties, excellent mechanical flexibility, solution treatability, and higher compatibility with semiconductors. However, certain key challenges associated with material preparation and device fabrication remain for the practical application of metal nanowire-based electrodes. In this review, we discuss state-of-the-art solution-processed metal nanowire-based FTEs and their applications in flexible and stretchable optoelectronic devices. Specifically, the important properties of FTEs and a cost-benefit analysis of existing technologies are introduced, followed by a summary of the synthesis strategy, key properties, and fabrication technologies of the nanowires. Subsequently, we explore the applications of metal-nanowire-based FTEs in different optoelectronic devices including solar cells, photodetectors, and light-emitting diodes. Finally, the current status, future challenges, and emerging strategies in this field are presented.

Plastic phase transitions in tris(hydroxymethyl)aminomethane perchlorate.

Organic crystal materials with metal-free feature and intrinsically low molecular mass are highly desirable for applications in flexible smart devices. Here, we reported a plastic crystal, tris(hydroxymethyl)aminomethane perchlorate (Tris-HClO4), which crystallizes in the R3̄ space group at room temperature and undergoes plastic phase transition at 369 K, showing a large entropy gain of 70.5 J mol-1 K-1, much higher than its fusion entropy gain (12.9 J mol-1 K-1). PXRD measurement indicates that it has cubic lattice symmetry in the high-temperature phase. Moreover, it exhibits excellent dielectric permittivity switching properties and robust cyclic stability. This work could be the pathway for chemical designing multifunctional switchable materials with the motive of combining the idea of symmetry breaking and plastic phase transition.

Strong, tough and conductive single-network hydrogels based on deswelling and the salting-out effect.

In recent years, the continuous attention given to increasing the fracture toughness and Young's modulus of polymeric gels has gradually shifted from toughening strategies on double-network (DN) gels to single-network (SN) gels. The salt-soaking method has been adopted to realize the toughening of SN gels through the salting-out effect and deswelling, constructing dense network structures with simultaneously precipitated polymer chains and cross-links. By comparing the mechanical properties between salt-treated hydrogels and air-dried hydrogels, the increased polymer chain concentration is proved to promote energy transfer by enlarging the dissipation region size due to the unwinding and slippage of coiled chains during stretching. The newly formed cross-link points in salt-treated hydrogels are considered to consume more deformation energy during stretching. The synergistic effect in energy transfer and dissipation arising from increases in polymer fraction and cross-linking plays an indispensable role in toughening SN hydrogels. In addition, the soaking process introduces abundant free ions to endow hydrogels with prominent conductivity. Thus, this salt-soaking method provides a general approach to synthesize strong, tough and conductive hydrogels with applications in flexible electrical devices.

Stability and photocurrent enhancement of photodetectors by using core/shell structured CsPbBr3/TiO2 quantum dots and 2D materials.

Ultra-stable CsPbBr3 perovskite quantum dots (QDs) were prepared, and the performance of the photodetector fabricated from them was enhanced by 2D material incorporation. This multi-component photodetector appears to have good stability in the ambient utilization environment. All inorganic CsPbBr3 QDs are potential candidates for application in photodetection devices. However, QDs have several issues such as defects on the QD surface, degradation under environmental conditions, and unfavorable carrier mobility limiting the high performance of the photodetectors. This work addresses these issues by fabricating a core/shell structure and introducing 2D materials (MXenes, Ti3C2Tx) into the device. Here, three types of photodetectors with QDs only, QDs with a core/shell structure, and QDs with a core/shell structure and MXenes are fabricated for systematic study. The CsPbBr3/TiO2 photodetector demonstrated a two times photocurrent enhancement compared to bare QDs and had good device stability after TiO2 shell coating. After introducing Ti3C2Tx into CsPbBr3/TiO2, a significant photocurrent enhancement from nanoampere (nA) to microampere (μA) was observed, revealing that MXenes can improve the photoelectric response of perovskite materials significantly. Higher photocurrent can avoid signal interference from environmental noise for better practical feasibility. This study provides a systematic understanding of the photocurrent conversion of perovskite quantum dots that is beneficial in advancing optoelectronic device integration, especially for flexible wearable device applications.

Anode-free lithium metal batteries: a promising flexible energy storage system

The anode-free lithium metal battery is characterized by light weight, low cost, high-energy density, and high safety and shows great potential for the application of flexible devices.

Van der Waals Epitaxy of Bismuth‐Based Multiferroic Layered Supercell Oxide Thin Films Integrated on Flexible Mica Substrate

Bi2NiMnO6 (BNMO) epitaxial thin films with a layered supercell (LSC) structure have emerged as a promising single‐phase multiferroic material recently. Because of the required strain state for the formation of the LSC structures, most of the previous BNMO films are demonstrated on rigid oxide substrates such as SrTiO3 and LaAlO3. Here, the potential of BNMO films grown on muscovite mica substrates via van der Waals epitaxy, spotlighting their suitability for cutting‐edge flexible device applications is delved. Comprehensive scanning transmission electron microscopy/energy‐dispersive X‐ray analyses reveal a layered structure in the BNMO film and a pristine interface with the mica substrate, indicating high‐quality deposition and minimal interfacial defects. Capitalizing on its unique property of easily cleavable layers due to weak van der Waals forces in mica substrates, flexible BNMO/mica samples are fixed. A standout feature of the BNMO film grown on mica substrate is its consistent multiferroic properties across varied mechanical conditions. A novel technique is introduced for thinning the mica substrate and subsequent transfer of the sample, with post‐transfer analyses validating the preserved structural and magnetic attributes of the film. Overall, this study illuminates the resilient multiferroic properties of BNMO films on mica, offering promising avenues for their integration for next‐generation flexible electronics.

Pom Functionalized Ionogels with Tunable Optical, Mechanical, Electrical, and Sensory Properties

AbstractIonogels, with wide applications in tissue engineering, soft robotics, and flexible iontronic devices, require tunable optical, mechanical, and electrical properties for advanced functionality applications. Here, a facile strategy is reported to tune a set of properties of ionogels via tuning the redox states of the added polyoxometalate (POM) clusters. Upon external electrical stimuli, the POM clusters in the ionogels can be reversibly tuned from a transparent, oxidized state to a blue, reduced state. The redox states of the POM anions influence the POM‐polymer interactions, which promotes the in situ modulation of the ionogel properties reversibly over a large window: optical transparency from 91% to 7%, dissipated energy from 0.9 to 3.1 MJ m−3, elastic modulus from 1.5 to 2 MPa, conductivity from 1.6 × 10−4 to 2.2 × 10−4 S cm−1. Meanwhile, the sensory properties of the ionogels can be modulated simultaneously. For strain sensing and pressure sensing, the GF can be tuned from 2.3 to 7.2, and the sensitivity can be tuned from 0.8 to 1.2 kPa−1. Such an ionogel with tunable optical, mechanical, and electrical properties may find a variety of applications meeting specific demands. The POM functionalization strategy may also bring new insights into the design of the stimuli‐responsive ionogels.

Research Progress in Special Engineering Plastic-Based Electrochromic Polymers.

SPECPs are electrochromic polymers that contain special engineering plastic structural characteristic groups (SPECPs). Due to their high thermal stability, mechanical properties, and weather resistance, they are also known as high-performance electrochromic polymer (HPEP or HPP). Meanwhile, due to the structural characteristics of their long polymer chains, these materials have natural advantages in the application of flexible electrochromic devices. According to the structure of special engineering plastic groups, SPECPs are divided into five categories: polyamide, polyimide, polyamide imide, polyarylsulfone, and polyarylketone. This article mainly introduces the latest research on SPECPs. The structural design, electrochromic properties, and applications of these materials are also introduced in this article, and the challenges and future development trends of SPECPs are prospected.

Ab Initio Molecular Dynamics Study on Self-Healing Solid Polymer Electrolyte for Lithium Metal Batteries

Lithium metal batteries (LMBs) have generally become potential candidates for energy storage devices because of their high energy density. However, the practical applications of LMBs have been limited due to the low safety of liquid electrolytes. Compared to liquid electrolytes, solid-state polymer electrolytes (SPEs) have excellent mechanical strength. However, there is room for improvement because traditional PEO-based SPEs need more mechanical properties and electrode contacts for flexible energy device applications. Self-healing solid polymer electrolytes (SHSPEs) have excellent flexibility and healing ability and can also suppress dendrite formation to increase the safety of LMBs. In this study, a novel SHSPE is designed by a combination of the zwitterionic copolymer, SBMA ([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide)-co-BA (Butyl Acrylate), and a lithium salt, LiTFSI. We explored their solvation structures and reactivity on the Li metal anode using Density functional theory (DFT) and ab initio molecular dynamics (AIMD) methods. Besides, we also studied the reactivity of the considered SHSPE on the Cu (100) surface to explore the SEI formation mechanisms. The cationic NR4 + and anionic SO3 - groups of SBMA interact electrostatically and form cross-linked network structures within the electrolyte framework, providing the designed SHSPE with prominent self-healing capacity. The decomposition reactions of SHSPE on the Li metal anode are explored, and the resultant decomposition products that contribute to the formation of the solid electrolyte interphase (SEI) are identified. Furthermore, AIMD results indicate that highly concentrated SO3 - groups in the SHSPE promote Li ion diffusion, which increases Li ionic conductivity. The present findings provide design criteria for developing highly conductive self-healing SPEs.

The Role of Self-Assembled Monolayers in the Surface Modification and Interfacial Contact of Copper Fillers in Electrically Conductive Adhesives.

Printing of electrical circuits and interconnects using isotropic conductive adhesives (ICAs) is of great interest due to their low-temperature processing and compatibility with substrates for applications in sensors, healthcare, and flexible devices. As a lower cost alternative to silver (Ag), copper (Cu)-filled ICAs are desirable but limited by the formation of high-resistivity Cu surface oxides. To overcome this limitation, self-assembled monolayers (SAMs) of octadecanethiol (ODT) have been demonstrated to reduce the oxidation of micrometer-scale Cu powder particles for use in ICAs. However, the deposition and function of the SAM require further investigation, as described in this paper. As part of this work, the stages of the SAM deposition process, which included etching with hydrochloric acid to remove pre-existing oxides, were studied using X-ray photoelectron spectroscopy (XPS), which showed low levels of subsequent Cu oxidation when ODT coated. The treated Cu powders were combined with one- or two-part epoxy resins to make Cu-ICAs, and the effect of the Cu surface condition and weight loading on electrical conductivity was examined. When thermally cured in an inert argon atmosphere, ICAs filled with Cu protected by ODT achieved electrical conductivity up to 20 × 105 S·m-1, comparable to Ag-ICAs, and were used to make a functional circuit. To understand the function of the SAM in these Cu-ICAs, scanning and transmission electron microscopy were used to examine the internal micro- and nano-structures along with the elemental distribution at the interfaces within sections taken from cured samples. Sulfur (S), indicative of the ODT, was still detected at the internal polymer-metal interface after curing, and particle-to-particle contacts were also examined. XPS also identified S on the surface of cured Cu-ICAs even after thermal treatment. Based on the observations, electrical contact and conduction mechanisms for these Cu-filled ICAs are proposed and discussed.

Modulating Quantum Well Width of Ferroelectric Ruddlesden–Popper Perovskites for Flexible Light Communication Device

Abstract2D Ruddlesden–Popper perovskites exhibit significant ferroelectricity due to the spontaneous polarization of organic molecules. By modulating the quantum well width in 2D Ruddlesden–Popper perovskites BA2MAn‐1PbnBr3n+1, a series of perovskites are adopted to realize adjustable polarization intensity and bandgap width. It is found that when n = 3, perovskite has the maximum polarization strength and optimal optoelectronic performance. In addition, flexible photodetectors with high mechanical stability are successfully fabricated based on n = 3 perovskite microplates. The fabricated flexible photodetectors exhibit high responsivity of 920 mA W−1 and detectivity of 1.02 × 1011 Jones, along with excellent flexibility and stability. After 3000 bending cycles, the photocurrent of n = 3 perovskites photodetector remains 81.8% of initial state. Besides, the photocurrent of n = 3 perovskites increase by 33 and 34 times after polarization at 0 and 3 V, respectively. And n = 3 perovskites exhibit a high polarization sensitivity with a current ratio of 2.09. On the basis of controllable regulation of the photocurrent through polarization, the application of flexible decoding optoelectronic devices by utilizing the correspondence between optical signals before and after polarization and binaries is achieved. These findings highlight the potential of modulating quantum well width in 2D Ruddlesden–Popper perovskites as a promising strategy for designing next‐generation flexible optoelectronic devices.

High-speed flexible near-infrared organic photodiode for optical communication.

Optical communication is a particularly compelling technology for tackling the speed and capacity bottlenecks in data communication in modern society. Currently, the silicon photodetector plays a dominant role in high-speed optical communication across the visible-near-infrared spectrum. However, its intrinsic rigid structure, high working bias and low responsivity essentially limit its application in next-generation flexible optoelectronic devices. Herein, we report a narrow-bandgap non-fullerene acceptor (NFA) with a remarkable π-extension in the direction of both central and end units (CH17) with respect to the Y6 series, which demonstrates a more effective and compact 3D molecular packing, leading to lower trap states and energetic disorders in the photoactive film. Consequently, the optimized solution-processed organic photodetector (OPD) with CH17 exhibits a remarkable response time of 91ns (λ = 880nm) due to the high charge mobility and low parasitic capacitance, exceeding the values of most commercial Si photodiodes and all NFA-based OPDs operating in self-powered mode. More significantly, the flexible OPD exhibits negligible performance attenuation (<1%) after bending for 500 cycles, and maintains 96% of its initial performance even after 550h of indoor exposure. Furthermore, the high-speed OPD demonstrates a high data transmission rate of 80MHz with a bit error rate of 3.5 [Formula: see text] 10-4, meaning it has great potential in next-generation high-speed flexible optical communication systems.

In situ reduction of Ag nanoparticles using okra polysaccharides for the preparation of flexible multifunctional sensors

This paper reports the fabrication of flexible films loaded with Ag nanoparticles (Ag NPs) and annotated as POPA films from polyvinyl alcohol, okra polysaccharides, phytic acid, and AgNO3 via an in situ reduction and solution-casting method. The prepared films exhibit strain, temperature, and humidity sensing. As a flexible strain sensor, the POPA sensor has a wide strain sensing range (1–250 %), and fast response/recovery (0.22/0.28 s), while as a temperature sensor, it senses the human body temperature and exhibits excellent temperature sensitivity (TCR = −1.401 % °C−1) and good linearity (R2 = 0.994) in the temperature range of 30–55 °C. Additionally, in the relative humidity (RH) of range 35–95 %, the POPA humidity sensor outputs stable electrical signals during adsorption and desorption. Moreover, it exhibits low hysteresis values (3.19 % RH) and good linearity (R2 = 0.989) for the detection of breathing rates during different human body states. Consequently, the POPA sensor exhibits good stability, repeatability, and reversibility for strain, temperature, and humidity sensing. The designed multifunctional POPA sensor thus holds great potential for its application in flexible wearable devices and electronics.

α-Fe2O3/ZnO nanocomposite as an efficient photocatalyst for wastewater treatment and flexible electronic device applications

α-Fe2O3/ZnO nanocomposite as an efficient photocatalyst for wastewater treatment and flexible electronic device applications

Tailoring Electrical Properties in Carbon Nanomaterial Patterns with Multimaterial Aerosol Jet Printing.

Multimaterial aerosol jet printing offers a unique capability to freely mix inks with different chemical compositions in the aerosol phase, enabling one-step digital fabrication with tailored compositions or functionally graded structures, including in the x-y plane. Here, in situ mixing of two carbon nanomaterial inks with distinct electrical properties is demonstrated. By tailoring the mixing ratio of the constituent inks, electrical conductivity is modulated by 130×, and sheet resistance values for a single pass span approximately 2 orders of magnitude. The ability to manufacture components with tailored electrical properties offers significant value for hybrid and flexible electronic device applications, such as microelectronics packaging. Moreover, grading properties within a part provides a new dimension of design freedom for complex assemblies.