Flexible Electronic Products Research Articles

Customizable Metal Micromesh Electrode Enabling Flexible Transparent Zn-Ion Hybrid Supercapacitors with High Energy Density.

Emerging flexible and wearable electronic products are placing a compelling demand on lightweight transparent energy storage devices. Owing to their distinguishing features of safety, high specific energy, cycling stability, and rapid charge/discharge advantages, Zn-ion hybrid supercapacitors are a current topic of discussion. However, the trade-off for optical transmittance and energy density remains a great challenge. Here, a high-performance Zn-ion hybrid supercapacitor based on the customizable ultrathin (5µm), ultralight (0.45mg cm-2), and ultra-transparent (87.6%) Ni micromesh based cathode and Zn micromesh anode with the highest figure of merit (84843) is proposed. The developed flexible transparent Zn-ion hybrid supercapacitors reveal excellent cycle stability (no decline after 20000 cycles), high areal energy density (31.69 µWh cm-2), and high power density (512 µW cm-2). In addition, the assembled solid flexible and transparent Zn-ion hybrid supercapacitor with polyacrylamide gel electrolyte shows extraordinary mechanical properties even under extreme bending and twisting operation. Furthermore, the full device displays a high optical transmittance over 55.04% and can be conformally integrated with diverse devices as a flexible transparent power supply. The fabrication technology offers seamless compatibility with industrial manufacturing, making it an ideal model for the advancement of portable and wearable devices.

PVF composite conductive nanofibers-based organic electrochemical transistors for lactate detection in human sweat

The detection of lactate and other bioactive molecules is of great significance in biological research, medical testing, and environmental monitoring. Organic electrochemical transistors are a kind of biosensor devices, which can convert biological signals into electrical signals. In recent years, fiber-based organic electrochemical transistors (FECTs) provide a new approach for the construction of flexible wearable biosensors, promoting greatly the development of flexible wearable electronic products. In this study, a multilayer composite electrode was first prepared by incorporating MXene and PEDOT:PSS onto electrospun oriented polyvinyl formal (PVF) nanofiber bundle, and then assembled into FECT with high sensitivity and selectivity. Meanwhile, a wearable real-time monitoring platform was built to detect the lactate concentrations in human sweat. The results showed that MXene could act as a bridge between PEDOT:PSS and PVF, and the sensing performance of PVF/MXene/PEDOT:PSS-based FECT was enhanced obviously. It had a wide linear response range of 1 nM-100 mM, a sensitivity of 0.442 NCR/decade, a quick response time of 0.5 s, a low detection concentration, an excellent reproducibility, and a superior anti-interference characteristic. Therefore, this work provided more possibilities for the development of wearable biosensor.

Fabrication of flexible planar micro-supercapacitors using laser scribed graphene electrodes incorporated with MXene

The surge in demand for personalized electronic products has fueled the emergence and development of flexible electronic technology, giving rise to flexible energy storage devices. An integral component in these devices is planar micro-supercapacitors (MSCs), which hold immense promise for compatibility with flexible electronic products, especially in terms of their miniaturization, flexibility, integration, and customization. In this study, a fast, efficient, and environmentally friendly laser scribing technique has been employed to pattern MXene and graphene oxide (MXene/GO) composite films to prepare shape-controllable MXene and laser scribed graphene (MXene/LSG) patterned electrodes on a flexible substrate, which were then constructed into flexible MSCs. Based on the synergistic effect of these two-dimensional materials, MXene and LSG, the resulting adaptable devices exhibit exceptional electrochemical performance, including high areal capacitance, long cycle stability, superior flexibility, and mechanical stability. Furthermore, the use of a laser scribing process has pivotal implications for the scalable production of patterned electrodes and modular integration.

In-situ twisted spiral fiber with tree-ring like structure for joule heating, photothermal and humidity sensing

Smart fibers are increasingly becoming an optimal material for producing the next generation of flexible wearable electronics. However, balancing practical functionality and comfort remains a major challenge at this stage. Herein, we have prepared a bacterial cellulose (BC)/MXene-30% composite fiber using an in-situ twisting method, as this fiber possessed excellent conductivity (4050 S/m) and mechanical strength (108 Mpa). In addition, this BC/MXene spiral fiber has excellent joule heating and photothermal performance, which can be rapidly heated up to 70 °C within 25 s under a low voltage of only 9 V. They also have a stable and repeatable light-induced heating capability under 250 W infrared light. This new fiber material has a simple preparation process and versatile functional characteristics, which broadens its application in the fields of intelligent hyperthermia, respiratory monitoring, water level warnings and so on. The BC/MXene spiral fiber exhibited in this work is expected to provide a powerful database and theoretical reference for the next generation of flexible wearable electronic products.

Graphene and its application in flexible electronics

With the rapid development of technology and the dramatic improvement of living quality in recent years, traditional electronic technology is increasingly difficult to meet people's needs, and more portable flexible electronic (FE) technology products also stand out. However, with the development of research and application in the field of FEs, people put forward higher requirements for FE products in terms of electronic performance, light transmission performance, and mechanical tensile performance. As a new carbon nanomaterial, graphene has great mechanical, thermal, electrical and optical properties and is an excellent raw material for preparing FE devices, which has broad application prospects. This paper introduces the development of graphene preparation and application and its application results in the field of FEs summarizes the current research progress of graphene in the field of FEs and focuses on discussing and comparing the technical characteristics and development potential of different methods in each application. This review is expected to provide theoretical and data support for the application and preparation of graphene, especially in the field of FEs and provide new ideas for the development of graphene applications in the field of FEs.

Process optimization of simple preparation of AgNPs by polyol method and performance study of a strain sensor

In this experiment, silver nanoparticles (AgNPs) were prepared by the polyol method, which is simple and low-cost. The AgNPs were characterized by SEM, UV–Vis, and XRD. It was determined that the prepared AgNPs had good morphology and the average particle size was about 53.01 nm. At the same time, the optimum conditions for preparation were determined: The molar ratio of polyvinylpyrrolidone K30 (PVP K-30) to AgNO3 was 6:1, the reaction time was 40 min, and the reaction temperature was 160 °C. Then the sintering process parameters were discussed. It was determined that when the content of AgNPs was 2.5%, the temperature of high-temperature sintering should reach 250 °C and above, the time should reach 30 min and above, and the lowest resistivity reaches 0.7 × 10−5 Ω·m under high-temperature sintering. In chemical sintering, Cl− replaces the N and O atoms of PVP K-30, induces spontaneous aggregation of Ag, and completes room temperature sintering. It is found that the sintering time needs to reach 30 min or more, and the resistivity is 3.325 × 10−5 Ω·m. Finally, the conductive region is printed by the material deposition system and the strain sensor is prepared by two sintering methods. The experimental test proves that the sensor prepared by high-temperature sintering has good cycle response and stability. The sensor prepared by chemical sintering has a good cycle response, but the repeatability is poor, which is not conducive to long-term high-strength use. The sensor can be applied to the field of flexible electronic products.

High-Sensitivity and Low-Cost Wearable Flexible Pressure Sensor Based on MOFs

With potential applications in artificial intelligence, health monitoring, and motion, flexible pressure sensors have attracted more and more attention and development. However, high material costs and complex manufacturing processes limit the application and development of flexible pressure sensors in society. Here, we propose a flexible pressure sensor based on carbonized cotton fiber (CF) coated with ZIF-67 (ZIF-67@CF). Benefitting from the synergistic effect of ZIF-67 and CF, this sensor exhibits high sensitivity (15.7 kPa–1), low detection limit (4.92 Pa), wide range detection (0–120 kPa), fast response/recovery time (40/30 ms), and excellent stability (3000 cycles). More importantly, the ZIF-67@CF flexible pressure sensor can detect various human movements, from wispy vital signs to obvious movements. These attractive properties coupled with a simple preparation process, low cost, and good sensing properties make it a good market competitor and endow it with potential applications in the next generation of flexible electronic products.

Unraveling the interlayer and intralayer coupling in two-dimensional layered MoS[formula omitted] by X-ray absorption spectroscopy and ab initio molecular dynamics simulations

Understanding interlayer and intralayer coupling in two-dimensional layered materials (2DLMs) has fundamental and technological importance for their large-scale production, engineering heterostructures, and development of flexible and transparent electronics. At the same time, the quantification of weak interlayer interactions in 2DMLs is a challenging task, especially, from the experimental point of view. Herein, we demonstrate that the use of X-ray absorption spectroscopy in combination with reverse Monte Carlo (RMC) and ab initio molecular dynamics (AIMD) simulations can provide useful information on both interlayer and intralayer coupling in 2DLM 2Hc-MoS2. The analysis of the low-temperature (10–300 K) Mo K-edge extended X-ray absorption fine structure (EXAFS) using RMC simulations allows for obtaining information on the means-squared relative displacements σ2 for nearest and distant Mo–S and Mo–Mo atom pairs. This information allowed us further to determine the strength of the interlayer and intralayer interactions in terms of the characteristic Einstein frequencies ωE and the effective force constants κ for the nearest ten coordination shells around molybdenum. The studied temperature range was extended up to 1200 K employing AIMD simulations which were validated at 300 K using the EXAFS data. Both RMC and AIMD results provide evidence of the reduction of correlation in thermal motion between distant atoms and suggest strong anisotropy of atom thermal vibrations within the plane of the layers and in the orthogonal direction.

High adhesion hydrogel electrolytes enhanced by multifunctional group polymer enable high performance of flexible zinc-air batteries in wide temperature range

With the development of flexible wearable electronic products, the demand for energy storage devices with high energy density and light weight is increasing, and flexible zinc-air batteries (ZABs) are expected to become a new generation of matching power source for wearable devices. The synthesis of hydrogel electrolytes with high ionic conductivity, excellent mechanical properties and strong alkali resistance is the key to the assembly of flexible ZABs. However, the conventional hydrogel electrolytes are very easy to detach from the electrode after being applied to the flexible ZABs through multiple bending, high temperature and low temperature environments, resulting in a large interfacial resistance, which limits the application of the batteries. Herein, a multifunctional group polymer, carboxymethyl chitosan (CMCS) is cross-linked with the copolymer of acrylamide (AM) and sodium acrylate (ANa) to form a high-performance double-network hydrogel with a high ionic conductivity of 145.63 mS cm−1. The optimal hydrogel electrolyte exhibits an admirable power density of 120.87 mW cm−2 when applying to a flexible ZABs. Meanwhile, the battery not only show remarkable electrochemical performance over a wide temperature range (−20 to 80 °C), but also possess good stability and practicality under various extreme conditions. This work opens up new ideas for the development of hydrogel electrolytes with high adhesion and performance, and provides new strategies for the research of flexible batteries with adaptability to extreme conditions.

Dual cross‐linked self‐healing temperature and pressure sensor based on PAM/ENR/h‐BN composite

AbstractSensor of monitor of temperature and pressure changes are garnering constant attention due to their wide applications. It is a challenge to synthesize dual‐functional material with the well‐balanced performance to temperature response and pressure changes. In this work, we have proposed a facile way to fabricate tough, flexible, and self‐healing composite with dually synergistic networks for pressure and temperature sensors, which are composed of polyacrylamide (PAM) and elastic epoxidized natural rubber (ENR). PAM networks are crosslinked by N,N‐methylenebisacrylamide (MBA) and physical crosslinking of hydrophilic hexagonal boron nitride (h‐BN) nanosheets, ENR network is further interlocked and PAM by physical entanglements, hydrogen bonds. It is found that the ternary PAM/ENR/h‐BN (PEB) composite is highly sensitive to temperature, making it can be exploited as a thermistor. This thermistor possesses high flexibility and appealing mechanical performance, with the sensitivity as high as 1.87%/°C at temperature range of −13 to 90°C. Furtherly, the PEB composite also can work as a flexible pressure sensor at operating range of ~80% strain and ~540 KPa. Our research work provides a guideline for the preparation of temperature monitor, piezoresistive pressure sensors, as well as flexible electronic products.

Environmentally friendlier wireless energy power systems: The coil on a paper approach

Paper is ubiquitous in everyday life and a low-cost environmentally friendly material. Thus, the printing of advanced conductive/magnetic nanomaterials on paper will allow the scalable production of flexible smart electronics, including energy-storage devices, sensors, inductors or antennas, among others, contributing towards more sustainable electronics. Particularly, wireless charging technologies are becoming essential for internet-of-things (IoT)-related electronic devices due to the ever-decreasing dimensions of portable/mobile devices that limit the quantity of energy that can be stored. Here, screen-printed paper-based coils and inductors operating on the 1–20 MHz range are presented based on Poly(vynil alcohol)/Fe3O4 and Ag inks. The ability of the printed cores and inductors to be incorporated on flexible wireless power transfer modules (WPTM) is technologically demonstrated by wireless powering light-emitting diodes (LEDs). The achieved induction efficiency of 94% is the highest reported on printed and flexible WPTM. The printed coils are also characterized by mechanical, hydrophobic and electrical properties that are suitable for IoT and industry 4.0 applications.

Silver-Nanowire-Based Elastic Conductors: Preparation Processes and Substrate Adhesion.

The production of flexible electronic systems includes stretchable electrical interconnections and flexible electronic components, promoting the research and development of flexible conductors and stretchable conductive materials with large bending deformation or torsion resistance. Silver nanowires have the advantages of high conductivity, good transparency and flexibility in the development of flexible electronic products. In order to further prepare system-level flexible systems (such as autonomous full-software robots, etc.), it is necessary to focus on the conductivity of the system's composite conductor and the robustness of the system at the physical level. In terms of conductor preparation processes and substrate adhesion strategies, the more commonly used solutions are selected. Four kinds of elastic preparation processes (pretensioned/geometrically topological matrix, conductive fiber, aerogel composite, mixed percolation dopant) and five kinds of processes (coating, embedding, changing surface energy, chemical bond and force, adjusting tension and diffusion) to enhance the adhesion of composite conductors using silver nanowires as current-carrying channel substrates were reviewed. It is recommended to use the preparation process of mixed percolation doping and the adhesion mode of embedding/chemical bonding under non-special conditions. Developments in 3D printing and soft robots are also discussed.

Super strong and tough anisotropic hydrogels through synergy of directional freeze-casting, metal complexation and salting out

Strong and tough ionic conductive hydrogel is one of the key raw materials for the development of high-performance flexible electronic products. However, it is still challenging to prepare ionic conductive hydrogel materials with the integration of ultra-high mechanical strength, extremely high toughness and ionic conductivity. In this work, a simple strategy is proposed to prepare super strong and tough hydrogels through multi-length scale synergistic strengthening. The directional freeze-casting would endow hydrogels with good anisotropic structure at the micro-scale and the post-treatment of soaking in the saturated Na3Cit and Al2(SO4)3 composite solution would introduce metal complexation and chain entanglement to realize network structure densification at the sub-micro and nano-scale. These effects have been proven to be positive and synergistic, which can significantly increase the tensile strength, toughness and Young's modulus of the poly(vinyl alcohol)/carboxymethyl chitosan (PVA/CMCS) hydrogel. The optimum tensile strength, toughness, Young's modulus and tear energy of PVA/CMCS/Na3Cit/Al2(SO4)3 hydrogel reach 25.9 MPa, 90.9 MJ/m3, 422.6 MPa and 118.2 MJ/m2. This super strong and tough conductive hydrogel was assembled into a sensor and combined with Morse code to realize information transmission, encryption and decryption. This work provides a new scheme for the preparation of ultra-strong ionic conductive hydrogel for flexible electronics.

Paradigm Changing Integration Technology for the Production of Flexible Electronics by Transferring Structures, Dies and Electrical Components from Rigid to Flexible Substrates

Emerging trends like the Internet of Things require an increasing number of different sensors, actuators and electronic devices. To enable new applications, such as wearables and electronic skins, flexible sensor technologies are required. However, established technologies for the fabrication of sensors and actuators, as well as the related packaging, are based on rigid substrates, i.e., silicon wafer substrates and printed circuit boards (PCB). Moreover, most of the flexible substrates investigated until now are not compatible with the aforementioned fabrication technologies on wafers due to their lack of chemical inertness and handling issues. In this presented paper, we demonstrate a conceptually new approach to transfer structures, dies, and electronic components to a flexible substrate by lift-off. The structures to be transferred, including the related electrical contacts and packaging, are fabricated on a rigid carrier substrate, coated with the flexible substrate and finally lifted off from the carrier. The benefits of this approach are the combined advantages of using established semiconductor and microsystem fabrication technologies as well as packaging technologies, such as high precision and miniaturization, as well as a variety of available materials and processes together with those of flexible substrates, such as a geometry adaptivity, lightweight structures and low costs.

Biodegradable Cellulose Nanocomposite Substrate for Recyclable Flexible Printed Electronics

AbstractPrinted, flexible, and hybrid electronic technologies are advancing rapidly leading to remarkable developments in smart wearables, intelligent textiles, and health monitoring systems. Flexible electronics are typically fabricated on petroleum‐derived polymeric substrates. However, in the light of global environmental concerns regarding fossil raw materials, there is a need to drive the production of flexible electronics devices based on sustainable materials. Additionally, there is a need to reduce the quantity of electronic waste by developing material recovery and recycling technologies. Here, a fully biobased and biodegradable substrate tailored for printed flexible electronic applications is developed. Based on a nanocomposite of cellulose nanofibril (CNF) and hydroxyethyl cellulose (HEC), the substrate shows excellent mechanical and optical properties for printed flexible electronics applications. High‐resolution screen printing of conductive ink and typical electronics assembly processes are possible to realize on the substrate. An electrocardiograph (ECG) device is fabricated on the cellulosic substrate as a technology demonstrator and its performance is confirmed on human volunteers. Last, end‐of‐life scenarios are studied for printed electronic devices where device degradation and subsequent material recovery concepts are presented. This work demonstrates that sustainable plant‐derived materials can play a big role toward a green transition in the electronics industry.

Triboelectric Nanogenerator-Based Near-Field Electrospinning System for Optimizing PVDF Fibers with High Piezoelectric Performance

Electrospinning is an effective method to prepare polyvinylidene fluoride (PVDF) piezoelectric fibers with a high-percentage β phase. However, as an energy conversion material for micro- and nanoscale diameters, PVDF fibers have not been widely used due to their disordered arrangement prepared by traditional electrospinning. Here, we designed a near-field electro-spinning (NFES) system driven by a triboelectric nanogenerator (TENG) to prepare PVDF fibers. The effects of five important parameters (PVDF concentration, needle inner diameter, TENG pulse DC voltage (TPD-voltage), flow rate, and drum speed) on the β phase fraction of PVDF fiber were optimized one by one. The results showed that the electrospun PVDF fibers had uniform diameter and controllable parallel arrangement. The β phase content of the optimized PVDF fiber reached 91.87 ± 0.61%. For the bending test of a single PVDF fiber piezoelectric device, when the strain is 0.098%, the electric energy of the single PVDF fiber device of NFES reaches 7.74 pJ and the energy conversion efficiency reaches 13.5%, which is comparable to the fibers prepared by the commercial power-driven NFES system. In 0.5 Hz, the best matching load resistance of a PVDF single fiber device is 10.6 MΩ, the voltage is 6.1 mV, and the maximum power is 3.52 pW. Considering that TENG can harvest micromechanical energy in the low frequency environment, the application scenario of the NFES system can be extended to the wild or remote mountainous areas without traditional high-voltage power supply. Therefore, the electrospun PVDF fibers in this system will have potential applications in high-precision 3D fabrication, self-powered sensors, and flexible wearable electronic products.

Flexible All-Solid-State Direct Methanol Fuel Cells with High Specific Power Density.

It is vital to create flexible batteries as power sources to suit the needs of flexible electronic devices because they are widely employed in wearable and portable electronics. The direct methanol fuel cell (DMFC) is a desirable alternative portable energy source since it is a clean, safe, and high energy density cell. The traditional DMFC in mechanical assembly and its unbending property, however, prevent it from being employed in flexible electrical devices. In this study, the flexible membrane electrode assembly (MEA) with superior electrical conductivity and nanoscale TiC-modified carbon cloth (TiC/CC) is used as supporting layer. Additionally, solid methanol fuels used in the manufacturing of flexible all-solid-state DMFC have the advantages of being tiny, light, and having high energy density. Furthermore, the DMFC's placement and bending angle have little effect on its performance, suggesting that DMFC is appropriate for flexible portable energy. The flexible all-solid-state DMFC's power density can reach 14.06mWcm-2 , and after 50 bends at 60°, its voltage loss can be disregarded. The flexible all-solid DMFC has an energy density that is 777.78WhKg-1 higher than flexible lithium-ion batteries, which is advantageous for the commercialization of flexible electronic products.

A cold spray-based novel manufacturing route for flexible electronics

In this research, we propose a cold spray-based novel manufacturing route that enables the custom production of flexible electronics (FE) at high spatial resolution without a need of high-temperature post-sintering process. The proposed manufacturing route sequentially comprises: (1) cold spray metallization; (2) femtosecond laser machining; and (3) ultrasonic plastic welding. First, the flexible polymer (i.e., PET) surface is metallized by cold spray direct writing of Tin (Sn) particles under vacuum-and mask-free conditions. The as-metallized polymer film is then precisely cut into arbitrarily designed high-resolution electrodes (i.e., 500 μm linewidth) by femtosecond laser machining. Lastly, the laser-cut electrodes are joined onto a base polymer substrate via ultrasonic plastic welding to constitute mechanically resilient and conformal FE. In this way, the proposed route enables exploiting the unique features of cold spray deposits in FE (e.g., strong adhesion, high conductivity, minimal thermal input). The resultant printings show excellent electrical conductivity (1.08 × 106 S·m−1), flexibility (60 % elongation), and adhesion strength without significantly compromising intrinsic polymer and functional coating properties. Moreover, a serpentine-shaped flexible microheater (10 × 10 mm2) is also fabricated to demonstrate the viability of the introduced platform in flexible microelectronics. This work potentially provides a promising route toward the rapid, scalable, and cost-effective production of high-resolution and high-performance FE in a mechanically resilient and conformal manner.

Static Control for Roll-to-Roll Manufacturing

Roll-to-Roll (R2R) manufacturing is used extensively in printing and flexible packaging industries. These commercially important markets exceeded $30B USD annually in the US in 2019 with employment of about 79,000. In addition, R2R operations are increasingly used to produce flexible electronic products and medical devices, which are easily damaged by electrostatic discharges (ESD). Many materials used in R2R operations such as polypropylene are insulating making them prone to accumulating static charges. Sparks from accumulated charges can ignite fires, injury employees, and damage products. Accumulated charges also cause static cling, which can disrupt machine operations. I estimate that waste caused by static electricity from injuries, damaged products, and machine downtime exceeds $600M USD annually in the US. This human suffering and waste may be eliminated by effective static control systems. Implementing effective static control on an R2R manufacturing line is a 4-step, data-driven process. First, identify sources of static charging with a static survey. Next, install static dissipaters forming a fault-tolerant, static control system. Once static dissipaters are operational, verify that static is well controlled with second static survey. Lastly, maintain static performance by regularly verifying static performance and by including static control in Management of Change procedures.

Durable, highly sensitive conductive elastomeric nanocomposite films containing various graphene nanoplatelets and their derivatives

AbstractIn recent years, the use of nano‐fillers in flexible polymer matrix to prepare highly flexible, stretchable, and multifunctional product has been widely studied. However, the uneven dispersion of nano‐fillers in polymer matrix is an important factor hindering their performance. In this study, a method to prepare graphene nanosheets by ball milling and modification with the silane coupling agent APTES is reported, and this method can reduce the thickness of the nanosheets, improving the dispersion effect and compatibility of the nanosheets in the PDMS matrix. The mechanical and conductive properties of the prepared composite films were further analyzed. The morphology showed that our modified graphene (MGE and BMGE) are more evenly dispersed in the PDMS matrix compared to the unmodified graphene (GNP). The MGE/PDMS composite film has significantly improved electrical conductivity. It has a wide sensing range (up to 48%), high sensitivity (GF of 152 in the 20%–40% strain range) and reliable cycle repeatability (>10,000 cycles) with a response time of 0.12 s. The results show that the modified graphene/PDMS conductive elastic nanocomposite film is an ideal material for making flexible electronic products.