Flexible Electronic Devices Research Articles

Preparation of CoNi‐LDH‐Modified Polypropylene‐Based Carbon Fiber Membranes for Flexible Supercapacitors

ABSTRACTThe rapid development of flexible electronic devices has placed higher demands on the development of high‐performance flexible supercapacitors. In this work, a safe and simple method was developed to prepare cobalt–nickel layered double hydroxide (CoNi‐LDH) flexible electrodes. Metal–organic framework (MOF)‐derived CoNi‐LDH was successfully grown on the surface of polypropylene nonwoven flexible carbon fiber membranes through plasma oxidation treatment, grafting of cobalt‐based MOFs, and room‐temperature etching in Ni2+ solution. The prepared flexible modified carbon fiber membrane (CPO‐CoNi‐40‐0.5) has good mechanical properties with a tensile strength of 159.26 ± 63.03 kPa. In addition, the CPO‐CoNi‐40‐0.5 electrode has a high specific capacitance of 580 F g−1 at 1 A g−1. The assembled supercapacitor maintains 99% of the initial specific capacity after 7000 cycles and 98% of the initial specific capacity when it is folded at 90°, showing excellent long cycle stability and bending resistance. This paper provides a new way to promote the development of high‐performance and low‐cost flexible electrodes.

Influences of carbon nanotubes as electrode materials on the energy storage for lithium-ion batteries

Due to inherent theoretical capacity limitations and safety issues associated with commonly used anode materials in lithium-ion batteries, carbon nanotubes (CNTs), with their unique one-dimensional tubular structure and superior mechanical, electrical, and thermal properties, can partially address these deficiencies and enhance lithium storage capacity. Therefore, this paper concentrates on the impacts of carbon nanotubes as electrode materials on energy storage for lithium-ion batteries. It discusses three aspects in detail: the use of CNTs as direct anode materials, as composite anode materials, and as flexible electrode materials. Each application will be examined in terms of its specific advantages, existing challenges, and corresponding solutions to improve battery performance. The paper also evaluates the role of CNTs in enhancing the electrochemical stability, improving cycle life, and achieving higher power densities, which makes them highly promising for next-generation energy storage solutions, particularly for portable and flexible electronic devices. Additionally, the unique ability of CNTs to form a highly conductive network facilitates efficient charge transport and reduces internal resistance, further contributing to the overall performance of the battery. Future research directions may focus on optimizing the synthesis methods and improving the interface interactions between CNTs and other active materials, to fully leverage their properties for enhanced safety, higher efficiency, and lower costs. As such, carbon nanotubes are seen as key materials that could play an important role in meeting the growing demand for advanced energy storage systems.

On Demand Copper Electrochemical Deposition on Laser Induced Graphene for Flexible Electronics.

The rapid development of flexible electronics necessitates simplified processes that integrate heterogeneous materials and structures. In this study, laser engraving is combined with electrochemical deposition (ECD) to directly fabricate various micro/nano-structured components and flexible electronic circuits. A theoretical framework and simulation model are developed to design the on-demand ECD on laser induced graphene (LIG), enabling the generation of multi-scale copper (Cu) materials with controllable oxidation states. The Cu-LIG composites exhibit high surface quality and reliability, meeting the requirements of flexible circuits. The study fabricates and characterizes multilayer circuits and complex functional devices, including electrochemical sensors, thin-film heaters, and wireless humidity sensors, to showcase the versatility of the LIG-ECD process. This approach can be extended to various polymer and metal deposition processes, paving the way for the development of high-performance flexible electronic devices.

High-Efficiency Intrinsically Thermoplastic Semiconducting Polymer with Excellent Strain-Tolerance Capacity for Flexible Ultra-Deep-Blue Polymer Light-Emitting Diodes.

Complex internal stresses that appear in flexible thin-film electronic devices under long-term deformation operation are associated with incompatible mechanical properties of the multiple layers, which potentially cause intralayer fracture and separation. These defects may result in device instability, performance loss, and failure. Herein, a thermoplastic functional strategy is proposed for manufacturing high-performance stretchable semiconducting polymers with excellent strain-tolerance capacities for flexible electronic devices. Internal plasticization is used to obtain a thermoplastic light-emitting polymer (N2) that can suppress intralayer tensile fracture and compressive separation to enhance the deformation stability of flexible thin-film optoelectronic devices, enabling outstanding energy dissipation capacity under stress. The thermoplastic films exhibit stable and efficient ultra-deep-blue emission with a high efficiency of ≈90% and chromaticity coordinates of (0.16, 0.04). Moreover, the N2-based rigid and flexible polymer light-emitting diodes (PLEDs) exhibit stable ultra-deep-blue electroluminescence properties with high EQEs of ≈2.4% and 1.9%, respectively. Compared with devices based on brittle PODPF, flexible PLEDs based on thermoplastic films effectively suppress performance degradation after hundreds of cycles of bending fatigue, even under extremely rigid conditions. Introducing intrinsically thermoplastic semiconducting polymers in flexible electronic devices can thus substantially enhance their operational stability under deformation.

Gum arabic-CNT reinforced hydrogels: dual-function materials for strain sensing and energy storage in next-generation supercapacitors

Recent advancements in the field of conductive hydrogels have made these promising candidates for the development of human motion sensors, for energy storage in soft and flexible electronic devices, owing to their excellent mechanical properties.

Carbon nanotube-doped Ag[formula omitted]O ink: A cost-effective method for strengthening inkjet-printed flexible circuits

Silver ink demonstrates significant potential in the field of printed electronics due to its excellent electrical conductivity and stability. However, traditional silver electrodes still face issues such as microscopic fractures under mechanical stresses like bending, twisting, and stretching, which are common in conformal circuits and flexible electronic devices. This study introduces a cost-effective, one-step method for synthesizing high stability carbon nanotube (CNT)-doped Ag2O ink. The feasibility of using CNTs as a scaffold with silver as the conductive network is validated. The study investigated the microscopic structural characteristics and composition of the printed films. It also analyzed their electrical conductivity and mechanical properties before and after annealing. A special surfactant ratio was employed to ensure the ink remains stable for an extended period of time. In testing, CNT-doped silver films exhibit exceptional electrical conductivity, and the printed lines achieve extremely low resistance after low-temperature (200 °C) annealing. The ink with a 5.45% mass fraction of CNTs achieved a minimum resistivity of approximately 1.4×10−7Ωm. Under external twisting forces, CNTs enhance the yield strength of the conductors by transferring and absorbing stress, refining the grain structure within the conductive network, and increasing the dislocation density. The printed circuits maintained nearly the initial resistivity even after multiple twists. The CNT-doped Ag2O ink demonstrates outstanding mechanical strength and flexibility, showcasing its potential for practical applications.

Application of organic semiconductors in flexible electronic devices

Application of organic semiconductors in flexible electronic devices

Laser writing of metal-oxide doped graphene films for tunable sensor applications.

Flexible and wearable devices play a pivotal role in the realm of smart portable electronics due to their diverse applications in healthcare monitoring, soft robotics, human-machine interfaces, and artificial intelligence. Nonetheless, the extensive integration of intelligent wearable sensors into mass production faces challenges within a resource-limited environment, necessitating low-cost manufacturing, high reliability, stability, and multi-functionality. In this study, a cost-effective fiber laser direct writing method (fLDW) was illustrated to create highly responsive and robust flexible sensors. These sensors integrate laser-induced graphene (LiG) with mixed metal oxides on a flexible polyimide film. fLDW simplifies the synthesis of graphene, functionalization of carbon structures into graphene oxides and reduced graphene oxides, and deposition of metal-oxide nanoparticles within a single experimental laser writing setup. The preparation and surface modification of dense oxygenated graphene networks and semiconducting metal oxide nanoparticles (CuO x , ZnO x , FeO x ) enables rapid fabrication of LiG/MO x composite sensors with the ability to detect and differentiate various stimuli, including visible light, UV light, temperature, humidity, and magnetic fluxes. Further, this in situ customizability of fLDW-produced sensors allows for tunable sensitivity, response time, recovery time, and selectivity. The normalized current gain of resistive LiG/MO x sensors can be controlled between -2.7 to 3.5, with response times ranging from 0.02 to 15 s, and recovery times from 0.04 to 6 s. Furthermore, the programmable properties showed great endurance after 200 days in air and extended bend cycles. Collectively, these LiG/MO x sensors stand as a testament to the effectiveness of fLDW in economically mass-producing flexible and wearable electronic devices to meet the explicit demands of the Internet of Things.

Carbon black-induced edge guided-metal lateral electrodeposition and its application in paper-based flexible electronic devices

Edge guided-metal lateral electrodeposition.

Blister test to measure the out-of-plane shear modulus of few-layer graphene.

We measure the out-of-plane shear modulus of few-layer graphene (FLG) by a blister test. During the test, we employed a monolayer molybdenum disulfide (MoS2) membrane stacked onto FLG wells to facilitate the separation of FLG from the silicon oxide (SiOx) substrate. Using the deflection profile of the blister, we determine an average shear modulus G of 0.97 ± 0.15 GPa, and a free energy model incorporating the interfacial shear force is developed to calculate the adhesion energy between FLG and SiOx substrate. The experimental protocol can be extended to other two-dimensional (2D) materials and layered structures (LS) made from other materials (WS2, hBN, etc.) to characterize their interlayer interactions. These results provide valuable insight into the mechanics of 2D nano devices which is important in designing more complex flexible electronic devices and nanoelectromechanical systems.

Unexpected piezoelectric properties of electrospun polyimide nanofibers for application in an extreme environment

The piezoelectric properties of FPI nanofibers were first discovered. This makes it a potential material for manufacturing wearable flexible electronic devices in extreme environments.

High‐Resolution Self‐Assembly of Functional Materials and Microscale Devices via Selective Plasma Induced Surface Energy Programming

AbstractCurrent technologies preclude effective and efficient self‐assembly of heterogeneous arrangements of functional materials between 10−1 and 10−5 m. Consequently, their fabrication is dominated by methods of direct material manipulation, which struggle to meet the designers’ demands regarding resolution, material freedom, production time, and cost. A two‐step, computer‐controlled is presented, multi‐material self‐assembly technique that allows heterogenous patterns of several centimeters with features down to 12.5 µm in size. First, a micro plasma jet selectively programs the surface energy of a polydimethylsiloxane substrate through localized chemical functionalization. Second, polar fluids containing functional materials are simplistically introduced which then self‐assemble according to the patterned regions of high surface energy over timescales of the order of seconds. In‐process control enables both high‐resolution patterning and high throughput. This approach is demonstrated to produce heterogenous patterns of materials with varying conductive, magnetic, and mechanical properties. These include magneto‐mechanical films and flexible electronic devices with unprecedented processing times and economy for high‐resolution patterns. This self‐assembly approach can disrupt the current lithography/direct write paradigm that dominates micro/meso‐fabrication, enabling the next generation of devices across a broad range of fields via a flexible, industrially scalable, and environmentally friendly manufacturing route.

Preparation and electromagnetic waves absorption performance of novel peanut shell/CoFe2O4/(RGO)x/PVA nanocomposites

Novel functional materials possessing the capability to attenuate electromagnetic energy are being increasingly incorporated into home decor as concerns over excessive electromagnetic radiation pollution continue to grow. The properties of magnetism and dielectricity in the flexible peanut shell/CoFe2O4/reduced graphene oxide/polyvinyl alcohol (PS/CF/(RGO)x/PVA) nanocomposites can be finely tuned by adjusting the amount of RGO in the mixture. An examination of the composite’s absorption capabilities revealed a direct link between higher RGO content and enhanced absorption. Due to the presence of multiple pathways for electromagnetic wave transmission through the three-dimensional porous structure, as well as the synergistic effects of dielectric-magnetic properties and various defects in the carbon derived from peanut shells, the PS/CF/(RGO)x/PVA nanocomposites exhibit remarkable impedance matching and exceptional attenuation capabilities to -20.98404 dB for a thickness of 1 mm. Additionally, the PS/CF/(RGO)x/PVA nanocomposites have shown great promise in the production of flexible electronic devices like light-dependent resistors. Their lightweight and flexible nature play a crucial role in their success in this application. It is worth mentioning, however, that these nanocomposites bear a resemblance to traditional absorber equipment used in the industry.

Fabrication of Nano Copper Highly Conductive and Flexible Printed Electronics by Direct Ink Writing.

Nanoscale metals have emerged as crucial materials for conductive inks in printed electronics due to their unique physical and chemical properties. However, the synthesis of high-precision and highly conductive copper ink remains a challenge. Herein, a high-precision, highly conductive, and oxidation-resistant nanocopper ink was synthesized to fabricate highly conductive and flexible printed electronic devices. Copper nanoparticles with a particle size of only 8.5 nm, a controllable structure, and excellent oxidation resistance were synthesized by the alcohol phase reduction method. The conductive ink was formulated with ethylene glycol, ethanol, and isopropanolamine (IPA) as the solvent, exhibiting excellent printability and sintering reducibility. Fluid dynamics simulations were employed to investigate the influence of printing parameters on the circuit forming performance, enabling precise control over the printing process. The sintering behavior of copper nanoparticles with varying particle sizes was investigated by combining experiments with molecular dynamics (MD) simulations. Highly conductive and flexible circuits were fabricated using direct ink writing (DIW) under low-temperature sintering, exhibiting a low resistance level as low as 1.9 μΩ·cm. Moreover, the circuit demonstrated an excellent adhesion performance and bending flexibility. The developed copper ink demonstrates outstanding printing potential for applications in flexible electronics, advancing the field of flexible printing and wearable electronic devices.

Development and Applications of Polypyrrole‐Based Conductive Inks: An Overview

AbstractDue to their flexibility, high conductivity, stability, monodispersity, and ease of processing; polypyrrole‐based conductive inks hold significant advancements in printing, biomedical and electronic applications. These inks enable innovative solutions in flexible electronics, wearable devices, sensors, and energy storage systems and also facilitate high‐quality printed films on various rigid and flexible substrates, supporting diverse applications from flexible circuits to smart textiles. Notably, in biomedicine, they exhibit excellent biocompatibility, and cell adhesion, aiding in tissue engineering and stem cell therapies. They serve as bioinks for 3D printing free‐standing scaffolds, showing potential for creating electrically active tissue constructs. Additionally, polypyrrole inks are crucial for developing highly specific and sensitive sensors for detecting gases, chemicals, and biological analytes and efficient energy storage devices like supercapacitors. As research progresses, these inks are pivotal in the future of lightweight, flexible, portable, and wearable electronic materials and devices. This review covers a general overview of various types of polypyrrole‐based conductive inks, highlighting their major applications and impacts.

Sustainable Soft Electronics with Biodegradable Regenerated Cellulose Films and Printed Recyclable Silver Nanowires

AbstractThis study describes the production of biodegradable and recyclable flexible electronic devices created by screen‐printing silver nanowires (AgNWs) onto regenerated cellulose films (RCFs). RCFs, derived from microcrystalline cellulose (MCC), are developed and further enhanced for flexibility with additives such as glycerol and poly(ethylene glycol) diglycidyl ether (PEGDE). The resulting cellulose films display relatively high tensile strength (up to 120 MPa), low Young's Modulus (down to 1500 MPa), and 90% optical transparency. Ink with AgNWs and poly(ethylene oxide) (PEO) as a binder is screen‐printed on regenerated cellulose films. The printed AgNWs patterns exhibit high electrical conductivity, excellent electromechanical performance, and strong interfacial adhesion with RCFs. To demonstrate the application of printed AgNWs on RCFs for soft electronics, transparent conductive electrodes (TCEs) are fabricated. Grid and honeycomb structures are printed separately and evaluated in terms of sheet resistance and optical transparency. TCEs with ≈80% transparency and very low sheet resistance (0.045 Ω sq−1) are obtained. Furthermore, enzymatic hydrolysis of the cellulose substrate and the recovery for reuse of the AgNWs are demonstrated, showing the potential of integrating natural polymers and recyclable nanomaterials for eco‐friendly and sustainable soft flexible electronics.

Response surface methodology assisted optimization of ultrafast laser lift-off micro-LEDs

ABSTRACT Ultrafast laser lift-off is an important step in manufacturing flexible electronic display devices. To improve the picosecond laser lift-off transfer quality of micro light emitting diodes (micro-LEDs), the response surface methodology (RSM) is employed for the optimization of multiple laser processing parameters, including laser power, scanning speed, spot diameter, and scanning distance. Transfer yield and residual stress are chosen as the performance evaluation metrics, as well as the lifted-off device element composition and transfer quality under different process parameters are characterized. The optimized maximum transfer yield is 95.84% and the minimum residual tensile stress is 0.589 GPa, which is less than 0.5% prediction error of the optimum transfer yield (95.67–95.74%) and residual stress (0.588–0.592 GPa) for ultrafast laser lift-off of micro-LEDs based on the central composite design of RSM, indicating the reliable guidance ability of this model. It develops a new way for quality improvement of the ultrafast laser lift-off process for micro-LEDs.

Liquid Crystal/Carbon Nanotube/Polyaniline Composites and Their Coating Orientation Patterning Applications

In this work, a coating method was used to prepare a liquid crystal physical gel with a high orientation of liquid crystal molecules, excellent electrical conductivity, and mechanical stability. The liquid crystal matrix used was nematic phase liquid crystal (5CB), the gel factor was polyvinyl alcohol (PVA), and the conductive filler was carbon nanotubes/polyaniline (CNT/PANI). Chemical in situ polymerization was used to create CNT/PANI composites, wherein polyaniline encapsulates the carbon nanotubes to enhance their dispersion. At 4 mm/s, 7.2 N of coating pressure, and 72 s of interval duration, the shear flow-induced orientation was achieved. The consistent and large-area orientation of the liquid crystal molecules was realized and the orientation direction of the liquid crystal molecules was parallel to the coating direction. Additionally, a type of stress sensor assembly based on multiple coating demonstrated a good sensor performance in the 90° bending test and high sensitivity in the 20% tensile test, with a sensor sensitivity of 23.25. Regarding the use of liquid crystal materials in flexible electronic devices, it is quite important.

Flexible and Multifunctional Biomass‐Based Chlorella Hydrogels for High‐Performance Wearable Electronics

AbstractBiomass‐based hydrogels have emerged as promising soft sensing materials to prepare the flexible biomimetic electronic devices for human health monitoring, due to their good stretchability, interfacial adhesion, and biocompatibility. Here, a simple and effective freeze‐thaw method is proposed to prepare the flexible and ductile biomass‐based Chlorella hydrogels for wearable capacitive strain sensor devices. Ascribing to the formation of dynamic physical cross‐linking (hydrogen bonding) between Chlorella and polyvinyl alcohol networks, the obtained Chlorella hydrogels exhibit considerable conductivity and good stretchability (tensile strain > 450%). Moreover, this hydrogel can be used as sensing materials to fabricate the capacitive strain sensor with considerable sensitivity, remarkable mechanical durability, wide working range, and good sensing stability. Furthermore, the conductive hydrogel electrolyte is paired with activated carbon electrodes to build a sandwich‐style supercapacitor. The flexible all‐solid‐state supercapacitor exhibits excellent cycling performance and outstanding stability. Intriguingly, the Chlorella hydrogels also reveal excellent antibacterial performance (against E. coli and S. aureus) and good pH response. These functional features make the biomass‐based Chlorella hydrogels valuable for practical healthcare applications.

Hybrid Strategies for Enhancing the Multifunctionality of Smart Dynamic Molecular Crystal Materials.

Dynamic molecular crystals are an emerging class of smart engineering materials that possess unique ability to convert external energy into mechanical motion. Moreover, they have being considered as strong candidates for dynamic elements in applications such as flexible electronic devices, artificial muscles, sensors, and soft robots. However, the inherent defects of molecular crystals like brittleness, short-life and fatigue, have significantly impeded their practical applications. Inspired by the concept of "the whole is greater than the sum of its parts" in the field of biology, building stimuli-response composites materials can be regarded as one of the ways to break through the current limitations of dynamic molecular crystals. Moreover, the hybrid materials can exhibit new functionalities that cannot be achieved by a single object. In this review, the focus was placed on the analysis and discussion of various hybrid strategies and options, as well as the functionalities of hybrid dynamic molecular crystal materials and the important practical applications of composite materials, with the introduction of photomechanical molecular crystals and flexible molecular crystals as a starting point. Moreover, the efficiency, limitations, and advantages of different hybrid methods were compared and discussed. Furthermore, the promising perspectives of smart dynamic molecular crystal materials were also discussed and the potential directions for future work were suggested.