Use In Flexible Electronics Research Articles

Molecularly engineered chitosan-derived poly(aprotic/protic ionic liquids) double-network hydrogel electrolytes for flexible supercapacitors and wearable strain sensors

Polymeric conductive hydrogels have been highlighted for use in flexible electronics, and there is still a challenge to design and fabricate a high-performance hydrogel electrolyte with integrated and multiple properties, such as sustainability, stretchability and compressibility, ionic conductivity, antibacterial property, strain sensitivity, and low-temperature tolerance. Herein, chitosan (CS) derived poly(aprotic/protic ionic liquids) (CS-PAPILs) are facilely prepared by taking the structural and sustainable features of chitosan and betaine hydrochloride, which are used as a functional component for the fabrication of CS-PAPILs/polyacrylamide (PAM)/LiCl (CS-PAPILs/PAM/LiCl) double-network (DN) hydrogel electrolyte via an in situ polymerization of AM and then a soaking strategy in LiCl aqueous solution. The achieved DN hydrogels exhibit tunable mechanical performance (tensile strength of 70–900 kPa, elastic modulus of 31.5–484 kPa, high compressibility (4450 kPa at 80 % strain), superior low-temperature tolerance (freezing point < -85 °C), anti-dehydration performance, high ionic conductivity at 25/-50 °C (94.8/4.6 mS cm−1), and excellent antibacterial activity. As a proof of concept, an assembled flexible and anti-freezing supercapacitor by the as-prepared DN hydrogel electrolyte demonstrated a high specific capacitance of 108.4F/g (at 2 A/g) and impressive cycling stability over 50,000 cycles at temperature as low as −50 °C. Furthermore, a wearable strain sensor based on the DN hydrogel was also demonstrated, and the sensor can be successfully attached to the human joints to monitor various human motions.

Flexible strained membranes of multiferroic TbMnO3

The multiferroic properties of TbMnO3 demonstrate high versatility under applied pressure, making the material potentially suitable for use in flexible electronics. Here, we report on the preparation of elastic freestanding TbMnO3 membranes with dominant (001) or (010) crystallographic out-of-plane orientation. Membranes with a thickness of 20 nm display orthorhombic bulk-like relaxed lattice parameters with strong suppression of twinning for the (010) oriented membranes. Strain in flexible membranes was tuned using a commercial strain cell device and characterized by Raman spectroscopy. The B1g out-of-phase oxygen-stretching mode, representative of the Mn–O bond distance, systematically shifts to lower energy with increasing strain (εmax ≈ 0.5%). The flexibility and elastic properties of the membranes allow for specific manipulation of the multiferroic state by strain, whereas the choice of the crystallographic orientation gives the possibility of an in- or out-of-plane electric polarization.

Graphene - Carbon Quantum Dot Ink Formulation: Porposal &amp; Conceptualization

This proposal presents a novel method to improve the conductivity and adaptability of conductive inks by using graphene and carbon quantum dots. The goal is to generate an ink formulation with improved mechanical flexibility, electrical conductivity, and charge transport by mixing these nanoparticles. Printability, adherence, and conductivity on a range of substrates—including paper, plastics, and textiles—will all be maximized for this formulation. To guarantee stability, rheological control, and compatibility with current printing technology, the ink will go through a thorough evaluation and characterization process. This ground-breaking conductive ink has the potential to transform a number of sectors and advance sustainable technology through its use in flexible electronics, energy storage devices, smart packaging, and other areas.

Hybrid Transfer Printing of Liquid Metals and Allied Inks for Rapid Fabrication of Multifunctional Soft Electronics.

The newly emerging liquid metal flexible electronics are gaining increasing applications over the world due to their outstanding adaptability and printability. Here, we proposed a generalized purpose thermo-activated hybrid transfer printing method for the rapid fabrication of multifunctional soft electronics, which can significantly reduce the difficulty facing existing technologies. This printing involves two delivery and deposition processes of liquid metals and the allied inks (toners) based on their adhesion selection mechanisms. Through developing office supplies, the laser printer could directly print toner masks on soft substrates, such as polydimethylsiloxane film. The heating plate was applied to remove the toner sacrificial mask after rolling liquid metal inks, resulting in retaining the liquid metal circuits on the target substrate. For illustration, diverse materials and inks are adapted to the strategy of constructing flexible electronics. Particularly, colorful circuits, flexible heaters, transparent circuitry, and soft programmable light-emitting diode array displays with multilayer circuits have been fabricated and tested. This general and easily accessible method allows for the rapid acquisition of user-designed soft electronics and is expected to promote the widespread use of flexible electronics in e-skin, sensing, displays, etc.

Self-supported flexible organic electrochemical synaptic transistors on self-healing composite electrolyte membranes

A variety of organic electrochemical transistors have been recently developed; however, their self-healing performance has been largely ignored. In this study, we propose the use of a lithium-ion composite electrolyte membrane as a dielectric layer and the use of poly(3-hexylthiophene) (P3HT) as a channel layer to fabricate flexible self-supporting organic synaptic transistors. A variety of synaptic behaviors were emulated within the proposed organic synaptic transistors. By leveraging the self-healing features of polymer electrolytes, along with cross-linking reactions and low-resistance lithium-ion transmission, the device maintained its electrical performance. Testing involving different curvatures also revealed the device's potential for use in flexible electronics. Significantly, due to the device's self-healing ability, consistent dataset recognition rates were sustained. This work highlights its vast prospects in the field of flexible and wearable electronics.

Study of electrical conductivity, biocompatibility and degradation effect of copper electrodes with hydrogel coatings for use in flexible electronics

Study of electrical conductivity, biocompatibility and degradation effect of copper electrodes with hydrogel coatings for use in flexible electronics

Simultaneously enhancing the mechanical robustness and conductivity of ionogels by in situ formation of coordination complexes as physical crosslinks

Ionogels with environmental tolerance have recently emerged as promising candidates for use in flexible electronics.

Deep eutectic solvent-based eutectogels consisting of ZnCl2 and lignin for quasi-solid-state supercapacitors

Eutectogels have attracted attention for use in flexible electronics and energy storage because of their high conductivity and good mechanical properties.

(Invited) Water-Based and Defect-Free 2D Material Inks for Printed Electronics

2D materials show great promise for use in flexible electronics because their atomic thickness allows for maximum electrostatic control, optical transparency, sensitivity and mechanical flexibility. In addition, different 2D crystals can be easily combined in one stack, offering unprecedented control on the performance and functionalities of the resulting heterostructure-based device. In addition, solution processing of 2D materials allows simple and low-cost techniques, such as ink-jet printing, to be used for fabrication of heterostructure-based devices of arbitrary complexity.Our group has developed highly concentrated, defect-free, biocompatible, inkjet printable and water-based 2D crystal formulations, by exploiting a supramolecular approach based on non-covalent functionalization of 2D materials with pyrene derivatives [1]. Examples of printed heterostructures, such as arrays of photosensors, programmable logic memories, transistors and memristors will be discussed [2-3]. I will show that inkjet printing can be easily combined with semiconducting 2D materials produced by chemical vapor deposition, allowing simple and quick fabrication of complex circuits on paper, compatible with CMOS technology [4-5] and also offers a simple way to integrate 2D materials into Si-based technology [6].

Self‐powered transparent photodetector for subretinal visual functions of wide‐field‐of‐view and broadband perception

AbstractNatural photoreceptors enable color vision in humans, wherein the eyes detect colors and their corresponding intensities via cone and rod photoreceptors, respectively. Herein, we developed an artificial broadband photoreceptor with light‐color intensity detection similar to that of natural photoreceptors. The developed photoreceptor operates in the self‐powered mode and is capable of broadband perception (365–940 nm). The designed metal‐oxide heterojunction (n‐ZnO/p‐NiO) photoreceptor with a thin tin sulfide layer embedded in between is capable of perceiving various colors. It exhibits good transparency in the visible range and displays excellent integration with flexible substrates, highlighting its potential for use in flexible electronics. The fabricated structure has an exceptional response time (≈1 ms) and a wide‐field‐of‐view (150°) compared to the human eye's sensing range (50–100 ms and 108°). The transparent photoreceptor mimics cones and rods to detect a various wavelength‐dependent signals and explicitly differentiate between the intensities of the detected signals, respectively. This is further illustrated by employing the developed photoreceptor to detect colors in real time by generating unique signals corresponding to each color. The demonstration provides the proof of concept for self‐biased flexible bioelectronics emulating high‐performing visual functions of artificial eyes.image

Estimation of the work of adhesion between ITO and polymer substrates: a surface thermodynamics approach.

Indium tin oxide (ITO) is one of the most widely used semiconductor among transparent conducting oxides (TCOs) due to their electrical conductivity and optical transparency properties. Since the development of low temperature deposition methods, coating of ITO on polymer substrates especially for use in flexible electronics has been a popular topic. The existence of adequate adhesion strength between ITO and polymer is critical in producing a successful film. Nowadays, polycarbonate (PC), poly(methyl methacrylate) (PMMA) and polyethyleneterephtalate (PET) are frequently used as substrates for such coatings. However, there may be other polymeric alternatives that have a potential to be used for this purpose in the future. To evaluate these alternatives, work of adhesion (Wa) knowledge between ITO and polymers is necessary, and it has not been handled systematically previously. In this study, the interphase interaction parameters and Wa values between ITO and various polymers were calculated based on the Dupré, Fowkes and Girifalco-Good equations. PC, PMMA, PET, polystyrene (PS), polyphenylene sulfide (PPS), Nylon 66, polypropylene (PP), polyvinylchloride (PVC), styrene-butadiene rubber (SBR), high density polyethylene (HDPE), low density polyethylene (LDPE), polyvinyl acetate (PVAc), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTrFE) and polyperfluoroalkylethyl acrylate (PPFA) were considered as substrate material. Surface free energy (SFE) components calculated by acid-base, geometric mean and harmonic mean approaches for polymeric substrates were used during the calculations. In the present study, the polymers that can be used as substrates were evaluated in terms of adhesion ability to ITO, the significance of calculation methods on Wa values were also investigated simultaneously. It was determined that the Wa between ITO and polymer substrates was directly related with the total SFE value of the polymers.

The development of graphene and its use in flexible electronics

In recent years, graphene has been deeply studied by scholars, and has attracted high attention in the field of flexible electronics. In order to better understand the properties and application of graphene, this article systematically summarized and analyzed the applications in the field of flexible electronics from multiple angles to better display its characteristics. It mainly introduces the development, preparation method, classification, and application of graphene. Since its discovery in 2004, it has become a special and useful nanomaterial. Graphene has been widely used in the field of flexible electronics in the past few years due to its excellent mechanical properties, electrical conductivity, and transparency. Moreover, we specifically show the development trends and application characteristics of graphene in flexible solar cells, field-effect transistors, nanogenerators. In addition, the problems facing graphene are also mentioned. Finally, the development prospects of graphene-based flexible electronics are presented and suggested for further studies.

(Digital Presentation) Enhanced Streaming Vibration Potential By Silane-Modificated Mxene/PVA Hydrogel for High-Performance Flexible Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) play a vital role in self-powered electronics, based on their superior energy harvesting ability and simple construction. In this work, polyvinyl alcohol (PVA) hydrogel is fabricated, exhibiting a three-dimensional (3D) network structure that allows PVA chains to be covered by a large amount of water. Combining MXene nanosheets with the hydrogel TENG, the composite improves the ion transport of the hydrogel and provides the streaming vibration potential (SVP) mechanism. This composite effectively enhances the output performance of hydrogel TENG. Furthermore, this work adopts different functional groups of silane (APTES, CPTMS, FOTS) to modify the surface work function of MXene nanosheets. The surface modification increases the charge density at the interface between MXene and water inside the hydrogel, improving the electrical output performance and mechanical sensitivity of MXene hydrogel TENG (MH-TENG). The result demonstrates that the electrical output performance of MH-TENGs modified by 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (FOTS) is approximately two times larger (output-voltage~85 V/output-current~240 nA) than pristine hydrogel TENG (output-voltage~40 V/output-current~100 nA). The MH-TENG behaves unlimited potential in the use of flexible electronics, such as movement monitoring electronics, strength sensors on the paddle, and wearable energy harvesting devices in the future.

Preparation of isolated semiconducting single-wall carbon nanotubes by oxygen-assisted floating catalyst chemical vapor deposition

Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising for use in flexible electronics as a channel material. However, it remains a big challenge to directly grow high purity, high-quality s-SWCNTs in large scale. Here we report the synthesis of isolated s-SWCNTs by an oxygen-assisted floating catalyst chemical vapor deposition method. By controlling the density of nucleated SWCNTs, isolated or small-bundled, rather than large-bundled SWCNTs were generated in a floating state, so that the oxygen introduced could more efficiently selectively etch the metallic-SWCNTs formed. In addition, it was found that the oxygen also functions in limiting the size of Fe catalyst nanoparticles in a narrow range of 5–8 nm. As a result, isolated s-SWCNTs with a narrow diameter distribution were synthesized. The content of s-SWCNTs reached ∼96%, and the percentage of isolated tubes was estimated to be ∼83%. Thin-film transistors (TFTs) constructed using the s-SWCNT film showed high on/off ratios ranging from 2.1 × 104 to 1.2 × 106, verifying the effective enrichment of s-SWCNTs.

Influence of interlayers on the interfacial behavior of Ag films on polymer substrates

With the wider use of flexible electronics and sensors it is necessary to better understand how the substrate chemistry as well as the use of relatively brittle interlayers influences the electro-mechanical and interfacial behavior of electrically conductive thin films. Here, silver (Ag) films sputter deposited on polyimide (PI) and polyethylene naphthalate (PEN) with and without a titanium (Ti) adhesion layer were studied with in-situ electrical resistance measurements during uniaxial straining to study the electro-mechanical response with the cracking factor. Additionally, a molybdenum (Mo) stressed overlayer was utilized with the tensile induced delamination method to quantitatively measure the adhesion energies of the different material systems. It is demonstrated that the substrate chemistry, in terms of the mechanical behavior and number of C = O groups, plays a significant role in how through thickness cracks elongate and how the Ag and Ti may chemically bond to the polymer substrates. In general, a Ti interlayer degrades the electrical behavior, but can improve the interface adhesion of Ag to PI substrates. For PEN substrates, Ti is found to lower the adhesion compared to Ag alone. This new knowledge on the material interactions can be used to improve future flexible electronic thin film systems.

Biocompatibility Testing of Liquid Metal as an Interconnection Material for Flexible Implant Technology.

Galinstan, a liquid metal at room temperature, is a promising material for use in flexible electronics. Since it has been successfully integrated in devices for external use, e.g., as stretchable electronic skin in tactile sensation, the possibility of using galinstan for flexible implant technology comes to mind. Usage of liquid metals in a flexible implant would reduce the risk of broken conductive pathways in the implants and therefore reduce the possibility of implant failure. However, the biocompatibility of the liquid metal under study, i.e., galinstan, has not been proven in state-of-the-art literature. Therefore, in this paper, a material combination of galinstan and silicone rubber is under investigation regarding the success of sterilization methods and to establish biocompatibility testing for an in vivo application. First cell biocompatibility tests (WST-1 assays) and cell toxicity tests (LDH assays) show promising results regarding biocompatibility. This work paves the way towards the successful integration of stretchable devices using liquid metals embedded in a silicone rubber encapsulant for flexible surface electro-cortical grid arrays and other flexible implants.

Conductive self-standing nanofiber fabric of fluorine-doped tin oxide prepared by electrospinning for use in flexible electronics

To realize a conductive substrate with heat resistance and flexibility for the application to flexible electronics, we aimed to reduce the resistance of the fluorine-doped tin oxide (FTO) ceramic nanofiber (NF) non-woven fabrics produced by the electrospinning method. Using NH4F and SnF2 as the raw materials for fluorine doping, the structure and electrical properties of FTO-NF non-woven fabric were compared. The non-woven fabrics obtained in both solutions were several cm square made by NFs with a diameter of 150~800 nm, and all NFs consisted of nanoparticles with a diameter of about 20 nm. The resistivity of the FTO-NF fabric could be reduced to $$5.19 ~\mathrm{\Omega \cdot cm}$$ by the improvements such as adding tin isopropoxide and mixing without using water for a solvent without making a precursor of FTO so that the raw material is uniformly adsorbed on the polymer in the solution. By considering the space occupancy of the NFs in the fabric, the minimum net resistivity of the FTO-NF fabric was estimated to be $$0.56 ~ \mathrm{\Omega \cdot cm}$$ . Since the obtained FTO fabric was brittle and cracked when bent, we made a prototype of a three-layer NF non-woven fabric composited with amorphous SiO2 NFs. The sheet resistance was $$6.4 ~\mathrm{k\Omega /sq}$$ , no cracks or breaks occurred even when wrapped around a glass rod with a diameter of 5 mm $$\phi$$ , and the rate of increase in the resistance after 100 bends could be suppressed to 4.9%.

One-step photonic curing of screen-printed conductive Ni flake electrodes for use in flexible electronics

Photonic curing has shown great promise in maintaining the integrity of flexible thin polymer substrates without structural degradation due to shrinkage, charring or decomposition during the sintering of printed functional ink films in milliseconds at high temperatures. In this paper, single-step photonic curing of screen-printed nickel (Ni) electrodes is reported for sensor, interconnector and printed electronics applications. Solid bleached sulphate paperboard (SBS) and polyethylene terephthalate polymer (PET) substrates are employed to investigate the electrical performance, ink transfer and ink spreading that directly affect the fabrication of homogeneous ink films. Ni flake ink is selected, particularly since its effects on sintering and rheology have not yet been examined. The viscosity of Ni flake ink yields shear-thinning behavior that is distinct from that of screen printing. The porous SBS substrate is allowed approximately 20% less ink usage. With one-step photonic curing, the electrodes on SBS and PET exhibited electrical performances of a minimum of 4 Ω/sq and 16 Ω/sq, respectively, at a pulse length of 1.6 ms, which is comparable to conventional thermal heating at 130 °C for 5 min. The results emphasize the suitability of Ni flake ink to fabricate electronic devices on flexible substrates by photonic curing.

Energetics of graphene origami and their “spatial resolution”

The extreme thinness of graphene combined with its tensile strength made it a material appealing for discussing and even making complex cut-kirigami or folded-only origami. In the case of origami, its stability is mainly defined by the positive energy of the single- or double-fold curvature deformation counterbalanced by the energy reduction due to favorable van der Waals contacts. These opposite sign contributions also have notably different scaling with the size L of the construction, the contacts contributing in proportion to area ~ L2, single folds as ~ L, and highly strained double-fold corners as only ~ L0 = const. Computational analysis with realistic atomistic-elastic representation of graphene allows one to quantify these energy contributions and to establish the length scale, where a single fold is favored (7 nm 21 nm), defining the size of the smallest possible complex origami designs as L ≫ 21 nm. The flexibility and foldability of graphene are some of its attractive properties inspiring the designs of origami structures with potential use in flexible electronics and electromechanical nanodevices. The aesthetics, precision, and ease of folding and stability, however, have limitations at the nanoscale. Here, by means of large-scale atomistic calculations and continuum models, it is quantified how the dimensions determine the relative robustness of the elementary folds of graphene (a single fold and a double-folded graphene forming a single order-four vertex), thereby mapping the spatial resolution limits and providing important guidance for graphene nano-origami realizations.

Fundamental Insights into Graphene Strain Sensing.

Graphene has been studied extensively for use in flexible electronics as ultrasensitive and wide-area strain sensors. Many sensors demonstrated so far rely on graphene networks, such that the spatial resolution is compromised, and they are unable to measure strain variations on a fine scale such as those resulting from substrate/interface failure. In this study, mono-/few-layer graphene are demonstrated to be good candidates for strain sensing with high spatial resolution to evaluate features <100 nm. The fundamentals of strain sensing-interaction with the target-have been discussed to shed light on the sensitivity and durability for future sensor fabrication. The proof-of-concept strain sensors have been shown to be able to monitor different states, e.g., the initiation and evolution, of crazes. The analysis also leads to the evaluation of interfacial energy and realization of high local strain in graphene that is applicable for other 2D materials for ultrasensitive strain sensing and bandgap opening applications.