Applications In Stretchable Electronics Research Articles

Stretchable Transparent Electrodes with Solution-Processed Regular Metal Mesh for an Electroluminescent Light-Emitting Film.

We report stretchable metal-mesh transparent electrodes (TEs) with excellent electrical conductivity (<2 Ω/sq) and optical transparency (>80%) under up to 55% strain. The figures of merit on these electrodes, as defined as the ratio between electrical conductivity and optical conductivity, are among the highest reported for stretchable TEs under moderate stretching. Moreover, we demonstrate their application in a stretchable electroluminescent (EL) light-emitting film as top and bottom electrodes. EL lighting devices require low-resistance electrodes to unleash their potential for large-area low-power-consumption applications, in which our highly conductive and transparent stretchable TEs provide an edge on other competitor approaches. Importantly, our stretchable metal-mesh electrodes are fabricated through a vacuum-free solution-processed approach that is scalable for cost-effective mass production. We also investigate the fracture and fatigue mechanisms of stretchable metal-mesh electrodes with various mesh patterns and observe different behaviors under one-time and cyclic stretching conditions. Our solution-processed fabrication method, failure mechanism investigation, and device demonstration for metal-mesh stretchable TEs will facilitate the adoption of this promising high-performance approach in stretchable and wearable electronics applications.

Review on flexible photonics/electronics integrated devices and fabrication strategy

In recent years, to meet the greater demand for next generation electronic devices that are transplantable, lightweight and portable, flexible and large-scale integrated electronics attract much more attention have been of interest in both industry and academia. Organic electronics and stretchable inorganic electronics are the two major branches of flexible electronics. With the semiconductive and flexible properties of the organic semiconductor materials, flexible organic electronics have become a mainstay of our technology. Compared to organic electronics, stretchable and flexible inorganic electronics are fabricated via mechanical design with inorganic electronic components on flexible substrates, which have stretchability and flexibility to enable very large deformations without degradation of performance. This review summarizes the recent progress on fabrication strategies, such as hydrodynamic organic nanowire printing and inkjet-assisted nanotransfer printing of flexible organic electronics, and screen printing, soft lithography and transfer printing of flexible inorganic electronics. In addition, this review considers large-scale organic and inorganic flexible electronic systems and the future applications of flexible and stretchable electronics.

A Sunlight-Degradable Autonomous Self-Healing Supramolecular Elastomer for Flexible Electronic Devices

Preparing an autonomous self-healing supramolecular elastomer with sunlight degradability is still a challenging task in related fields. In this work, we report a supramolecular elastomer by using the classic host–guest complexation of visible-light-photolabile picolinium-containing adamantanes (Ad) and β-cyclodextrin nanogels (β-CD). The as-synthesized elastomer possesses merits of high mechanical strength, excellent stretchability (>1500% strain), efficient self-healing (>85% at 60 min), ultrastability against electrolytes, and photodegradation properties, implying versatile applications in flexible and stretchable electronics. As proofs-of-concept, self-healable strain and pressure sensors using conductive elastomers are first fabricated, which feature exceptionally high sensitivity (e.g., 0.1% in capacitance at 0.2 kPa) and fast response to detect human body motions. A degradable and flexible supercapacitor is also fabricated using the conductive elastomer as the flexible matrix. Remarkably, both the ...

Extreme Toughening of Soft Materials with Liquid Metal.

Soft and tough materials are critical for engineering applications in medical devices, stretchable and wearable electronics, and soft robotics. Toughness in synthetic materials is mostly accomplished by increasing energy dissipation near the crack tip with various energy dissipation techniques. However, bio-materials exhibit extreme toughness by combining multi-scale energy dissipation with the ability to deflect and blunt an advancing crack tip. Here, we demonstrate a synthetic materials architecture that also exhibits multi-modal toughening, whereby embedding a suspension of micron sized and highly deformable liquid metal (LM) droplets inside a soft elastomer, the fracture energy dramatically increases by up to 50x (from 250 ± 50 J m-2 to 11,900 ± 2600 J m-2 ) over an unfilled polymer. For some LM-embedded elastomer (LMEE) compositions, the toughness is measured to be 33,500 ± 4300 J m-2 , which far exceeds the highest value previously reported for a soft elastic material. This extreme toughening is achieved by (i) increasing energy dissipation, (ii) adaptive crack movement, and (iii) effective elimination of the crack tip. Such properties arise from the deformability of the LM inclusions during loading, providing a new mechanism to not only prevent crack initiation, but also resist the propagation of existing tears for ultra tough, soft materials.

Direct Printing of Stretchable Elastomers for Highly Sensitive Capillary Pressure Sensors.

We demonstrate the successful fabrication of highly sensitive capillary pressure sensors using an innovative 3D printing method. Unlike conventional capacitive pressure sensors where the capacitance changes were due to the pressure-induced interspace variations between the parallel plate electrodes, in our capillary sensors the capacitance was determined by the extrusion and extraction of liquid medium and consequent changes of dielectric constants. Significant pressure sensitivity advances up to 547.9 KPa−1 were achieved. Moreover, we suggest that our innovative capillary pressure sensors can adopt a wide range of liquid mediums, such as ethanol, deionized water, and their mixtures. The devices also showed stable performances upon repeated pressing cycles. The direct and versatile printing method combined with the significant performance advances are expected to find important applications in future stretchable and wearable electronics.

Facile Fabrication of Stretchable Electrodes by Sedimentation of Ag Nanoparticles in PDMS Matrix

This study reports a facile fabrication method for highly conductive stretchable electrodes composed of a conductive 0D nanomaterial filler and an elastomer matrix. The local volume fraction of the Ag nanoparticles at the composite surface could be significantly increased by the sedimentation of Ag nanoparticles in uncured polydimethylsiloxane (PDMS) fluid. The stretchable electrodes had a surface resistance of 0.910±0.509 Ω/sq and were stretchable up to 100% of strain without the reduction of the electrical conductivity, demonstrating their potential as high-performance electrodes for applications in stretchable electronics.

Multifunctional electromechanical and thermoelectric polyaniline–poly(vinyl acetate) latex composites for wearable devices

Polyaniline–poly(vinylacetate) nanocomposites with a 3D segregated architecture have suitable electromechanical and thermoresistive properties for sensor applications in stretchable and wearable electronics.

Direct Printing for Additive Patterning of Silver Nanowires for Stretchable Sensor and Display Applications

AbstractA unique direct printing method is developed to additively pattern silver nanowires (AgNWs) with length of up to ≈40 µm. Uniform and well‐defined AgNW features are printed on various substrates by optimizing a series of parameters including ink composition, printing speed, nozzle size, substrate temperature, and hydrophobicity of the substrate surface. The capability of directly printing such long AgNWs is essential for stretchable electronics applications where mechanical compliance is required as manifested by a systematic study comparing the electrical and electromechanical performance of printed AgNW features with different nanowire lengths. Such printed AgNWs are used to demonstrate biaxially stretchable conductors, ultrasensitive capacitive pressure sensor arrays, and stretchable electroluminescent displays, indicating their great potential for applications in low‐cost wearable electronics. This strategy is adaptable to other material platforms like semiconducting nanowires, which may offer a cost‐effective entry to various nanowire‐based mechanically compliant sensory and optoelectronic systems.

2.5/3D dynamically stretchable and permanently shaped electronic circuits

Conventional electronic circuits are made up of electronic components assembled on either rigid substrates like FR4 and ceramic or on flexible substrates based on polymers such as polyimide, PET and PEN foils. The latter type of substrates offers considerable improvements in freedom of motion over its rigid complement although the deformations are still pretty limited due to the inability of common electronic materials, such as metals, to cope with the corresponding deformation. Moreover, the assembly of rigid electronic components can often reduce the circuit’s ability to bend. The current trend towards increased component density on substrates makes the final assembly even less flexible. However, electronic circuits which can fully conform and easily fit in the arbitrary curved surface topologies are of keen interest in various areas of applications. Aside from flexibility, a certain degree of stretching is required for the three-dimensional shaping of electronic systems. Hence, deformability will offer electronics a number of additional features like bendability, conformability shaping and lightweight. Three-dimensional shaped electronics can be obtained either by multi-time (dynamic or elastic) or one time (static, permanent) stretching. In this paper an introduction on deformable and conformable electronics is outlined highlighting the different existing approaches. Some examples of flexible and stretchable electronic applications will be provided in various fields.

Buckled Thin-Film Transistors and Circuits on Soft Elastomers for Stretchable Electronics.

Although recent progress in the field of flexible electronics has allowed the realization of biocompatible and conformable electronics, systematic approaches which combine high bendability (<3 mm bending radius), high stretchability (>3-4%), and low complexity in the fabrication process are still missing. Here, we show a technique to induce randomly oriented and customized wrinkles on the surface of a biocompatible elastomeric substrate, where Thin-Film Transistors (TFTs) and circuits (inverter and logic NAND gates) based on amorphous-IGZO are fabricated. By tuning the wavelength and the amplitude of the wrinkles, the devices are fully operational while bent to 13 μm bending radii as well as while stretched up to 5%, keeping unchanged electrical properties. Moreover, a flexible rectifier is also realized, showing no degradation in the performances while flat or wrapped on an artificial human wrist. As proof of concept, transparent TFTs are also fabricated, presenting comparable electrical performances to the nontransparent ones. The extension of the buckling approach from our TFTs to circuits demonstrates the scalability of the process, prospecting applications in wireless stretchable electronics to be worn or implanted.

Electronic Muscles and Skins: A Review of Soft Sensors and Actuators

This article reviews several classes of compliant materials that can be utilized to fabricate electronic muscles and skins. Different classes of materials range from compliant conductors, semiconductors, to dielectrics, all of which play a vital and cohesive role in the development of next generation electronics. This paper covers recent advances in the development of new materials, as well as the engineering of well-characterized materials for the repurposing in applications of flexible and stretchable electronics. In addition to compliant materials, this article further discusses the use of these materials for integrated systems to develop soft sensors and actuators. These new materials and new devices pave the way for a new generation of electronics that will change the way we see and interact with our devices for decades to come.

Liquid metals catalyze industrial reactions

Gallium’s quirky liquid-state properties have pushed that element into the scientific spotlight recently, as researchers have tapped the liquid metal for applications in stretchable electronics and three-dimensional printing. Now gallium is back in the news, this time as a catalyst. Researchers in Germany report that liquid droplets of Ga-Pd alloys function as active and durable catalysts for alkane dehydrogenation. That industrial-scale reaction converts low-value alkanes to higher-value olefins, compounds with C=C bonds that are used to make polymers and chemicals (Nat. Chem. 2017, DOI: 10.1038/nchem.2822). Gallium and some of its alloys exhibit a handful of unique properties, such as a tendency to remain liquid over an enormous temperature range—about 2,000 °C. The metal also has a knack for spontaneously forming an ultrathin oxide skin that stabilizes liquid droplets but easily breaks, allowing the metal to flow momentarily until the skin re-forms around the liquid. A team including Nicola Taccardi and

Assembly of highly stable aqueous dispersions and flexible films of nitrogen-doped graphene for high-performance stretchable supercapacitors

Here, we propose a route for production of highly stable nitrogen-doped graphene (NG) aqueous dispersions and flexible NG films. The NG dispersions are formed through sonication of NG hydrogels in methyl orange solution and stabilized through electrostatic repulsion without using any polymeric or surfactant stabilizer. The flexible NG films are formed by vacuum filtration of as-prepared NG dispersions and transferred onto stretchable and adhesive polyacrylate for the fabrication of stretchable supercapacitors. The supercapacitor exhibits high gravimetric specific capacitances of 315 F g−1 under no strain and 300 F g−1 under 30% applied strain at a current density of 1 A g−1. The fabrication of aqueous dispersions and stretchable NG films makes NG materials attractive for a diversity of applications in stretchable electronics.

Highly flexible fabric strain sensor based on graphene nanoplatelet–polyaniline nanocomposites for human gesture recognition

ABSTRACTFlexible and wearable smart fabrics are becoming increasingly popular in healthcare and motion monitoring because of their potential applications in flexible and stretchable electronics. The integration of ordinary fabric with conductive fillers provides the fabric with new and intriguing functions, such as sensation. In this study, a low‐cost and efficient manner was used to fabricate a highly reliable conductive composite on fabric as an effective sensing material for gesture recognition. A strain sensor was fabricated by the incorporation of the highly conductive polyaniline (PANI) polymer, graphene nanoplatelets (GNPs), and a handful of silicon rubber (SR) onto elastic Lycra fabric via a spin‐coating method. We demonstrated that the fabric strain sensor was able to detect and monitor the bending angle of a human finger. By means of the covered structure of the PANI and GNPs, the composite fabric could bear a 40% maximum strain and possess the pleasant characteristic of stretching and bending. The gauge factor of the fabric strain sensor reached 67.3; this was an improvement of approximately four times compared to sensors without PANI microparticles. Finally, the superior performance of our strain sensor through the integration of five strain sensors on a glove for the motion detection of fingers was demonstrated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45340.

Soft Poly(butyl acrylate) Side Chains toward Intrinsically Stretchable Polymeric Semiconductors for Field-Effect Transistor Applications

Poly(butyl acrylate) (PBA) side chain equipped isoindigo-bithiophene (II2T) conjugated polymers have been designed and synthesized for stretchable electronic applications. The PBA segment possesses low glass transition temperature and high softness, offering a great opportunity to improve the mechanical property of semiconducting polymer thin films that typically contain lots of rigid conjugated rings. Polymers with 0, 5, 10, 20 and 100% of PBA side chains, named PII2T, PII2T-PBA5, PII2T-PBA10, PII2T-PBA20, and PII2T-PBA100, were explored, and their polymer properties, surface morphology, electrical characteristics, and strain-dependent performance were investigated systematically. The series polymers showed a charge carrier mobility of 0.06–0.8 cm2 V–1 s–1 with an on/off current ratio over 105 dependent on different amounts of PBA chains as probed using a top-contact transistor device. Moreover, we can still achieve a mobility higher than 0.2 cm2 V–1 s–1 even if 10% of PBA side chains were added (i.e., P...

A Free-Standing and Self-Healable 2D Supramolecular Material Based on Hydrogen Bonding: A Nanowire Array with Sub-2-nm Resolution.

In many 2D materials reported thus far, the forces confining atoms in a 2D plane are often strong interactions, such as covalent bonding. Herein, the first demonstration that hydrogen (H)-bonding can be utilized to assemble polydiacetylene (a conductive polymer) toward a 2D material, which is stable enough to be free-standing, is shown. The 2D material is well characterized by a large number of techniques (mainly different microscopy techniques). The H-bonding allows splitting of the material into ribbons, which can reassemble, similar to a zipper, leading to the first example of a healable 2D material. Moreover, such technology can easily create 2D, organic, conductive nanowire arrays with sub-2-nm resolution. This material may have potential applications in stretchable electronics and nanowire cross-bar arrays.

Development of strong, biodegradable and highly elastomeric polycitrate-gelatin hybrid polymer with enhanced cellular biocompatibility

Native human tissues possess incomparable biological performance due to their strong and viscoelastic mechanical properties, and biocompatible compositions. Herein, by a thermal polymerization and solvent hybridization method, we develop biomimetic polycitrate-gelatin hybrid polymers (PC-GT) with strong mechanical properties and tailored elastomeric behavior for tissue regeneration applications. The incorporation of gelatin significantly enhanced the mechanical properties and cellular biocompatibility of PC. PC-GT hybrids demonstrated the 135 times (from 7.5 to 1015MPa) and 11 times (from 4 to 46MPa) improvement for the elastomeric modulus and tensile strength respectively as compared with PC elastomers, while showing controlled stretchable and elastomeric behavior. In addition, PC-GT hybrids significantly improved the fibroblasts (L929) attachment and proliferation, suggesting their high biocompatibility. This study may provide a novel strategy to design biocompatible hybrid polymers with strong and elastomeric behavior for tissue regeneration and stretchable electronic devices applications.

Stretchable Conjugated Rod–Coil Poly(3-hexylthiophene)-block-poly(butyl acrylate) Thin Films for Field Effect Transistor Applications

We report the synthesis, morphology, and properties of poly(3-hexylthiophene)-block-poly(butyl acrylate) (P3HT-b-PBA) for stretchable electronics applications, which are consisted of semiconducting P3HT and low glass transistion temperature (Tg) PBA blocks. The P3HT-b-PBA thin films self-assembled into fibrillar-like nanostructures and maintained the edge-on oreientation even at a low P3HT composition, based on the results from atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). By varying the P3HT/PBA ratio, the tensile modulus decreased as the block length of PBA increased, from 0.93 GPa for P3HT to 0.19 GPa for P3HT-b-PBA12k. The field effect transistor (FET) using P3HT-b-PBA as the active layer exhibited a high p-type mobility over 10–2 cm2 V–1 s–1, indicating its good charge transporting ability. Furthermore, the P3HT-b-PBA6k based FET under 100% strain had a high mobility of 2.5 × 10–2 cm2 V–1 s–1 with an on/off ratio of 7.2 × 106, and it maintained over 10–2 cm2 V–1 s–1 fo...

Highly efficient and mechanically robust stretchable polymer solar cells with random buckling

Stretchable polymer solar cells have shown great potential as stretchable power generators for applications in stretchable electronics, such as wearable electronics, electronic skins and stretchable displays. However, their mechanical stability and power conversion efficiency (PCE) thus are still far below the requirement for the practical applications. Here, we have developed highly efficient and stretchable polymer solar cells (PSCs) based on a random buckling process. The stretchable PSCs are fabricated by attaching the ultrathin PSC onto a pre-stretched elastomeric substrate and then releasing the prestrain to form random bucklings. Its PCE of 5.8% under 70% tensile strain is the largest to date among the reported PSCs. The stretchable PSCs exhibit small fluctuations in performance after 400 stretching-releasing cycles. This is an important step towards producing stretchable PSCs for commercial applications.

Laser-engraved carbon nanotube paper for instilling high sensitivity, high stretchability, and high linearity in strain sensors.

There is an increasing demand for strain sensors with high sensitivity and high stretchability for new applications such as robotics or wearable electronics. However, for the available technologies, the sensitivity of the sensors varies widely. These sensors are also highly nonlinear, making reliable measurement challenging. Here we introduce a new family of sensors composed of a laser-engraved carbon nanotube paper embedded in an elastomer. A roll-to-roll pressing of these sensors activates a pre-defined fragmentation process, which results in a well-controlled, fragmented microstructure. Such sensors are reproducible and durable and can attain ultrahigh sensitivity and high stretchability (with a gauge factor of over 4.2 × 104 at 150% strain). Moreover, they can attain high linearity from 0% to 15% and from 22% to 150% strain. They are good candidates for stretchable electronic applications that require high sensitivity and linearity at large strains.