Highly Stretchable and Waterproof Electroluminescence Device Based on Superstable Stretchable Transparent Electrode

Realization of devices with enhanced stretchability and waterproof properties will significantly expand the reach of electronics. To this end, we herein fabricate an elastic transparent conductor that comprises silver nanowires (AgNWs) on a hydroxylated polydimethylsiloxane (PDMS) substrate covered by polyurethane urea (PUU), which is fully compatible with both materials. Carboxylic acid groups of PUU was designed to form hydrogen bonds with the carbonyl groups of poly­(vinylpyrrolidone) on the AgNW surface, resulting in an enhanced affinity of AgNWs for PUU. Exceptionally strong hydrogen bonds between PUU and the hydroxylated PDMS thus facilitate the achievement of water sealable, mechanically stable, and stretchable transparent electrodes. To fabricate stretchable electroluminescence (EL) devices, ZnS particles were mixed with PUU, and the mixture was coated onto the AgNWs/hydroxylated PDMS, followed by a face-to-face lamination with another identical electrode. The devices could be stretched up to 150% without a severe reduction in the emission intensity, and they survived 5000 cycles of 100% stretch–release testing. The high adhesion between PUU and PDMS even in water is responsible for the good waterproof characteristics of the EL devices. These results pave the way for realization of fully stretchable and waterproof electronic devices

Heterogeneous Configuration of a Ag Nanowire/Polymer Composite Structure for Selectively Stretchable Transparent Electrodes

One of the most important aspects that we need to consider in the design of intrinsically stretchable electrodes is that most electronic devices that can be formed on them are not stretchable themselves. This discrepancy can induce severe stress singularities at the interfaces between stiff devices and stretchable electrodes, leading to catastrophic device delamination when the substrate is stretched. Here, we suggest a novel solution to this challenge which involves introducing a photolithography-based rigid-island approach to fabricate the heterogeneous configuration of a silver nanowire (AgNW)/polymer composite structure. For this, we designed two new transparent polymers: a photopatternable polymer that is rigid yet flexible, and a stretchable polymer, both of which have identical acrylate functional groups. Patterning of the rigid polymer and subsequent overcoating of the soft polymer formed rigid island disks embedded in the soft polymer, resulting in a selectively stretchable transparent film. Strong covalent bonds instead of weak physical interactions between the polymers strengthened the cohesive force at the interface of the rigid/soft polymers. Inverted-layer processing with a percolated AgNW network was used to form a heterogeneous AgNW/polymer composite structure that can be used as a selectively stretchable transparent electrode. An optimized structural configuration prevented the resistance of the rigid electrode from varying up to a lateral strain of 70%. A repeated stretch/release test with 60% strain for 5000 cycles did not cause any severe damage to the structure, revealing that the fabricated structure was mechanically stable and reliable

Highly Stretchable and Mechanically Stable Transparent Electrode Based on Composite of Silver Nanowires and Polyurethane–Urea

Transparent electrodes based on conventional indium–tin oxide (ITO) can hardly meet the requirements of future generations of stretchable electronic devices, including artificial skins, stretchable displays, sensors, and actuators, because they cannot retain high conductivity under substantial stretching and bending deformation. Here we suggest a new approach for fabricating highly stretchable and transparent electrodes with good stability in environments where they would be stretched repeatedly. We designed polyurethane–urea (PUU), a urethane-based polymer, to enhance the adhesion between Ag nanowires (AgNWs) and poly­(dimethylsiloxane) (PDMS). The adhesion could be further improved when irradiated by intense pulsed light (IPL). After delicate optimization of the layered AgNW/PUU/PDMS structure, we fabricated a stretchable transparent electrode that could withstand 100 cycles of 50% stretching–releasing, with exceptionally high stability and reversibility. This newly developed electrode is therefore expected to be directly applicable to a wide range of high-performance, low-cost, stretchable electronic devices

Photoenhanced Patterning of Metal Nanowire Networks for Fabrication of Ultraflexible Transparent Devices

Network structures of metal nanowires are a promising candidate for producing a wide range of flexible electronic devices, but only if they can be suitably patterned and retained on various materials. Here we present a new approach to the patterning of metal nanowires by employing intense-pulsed-light (IPL) irradiation to reduce the process to just two steps: irradiation and the subsequent removal of nonirradiated nanowires. This ultrasimple method eliminates the need to employ chemical reagents for etching or improving the adhesion of nanowires, and is compatible with Ag nanowires (AgNWs), Cu nanowires (CuNWs), and most transparent polymers. Furthermore, it is not reliant on additional processes, such as coating, heating, developing, and etching to make a patterned nanowire structure. Using this simple method, ultraflexible and transparent devices such as touch sensor, heater and light emitting diode with an exceptionally high mechanical stability have been successfully fabricated. This new method is expected to be directly applicable to the fabrication of a wide range of high-performance, low-cost, biocompatible, and wearable devices

Photoenhanced Patterning of Metal Nanowire Networks for Fabrication of Ultraflexible Transparent Devices

Network structures of metal nanowires are a promising candidate for producing a wide range of flexible electronic devices, but only if they can be suitably patterned and retained on various materials. Here we present a new approach to the patterning of metal nanowires by employing intense-pulsed-light (IPL) irradiation to reduce the process to just two steps: irradiation and the subsequent removal of nonirradiated nanowires. This ultrasimple method eliminates the need to employ chemical reagents for etching or improving the adhesion of nanowires, and is compatible with Ag nanowires (AgNWs), Cu nanowires (CuNWs), and most transparent polymers. Furthermore, it is not reliant on additional processes, such as coating, heating, developing, and etching to make a patterned nanowire structure. Using this simple method, ultraflexible and transparent devices such as touch sensor, heater and light emitting diode with an exceptionally high mechanical stability have been successfully fabricated. This new method is expected to be directly applicable to the fabrication of a wide range of high-performance, low-cost, biocompatible, and wearable devices

Mechanically Robust and Healable Transparent Electrode Fabricated via Vapor-Assisted Solution Process

A mechanically robust, transparent, and healable electrode was successfully developed by embedding Ag nanowires (AgNWs) on the surface of polydimethylsiloxane-based polyurethane (PDMS-CPU) cross-linked by Diels–Alder (DA) adducts. The reversibility of the DA reaction enabled the heated dimethylformamide (DMF) vapor to induce de-cross-linking of the PDMS-CPU preformed as a substrate. A combination of the retro-DA reaction and the plasticizer effect softened the polymer surface, embedding the coated AgNWs on the surface of the polymer. With this simple postprocessing, the surface roughness and mechanical stability of the electrode were largely enhanced. Even with a 55 μm bending radius, which corresponds to a strain of 90%, the resistance of the electrode after 10 min of vapor treatment increased by 2.1% for inward bending and 5.3% for outward bending. This result shows a great potential of the proposed method, as it can also be used to fabricate various mechanically deformable transparent electrode. Furthermore, swelling of the PDMS-CPU film owing to the DMF vapor facilitated the healing properties of the scratched electrodes