Optically Transparent and Mechanically Robust Ionic Hydrogel Electrodes for Bright Electroluminescent Devices Achieving High Stretchability Over 1400%

Abstract

To realize wearable displays and interactive soft robots, significant research efforts are focused on developing highly deformable alternating‐current electroluminescent (ACEL) devices. Although soft emission layers are well developed, designing stretchable, conductive, and transparent soft electrodes remains challenging. In this study, ionic hydrogels are prepared comprising a double network (DN) of poly(N‐hydroxyethylacrylamide‐co‐acrylamide)/crosslinked chitosan swollen in aqueous lithium bis(trifluoromethanesulfonyl) imide. Owing to the finely tuned DN structure of the polymeric crosslinker and transparent electrolyte, the developed ionic hydrogels exhibit remarkable stretchability (1400%), excellent optical transmittance (>99%), and high conductivity (1.95 × 10−2 Sm−1). Based on the high performance of the ionic hydrogels, ACEL devices are fabricated with an emission layer containing phosphor microparticles and demonstrate stable, high luminance under extreme deformation, and ultra‐high elongation. The excellent transparency of the ionic hydrogel further enables the fabrication of novel soft ACEL devices with tandem structures by stacking several emission and electrode layers, in which each emission layer is independently controlled with a switch circuit.

Continuous Melt Spinning of Adaptable Covalently Cross‐Linked Self‐Healing Ionogel Fibers for Multi‐Functional Ionotronics

“…As the applied voltage increased from 0.5 to 4 V μm −1 , the luminance of emissive layer increased from 1.1 ± 0.1 to 171.5 ± 12.4 cd m −2 , which was similar to previously reported bulk ionogel-based electroluminescent device. [42,43] When the DOU-IG-30 fiber contacted different places of DOU-IG-30@ZnS:Cu fiber, the luminescence intensities of electroluminescence fibers exhibited relatively minor variations (Figure 3f; Figure S17, Supporting Information), which was attributed to the uniformity of WPU@ZnS:Cu coating. DOU-IG-30 fibers and DOU-IG-30@ZnS:Cu fibers could be rationally woven and integrate into traditional fabrics to design different luminescent patterns such as "Z" (Figure 3g; Figure S18, Supporting Information).…”

A Transparent Hydrogel-Ionic Conductor with High Water Retention and Self-Healing Ability

“…Ionic conductors are expected to resolve issues in relation to hydrogels, such as drying out and low mechanical strength, and could be applied to various hydrogel ionics, such as wearable/implantable devices and sensors [42][43][44][45][46], soft robotics [47,48], and energy devices [18,49]. In particular, the gels discussed in this paper possess both high ionic conductivity and optical transparency, allowing them to be utilized as transparent electrodes and electrolytes in applications such as displays, solar cells, and optical sensors where light transmission is critical [50,51]. Additionally, the gel, which is composed of naturally derived agarose polymer, sucrose, and salt, is expected to be highly biocompatible, which would allow it to be actively utilized in applications that require human interfaces.…”

Seamless Integration of Conducting Hydrogels in Daily Life: From Preparation to Wearable Application

“…These hydrogels can be used as electrodes in supercapacitors and batteries by incorporating conducting fillers and immersing them in electrolytes. [10,45] The high surface area of the hydrogel matrix, coupled with its conductivity, allows efficient charge storage and rapid ion transport, leading to enhanced energy-storage performance. Specific biomolecules or enzymes incorporated into a hydrogel matrix can be used as biosensors for detecting analytes in biological fluids.…”

“…By manipulating the chemical structure of CHs, their mechanical properties can also be tuned to obtain softness, flexibility, and stretchability, which are important characteristics of conformal and deformable wearable devices. [10] Using recently developed advanced techniques, including various 3D printing methods and microfluidic spinning, CHs can be fabricated into controlled shapes and precise geometries. [11] Additionally, CHs can be further developed to possess self-adhesive, [12] self-healing, [1] antibacterial, [13] antifreezing, and anti-drying [14] functionalities, among others.…”