Alternating-current Electroluminescent Device Research Articles

Bright Bifacial White-Light Illumination by Highly Deformable Electroluminescent Devices Based on Transparent Ionic-Hydrogel Electrodes and Quantum-Dot Color Conversion.

Deformable alternating-current electroluminescent (ACEL) devices are of increasing interest because of their potential to drive innovation in soft optoelectronics. Despite the research focus on efficient white ACEL devices, achieving deformable devices with high luminance remains difficult. In this study, this challenge is addressed by fabricating white ACEL devices using color-conversion materials, transparent and durable hydrogel electrodes, and high-k nanoparticles. The incorporation of quantum dots enables the highly efficient generation of red and green light through the color conversion of blue electroluminescence. Although the ionic-hydrogel electrode provides high toughness, excellent light transmittance, and superior conductivity, the luminance of the device is remarkably enhanced by the incorporation of a high-k dielectric, BaTiO3. The fabricated ACEL device uniformly emits very bright white light (489cdm-2) with a high color-rendering index (91) from both the top and bottom. The soft and tough characteristics of the device allow seamless operation in various deformed states, including bending, twisting, and stretching up to 400%, providing a promising platform for applications in a wide array of soft optoelectronics.

Dual functions of alternating current electroluminescent device for light emission and humidity detection

Alternating current electroluminescent (AC-EL) device can be considered as a potential candidate for next generation of multifunctional light-emitting sources. In this work, we present a new design of AC-EL device with inclusion of a silver oxide humidity-sensing layer instead of an insulating buffer layer for humidity detection. The ZnS:Cu, Cl and ZnS:Ag+(Zn,Cd)S:Ag phosphors were used as an emissive layer prepared by screen printing method. The silver oxide (AgO/Ag2O) nanoparticles synthesized via a green method were employed as a humidity sensing layer. The developed AC-EL devices exhibited high response, good productivity, high stability, high repeatability and linear relationship with humidity in range of 10%–90% RH as well as no significant effects with several VOCs/gases such as NH3, CO2, acetone, methanol, toluene and propan at room temperature. The effects of parameters such as excitation frequency, applied voltage, and waveforms on the luminance intensity are discussed. The development of the present AC-EL device offers a simplified architecture to enable sensing functions of the AC-EL device via monitoring of light emission changing.

Flexible Alternating‐Current Electroluminescence Plunging to Below 1 Hz Frequency by Triboelectrification

AbstractLow frequency, portable power source is one of the key challenges for applications of wearable alternating‐current electroluminescent (ACEL) device because it typically requires a working frequency above 500 Hz. Here, an extremely low frequency self‐powered ACEL system is proposed, which consists of a vertical contact‐separation triboelectric nanogenerator and a self‐made flexible ACEL device. It achieves directly‐driven electroluminescence phenomenon in real‐time by triboelectrification and works completely self‐powered through converting kinetic energy of human body into electricity. The working frequency has fallen from 500 to 1 Hz, i.e., the real frequency needed for electroluminescence has dropped 500 times, which is due to the favorable low‐frequency high‐voltage advantages of the triboelectric nanogenerator. It delivers a stabilized open‐circuit voltage of 160 V and a short‐circuit current of 6 µA for applied force of 0.1 N. Meanwhile, a strong blueshift is also observed experimentally with the change of working frequency. Furthermore, a self‐powered medical protective gown is demonstrated that is real‐time monitoring both the temperature and humidity. This work breaking the bottleneck of high‐frequency driving, demonstrates the great potential of self‐powered ACEL systems in wearable electronics and medical health.

All-Solid-State Self-Healing Ionic Conductors Enabled by Ion-Dipole Interactions within Fluorinated Poly(Ionic Liquid) Copolymers.

Self-healing ionic conductors in all solid state without evaporation or leakage offers great potential for the next-generation soft ionotronics. However, it remains challenging to endow ionic conductors with all solid state while keeping their essential features. In this study, an intrinsically conducting polymer is developed as all-solid-state self-healing ionic conductors based on ion-dipole interactions within a fluorinated poly(ionic liquid) copolymer. This unique material possesses good self-healing ability at room temperature (96% of healing efficiency in 24 h), large strain (1800%), optical transparency (96%), and ionic conductivity (1.62 × 10-6 S/cm). The self-healing polymer itself is intrinsically conductive without any additives or fillers, thus it is almost free of evaporation or leaking issues of traditional conducting gels. An alternating-current electroluminescent device with self-healing performance is demonstrated. It is anticipated that this strategy would provide new opportunities for the development of novel self-healing ionotronics.

Super Stretchable and Durable Electroluminescent Devices Based on Double-Network Ionogels.

Ionogels are good candidates for flexible electronics owing to their excellent mechanical and electrical properties, including stretchability, high conductivity, and stability. In this study, conducting ionogels comprising a double network (DN) of poly(N-isopropylacrylamide-co-N,N'-diethylacrylamide)/chitosan which are further reinforced by the ionic and covalent crosslinking of the chitosan network by tripolyphosphate and glutaraldehyde, respectively, are prepared. Based on their excellent mechanical properties and high conductivity, the developed DN ionogels are envisioned as stretchable ionic conductors for extremely stretchable alternating-current electroluminescent (ACEL) devices. The ACEL device fabricated with the developed ionogel exhibits stable working operation under an ultrahigh elongation of over 1200% as well as severe mechanical deformations such as bending, rolling, and twisting. Furthermore, the developed ACEL devices also display stable luminescence over 1000 stretch/release cycles or at temperatures as harsh as 200 °C.

Facile and Efficient Patterning Method for Silver Nanowires and Its Application to Stretchable Electroluminescent Displays.

The patterning of silver nanowires (AgNWs) is subject to critical challenges, which have seriously limited their practical applications. This work describes a simple and efficient method combining screen printing with vacuum filtration for patterning AgNW networks. The screen-printed poly(dimethylsiloxane) (PDMS) mask layer was shown to be strongly adhered to the filtration membrane, which resulted in well-defined sharp edges of the deposited AgNW patterns, and a 50 μm patterning resolution was achieved. The patterned films with low densities of AgNWs (≤15 μg/cm2) were transferred to the surface of PDMS to make patterned stretchable transparent conductive films (TCFs). The low sheet resistance of 7.3 Ω/sq was achieved at an optical transmittance of 79.6% (at 550 nm wavelength) with a AgNW deposition density of only 12.5 μg/cm2. As an application example, the patterned TCFs were used as the top electrodes to fabricate stretchable alternating current electroluminescent (ACEL) displays with stretchability up to 70% of their original dimension, which were applied to a smart system for simulating heart beats together with a digitally operated flexible circuit. The ACEL device exhibited a bright and uniform emission with a clear and smooth edge even with a pattern width as narrow as 100 μm, as well as exceptional elasticity and durability in spite of bending, stretching, and twisting. The present work provides a new way of patterning AgNWs and can be extended to a variety of applications.

Sustainable and Transparent Fish Gelatin Films for Flexible Electroluminescent Devices.

In the past decades, various alternating current electroluminescent (ACEL) devices, especially the flexible ones, have been developed and used in flat panel display, large-scale decorating, logo display lighting, optical signaling, etc. Transparent plastics are usually used as substrates in ACEL devices; however, they are undegradable and may cause serious environmental pollution. Herein, we have developed a flexible transient ACEL device based on transparent fish gelatin (FG) films. The FG films were made from fish scales, which are sustainable, cost-efficient, and eco-friendly. These films could dissolve in water within seconds at 60 °C and degrade completely within 24 days in soil. The transmittance of these FG films was up to 91.1% in the visible spectrum, comparable to that of polyethylene terephthalate (PET) (90.4%). After forming a composite with silver nanowires (Ag NWs), the Ag NWs-FG film showed a transmittance up to 82.3% and a sheet resistance down to 22.4 Ω sq-1. The fabricated ACEL device based on the Ag NWs-FG film exhibited high flexibility and luminance up to 56.0 cd m-2. The device could be dissolved in water within 3 min. Our work demonstrates that the sustainable, flexible, and transparent FG films are a promising alternative for green and degradable substrates in the field of flexible electronics, including foldable displays, wearable devices, and health monitoring.

Constructing a Novel Electroluminescent Device with High-Temperature and High-Humidity Resistance based on a Flexible Transparent Wood Film.

Plastic-based electroluminescent devices generally suffer from thermal expansion owing to the high coefficient of thermal expansion (CTE) of the plastic substrate, which reduces the service lifetime of the electroluminescent device. In this study, we employed a delignified veneer synergistically reinforced with epoxy resin as a low-cost substrate for alternating current electroluminescent (ACEL) devices. In brief, the natural interconnected porous structure of wood had a good antideformation capacity to restrict the volume expansion of the epoxy resin under thermal conditions. Furthermore, the impregnation of epoxy resin dramatically improved the optical transmittance of delignified veneer. Considering its low CTE and antideformation capability, the intrinsically high-temperature and high-humidity resistance device based on transparent sliced veneer (TSV) was constructed. Remarkably, the TSV-ACEL device exhibited excellent stability and maintained good luminescence performance even at a high temperature (100 °C, 30 min; as a reference, the poly(ethylene terephthalate)-based ACEL device has stopped operating), completely submerged in water (30 min), or under high-temperature and high-humidity conditions (90 °C, relative humidity: >90%, 30 min). These results pave the way for the realization of flexible and high-temperature resistance ACEL devices.

Solution‐Processable, High‐Performance Flexible Electroluminescent Devices Based on High‐k Nanodielectrics

AbstractFlexible alternating‐current electroluminescent (ACEL) devices have attracted considerable attention for their ability to produce uniform light emission under bent conditions and have enormous potential for applications in back lighting panels, decorative lighting in automobiles, and panel displays. Nevertheless, flexible ACEL devices generally require a high operating bias, which precludes their implementation in low power devices. Herein, solution‐processed La‐doped barium titanate (BTO:La) nanocuboids (≈150 nm) are presented as high dielectric constant (high‐k) nanodielectrics, which can enhance the dielectric constant of an ACEL device from 2.6 to 21 (at 1 kHz), enabling the fabrication of high‐performance flexible ACEL devices with a lower operating voltage as well as higher brightness (≈57.54 cd m−2 at 240 V, 1 kHz) than devices using undoped BTO nanodielectrics (≈14.3 cd m−2 at 240 V, 1 kHz). Furthermore, a uniform brightness across the whole panel surface of the flexible ACEL devices and excellent device reliability are achieved via the use of uniform networks of crossaligned silver nanowires as highly conductive and flexible electrodes. The results offer experimental validation of high‐brightness flexible ACELs using solution‐processed BTO:La nanodielectrics, which constitutes an important milestone toward the implementation of high‐k nanodielectrics in flexible displays.

Transient Light Emitting Devices Based on Soluble Polymer Composites

Building transient electronics are promising and emerging strategy to alleviate the pollution issues from electronic waste (e-waste). Although a variety of transient devices comprising organic and inorganic materials have been described, transient light emitting devices are still elusive but highly desirable because of the huge amount of lighting and display related consumer electronics. Here we report a simple and efficient fabrication of large-area flexible transient alternating current electroluminescent (ACEL) device through a full-solution processing method. Using transparent flexible AgNW-polymer as both electrodes, the devices exhibit high flexibility and both ends side light emission, with the features of controlled size and patterned structure. By modulating the mass ratio of blue and yellow phosphors, the emission color is changed from white to blue. Impressively, the fabricated ACEL device can be thoroughly dissolved in water within 30 min. Our strategy combining such advances in transient light emitting devices with simple structure, widely used materials, full solution process, and high solubility will demonstrate great potential in resolving the e-waste from abandoned light-emitting products and expand the opportunities for air-stable flexible light emitting devices.

Extremely Stretchable Electroluminescent Devices with Ionic Conductors.

An extremely stretchable electroluminescent device is fabricated based on alternating-current electroluminescent (ACEL) materials and ionic conductors. The stretchable ACEL device possesses extremely high stretchability, and can be linearly stretched to 700% with the luminance being maintained at 70% of the initial value before stretching. The ACEL device can be repetitively stretched to 400% with stable emission behavior.

Highly stretchable and self-deformable alternating current electroluminescent devices.

A highly stretchable light-emitting device based on an alternating current electroluminescent (ACEL) material is fabricated by a simple and all-solution processable method. The ACEL device shows stable emission performance with strain up to 100%, which can be repetitively stretched to 80% strain. Furthermore, a novel self-deformable EL device that can be electrically driven into dynamic shapes is demonstrated by integrating the device with dielectric elastomer actuators. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.