Flexible Electroluminescent Devices Research Articles

Kill Two Birds with One Stone: Cracking Lithography Technology for High-Performance Flexible Metallic Network Transparent Conductors and Metallic Micronano Sheets.

Flexible electronics have sparked a wide range of exciting applications, such as flexible display technologies, lighting, sensing, etc. Flexible conductors are essential components of flexible electronics and seriously affect efficiency and overall performance. Here, a facile and kill-two-birds-with-one-stone strategy of cracking lithography technology has been proposed to simultaneously fabricate two high-performance flexible conductors, flexible metallic network transparent conductors (f-NTCs) and metallic micronano sheets (MMNSs). The PET substrate flexible transparent conductors (FTCs) based on this strategy yield 88.1% transparency within the visible spectrum and a sheet resistance of 9 Ω/sq. In addition, the FTCs show exceptional mechanical stability, with the sheet resistance remaining virtually unchanged even after 6000 s of bending tests. Subsequently, the remaining MMNSs are recycled to manufacture a Ag paste, showing a very low conductive percolation threshold (∼13%) and excellent flexibility with 140% breaking elongation. After 1000 s of stretching tests, it showed excellent mechanical stability. Furthermore, flexible electroluminescent devices based on the FTCs and sensors fabricated with MMNSs both show excellent performance, demonstrating their potential wide applications in flexible electronics.

Recent Advances in Perovskite-Based Flexible Electroluminescent Devices.

Perovskite-based flexible electroluminescent (EL) devices are emerging as promising candidates in the display field due to their exceptional optoelectronic properties and potential for cost-effective production. However, simultaneously achieving high EL performance, excellent flexibility and stretchability, robust mechanical strength, and diverse applications remains a significant challenge. In this review, we provide a comprehensive overview of the latest developments in perovskite-based flexible EL devices, covering both direct-current (DC) and alternating-current (AC) electroluminescent formats. Our discussion encompasses the materials, working principles, device architectures, failure mechanisms, optimization strategies, and practical applications. Through this review, we aim to deepen our understanding of the current challenges and future directions of perovskite-based flexible light-emitting technologies, hoping to facilitate their potential commercial applications.

Fabrication and characterization of bacterial cellulose/carbon nanotube composite conductive film and its impact on the luminance of flexible electroluminescent devices as the bottom electrode

Flexible conductive films (BC/CNTs) were fabricated via a straightforward vacuum filtration method using bacterial cellulose (BC) as the substrate and single-walled carbon nanotubes (SWCNTs) as the conductive filler. The resulting BC/CNTs composite films were characterized for the morphology, structure, thermal properties and electrical conductivity using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and X-ray photoelectron spectroscopy (XPS). The study revealed that, the addition of SWCNTs significantly improved the mechanical properties of films. Among the BC/CNTs composite films, the one with the SWCNTs concentration of 0.36 wt% exhibited the best mechanical properties. Incorporating SWCNTs also enhanced the thermal stability and improved electrical conductivity of the composite films. Notably, higher SWCNTs concentrations led to better thermal stability and lower electrical resistance. Ultimately, these BC/CNTs composite films were successfully employed in flexible electroluminescent devices, demonstrating good luminescence.

Green Fabrication of All-Nanocellulose-Based Flexible Electroluminescent Devices with Biodegradability, Recyclability, and Extreme Environment Tolerance

Green Fabrication of All-Nanocellulose-Based Flexible Electroluminescent Devices with Biodegradability, Recyclability, and Extreme Environment Tolerance

Study on Preparation and Ink Performance of Flexible Electro-luminescent Devices

Study on Preparation and Ink Performance of Flexible Electro-luminescent Devices

Flexible electroluminescent device based on ZnS:Cu-polyurethane composite and silver nanowires

Flexible electroluminescent device based on ZnS:Cu-polyurethane composite and silver nanowires

A hydrophobic eutectogel with excellent underwater Self-adhesion, Self-healing, Transparency, Stretchability, ionic Conductivity, and fully recyclability

As an emerging soft material, eutectogels have attracted widespread interest for their excellent optical, mechanical, ion-conductive, self-adhesive, and self-healing properties. However, these properties of eutectogels are usually heavily affected by water molecules, leading to functionality failure in wet or underwater environments. Here, a novel hydrophobic eutectogel (HEG) is rapidly prepared with the help of photopolymerization by simultaneously introducing soft and hard acrylate monomers in a hydrophobic benzyltriethylammonium chloride/thymol deep eutectic solvent. Due to the abundant non-covalent and hydrophobic interactions within the polymer network, the synthesized HEG addresses the shortcomings of conventional eutectogels that are sensitive to water, while enabling good self-healing and self-adhesive properties both in air and underwater. Typical HEGs also exhibit high transparency, tunable mechanical properties, and ionic conductivities. The combination of these advantages makes HEG very suitable for the use of underwater adhesives and sensors with stable performance. In addition, it can be also used to prepare fully self-healing, recyclable and flexible electroluminescent devices. The design and applications based on HEGs show great promise for wearable sensors, self-healing flexible devices, and iontronics.

Fabrication of flexible optoelectronics based on in-situ-grown customized graphene patterns

The unique physical and chemical properties of graphene enable it to be widely used in optoelectronic devices, and the important prerequisite for its functionalization and application is the hene patterning technique. However, traditional patterned graphene preparation methods will introduce impurities and defects in the process, which will affect the performance of devices. We developed a method to directly grow patterned graphene, and then transfer it to a flexible substrate to fabricate optoelectronic devices. Flexible electroluminescent devices were fabricated and functionally tested.

Microscale Hybrid Additive Manufacturing of Ultra‐Fine, Embedded Cu/Ag(shell)–P4VP(core) Grid for Flexible Transparent Electrodes

AbstractFlexible transparent electrodes (FTEs) with embedded metal mesh composed of composite materials or structures have excellent comprehensive performance, which has attracted extensive attention, but it also brings great challenges to its manufacturing. Herein, a simple and cost‐effective fabrication process free of template, vacuum processes is proposed for high‐performance FTEs with ultra‐fine embedded Cu/Ag(shell)–P4VP(core) conductive grid via a microscale hybrid additive manufacturing technique. The produced FTE exhibits excellent properties with a sheet resistance of 2.5 Ω, a transmittance of 93% at a line pitch of 250 µm, and an ultra‐fine line width of 4 µm, low surface roughness (Ra ≈ 5.28 nm), and excellent mechanical stability (no change in Rs after 100 adhesion and 150 scratch tests). The FTEs expose only a few conductive areas, which make it excellent environmental stability (no change in Rs after exposure to humidity environment for 72 h). The flexible electroluminescent device fabricated with this FTE has good bending and luminescent properties, showing great potential for flexible optoelectronic applications.

CsPbBr3/CsCaAl2O4:Nd,Er Nanoriveted Structure Perovskites with Long Afterglow Dual-Wavelength Emission for Flexible Photoelectric Devices

Lead halide perovskites have garnered widespread attention because of their excellent photoelectric and photonic properties. However, their material fabrications and optoelectronic applications are hindered by low stability. Nanoriveted structure perovskites with high stability and long afterglow dual-wavelength emission are synthesized using a shared ion strategy of perovskites and phosphors. The CsPbBr3/CsCaAl2O4:Nd,Er nanoriveted structure perovskites exhibit dual-wavelength emission of blue and green during photoexcitation, as well as a prolonged afterglow. The fabricated flexible electroluminescent devices have spectrally tunable and dual-wavelength emissions even at 60° bending. Because the CsPbBr3 quantum dots (QDs) capture the photon emitted from Er element, the electroluminescent devices retain observable dual-wavelength emissions and high synchronization in their afterglow, which decays after the removal of power. The CsPbBr3/CsCaAl2O4:Nd,Er nanoriveted structure perovskites can also be used as the light-emitting downshift layers to improve the performance of photovoltaic modules in photovoltaic devices. At cryogenic temperatures, the temperature-dependent photoluminescence spectra test reveals the energy transfer between CsPbBr3 QDs and CsCaAl2O4:Nd,Er (contradicts the energy transfer in the afterglow state). These discoveries overcome the limitations of conventional afterglow phosphors, provide new applications for long afterglow materials, and introduce an innovative approach to energy conservation.

Flexible multi-color electroluminescent devices with a high transmission conducting hydrogel and an organic dielectric.

Flexible electroluminescent devices have sparked widespread interest due to their tremendous applications in bioinspired electronics, smart wearables, and human-machine interfaces. In these applications, it is important to reduce the operating electrical frequency and realize color modulation. Herein, flexible electroluminescent devices have been fabricated with phosphor layers by a solution method. Using polyvinylidene difluoride as a dielectric layer and ionic hydrogels as electrodes, the devices can be effectively driven even when the operating frequency is 0.1 kHz. More importantly, the devices can exhibit multi-color emission, including blue, green, red and white. The results show that the developed devices are promising for flexible optoelectronics.

Blue and white light modulation of a flexible electroluminescent device based on phosphors.

Flexibility, certain mechanical strength, and color modulation are significant elements for flexible optoelectronic devices. However, it is laborious to fabricate a flexible electroluminescent device with balanceable flexibility and color modulation. Here, we mix a conductive nonopaque hydrogel and phosphors to fabricate a flexible alternating current electroluminescence (ACEL) device with color modulation ability. This device realizes flexible strain based on polydimethylsiloxane and carboxymethyl cellulose/polyvinyl alcohol ionic conductive hydrogel. The color modulation ability is achieved by varying the voltage frequency applied on the electroluminescent phosphors. The color modulation could realize blue and white light modulation. Our electroluminescent device exhibits great potential in artificial flexible optoelectronics.

Screen-printed, erasable mask on filter membrane for silver nanowires patterning and application in flexible electroluminescent devices

Silver nanowires (AgNWs) have been widely used in transparent conductive films (TCFs) for wearable optoelectronic devices due to their high transmittance, high conductivity. Mask-assisted vacuum filtration is a straightforward and effective patterning strategy for AgNWs with high aspect ratio. However, currently reported non-erasable masks result in the filter membrane being unable to be recycled, which greatly increase the manufacturing cost of patterned TCFs. Herein, we propose an improved method to construct an erasable mask on the filter membrane by screen printing polyvinyl alcohol (PVA) solution. The printed PVA mask is strongly attached to the filter membrane, which lead to the AgNWs pattern with smooth and distinct edges after vacuum filtration. The deposited AgNWs patterns can be transferred to the polydimethylsiloxane film by hot pressing to prepare the patterned TCFs. After the transfer, the printed PVA mask can be easily erased or cleaned from the filter membrane in hot water without damaging its pore structure, enabling the recycling of the filter membrane. As a proof, ten pieces of TCFs with square shape were prepared by recycling one filter membrane and all of them had excellent consistency in sheet resistance, optical transmittance and bending durability. Alternating current electroluminescence devices made from the TCFs were consistent in luminance, emission spectrum and Commission Internationale de l’eclairage coordinates. The erasable mask technique can be extended to patterning process of various nanomaterials other than AgNWs under vacuum filtration to enhance the utilization efficiency of filter membrane and to reduce the manufacturing cost.

Integrated 3D printing of flexible electroluminescent devices and soft robots

Flexible and stretchable light emitting devices are driving innovation in myriad applications, such as wearable and functional electronics, displays and soft robotics. However, the development of flexible electroluminescent devices via conventional techniques remains laborious and cost-prohibitive. Here, we report a facile and easily-accessible route for fabricating a class of flexible electroluminescent devices and soft robotics via direct ink writing-based 3D printing. 3D printable ion conducting, electroluminescent and insulating dielectric inks were developed, enabling facile and on-demand creation of flexible and stretchable electroluminescent devices with good fidelity. Robust interfacial adhesion with the multilayer electroluminescent devices endowed the 3D printed devices with attractive electroluminescent performance. Integrated our 3D printed electroluminescent devices with a soft quadrupedal robot and sensing units, an artificial camouflage that can instantly self-adapt to the environment by displaying matching color was fabricated, laying an efficient framework for the next generation soft camouflages.

Solution-processed green and blue quantum-dot light-emitting diodes with eliminated charge leakage

Quantum-dot light-emitting diodes (QD-LEDs) promise a new generation of efficient, low-cost, large-area and flexible electroluminescent devices. However, the inferior performance of green and blue QD-LEDs compared with their red counterpart is hindering the commercialization of QD-LEDs in display and solid-state lighting applications. Here we demonstrate green and blue QD-LEDs with ~100% conversion of the injected charge carriers into emissive excitons. The key to success is the elimination of electron leakage at the organic/inorganic interface by using hole-transport polymers with simultaneous low electron affinity and reduced energetic disorder. Our devices exhibit high external quantum efficiencies over a wide range of luminance values (peak external quantum efficiencies of 28.7% for green and 21.9% for blue) and excellent stability (extrapolated T95 lifetime is 580,000 h for green and 4,400 h for blue QD-LEDs). We expect our work to provide a general strategy for eliminating charge leakage in solution-processed LEDs featuring organic/inorganic interfaces.

Thiochromenocarbazole imide: a new organic dye with first utility in large area flexible electroluminescent devices

Synthesis and use of the unprecedented thiochromenocarbazole imide (TCI) for the preparation of printed, large-area and flexible OLEDs.

Multifunctional Liquid‐Free Ionic Conductive Elastomer Fabricated by Liquid Metal Induced Polymerization

AbstractNovel liquid‐free ionic conductive elastomers are fabricated by the polymerization of acrylic acid (AA) in polymerizable deep eutectic solvent (PDES). Liquid metal (LM) nanodroplets are used to initiate and further cross‐link polyacrylic acid (PAA) chains into a liquid‐free polymeric network without any extra initiators and cross‐linkers. The resulting liquid‐free ionic conductive elastomers exhibit high transparency (94.1%), ultra‐stretchability (2600%), and autonomous self‐healing. Spin trapping electron paramagnetic resonance and dye fading experiments reveal the generation of free radicals. UV–visible spectrometry and viscosity tests demonstrate the cross‐linking effect of Ga3+. The gelation time is much shorter than that of the conventional ammonium persulfate thermal initiation process. Furthermore, this liquid‐free polymer material is intrinsically resistant to freezing and drying, enabling it to operate under harsh conditions. In consideration of transparency, self‐healing, ultra‐stretchability, moldability, and sensory features, the resulting elastomeric conductor may hold promise for industrial applications in wearable devices, force mapping, and flexible electroluminescent devices.

Improving Dielectric Constant of Polymers through Liquid Electrolyte Inclusion

AbstractDifferent from the traditional ways for enhancing the dielectric properties of polymers by compositing with rigid electronic conductors, here an alternative strategy is reported via introducing ionically conductive liquid electrolytes as functional fillers. Dielectric constant has significantly improved (up to 600%) by liquid electrolyte inclusions in an elastomer matrix. Moreover, by taking advantage of the inherent transparency of liquid electrolyte fillers, high transparency, good stretchability, and high dielectric constant are achieved simultaneously. Using the composite elastomer, the fabrication of highly sensitive strain sensor is demonstrated with 5–6 times higher sensitivity than the pristine elastomer, and flexible electroluminescent device with greatly lowed driving voltage. The strategy provides new opportunities for novel electroactive polymers, including flexible touchscreen panels and displays, biomimetic soft machines, and smart optics.

Flexible Multicolor Electroluminescent Devices on Cellulose Nanocrystal Platform

In this work, flexible electroluminescent devices (FELDs) are demonstrated using environmentally‐friendly cellulose nanocrystal (CNC) substrates with a silver nanowire conductive network. The CNC sheets with drop‐casted silver nanowires act as highly transparent conductive electrodes for an electroluminescent layer (a phosphorescent ink containing Cu/Br‐doped ZnS microparticles). This phosphorescent device requires operating voltages as low as 7 V and achieves high luminance of up to 43 Cd m−2 (at 50 V). Furthermore, through impregnating the CNC host material with Rhodamine 6G or Thiazol Yellow G, different emission colors are achieved: blue, turquoise, green, and purple light emission having a broad (400–650 nm) luminescence spectrum are obtained. This device, which uses earth‐abundant, cost‐effective, and recyclable materials, is envisioned to lead to advancements in the areas of electronics and lighting technology.

Fabrication of architectural structured polydopamine-functionalized reduced graphene oxide/carbon nanotube/PEDOT:PSS nanocomposites as flexible transparent electrodes for OLEDs

High performance, flexible transparent conductive films with a structure similar to that of reinforced concrete and constructed by sandwiching single-walled carbon nanotubes (SWCNT) between poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and polydopamine functionalized reduced graphene oxide (PDA-RGO) were fabricated using simple spray coating. Mussel-inspired polydopamine was introduced as a graphene oxide reducing agent and modifier; the obtained PDA-RGO improved the interfacial adhesion between the conductive coating layers and substrate, and an effective post fabrication treatment method was performed on the hybrid film to achieve better conductivity. It was found that the resulting electrode exhibited a low sheet resistance of 52.2 Ω/sq. with a high optical transmittance of 88.7% at 550 nm. Moreover, the transparent film exhibited long-term stability with a relatively low roughness (ca. 2.41 nm), and its architectural structure sustained the flexibility of the film during bending. The organic light emitting diodes which using PDA-RGO/SWCNT/PEDOT:PSS film as anode was successfully fabricated, the luminance of the device was 2032 cd/cm2 at 15 V and the maximum current efficiency was 2.13 cd/A at 14 V, indicating the strong potential of this type of transparent electrode for flexible electroluminescent devices.