Homogeneously Bright, Flexible, and Foldable Lighting Devices with Functionalized Graphene Electrodes

Abstract

Alternating current electroluminescent technology allows the fabrication of large area, flat and flexible lights. Presently the maximum size of a continuous panel is limited by the high resistivity of available transparent electrode materials causing a visible gradient of brightness.Here, we demonstrate that the use of the best known transparent conductor FeCl 3 -intercalated few-layer graphene boosts the brightness of electroluminescent devices by 49% compared to pristine graphene. Intensity gradients observed for high aspect ratio devices are undetectable when using these highly conductive electrodes. Flat lights on polymer substrates are found to be resilient to repeated and flexural strains. * To whom correspondence should be addressed 1 arXiv:1606.05482v1 [cond-mat.mtrl-sci] Jun 2016Displays and screens are some of the most important devices within the field of optoelectronics.Large-area displays are ubiquitous in advertising, ambient lighting, television, computer screens and almost every device with an interface for its control. Current research is focused on making these devices suitable for the next generation of flexible and foldable optoelectronics. In particular, foldable displays and lighting systems would allow expandable screens for smart phones and electronic paper, wearable optoelectronics, rollable or collapsible wallpaper lights, and biocompatible light sources for medical devices. To date, alternating current electroluminescent (ACEL) technology uniquely enables the realization of flat, large-area (≈ 1m 2 ) and flexible light sources. 1 ACEL devices have good contrast and uniform brightness. They can display images with high resolution when employing nano-patterned electrodes and they can withstand mechanical shocks as well as a wide range of temperatures. 2,3 Presently, the maximum size of ACEL lighting panels is still limited to less than a square meter under practical operational conditions. This is due to the visible gradient of brightness which develops across a panel induced by the high sheet resistance (typically larger than 100Ω/2) of the transparent electrode materials. 4,5 Highly resistive electrodes also require a high operational voltage and frequency, leading to increased power consumption and accelerated device degradation. 1,5 Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a transparent and conductive polymer widely used by the printed electronics industry owing to its high mechanical flexibility. However, PEDOT:PSS has a high sheet resistance of 850Ω/2 for an optical transparency of 90%, 6-8 an unwanted blue tinge 8 and limited environmental stability. 6-8 When exposed to relative humidity of just 40%, the uptake of water by the hygroscopic PSS leads to the development of shear lips when the films are deformed, greatly increasing the sheet resistance. 7 Moreover, the absorption of water combined with the acidity of PSS is a well-known cause of degradation in device components. 9,10 Atomically thin conductors such as graphene possess many attrac...

Efficient Solid‐State Photoluminescence of Graphene Quantum Dots Embedded in Boron Oxynitride for AC‐Electroluminescent Device

“…The EL spectrum of the AC‐GPEL device in Figure d shows clear blue emission (see inset image) with a peak wavelength of 423 nm, which is consistent with the PL spectrum considering that the PL peak ranged within 400–450 nm. The EL intensity increased with increasing driving voltage, similar to archetypal AC‐driven EL devices . Due to the role of the localized dielectric medium, BNO not only contributes to electron tunneling into GQDs that occurs via electrical excitation but can also prevent dielectric breakdown under a high electric field, enabling efficient EL emission (Figure c).…”

Flexible Multicolor Electroluminescent Devices on Cellulose Nanocrystal Platform

“…The optical transmittance and electrical resistance of the CNC sheets with drop‐casted Ag NWs are listed along with those of other potential electrodes (e.g., PEDOT:PSS, CNTs, and graphene (Table )). In comparison with the EL cellulose‐based device from Zhang et al, the CNC sheet prepared by our process exhibits a much higher optical transmission (81–90%) over the 350–800 nm wavelength range.…”

New routes to the functionalization patterning and manufacture of graphene-based materials for biomedical applications

“…Examples include an unforeseen stability to harsh environmental conditions [31], ease of large-area processing [32], the realization of allgraphene photodetectors [32] and the potential to enhance the efficiency of photovoltaic and organic light-emitting devices [32,33]. When used as a transparent electrode in electroluminescent devices, FeCl 3 -functionalized graphene also increases the brightness of the emitted light by up to 50% when compared with pristine graphene, and up to 30% compared with stateof-the-art commercial electrodes [34]. Furthermore, the record high charge density achieved in FeCl 3 -functionalized graphene [13,35] makes it an attractive platform for the production of high-responsivity, high-resolution photodetectors.…”

“…Many of the above issues have been recently tackled using FeCl 3 -intercalated FLG [13,[31][32][33][34][35]42] (FeCl 3 -FLG), together with a new way to define optically active junctions [43]. As shown in figure 2a, a laser beam is used to control the [13,32] and consequent p-type doping of the graphene.…”