On Organic Light Emitting Diode Research Articles

Creating Efficient Red Thermally Activated Delayed Fluorescence Materials with Cyano-Substituted 11,12-Diphenyldipyrido[3,2-a:2',3'-c]phenazine Acceptors.

Red luminescent materials are essential components for full color display and white lightening based on organic light-emitting diode (OLED) technology, but the extension of emission color towards red or deep red region generally leads to decreased photoluminescence and electroluminescence efficiencies. Herein, we wish to report two new luminescent molecules (2CNDPBPPr-TPA and 4CNDPBPPr-TPA) consisting of cyano-substituted 11,12-diphenyldipyrido[3,2-a:2',3'-c]phenazine acceptors and triphenylamine donors. As the increase of cyano substituents, the emission wavelength is greatly red-shifted and the reverse intersystem crossing process is promoted, resulting in strong red delayed fluorescence. Meanwhile, due to the formation of intramolecular hydrogen bonds, the molecular structures become rigidified and planarized, which brings about large horizontal dipole ratios. As a result, 2CNDPBPPr-TPA and 4CNDPBPPr-TPA can perform as emitters efficiently in OLEDs, furnishing excellent external quantum efficiencies of 28.8 % at 616 nm and 20.2 % at 648 nm, which are significantly improved in comparison with that of the control molecule without cyano substituents. The findings in this work demonstrate that the introduction of cyano substituents to the acceptors of delayed fluorescence molecules could be a facile and effective approach to explore high-efficiency red or deep red delayed fluorescence materials.

Measuring visual acuity and spherical refraction with smartphone screens emitting blue light

IntroductionA periodical self-monitoring of spherical refraction using smartphones may potentially allow a quicker intervention by eye care professionals to reduce myopia progression. Unfortunately, at low levels of myopia, the far point (FP) can be located far away from the eye which can make interactions with the device difficult. To partially remedy this issue, a novel method is proposed and tested wherein the longitudinal chromatic aberration (LCA) of blue light is leveraged to optically bring the FP closer to the eye. MethodsFirstly, LCA was obtained by measuring spherical refraction subjectively using blue pixels in stimuli shown on organic light-emitting diode (OLED) screens and also grey stimuli with matching luminance. Secondly, the visual acuity (VA) measured with a smartphone located at 1.0 m and 1.5 m and displaying blue optotypes was compared with that obtained clinically standard measurements. Finally, the spherical over refraction obtained in blue light with a smartphone was compared with clinical over-refraction with black and white (B&W) optotypes placed at 6 m. ResultsMean LCA of blue OLED smartphone screens was −0.67 ± 0.11 D. No significant differences (p > 0.05) were found between the VA measured with blue optotypes on a smartphone screen and an eye chart. Mean difference between spherical over-refraction measured subjectively by experienced subjects with smartphones and the one obtained clinically was 0.08 ± 0.34 D. ConclusionsSmartphones using blue light can be used as a tool to detect changes in visual acuity and spherical refraction and facilitate monitoring of myopia progression.

81‐2: Invited Paper: Highly Stretchable Color MicroLED Meta‐Display Without Image Distortion

Recently, rollable and foldable displays have been commercialized based on organic light‐emitting diode (OLED) display technology. The next form‐factor challenge would be the realization of stretchable displays. Though many studies have targeted stretchable OLED displays, they have an intrinsic issue with the inextensible barrier coating. The micro‐LED displays are considered a promising solution for stretchable displays because of their high reliability without the barrier coating. This talk presents a highly stretchable micro‐LED display manufacturing technology with RGB micro‐LED pixels. We designed circuit boards made of the auxetic meta‐material with a Poisson's ratio of ‐1. These auxetic circuit boards provided our micro‐LED displays with high stretchability and distortion‐free images. We designed and developed a meta‐display manufacturing process for mass production, which is highly compatible with the conventional display manufacturing process on polyimide substrates.

Micro-resonant cavity organic light-emitting diode with high refractive index contrast dielectric metasurfaces for naked-eye 3D display

Conventional naked-eye three-dimensional (3D) display technology based on organic light-emitting diode (OLED) combines reconstructing 3D scenes and advantages of OLED simultaneously, however, it requires multiple separate optical components, resulting in complex systems and bulky volumes. In this study, we propose a solution for the integration of resonant cavity and high refractive index contrast dielectric metasurfaces on OLED to endow the device with unidirectional light emission for naked-eye 3D display. We perform a systematical analysis on the effect of structure parameters of OLED that integrated distributed Bragg reflector and metasurfaces on its performance by employing the 3D finite-difference time-domain method. The simulation results show that top crystalline silicon (c-Si) metasurfaces are superior to the other metasurfaces structures, which can provide a larger deflection efficiency while remaining a small aspect ratio. We believe that this proposed single-chip resonant cavity OLED integrated a top c-Si metasurfaces structure could be a very promising candidate for naked-eye 3D OLED display.

Ink Formulation and Optimum Surface Condition for a Printed Organic Light-Emitting Diode with High Boiling Point and Surface Tension Solvents

Ink formulation with the benzoate-type solvent mixture was designed to provide a mismatch in the surface tension, boiling point, and viscosity toward a stable jet printing on organic light-emitting diode (OLED) pixel pattern cell. Compared with a single component solvent ink, the mixtures showed smoother surface roughness and uniform line printed, while the dried film roughness was further improved by solvent-vapor annealing. Inkjet OLEDs on the 60 to 80 μm-scale pixels were fabricated, and the luminous quantum efficiency behavior of the printed OLEDs were characterized in terms of structural perfection of patterns and in-pixel coverage for different bank boundaries. With the optimum printing recipe and pattern-receptor surface condition, an external quantum efficiency of inkjet device was more than 82% of the value for spin-coating reference.

22‐5: Late‐News Paper: Silicone‐based Low‐k Material for Display

The encapsulation and insulation layers, which are typically located between a data electrode and a pixel electrode, should have low parasitic capacitance and enough electrical insulation to minimize signal distortion and crosstalk. Low dielectric constant (Dk) material reduces the parasitic capacitance and improve the insulation performance. New OLED flexible displays need organic‐based passivation and insulation materials for flexibility, light weight and productivity. Epoxy and acryl‐based materials were widely used in display industry for this purpose, but both have relatively higher Dk greater than 3.0, which limits to design new flexible displays and touch screen panels.DOW has invented a low Dk optical material based on silicone technology. A Dk value of 2.5 was achieved with a low viscosity of 12–18 mPa.s at 25°C for jetting without solvent. The newly developed product can be cured at 1,000 mJ/cm2 energy density at 395 nm with a light emitting diode (LED) ultraviolet (UV) lamp. One of the target applications is a dielectric layer for touch screen panels on organic light emitting diode (OLED) displays, but it is not limited to this. This material enables display manufacturers to develop and design ultrathin and innovative touch screen panels; and the novel and patented technology can be applied to various applications that require low dielectric constant.

Modeling and Analysis of Organic Light Emitting Diode with Thin Film Anti-Reflective Coatings

The effects of anti-reflective coatings (ARC) on organic light emitting diode (OLED) optical characteristics are reported in this paper. The light output produced from the OLED is not 100%. But the emitted light is trapped due to various Modes. The losses at the glass air substrate interfaces of an OLED are addressed in this work. The Anti-Reflective coatings increase the light output by reducing OLED reflections at the interface between glass and air. The Finite Difference Time Domain (FDTD) method and the Fresnel theory have been used to design the device and study the effects on OLED of the Single Layer Anti-Reflective Coating (SLAR) and Double Layer Anti-Reflective Coating (DLAR). The thicknesses and refractive indices of the layers of the anti-reflective coatings were optimized. We also compared the light out coupling power efficiency of the SLAR coated OLED with that of an OLED with a DLAR coating and also with Conventional OLED. The results show that the enhancement in light output efficiency of the DLAR coated OLED was slightly higher than that of the SLAR coated OLED.

Perceived-Color Approximation Transforms for Programs that Draw

Human color perception acuity is not uniform across colors. This makes it possible to transform drawing programs to generate outputs whose colors are perceptually equivalent but numerically distinct. One benet of such transformations is lower display power dissipation on organic light-emitting diode (OLED) displays. We introduce Ishihara, a language for 2D drawing that lets programs specify perceptual-color equivalence classes to use in drawing operations enabling compile-time and runtime transformations that trade perceived color accuracy for lower OLED display power dissipation.

Domain Adaptation for Automatic OLED Panel Defect Detection Using Adaptive Support Vector Data Description

Detection of surface defects on organic light emitting diode (OLED) panels pose challenges such as irregular shapes and sizes along with varying textures and patterns on the panels. These challenges can be addressed by designing invariant features and training an anomaly detection algorithm such as support vector data description (SVDD). However, these hand designed features may not be capable of handling test datasets that have undergone distributional shift due to changes in lighting configuration or panel specification. This leads to a degradation of the classifier performance. In this paper, we propose a domain adaptation technique for outlier detection called as adaptive support vector data description (A-SVDD) to tackle distributional change in OLED panel datasets. The proposed method aims to learn an incremental classifier based on the existing classifier using an objective function similar to SVDD. We also investigate the application of features called as local inlier---outlier ratios augmented with modified local binary pattern (LBP) for detection of OLED panel defects in the context of SVDD and A-SVDD. In the experiments, the proposed domain adaptation technique is compared with baseline methods and existing approaches to demonstrate its effectiveness. A detailed evaluation of the features was performed in the context of A-SVDD and SVDD on several defects like scratch, spot, stain and pit to demonstrate that the combination of local inlier---outlier ratios and modified LBP significantly increases the detection accuracy.

Study of Effect of Environmental Factors on Organic Light Emitting Diode (OLED) Displays: A Review

Organic Light Emitting Diode Display is the most emerging technology in today’s era for the flexible, lightweight, and thinner display systems. OLEDs are admirable as compared with other displays in number of attributes. It can be thought of to use OLED in many specialized applications such as mobile phones, cockpit instrumentation for surface transport and probably also for aviation because of its features such as low power required, better contrast ratio, wide viewing angle, high luminance, etc. However, there are many technical challenges faced by OLED display technology when applied for aerospace applications. These challenges include effect of environmental factors such as water vapor, oxygen i.e. humidity, harsh temperatures, solar radiation, vibration, etc. Luckily there are different technologies available to overcome these challenges such as use of desiccators and encapsulation methods. Different approaches to prevent OLED from degradation have different effects and requirements. The paper reviewed such different approaches and methods in respect of humidity and water vapour.

Candlelight style organic light-emitting diode: a plausibly human-friendly safe night light

Candles emit sensationally warm light with a very low color temperature, comparatively most suitable for use at night. In response to the need for such a human-friendly night light, we demonstrate the employment of a high number of candlelight complementary organic emitters to generate and mimic candlelight based on organic light emitting diode (OLED). One resultant candlelight style OLED shows a very-high color rendering index (CRI), with an efficacy at least 300 times that of a candle or at least two times that of an incandescent bulb. The device can be fabricated, for example, by using four candlelight complementary emitters: red, yellow, green, and sky-blue phosphorescent dyes. These dyes, in the present system, can be vacuum deposited into two emission layers that are separated by a nanolayer of carrier modulation material that is used to maximize very high CRI and energy efficiency. A nano carrier modulation layer also played a significant role in maintaining the low blue emission and high-red emission, the low color temperature of device was obtained. Importantly, a romantic sensation giving and supposedly physiologically friendly candlelight style emission can hence be driven by electricity in lieu of hydrocarbon burning and greenhouse gas-releasing candles that were invented 5000 years ago.

Assessment of OLED displays for vision research

Vision researchers rely on visual display technology for the presentation of stimuli to human and nonhuman observers. Verifying that the desired and displayed visual patterns match along dimensions such as luminance, spectrum, and spatial and temporal frequency is an essential part of developing controlled experiments. With cathode-ray tubes (CRTs) becoming virtually unavailable on the commercial market, it is useful to determine the characteristics of newly available displays based on organic light emitting diode (OLED) panels to determine how well they may serve to produce visual stimuli. This report describes a series of measurements summarizing the properties of images displayed on two commercially available OLED displays: the Sony Trimaster EL BVM-F250 and PVM-2541. The results show that the OLED displays have large contrast ratios, wide color gamuts, and precise, well-behaved temporal responses. Correct adjustment of the settings on both models produced luminance nonlinearities that were well predicted by a power function ("gamma correction"). Both displays have adjustable pixel independence and can be set to have little to no spatial pixel interactions. OLED displays appear to be a suitable, or even preferable, option for many vision research applications.

Chameleon: A Color-Adaptive Web Browser for Mobile OLED Displays

Displays based on organic light-emitting diode (OLED) technology are appearing on many mobile devices. Unlike liquid crystal displays (LCD), OLED displays consume dramatically different power for showing different colors. In particular, OLED displays are inefficient for showing bright colors. This has made them undesirable for mobile devices because much of the web content is of bright colors. To tackle this problem, we present the motivational studies, design, and realization of Chameleon, a color adaptive web browser that renders webpages with power-optimized color schemes under user-supplied constraints. Driven by the findings from our motivational studies, Chameleon provides end users with important options, offloads tasks that are not absolutely needed in real time, and accomplishes real-time tasks by carefully enhancing the codebase of a browser engine. According to measurements with OLED smartphones, Chameleon is able to reduce average system power consumption for web browsing by 41 percent and is able to reduce display power consumption by 64 percent without introducing any noticeable delay.

40.1: Invited Paper: AMOLED Technology for Mobile Displays

In this paper we describe current trends in mobile display technology, and analyze the requirements for those displays as well as the ways of their fulfillment. We also show how active matrix displays based on organic light emitting diode (OLED) technology should provide basis for the economic manufacture of displays for mobile applications.

New emission band of PtOEP phosphor in organic LED devices

Electroluminescence (EL) and transient EL response have been studied on organic light-emitting diode (OLED) devices based on phosphorescent PtOEP molecule. As the emitting layer, we used layer of PtOEP doped in CBP host material and layer formed by 100%PtOEP (without doping in host). Three EL bands are observed at 500, 527 and 570 nm in the latter device besides red EL due to PtOEP. The 500 and 527 nm ELs are attributed to emission from hole- and electron-transport layers, respectively, while the 570 nm EL to emission from exciplex formed at the interface between the hole-blocking layer and emitting layer. Weak emission from the thermally populated triplet state is observed in single layer OLED device with 100%PtOEP layer and multi-layer device with PtOEP doped in host. Double exponential decay is observed in the electrophoresecence in the 100%PtOEP layer device, while a single exponential decay is observed in the device with PtOEP doped in host.

Application of radiative transport theory to light extraction from organic light emitting diodes

One limitation on organic light emitting diode (OLED) performance is the optical extraction efficiency ηex, which is defined as the ratio of light generated within the device to light emitted into the ambient. Typical estimates for ηex, in OLEDs range between 0.17 and 0.5. We develop a simple radiative transport model that quantifies the effect of volumetric light scattering on light output in OLEDs in terms of a small set of readily measured parameters. The methodology is sufficiently general to parametrize and describe many of the light extraction schemes found in the literature. A set of model calculations is presented using typical OLED parameters; these calculations show that the introduction of light scattering sites within the otherwise transparent substrate can increase light extraction efficiencies to values between 0.55 and 1.

The conjugation effects on the luminescence properties of oligophenylenes for the OLED

We synthesized novel phenyl-complexes as blue-emitting materials. The absorption maximum of 1,4′:1′,1ʺ:2ʺ,1‴,4⁗,1⁗—quinquephenyl (BBPB) and 2ʺ,5ʺ-bis(1,1′-biphenyl-4-yl)—1,4′:1′,1ʺ:4ʺ,1‴:4‴,1⁗-quinquephenyl (TTBPB) were located at 290 and 276 nm. The peak PL emission of TTBPB appears at 410 nm and that of BBPB appears at 374 nm with a shoulder at 398 nm, which indicate that the two types of aggregations are formed at the solid state. The dramatic difference in fluorescence quantum yield of the oligophenylenes is due to the steric twist of the two biphenyl groups of BBPB. The four biphenyl groups of TTBPB are conjugated to a generated pentaphenylene moiety. As expected, the oligophenylene derivatives exhibit low current density and the electroluminescence intensity is not high, due to less extended conjugation effects of phenylene groups. The relatively high intensity of TTBPB on organic light-emitting diode (OLED) can be explained by the conjugation effects of biphenyl groups of oligophenylenes.

Thermal effects and scaling in organic light-emitting flat-panel displays

The temperature rise in flat-panel displays without forced air cooling has been both modeled and experimentally measured as a function of the display size. Both radiation and convection are important processes for the transfer of heat to the ambient. Because of much poorer convection and the lack of lateral heat transport at large dimensions, for a fixed power density large displays are expected to be substantially hotter than small displays. This could adversely impact the reliability of large displays based on organic light-emitting diode (OLED) technology.