Single emitting layer white organic light-emitting device with high color stability to applied voltage

A new type of white organic light-emitting device has been fabricated incorporating a single light-emitting layer of bis(2-methyl-8-quinolinolato) (para-phenylphenolato) aluminum (III) (BAlq) doped with 2,5,8,11-tetra-tert-butylperylene (TBPe) and 5,6,11,12-tetraphenyl-naphthacene (rubrene). The configuration of the device was ITO/PVK:TPD/BAlq:TBPe:rubrene/Alq₃/Mg:Ag. By adjusting the proportion of the dopants (TBPe and rubrene) in the light-emitting layer, white light with Commission Internationale de l’Eclairage (CIE) coordinates of (0.34, 0.39) was obtained at an applied voltage of 8 V; the change of emission spectra was minimal when the voltage increased from 5 to 20 V. The device exhibited a maximum external quantum efficiency of 0.68% and a brightness of 1020 cd/m² at 8 V, the brightness increasing to 5723 cd/m² at 17 V.     

Red light emission from hybrid organic/inorganic quantum dot AC light emitting displays

An alternating current electroluminescent display has been direct written onto a flexible plastic substrate. A hybrid layer of poly(2-methoxy,5(2-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) and CdSe quantum dots (QDs) were used to convert the light emitted by electroluminescent ZnS phosphor into red light. The emission wavelength of the display is found to be directly related to the emission of CdSe quantum dots. The integration of QDs into thin film electroluminescent (TFEL) displays has the potential to enhance its color spectrum.     

Spectral studies of white organic light-emitting devices based on multi-emitting layers

White organic light emitting devices (WOLEDs) with an RBG stacked multilayer structure were demonstrated. In RGB stacked OLEDs, blue emitting, 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN) doped with p-bis(p-N,N-diphenyl-amono-styryl)benzene (DSA-Ph), green emitting, tris-(8-hydroxyquinoline)aluminum (Alq) doped with C545, and red emitting, tris-[8-hydroxyquinoline]aluminum (Alq) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)- 4H-pyran (DCJTB), were used. By adjusting the order and thickness of emitting layer in RBG structure, we got a white OLED with current efficiency of 5.60 cd/A and Commission Internationale De L’Eclairage (CIE) coordinates of (0.34, 0.34) at 200 mA/cm². Its maximum luminance was 20,700 cd/m² at current density of 400 mA/cm². The results have been explained on the basis of the theory of excitons generation and diffusion. According to the theory of excitons generation and diffusion, an equation has been set up which relates EL spectra to the thickness of every layer and to the exciton diffusion length.     

Neuro-controller for broadcast lighting light-emitting diode to express white light with high color rendering index

Technical characteristics analysis related to correlated color temperature (CCT), color rendering, and illuminance is required to use light-emitting diode (LED) as broadcast lighting. In general, to realize a white light source with a high color rendering index (CRI), we selected the appropriate emission intensity of RGBW LED through trial and error. However, the characteristics of the LED light source and environmental conditions make it difficult to perform the procedure several times. The objective of this study was to design a system that could control illuminance, CCT, and ∆uv while having high CRI, as an LED control method for broadcasting lighting. The controller implements using a feed-forward neural network with excellent nonlinear function approximation capability. We measure data directly from the red green blue white (RGBW) LED system for neural network training. We then select data with high CRI from the measured raw data and choose data for neural network learning by removing measurement noise using the quadratic polynomial interpolation method. The performance evaluation confirms that the proposed neural network controller shows excellent results as an RGBW LED controller for broadcast lighting in the Planckian locus and all regions of white light.     

Highly efficient single‐unit white OLED device with emission from both singlet and triplet excitons

We succeeded in developing a single‐unit hybrid organic light‐emitting diode (OLED) device with efficient light emission from both a phosphorescent layer and a fluorescent layer. The single‐unit hybrid OLED achieved a power efficiency higher than that of a two‐unit hybrid tandem OLED with phosphorescent and fluorescent layers.     

Enhancement of emission efficiency in white OLED device by highly efficient narrow spectrum red‐emission material

Newly developed red‐emission material with a narrow spectrum enhanced the current efficiency of a red OLED 1.3 times greater than a conventional material while maintaining chromaticity of red. This material also increased the power efficiency of a white OLED 1.2 times greater than the conventional material without impairing color rendering.     

Small molecules with pyridine backbone modified with carbazole,fluorine and bromine for white light-emitting diode applications

Seven compounds with pyridine as the backbone modified by carbazole moiety, bromine atom and fluorine atom were synthesized. Compounds 1, 2, 3 with bromo substitution at the 2-position and carbazole modification at the 5-position of pyridine emit not only a sharp blue singlet fluorescence but also a wide banded excimer-based orange emission. The two colors coming from a single molecule can be used to fabricate a simplified white light emitting device. The electroluminescence based on 1 and 2 exhibits white-light emission with CIE coordinates of x = 0.25 and y = 0.30 for 1 and x = 0.33 and y = 0.37 for 2 at high current densities, very close to pure white emission. In addition, the role of bromo-substitution at pyridine is concluded to be essential to generate molecular interaction thus an excimer emission.     

Realization of high efficacy white organic light emitting diode by controlling internal light absorption and angular distribution

We investigated highly efficient organic light emitting diode (OLED) with advanced optical designs of organic layers to convert evanescent mode (internal absorption) into guided light and micro structure to extract the specifically distributed guided light dominated by wide angular substrate mode. White OLED device based on these optical designs realized high efficacy of 133 lm/W and external quantum efficiency of 56 % at 1000 cd/m².     

Highly efficient and stable white organic light emitting diode with triply doped structure

A triply doped white organic light emitting diode with red and blue dyes in the light emitting layer and a green dye in another layer is proposed. The device structure was CuPc(12 nm)/NPB(40 nm)/ADN:DCJTB(0.2%):TBPe(1%)(50 nm)/Alq:C545(0.5%)(12 nm)/LiF(4 nm)/Al. Here copper phthalocyanine (CuPc) is a buffer layer, N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) is a hole transporting layer, 9,10-di-(2-naphthyl) anthracene (ADN) is blue emitting layer, tris (8-quinolinolato)aluminium complex (Alq) is an electron transporting layer, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidy1-9-enyl)-4H- pyran (DCJTB), 2,5,8,11-tetra-butylperylene (TBPe), Coumarin6 and deveriative (C545) are red, blue and green dyes, respectively. This device shows a luminance of 21200 cd/m² at driving current of 400 mA/cm² and 1026 cd/m² at 20 mA/cm². Its efficiency is 6 cd/A and 3.11 Lm/W. It also shows a higher operating stability: the half lifetime is 22,245 h at an initial luminance of 100 cd/m², while the driving voltage increased only 0.3 V.     

The liquid crystal light valve,an optical-to-optical interface device

A new device is described that transfers high resolution, two-state (black and white) images from a noncoherent beam of light to a fully coherent beam of light in quasi real-time (less than 1 sec). The device is a photoconductor activated liquid crystal light valve that operates in the dynamic scattering mode of the liquid crystal. It has sensitivity of 1–10 μW/cm² (at 5100 Å), resolution of 100 lines/mm and cycles on and off in 0.25 sec or less. This paper describes the construction and operation of the device and discusses its application to coherent optical data processing.     

Organic light-emitting diodes with improved hole–electron balance and tunable light emission with aromatic diamine/bathocuproine multiple hole-trapping-layer

Organic light-emitting diodes (OLEDs) with multiple hole-trapping-layer (HTL) structures, which consist of N,N′-bis-(1-naphthyl)-N, N′-diphenyl-1,1′-biphenyl 4,4′-diamine (NPB), bathocuproine (BCP) and tris(8-hydroxy-quinoline)aluminum (Alq₃) have been fabricated. The emitting zone of the device with the structure of ITO/[NPB/BCP]_n/Alq₃/LiF/Al can be changed by the number n of HTL. The effect of the multiple HTL structure upon the performance of OLEDs with tris(8-hydroxyquinoline) aluminum as the emitting material has been investigated. Compared with the brightness of the conventional green emitting diode without the multiple HTL structure, that of the diode with periodic number of five has been increased from 2512.8 cd/m² to 8661.0 cd/m². Such an improvement in the device performance was attributed to the improved hole–electron balance, which can be further attributed to the introduction of the multiple HTL structure.     

Microwave emission from an irregular snow layer

Emission from an irregular snow layer is modeled by a layer of Mie scatterers using the radiative transfer method. Comparisons are made with measurements showing snow wetness effects and rough air-snow boundary effects. For convenience of reference, theoretical model behavior is also illustrated.     

Artificial intelligence-assisted auto-optical inspection toward the stain detection of an organic light-emitting diode panel at the backplane fabrication step

This paper attempts to implement an auto-optical inspection (AOI) system using artificial intelligence (AI) technology for cost reduction in the production of organic light emitting diode (OLED) panels, specifically at the production stage of the thin film transistor (TFT) . Further, to improve the accuracy of mura detection, the possible causes of mura were properly identified, and a model to control and predict mura occurrence was realized based on the sufficient analysis of these causes. More specifically, an explainable AI (XAI) prediction model was developed using the fab image and test element group (TEG) engineering methods, which could be applied as input data for the circuit simulations to improve the accuracy of the overall simulations. Initially, we attempted to predict backplane stain using only the TFT width, length dimension, and resistance–capacitance (RC) extraction data, but the results were not accurate. Consequently, we identified, via sufficient analysis, that the correlation between the dehydrogenation and stain, and introduced an AI model. As a result, the accuracy was improved from 50 to 80%, which is more effective in terms of time and cost, compared to conventional simulation through the TCAD analysis. Overall, by implementing the inspection method described in this paper, it was possible to detect stains at the backplane stage, which was only possible during the final test stage, thereby resulting in significant cost savings.     

Multifunctional device with an integration of light emitting,photo detective,and energy harvesting

In this work, we present a multifunctional device based on a heterojunction active layer formed between the halide perovskite and chalcogenide quantum dots. The device is demonstrated with an integration of proof‐of‐concept functions, including a voltage controllable multicolor light‐emitting diode, an efficient energy harvesting device, and a photosensitive detector. The concept of the heterojunction active layer provides a feasible route to design efficient multifunctional devices in the future.     

The suppression of viewing angle dependence of top emission organic light emitting diodes having strong microcavity characteristics by applying concave patterned anode

In order to obtain the stable viewing angle characteristics of top emission organic light emitting diodes (TEOLEDs) having strong microcavity characteristics, we fabricated nano‐porous film on the glass substrate before depositing highly reflective anode. And then, we could obtain the concave patterned anode by depositing anode on the nano‐porous film and fabricated TEOLED composed of concave patterned layers. From this approach, we could successfully obtain not only the stable color shift and luminance distribution with viewing angle but also high efficiency caused by uneven morphology. In addition, we found that the driving voltage of TEOLED could be reduced due to increased surface area effect of the concave patterned anode, so that the power efficiency was enhanced by about 15% in comparison with reference device.     

Thin‐film encapsulated white organic light top‐emitting diodes using a WO3/Ag/WO3 cathode to enhance light out‐coupling

An alternative design of a semitransparent cathode for top‐emission white‐fluorescent organic light‐emitting diodes (OLEDs) has been investigated. The scope of this study was to improve the luminance of OLEDs used for displays while keeping the current density versus voltage characteristic unchanged for addressing purposes. The use of an optical simulation tool allowed the optimization of the tri‐layer cathode WO₃/Ag/WO₃ to increase the light out‐coupling coefficient of the device leading to an increased white emission compared with a reference device with a Ca/Ag cathode. An increase of ~40% in luminance has been calculated by simulation and experimentally confirmed. The p‐i‐n OLED structure underneath the tri‐layer cathode allowed an efficient injection of electrons independently from the work function of WO₃. The WO₃/Ag/WO₃ cathode has been also confirmed to be compatible with the atomic layer deposition technique for thin film encapsulation. Finally, lifetime measurements up to 600 h have been carried out to quantify the enhancements induced by the new cathode compared with the control device. It has been found that lifetimes of both cathode architectures are similar on this time scale, while the WO₃/Ag/WO₃ cathode shows a lower voltage drift versus aging.     

A modified transfer function obtained from the commutating contact of an N-path filter†

The realization of network transfer functions by commutating the input signal to a number of low-pass filters is well established. This paper shows that such an arrangement produces more than one transfer function, depending on the phase of the output brush with respect to the input brush. It is shown that when the output is picked up from the contact undergoing commutation the output is not only of different phase but also of different magnitude from that obtained from any of the other contacts.     

Direct excitation of xenon by ballistic electrons emitted from nanocrystalline‐silicon planar cathode and vacuum‐ultraviolet light emission

Abstract— To verify the possible use of energetic electrons for direct excitation of inert gas molecules, a nanocrystalline‐silicon (nc‐Si) planar ballistic emitter is operated in a high‐pressure xenon gas ambience. Under the pulse drive, vacuum‐ultraviolet (VUV) light emission is detected without any signs of discharge. The transient behavior of the VUV light emission properly corresponds to that of the nc‐Si emitter. In accordance with quantitative analyses of electron‐emission characteristics and the VUV output, the electron‐to‐photon conversion efficiency reaches 81% in the relatively efficient emitter case. The VUV output power is mainly determined from the number of electrons with energies compatible the with internal excitation of xenon. The emission spectrum observed at a pressure of 10 kPa shows peaks at 152 and 172 nm, which are thought to be originated from metastable Xe²* states. In contrast to the case of conventional impact ionization, no near‐infrared (NIR) peaks are seen in the spectrum. These results strongly suggest that the incidence of energetic electrons causes direct excitation of xenon molecules followed by radiative relaxation through intermediate states. The generated VUV light can be easily converted to visible light using a phosphor screen. As a discharge‐free VUV light emission, this phenomenon is potentially applicable to mercury‐free, high‐efficacy, and high‐stability flat‐panel light‐emitting device.     

High color purity emission from quantum dots by optimizing the full width at half the maximum and optical density to blue light

In this paper, we got wide color gamut of quantum dot (QD) films by optimizing the spectra width and optical density (OD) of quantum dots. The specific methods to achieve the following: QD R: one layer of color filter R film was coated below the QD R layer. QD G: one layer of yellow‐green film was coated below the QD G film. By a structure optimal design, we got wide color gamut up to 99.2% BT2020 (equal to 132.86% NTSC) in Cd‐based QD and 93.6% BT2020 (equal to 125.35% NTSC) in Cd‐free QD. Furthermore, the gamut of QD display will continue to be improved by continuous refining the structure of QD display.