Organic Light-emitting Diode Lighting Research Articles

Paper] High-Gas-Barrier Film for Organic Light-Emitting Diode Lighting

Paper] High-Gas-Barrier Film for Organic Light-Emitting Diode Lighting

Organic light-emitting diodes, what’s next?

Organic light-emitting diode (OLED) technology has made significant advances in performance and becoming widely used in smartphone displays. However, the stability of efficient blue emitters, such as phosphorescent and thermally activated delayed fluorescent emitters, remains a challenge. While white OLEDs have the potential to revolutionize indoor lighting, their high cost per lumen due to efficiency roll-off and manufacturing costs is a limiting factor. To overcome these challenges, researchers must explore new material systems and device architectures to reduce efficiency roll-off and develop cost-effective film preparation processes. With continued increases in stability and decreases in cost, there is significant interest in scaling up OLED lighting and exploring its applications in other fields such as biomedical devices, anti-counterfeit labels, and optical communication.

Wearable devices for photodynamic therapy – A systematic review

Wearable devices for photodynamic therapy – A systematic review

Metabolic responses to polychromatic LED and OLED light at night

Light exposure at night has various implications for human health, but little is known about its effects on energy metabolism during subsequent sleep. We investigated the effects of polychromatic white light using conventional light-emitting diodes (LED) and an alternative light source, organic light-emitting diodes (OLED), producing reduced spectral content in the short wavelength of blue light (455 nm). Ten male participants were exposed to either LED, OLED (1000 lx), or dim (< 10 lx) light for 4 h before sleep in a metabolic chamber. Following OLED exposure, energy expenditure and core body temperature during sleep were significantly decreased (p < 0.001). Fat oxidation during sleep was significantly reduced (p = 0.001) after the exposure to LED compared with OLED. Following exposure to OLED, fat oxidation positively correlated with the 6-sulfatoxymelatonin levels, suggesting that the role of melatonin in lipolysis differs depending on the light. These findings advance our knowledge regarding the role of light in energy metabolism during sleep and provide a potential alternative to mitigate the negative consequences of light exposure at night.

Performance Enhancement and Bending Restoration for Flexible Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors by Low-Temperature Supercritical Dehydration Treatment.

For high-performance and high-lifetime flexible and wearable electronic applications, a low-temperature posttreatment method is highly expected to enhance the device performance and repair the defects induced by the low-temperature fabrication process intrinsically. Particularly, if the method can repair the traces induced by the multiple cycles of bending or deforming, it would overcome current fatal obstacles and provide a vital solution to the rapid development of flexible electronics. In this work, we propose a method to apply low-temperature supercritical CO2 fluid with a dehydration function to improve or even restore the performance of flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). After the treatment, the a-IGZO TFT exhibits 3 times improvement drivability up to 0.24 μA/μm, a smaller subthreshold swing of 0.18 V dec-1, a smaller Vth of 0.25 V, and a larger Ion/Ioff ratio of 3.8 × 107. Additionally, the posttreated a-IGZO TFTs possess relatively good uniformity and reproducibility with an on-current standard deviation of 0.047 μA/μm, and the performance of the a-IGZO TFT after the treatment remains almost unchanged even after bending 2500 times at a bending radius of 5 mm. These characteristics are attributed to the improved quality of the channel and gate dielectric. It is worth noting that when this is applied to a flexible TFT-driven organic light-emitting diode lighting system, this treatment method can restore the performance of not only the TFT but also the lighting system, even after the system has been bent more than 600 times and has failed. To date, this is the first time that the bending-track erasing function of the supercritical fluid for flexible systems has been reported, which has the potential to prolong the lifetime of flexible electronics.

Design and Implementation of Solar OLED Lighting Driver Circuit with Frequency Modulation Control

This paper proposes a single-stage single-ended primary inductor converter (SEPIC) converter circuit, which is applied to the organic light-emitting diodes (OLED) driver circuit. The circuit proposed in this paper replaces the output Schottky diode from the original SEPIC with a power switch. Deadtime is added to prevent the on-state overlapping of two switches with zero voltage switching (ZVS), and the circuit operates in triangular current mode. The digital control methods are maximum power point tracking and frequency modulation using a battery to supply the converter and illuminate the OLED at night. Finally, a prototype is implemented to show the feasibility under the DC input voltage range of 10–40 V. The DC output is 12 V/1 A/12 W, and the conversion efficiency is up to 96.3%.

Enhanced optical efficiency and color purity for organic light-emitting diodes by finely optimizing parameters of nanoscale low-refractive index grid

To extract the confined waveguided light in organic light-emitting diodes (OLEDs), inserting a low refractive index (RI) periodic structure between the anode and organic layer has been widely investigated as a promising technology. However, the periodic-structure-based light extraction applied inside devices has been shown to severely distort spectrum and affect EL characteristics. In this study, a simple light extraction technology using periodic low-RI nanodot array (NDA) as internal light extraction layer has been demonstrated. The NDA was fabricated simply via laser interference lithography (LIL). The structural parameters of periodic pattern, distance, and height were easily controlled by the LIL process. From computational analysis using finite-difference time-domain (FDTD) method, the NDA with 300 nm pitch and 0.3 coverage ratio per unit cell with 60 nm height showed the highest enhancement with spectral-distortion-minimized characteristics. Through both computational and experimental systematic analysis on the structural parameters of low-RI NDA-embedded OLEDs, highly efficient OLEDs have been fabricated. Finally, as representative indicators, hexagonal and rectangular positioned NDA-embedded OLEDs showed highly improved external quantum efficiencies of 2.44 (+29.55%) and 2.77 (+57.38%), respectively. Furthermore, the disadvantage originating from the nanoscale surface roughness on the transparent conductive oxide was minimized.

Effects of Different Light Sources on Neural Activity of the Paraventricular Nucleus in the Hypothalamus.

Background and Objectives: Physical function is influenced by light irradiation, and interest in the influence of light irradiation on health is high. Light signals are transmitted from the retina to the suprachiasmatic nucleus (SCN) via the retinal hypothalamic tract as non-image vision. Additionally, the SCN projects a nerve to the paraventricular nucleus (PVN) which acts as a stress center. This study examined the influences of three different light sources on neural activity in the PVN region using two different color temperatures. Materials and Methods: Experiments were conducted using twenty-eight Institute of Cancer Research (ICR) mice (10 week old males). Three light sources were used: (1) organic light-emitting diode (OLED) lighting, (2) LED lighting, and (3) fluorescent lighting. We examined the effects of light irradiation from the three light sources using two different color temperatures (2800 K and 4000 K). Perfusion was done 60 min after light irradiation, and then the brain was removed from the mouse for an immunohistochemistry analysis. c-Fos was immunohistochemically visualized as a marker of neural activity in the PVN region. Results: The number of c-Fos-positive cells was found to be significantly lower under OLED lighting and LED lighting conditions than under fluorescent lighting at a color temperature of 2800 K, and significantly lower under OLED lighting than LED lighting conditions at a color temperature of 4000 K. Conclusions: This study reveals that different light sources and color temperatures alter the neural activity of the PVN region. These results suggest that differences in the light source or color temperature may affect the stress response.

Formation of nanopore and nanopillar patterned polymer films from mixed PAA-PI solutions by phase separation method

Random nanopore and nanopillar patterns were prepared by using simple spin-coating technique based on the phase separation of a binary immiscible polymer blend of poly(amic acid) (PAA) and polyimide (PI). The pattern structure was spontaneously formed upon spin-coating of a mixed solution of PAA and PI on a glass substarte followed by thermal annealing, whose morphology was investigated by atomic force microscope and field emission scanning electron microscope technique. The results showed that not only the size of the patterns was the nanoscale of around 200 nm but also their shape was very uniform without requiring conventional patterning or photolithography processes. Two different morphologies, nanopore and nanopillar arrays were obtained for the PAA:PI volume ratio of 1:9 and 9:1, respectively. The flexible characteristic of nanopore and nanopillar films could be an interesting feature to be applied to organic light-emitting diodes lighting and displays.

Encapsulation requirements to enable stable organic ultra-thin and stretchable devices

Abstract

Reshaping the luminance distribution of OLED lighting using optical films

ABSTRACTThe angular distribution of luminance on a combination of a white organic light-emitting diode (OLED) panel and optical films was investigated through an experiment and through optical simulation. Applying an appropriate combination of separate optical films onto the OLED panel provided a great deal of flexibility in shaping the luminance profile of OLED lighting. This was due to the existence of thin air gaps between the OLED and the optical film on it as well as between the optical films, as supported by optical simulation. This flexibility may supply the OLED lighting with an additional degree of freedom, which is effective in adjusting the luminance profile freely.

Organic light-emitting diode lighting with high out-coupling and reliability: Application of transparent amorphous ZnO–SiO2 semiconductor thick film

Abstract We report that combination of high refractive index scattering layer made of glass and very thick amorphous ZnO-SiO2 (a-ZSO) semiconductor film is a route for obtaining both high out-coupling and reliability. a-ZSO is a promising material for electron injection/transport layer (EIL/ETL) in OLEDs; it has exceptionally small work function of ∼3.5 eV and high electron mobility of ∼1cm2/(Vs) (conductivity = 3.4 × 10−4 Scm−1), and can form ohmic contact with ITO. Thus, very thick a-ZSO film is applicable for EIL/ETL with no increase in turn-on voltage. Furthermore, a-ZSO has high transparency in the visible light region and a good index matching with the high index scattering layer, which is the most critical criterion to keep high out-coupling efficiency. Consequently, we succeeded in fabricating very stable and efficient OLED using 245 nm thick a-ZSO with the scattering layer which indicates ∼1.7 times higher out-coupling efficiency and smaller leakage current than the OLED with conventional glass substrate and a-ZSO thin film. This technology will be efficient for practical OLED lighting, and the durability against short circuit is also expected to improve.

Enhancement of autonomic and psychomotor arousal by exposures to blue wavelength light: importance of both absolute and relative contents of melanopic component

BackgroundBlue light containing rich melanopsin-stimulating (melanopic) component has been reported to enhance arousal level, but it is unclear whether the determinant of the effects is the absolute or relative content of melanopic component. We compared the autonomic and psychomotor arousal effects of melanopic-enriched blue light of organic light-emitting diode (OLED) with those of OLED lights with lesser absolute amount of melanopic component (green light) and with greater absolute but lesser relative content (white light).MethodsUsing a ceiling light consisting of 120 panels (55 × 55 mm square) of OLED modules with adjustable color and brightness, we examined the effects of blue, green, and white lights (melanopic photon flux densities, 0.23, 0.14, and 0.38 μmol/m2/s and its relative content ratios, 72, 17, and 14%, respectively) on heart rate variability (HRV) during exposures and on the performance of psychomotor vigilance test (PVT) after exposures in ten healthy subjects with normal color vision. For each of the three colors, five consecutive 10-min sessions of light exposures were performed in the supine position, interleaved by four 10-min intervals during which 5-min PVT was performed under usual fluorescent light in sitting position. Low-frequency (LF, 0.04–0.15 Hz) and high-frequency (HF, 0.15–0.40 Hz) power and LF-to-HF ratio (LF/HF) of HRV during light exposures and reaction time (RT) and minor lapse (RT >500 ms) of PVT were analyzed.ResultsHeart rate was higher and the HF power reflecting autonomic resting was lower during exposures to the blue light than the green and white lights, while LF/HF did not differ significantly. Also, the number of minor lapse and the variation of reaction time reflecting decreased vigilance were lower after exposures to the blue light than the green light.ConclusionsThe effects of blue OLED light for maintaining autonomic and psychomotor arousal levels depend on both absolute and relative contents of melanopic component in the light.

Recent Advances in Organic Electroluminescent Materials and Devices

Since the invention of organic light-emitting diodes(OLEDs) by Dr. CW Tang in 1987, researches in related fields have been developed rapidly. Now, small to medium size OLED displays have already been commercialized. Large OLED TVs and OLED lightings have also emerged in real applications. The further development of the OLED technology calls for intensive research on organic light-emitting materials and devices. This report reviewed the most focused issues as well as the main progress in the field of OLEDs in the recent years. It is shown that researchers have paid attentions to both technical innovations and theoretical researches, such as the design of new molecules, developing of new device technology, and understanding of light-emitting and transporting mechanisms of organic semiconductors.The developing trends of organic light-emitting materials and devices are summarized as follows: 1) molecular design for high performance phosphorescent materials; 2) novel fluorescent materials and their light emitting mechanisms; 3) new technologies for high performance white OLEDs; 4) new technologies for solution-processed devices and flexible devices; 5) the influences of molecular packing, disorder and doping on the charge transporting properties of organic semiconductors. Moreover, the current situations and developing trends of international OLED display and lighting industries are discussed.

OLED 조명을 위한 Yellow, Orange, Red 인광 재료

Organic light-emitting diode (OLED) research field has received great attention from academic and industrial circles. Recently, The technical feature of OLEDs is more and more attractive in the lighting market, including area emission characteristics different from other existing light sources. Features are environmentally friendly and efficient use of energy, large area, ultra-light weight, and ultrathin shape, etc. Furthermore, OLED light became the mainstream of next-generation lighting to replace the light emitting diode (LED) fluorescent light. This article summarizes phosphorescent emitting materials that have been applied to white OLEDs. In particular, the chemical structures and device performances of the important yellow, orange, and red phosphorescent emitting materials is discussed. Systematic classification and understanding of the phosphorescent materials can aid the development of new light-emitting materials.

Recent progress in the use of fluorescent and phosphorescent organic compounds for organic light-emitting diode lighting

Organic light-emitting diodes (OLEDs) have attracted considerable attention in both academic and industrial circles. Certain properties of OLEDs make them especially attractive in the lighting market, including area emission characteristics not found in other existing light sources, environmentally friendly efficient use of energy, large area, ultra-light weight, and ultra-thin shape. Fluorescent and phosphorescent materials that are being applied to white OLEDs have been categorized, and the chemical structures and device performances of the important blue, orange, and red light-emitting materials have been summarized. Such a systematic classification and understanding of the materials that have already been reported can aid the development and study of new light-emitting materials through quantitative and qualitative approaches.

Improvement of light extraction in organic light-emitting diodes using a corrugated microcavity.

Based on the phase separation effect in the film formation process of Polystyrene and Poly(methyl methacrylate) blend solution, bottom-emitting organic light-emitting diodes (OLEDs) with corrugated microcavity was demonstrated. This device exhibited high efficiency, broad spectra and Lambertian angular emission. Compared with the traditional bottom-emitting OLEDs with ITO anode and the planar microcavity OLEDs, about 57% and 41% enhancement for external quantum efficiency was achieved in this corrugated microcavity OLEDs respectively. This improvement can be understood by the scattering effect of the quasi-periodic characteristic of this corrugated microcavity which reduces the optical loss at surface plasmon polariton modes and wave-guided modes. This work provides a simple as well as efficienct method to recover trapped light in OLEDs, which will benefit the low cost fabrication process.

An Inductive Power Transfer System for Driving Multiple OLED Light Panels

An inductive power transfer system for driving multiple organic light-emitting diode (OLED) light panels is presented. Each light panel is driven by an output in a daisy-chained transformer (DCT) structure through a detachable transformer. The DCT structure allows using a single switching network to drive multiple light panels with good current balancing. A primary-side freewheeling (FW) circuit and an open-load protection network are introduced to maintain the current-balancing function of the DCT structure upon abnormal power transfer from the primary side to the secondary side of the detachable transformer. Apart from easy and safe operation, the proposed system also offers a modular, scalable, maintenance-free, and hot-swappable platform for large-area illumination. Modeling, design, and analysis of the system under normal and faulty operating conditions and misalignment of the detachable transformer will be given. A prototype system with four OLED light panels has been built and evaluated. The experimental results show that the circuit has a robust current balancing ability and fault condition tolerance. In addition, a comparison on the cost effectiveness between DCT structure and “one-drive-to-one-load” structure is investigated.

Enhancement of organic light-emitting diode light extraction by texturing PDMS layers

We have used different methods to produce a texture on the surface of polydimethylsiloxane layers. The layers were produced by spin coating on templates such as sandblasted and lithographed glass and sandpaper. The most striking result was obtained on layers templated on sandblasted glass surfaces, where an increase in luminous efficacy of 36% was observed.

Fabrication of Multiple Gas Barrier Layers Utilizing Roll-to-Roll Sputter and Performance

Flexible organic light emitting diodes (OLEDs) have been studied actively for the potential application to OLED display and OLED lighting. One of the key materials for flexible OLED is the flexible and transparent film substrate which can substitute ITO glass in flat panel OLEDs.In this work we deposited silicon and aluminium oxide and nitride single layer thin films on different flexible substrates such as poly(polyethylene terephthalate) (PET) and poly(polyethylene naphthalate (PEN) to investigate the gas barrier properties. After selecting the polymer film substrate and thin inorganic layer material, the inorganic/organic/inorganic multiple gas barrier was formed on film substrate by using roll-to-roll sputter and their property was examined from the viewpoint of multilayer structure and gas barrier properties for application to flexible substrate of OLED devices.