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Planarization of Slot-Die Coated Multilayer Stripes via Pre-drying by a Heating Roll for Organic Light-Emitting Diodes
摘要： Micro-patterning of single-layer thin films in the cross-web (transverse) direction is feasible using a slot-die coating system. For its practical applications in organic light-emitting diodes (OLEDs), however, the fabrication and planarization of multilayer thin-film stripes are indispensable. We have coated multilayer stripes using an aqueous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and non-aqueous poly(N-vinylcarbazole) (PVK) and planarized them via pre-drying by a heating roll in a roll-to-roll slot-die coating system. It is demonstrated that the PEDOT:PSS stripe can be planarized at a pre-drying (heating roll) temperature of 40 °C. At higher temperatures, it is found that there appear the evaporation-induced inward and/or outward capillary flows depending on the wet film thickness. Using a low-boiling-point solvent, the PVK stripe coated atop the planarized PEDOT:PSS stripe is shown to be planarized at a pre-drying temperature of 65 °C, the step coverage and thickness uniformity by which are substantially enhanced. Such a planarization scheme also brings in the positive effect on the surface morphology of those stripes. To verify the planarization effect at the device level, we have fabricated phosphorescent OLED stripes. Without planarization, the light-emitting area shrinks and a spot with strong light emission appears, increasing the probability of a short circuit in OLEDs. With planarization, however, we can achieve brighter light emission from OLED stripes with high inter-stripe emission uniformity.
关键词： planarization,Slot-die coating,organic light-emitting diode,heating roll,multilayer stripes
更新于2025-09-11 14:15:04
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Fundamentals and Applications of Red Light-Emitting Diodes (LEDs) <i>In Vitro</i> Plant Growth on Tomato <i>Lycopersicon esculentum Mill</i>
摘要： The aim of these studies was mainly to investigate the effects of monochromatic LEDs applied singly on the in vitro plant growth and morphogenesis. Various morphological and physiological parameters are considered that influence the growth and development of plants in vitro under red LED light as compared to those under normal light. Upon exposure to LED, in vitro-raised plants have shown significant improvements in growth and morphogenesis. In particular, red and blue lights, either alone or in combination, have a significant influence on plant growth. The present study gives an overview of the fundamentals of LEDs and describes their effects on in vitro plant growth and morphogenesis and their future potentials. The main objective of this study was to carry out line and combing ability of plant growth on tomato.
关键词： Solid-state lighting,Light-emitting diode,In vitro morphogenesis,Spectral quality
更新于2025-09-11 14:15:04
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Synthesis and Properties of New Imidazole Derivatives Including Various Chromophore for OLEDs
摘要： Two new blue compounds were successfully synthesized by introducing phenanthroimidazole group as a side group into pyrene, a chromophore with good luminous efficiency: 1-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazole (NA-PPI) and 1-(4’-(9H-carbazol-9-yl)-[1,1’-biphenyl]-4-yl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazole (CP-PPI). The optical and electroluminescence properties of newly synthesized materials were measured. Both materials emit blue or sky-blue photoluminescence in the film state and have a high PLQY value of over 80% in solution state. The synthesized materials were applied as EML in non-doped devices, and high efficiency of 3.51 cd/A and EQE of 2.39% in CP-PPI device were achieved.
关键词： pyrene,blue emission,Organic light-emitting diode,imidazole,fluorescence
更新于2025-09-11 14:15:04
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Femtosecond Laser Lift‐Off with Sub‐Band Gap Excitation for Production of Free‐Standing GaN LED Chips
摘要： A novel method for lifting-off GaN-based LED structures from sapphire substrates is demonstrated. In this approach, ultrashort (350 fs) green pulses are scanned across the sample backside to lift-off the LED, utilizing two-photon absorption at the GaN/sapphire interface. The corresponding fluence regime is carefully investigated. Stable emission properties after laser lift-off are proven by cathodoluminescense measurements.
关键词： GaN,light-emitting diode,femtosecond laser,non-linear optics,laser lift-off
更新于2025-09-11 14:15:04
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Value Retention Options in Circular Economy: Issues and Challenges of LED Lamp Preprocessing
摘要： The Circular Economy is gaining recognition for its attention to increasing material circularity by proposing a set of value retention options, and organizing business, institutions, and policies for their implementation. Light emitting diode (LED) lamp recycling is becoming increasingly important due to their growing market share and precious metal content. Instead of the current shredding approach, this study applied higher value retention options, such as testing for the functionality of the bulb at the product level, manual disassembly to reuse parts at the component level, and automatic disassembly for industrial scale reuse. This study ?nds that the e?ort that is needed to implement higher value retention options (such as reuse) requires a new form of secondary business, wider networks of recycling chains, and favorable policies. It also shows that about 50% of the lamp waste stream is still functioning and economically attractive if they are remarketed. However, the demand-pull market conditions seem to be missing. For manual disassembly, the output fractions are cleaner, but it is not economically feasible due to high labor cost. On the other hand, automatic disassembly does not produce cleaner fractions due to wide design variability. Thus, this study suggests that shifting from shredding-focused-resource recovery to reuse-based-resource circularity requires a comprehensive framework that simultaneously encourages secondary market formation, collaboration between manufacturers, recyclers and companies, and the formulation of favorable reuse policies. This study applies insights from circular economy principles to LED lamp recycling, and it also contributes to the latter by identifying challenges and possible solutions.
关键词： circular economy,light emitting diode (LED) lamp,value retention options,disassembly,recycling
更新于2025-09-11 14:15:04
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Dopant-Free Squaraine-Based Polymeric Hole-Transporting Materials with Comprehensive Passivation Effects for Efficient All-Inorganic Perovskite Solar Cells
摘要： Quantum-dot (QD) white light-emitting diodes (LEDs) are promising for illumination and display applications due to their excellent color quality. Although they have a high quantum yield close to unity, the reabsorption of QD light leads to high conversion loss, significantly reducing the luminous efficacy and stability of QD white LEDs. In this report, SBA-15 mesoporous particles (MPs) with two-dimensional hexagonal pore structures (2D-HPS) are utilized to largely enhance the luminous efficacy and color-conversion efficiency of QD white LEDs in excess of 50%. The reduction in conversion loss also helps QD white LEDs to achieve a lifetime 1.9 times longer than that of LEDs using QD-only composites at harsh aging conditions. Simulation and testing results suggest that the waveguide effect of 2D-HPS helps in reducing the reabsorption loss by constraining the QD light inside the wall of 2D-HPS, decreasing the probability of being captured by QDs inside the hole of 2D-HPS. As such, materials and mechanisms like SBA-15 MPs with 2D-HPS could provide a new path to improve the photon management of QD light, comprehensively enhancing the performances of QD white LEDs.
关键词： stability,two-dimensional hexagonal pore structure,reabsorption,luminous efficacy,SBA-15 mesoporous particle,quantum-dot white light-emitting diode
更新于2025-09-11 14:15:04
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Uncommon Intramolecular Charge Transfer Effect and Its Potential Application in OLED Emitters
摘要： Planarized intramolecular charge transfer(PLICT) state can facilitate the fluorescence process thanks to the relative excellent planarity. Recently, we have discovered that the excited state quinone -conformation induced planarization(ESQIP) occurring on tetraphenylpyrazine(TPP) based derivatives could furnish them with PLICT feature. Unlike to the well-known intramolecular charge transfer, strengthening the electron-donating nature on the donor(D) moiety did not impair the PLICT. The calculation results showed that planarization of the TPP based compounds scarcely accompanied with energy wastage while amount of energy was required for the torsion on geometries. In the polar solvents, the energy consumption for planarization could further decrease, but that for twisting structure would increase. To take advantage of the transformation of the frontier orbitals’ distribution, the PLICT type materials would perform a potential application on organic light-emitting diodes(OLEDs).
关键词： Tetraphenylpyrazine,Organic light-emitting diode,Planarized intramolecular charge transfer,Excited state quinone-conformation induced planarization
更新于2025-09-11 14:15:04
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White organic light-emitting diode (OLED) microdisplay with a tandem structure
摘要： Microdisplay is a key technology for realizing augmented reality (AR) and mixed reality (MR) devices, which have attracted much attention of late. Even though the operating voltage in the tandem structure is higher than that in the single structure, 2-stack tandem OLED exhibited 20,000 cd/m2 at 9 V, which is compatible with CMOS circuit driving. Due to its top-emitting geometry with a tandem structure, the OLED device with a well-controlled thickness exhibited a white spectrum with (0.26, 0.26) color coordinates. The pixel density of the fabricated microdisplay panel with a white tandem OLED was about 2350 pixels per inch, and the active area of the panel was 0.7 inch diagonally. The resolution of the panel was 1280 × 1024, corresponding to SXGA, and the maximal luminance was 3,000 cd/m2.
关键词： white OLED,tandem,Organic light-emitting diode (OLED),microdisplay
更新于2025-09-11 14:15:04
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An efficient cadmium free inverted red quantum dot light emitting diodes
摘要： Here, we report an efficient inverted red indium phosphide (InP) comprised QD (InP/ZnSe/ZnS, core/shell structure) light-emitting diode (QLED) by modulating an interfacial contact between the electron transport layer and emissive InP-QDs and applying self-aging approach. The red InP-QLED with optimized interfacial contact exhibits a significant improvement in maximum external quantum efficiency and current efficiency from 4.42% to 10.2% and 4.70 cd/A to 10.8 cd/A, respectively, after 69 days of self-aging, which is an almost 2.3-fold improvement compared with the fresh device. The analysis indicates the consecutive reduction in electron injection and accumulation in the emissive QD due to changes in the conduction band minimum of ZnMgO (0.1 eV after 10 days of storage times) through a downward vacuum level shift according to the aging times. During the device aging periods, the oxygen vacancies of ZnMgO reduces, which leads to lower the conductivity of ZnMgO. As a result, the improvement of charge balance in the device with the suppression of exciton quenching at the interface of ZnMgO and InP-QD.
关键词： Cadmium-free quantum dots,charge balance,charge carrier injection layers,inverted structure,light emitting diode
更新于2025-09-11 14:15:04
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Adaptive Thresholding Scheme for Demodulation of Rolling-Shutter Images Obtained in CMOS Image Sensor Based Visible Light Communications
摘要： Light-emitting-diode transmitter and complementary-metal–oxide–semiconductor (CMOS) image sensor receiver based visible light communication is a promising scheme for an optical wireless communication. During the demodulation of the rolling shutter pattern obtained from the CMOS image sensor Rx, due to the high signal fluctuation introduced by the uneven light exposure, special thresholding schemes are needed to correctly identify the data logic. In this work, we propose and demonstrate a modified adaptive scheme (MQA) for the demodulation of the rolling shutter pattern. Experimental bit-error-ratio (BER) measurements using different thresholding schemes at different illuminance are analyzed. The results show that the proposed MQA scheme can provide much lower BER, with similar process latencies when compared with other schemes.
关键词： visible light communication (VLC),Light emitting diode (LED),CMOS image sensor.
更新于2025-09-10 09:29:36