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High Emission Quantum Yield Tb <sup>3+</sup> -Activated Organic-Inorganic Hybrids for UV-Down-Shifting Green Light-Emitting Diodes
摘要： Solid-state light-emitting diodes (LEDs) are driving the lighting industry towards efficient and environmentally friendly lighting and displays. Current challenges encompass efficient and low-cost down-shifting phosphors with tuned emission colors. Green light lies on the low-loss optical transmission window in plastic optical fibers and plays a special role in human and plants circadian rhythm regulation. Moreover, green-emitting phosphors may suppress the ‘green gap’ found in semiconductor-based LEDs. In this work, a UV-photostable Tb(NaI)3(H2O)2, with (1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-NaI= nalidixic naftiridine-3-carboxylic acid), was incorporated into tripodal organic-inorganic hybrid materials. The hybrid hosts boost the absolute emission quantum yield from ~0.11 (isolated complex) to ~0.82 (doped hybrid), being the largest value reported for Tb3+-based hybrid phosphors. A green-emitting LED was fabricated by coating a near-UV LED (365 nm) with a Tb3+-activated organic-inorganic hybrid showing pure-green light with Commission International de l’Eclairage color coordinates and an efficacy value of (0.33, 0.59) and 1.3 lm·W?1, respectively.
关键词： near-UV light-emitting diodes,green light-emitting diodes,lanthanides,solid-state lighting,organic-inorganic hybrids
更新于2025-09-23 15:21:01
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[IEEE 2018 4th IEEE International Conference on Emerging Electronics (ICEE) - Bengaluru, India (2018.12.17-2018.12.19)] 2018 4th IEEE International Conference on Emerging Electronics (ICEE) - Development of New Blue-Light Emitting PPV Block Copolymer: Synthesis, Characterization and Electro-Optical Studies
摘要： New soluble intense blue light emitting bulky ring substituted segmented PPV block copolymer was synthesized by synthesized condensation polymerization. Rigid cyclohexyl methoxy group substituted distyrylbenzene unit was the chromophore group present in the synthesized segmented block copolymer. The obtained copolymer was dissolved in all common organic solvents. The structure of the copolymer was characterized by using FT-IR, NMR techniques, and elemental analysis. GPC analysis shows that the copolymer has narrow polydispersity index. Thermal gravimetric analysis shows it has excellent thermal stability with maximum decomposition temperature obtained as 4220C. The HOMO and LUMO values of copolymer were estimated from the cyclic voltammograms. Photoluminescence studies show that copolymer gives blue emission. XRD and DSC studies give information about the semi-crystalline nature of the present copolymer. Overall results such as thermal properties, photoluminescence characteristics and low onset voltage from Voltage vs. Current data are confirmed the suitability of the copolymer for fabricating PLEDs.
关键词： polymer light emitting diodes,light emitting polymers,segmented block copolymer
更新于2025-09-23 15:21:01
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Bright CsPbI <sub/>3</sub> Perovskite Quantum Dot Light-Emitting Diodes with Top-Emitting Structure and a Low Efficiency Roll-Off Realized by Applying Zirconium Acetylacetonate Surface Modification
摘要： Zirconium acetylacetonate used as a co-precursor in the synthesis of CsPbI3 quantum dots (QDs) increased their photoluminescence quantum efficiency to values over 90%. The top-emitting device structure on a Si substrate with high thermal conductivity (to better dissipate Joule heat generated at high current density) was designed to improve the light extraction efficiency making use of a strong microcavity resonance between the bottom and top electrodes. As a result of these improvements, light-emitting diodes (LEDs) utilizing Zr-modified CsPbI3 QDs with an electroluminescence at 686 nm showed external quantum efficiency (EQE) of 13.7% at a current density of 108 mA cm?2, which was combined with low efficiency roll-off (maintaining an EQE of 12.5% at a high current density of 500 mA cm?2) and a high luminance of 14 725 cd m?2, and the stability of the devices being repeatedly lit (cycled on and off at high drive current density) has been greatly enhanced.
关键词： CsPbI3 perovskite quantum dots,top-emitting light-emitting diodes,surface modification,zirconium acetylacetonate,efficiency roll-off
更新于2025-09-23 15:21:01
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Subwavelength-scale nanorods implemented hexagonal pyramids structure as efficient light-extraction in Light-emitting diodes
摘要： Subwavelength-scale nanorods were implemented on the hexagonal pyramid of photochemically etched light-emitting diodes (LEDs) to improve light extraction efficiency (LEE). Sequential processes of Ag deposition and inductively coupled plasma etching successfully produce nanorods on both locally unetched flat surface and sidewall of hexagonal pyramids. The subwavelength-scale structures on flat surface offer gradually changed refractive index, and the structures on side wall of hexagonal pyramid reduce backward reflection, thereby enhancing further enhancement of the light extraction efficiency. Consequently, the nanorods implemented LED shows a remarkable enhancement in the light output power by 14% compared with that of the photochemically etched LEDs which is known to exhibit the highest light output power. Theoretical calculations using a rigorous coupled wave analysis method reveal that the subwavelength-scale nanorods are very effective in the elimination of TIR as well as backward reflections, thereby further enhancing LEE of the LEDs.
关键词： subwavelength-scale nanorods,light-emitting diodes,light extraction efficiency,hexagonal pyramids,photochemical etching
更新于2025-09-23 15:21:01
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Enhanced optical efficiency and color purity for organic light-emitting diodes by finely optimizing parameters of nanoscale low-refractive index grid
摘要： 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.
关键词： organic light-emitting diodes,nanodot array,FDTD simulation,laser interference lithography,light extraction,low refractive index
更新于2025-09-23 15:21:01
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Improving the out-coupling efficiency of polymer light-emitting diodes with soft nanoimprinted random corrugated structures
摘要： A simple method is demonstrated in this study by applying random corrugated structures into the polymer emitting layer via soft nanoimprint technology to enhance the light out-coupling efficiency of polymer light-emitting diodes (PLEDs). The device with the random corrugated structures presents high efficiency and stable emission close to the Lambertian pattern. Compared with the flat device, about 52% efficiency enhancement is achieved in the PLEDs with the random corrugated structures, which can be understood by extraction of waveguide mode and surface plasmon polariton mode losses simultaneously. With these advantages, the simple random corrugated structures have the potential to stimulate the development of low-cost and large-area flexible PLEDs with high efficiency in the applications of solid-state light sources and full-color displays.
关键词： surface plasmon polariton mode,soft nanoimprint,light out-coupling efficiency,random corrugated structures,polymer light-emitting diodes,waveguide mode
更新于2025-09-23 15:21:01
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Improved Color Purity of Monolithic Full Color Micro-LEDs Using Distributed Bragg Reflector and Blue Light Absorption Material
摘要： In this study, CdSe/ZnS core-shell quantum dots (QDs) with various dimensions were used as the color conversion materials. QDs with dimensions of 3 nm and 5 nm were excited by gallium nitride (GaN)-based blue micro-light-emitting diodes (micro-LEDs) with a size of 30 μm × 30 μm to respectively form the green and red lights. The hybrid Bragg re?ector (HBR) with high re?ectivity at the regions of the blue, green, and red lights was fabricated on the bottom side of the micro-LEDs to re?ect the downward light. This could enhance the intensity of the green and red lights for the green and red QDs/micro-LEDs to 11% and 10%. The distributed Bragg re?ector (DBR) was fabricated on the QDs color conversion layers to re?ect the non-absorbed blue light that was not absorbed by the QDs, which could increase the probability of the QDs excited by the re?ected blue light. The blue light absorption material was deposited on the DBR to absorb the blue light that escaped from the DBR, which could enhance the color purity of the resulting green and red QDs/micro-LEDs to 90.9% and 90.3%, respectively.
关键词： micro-light-emitting diodes,color conversion layer,distributed Bragg re?ector,quantum dots,hybrid Bragg re?ector,blue light absorption material
更新于2025-09-23 15:21:01
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Novel strategy to improve the efficiency roll-off at high luminance and operational lifetime of hybrid white OLEDs via employing an assistant layer with triplet-triplet annihilation up-conversion characteristics
摘要： The efficiency roll-off at high luminance and operational lifetime remain a major challenge before the wide applications of white organic light-emitting diodes (WOLEDs) technology. Here we present a novel strategy to improve the efficiency roll-off at high luminance and operational lifetime by employing an assistant layer with triplet-triplet annihilation (TTA) up-conversion characteristics in emitters. It can be seen that at high luminance, the partial triplet energies in emitters will transfer to the TTA assistant layer and finally lead to the TTA emission, which reduces the exciton quenching at high luminance. Therefore, not only the efficiency roll-off, but also the operational lifetime are greatly improved. The resulting hybrid WOLEDs exhibited the maximum forward-viewing external quantum efficiency and power efficiency of 23.6% and 68.8 lm W?1, and they only dropped to 18.3% and 38.1 lm W?1 at 1000 cd m?2 and 17.1% and 25.9 lm W?1 at 5000 cd m?2, which are significantly higher than 10.5% and 17.9 lm W?1 at 5000 cd m?2 of WOLEDs without TTA assistant layer. Furthermore, the operational half-lifetime of the resulting hybrid WOLEDs also reached 600 hours at the luminance of 1000 cd m?2, which is nearly two-fold longer than that of the reference WOLEDs.
关键词： exciton diffusion,triplet-triplet annihilation up-conversion,Efficiency roll-off,white organic light-emitting diodes,lifetime
更新于2025-09-23 15:21:01
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Concentration quenching resistant donor-acceptor molecular structure for high efficiency and long lifetime thermally activated delayed fluorescent organic light-emitting diodes via suppressed non-radiative channel
摘要： A molecular design having t-butyl groups surrounding a donor-acceptor type core structure was developed as an approach to obtain high external quantum efficiency by suppressing concentration quenching effect caused by strong intermolecular interaction. The donor-acceptor type core structure was surrounded by six t-butyl groups to separate the donor-acceptor core structure between molecules. A heptazine acceptor and a diphenylamine donor based thermally activated delayed fluorescent emitter protected by the multiple t-butyl units achieved maximum external quantum efficiency of 32.6% at 1% doping concentration and 23.0% even at a high doping concentration of 20% by reducing concentration quenching effect. Furthermore, the lifetime of the thermally activated delayed fluorescent devices was also improved relative to that of the previous emitter with the same acceptor. The external quantum efficiency and device lifetime are better than any other results reported in the orange TADF OLEDs.
关键词： Thermally activated delayed fluorescence,Lifetime,T-butyl,Organic light-emitting diodes,High efficiency
更新于2025-09-23 15:21:01
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Interface Engineering of CsPbBr <sub/>3</sub> Nanocrystal Light-Emitting Diodes via Atomic Layer Deposition
摘要： Perovskite nanocrystal (PNC) suffers from solution corrosion and water/oxygen oxidation when used in light-emitting diodes (LEDs). Atomic layer deposition (ALD) is applied to introduce Al2O3 infilling and interface engineering for the CsPbBr3 nanocrystal emission layers, and the inorganic electron transport layer-based CsPbBr3–ZnMgO LED device is fabricated. The introduction of Al2O3 ALD layers significantly improves the tolerance of CsPbBr3 PNC thin films to polar solvents ethanol of ZnMgO during spin coating. The operation lifetime of ALD-treated CsPbBr3 PNC–ZnMgO LED is prolonged to about two orders of magnitude greater than that of the CsPbBr3 PNC-TPBi LED device with a largely improved external quantum efficiency (EQE) value. Moreover, the infilling of Al2O3 into the CsPbBr3 layer boosts the carrier mobility for more than 40 times inside the light-emission layer. However, the interfacial carrier transport between different functional layers is hindered by the insulated Al2O3 layer, which provides an effective barrier for excess electron transport. Such a favorable band alignment facilitates the carrier balance of the device and contributes to the improved electroluminescent performance of the device with ALD Al2O3 interface engineering, which is further supported by theoretical device modeling. Herein, a facile method is provided to fabricate PNC-LED devices with both high efficiency and long-term lifetime.
关键词： light emitting diodes,working stability,interface engineering,atomic layer deposition,CsPbBr3 perovskite nanocrystals
更新于2025-09-23 15:21:01