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An effective thermally activated delayed fluorescence host material for highly efficient blue phosphorescent organic light-emitting diodes with low doping concentration
摘要： A thermally activated delayed fluorescence (TADF) material BCz-2SO has been designed and synthesized as host for blue phosphorescent organic light-emitting diodes (OLEDs). Photophysical studies and theoretical calculations show that the molecule has a small singlet-triplet energy gap (ΔEST) of 0.345 eV, which is beneficial to the reverse energy transferring between the singlet and triplet state. Thanks to the TADF property, the triplet energy can be transmitted to the singlet state through reverse intersystem crossing (RISC), and then transmitted to the guest through the Fo?rster energy transfer (FET) to achieve 100% utilization of energy. Thus, the triplet–triplet annihilation (TTA) of the blue phosphor can be avoided by the extremely low doping concentration of 1%. By using BCz-2SO as the host of FIrpic, the solution-processed blue phosphorescent device achieves the maximum current efficiency (CE), power efficiency (PE), external quantum efficiency (EQE) and highest brightness of 16.38 cd A-1, 9.04 lm W-1, 7.8% and 16537 cd m-2, respectively. It demonstrates that one can employ the solution-processed method to prepare the high performance phosphorescent OLEDs using the TADF host material we have developed.
关键词： TADF,blue emission,organic light-emitting diodes,low doping concentration,solution-process
更新于2025-09-11 14:15:04
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Novel ultra-stable and highly luminescent white light-emitting diodes from perovskite quantum dots—Polymer nanofibers through biaxial electrospinning
摘要： Cesium lead halide perovskite quantum dots (QDs) have drawn extensive attention due to their excellent optical properties. However, their use is limited by poor stability. To enhance their stability, we electrospun perovskite-embedded fibers from composite CsPbX3 (X = Cl, Br, and I) perovskite QDs, blending with three polymers, poly(styrene-butadiene-styrene) (SBS), poly(methyl methacrylate) (PMMA), or polystyrene (PS), for the light-emitting diode (LED) applications. We found that the stretchable CsPbBr3@SBS fibers revealed the highest photoluminescence quantum yield, the CsPbBr3@PMMA fibers demonstrated a high thermal stability, and the CsPbBr3@PS fibers exhibited the best water-resistant stability. The photoluminescence intensity maintained 83% of its initial intensity for more than 3 months in water. Furthermore, the LED devices are manufactured from the blue chips and packaged with the core/shell red and green perovskite-based fibers by using biaxial electrospinning exhibited stable and highly efficient white luminescence. The luminance and efficiency are higher than 400% of the values of multilayered structures.
关键词： biaxial electrospinning,luminescence,stability,white light-emitting diodes,polymer nanofibers,perovskite quantum dots
更新于2025-09-11 14:15:04
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Effects of alkylamine chain length on perovskite nanocrystals after washing and perovskite light-emitting diodes
摘要： Organic-inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have great attention as a light source for perovskite light-emitting diodes (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short-alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as a one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short-alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd/cm2, indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film.
关键词： optical properties,light-emitting diodes,perovskite nanocrystals,washing process,alkylamine chain length
更新于2025-09-11 14:15:04
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16.3: <i>Invited Paper:</i> New development in Red Light‐emitting Diodes (LEDs) using Eu‐doped GaN for Monolithic Micro‐LED Displays
摘要： There has been a strong demand to develop red light-emitting nitride semiconductors for the monolithic integration of the three primary colors (RGB) and the development of a high-resolution display. Such a display is a key device for 'a smart society', in which cyberspace (information processing) and physical space (things) interactively fuse. The ongoing search for an efficient red LED based on GaN is pivotal to those efforts. In blue and green LEDs, InxGa1-xN /GaN multi-quantum wells are used as an active layer. Emission wavelength is determined by In composition in the InGaN. A simple way to realize the red LED is to increase In composition to 0.5. However, lattice mismatch between InGaN and GaN becomes large in InGaN with high In composition, which leads to severe degradation of crystalline quality of InGaN quantum wells. Furthermore, lattice mismatch also induces huge piezoelectric field, resulting in poor radiative recombination due to quantum-confined Stark effects. We have worked on the development of semiconductors intra-center photonics. This novel photonics uses the intra-4f shell transitions of rare-earth ions doped in semiconductors. In 2009, we invented a narrow-band red LED using Eu-doped GaN (GaN:Eu). A main emission line with a half width of less than 1 nm is observed at 621 nm, which can be assigned to the 5D0–7F2 transition of Eu3+ ions. The wavelength is extremely stable against the ambient temperature. Due to optimization of the device processing, the output power of the LED has been increasing steadily to over 1 mW. Utilizing this red LED, small nitride-based monolithic high-resolution optical devices that comprise RGB GaN-based LEDs can be realized for micro-LED displays and/or lighting technology. One of limiting factors for more enhanced light output power is a relatively long radiative lifetime of the Eu emission in GaN:Eu (～300 μs). According to the Fermi’s golden rule, modifying the spontaneous emission rate of Eu ions can be achieved by increasing the photonic density of states at the frequency of spontaneous emission, as already demonstrated with a planar Fabry-Perot cavity. We have boosted the output power by actively manipulating radiative recombination probability at the atomic level of the Eu ions, which can be achieved through control of their photon fields in micro- and nano-cavities. In a GaN:Eu layer embedded in a microcavity consisting of an AlGaN/GaN distributed Bragg reflector (DBR) and a Ag reflecting mirror, a 21-fold increase of the Eu emission intensity was obtained under optical pumping at room temperature. Furthermore, in a preliminary LED with a microcavity consisting of ZrO2/SiO2 and AlInN/GaN DBRs, the output power was enhanced by 10 times. In the talk, current status of the LED and strategies for more improved output power will be presented.
关键词： Monolithic Micro-LED Displays,Eu-doped GaN,Intra-center photonics,Red Light-emitting Diodes,Nitride semiconductors
更新于2025-09-11 14:15:04
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Near-infrared polymer light-emitting diodes based on an inverted device structure
摘要： Near-infrared polymer light-emitting diodes (NIR-PLEDs) possess great potential in applications ranging from night-vision device to optical communications. Here we obtained NIR emission from normal red fluorescent polymers by using an inverted device structure with the aid of micro-cavity effects. By tuning the thickness of the emissive layer, the inverted NIR-PLED based on PPF-FSO15-DHTBT10 and MEH-PPV got a near-infrared emission with the main peak located at 700 nm and 706 nm, and the maximum external quantum efficiency (EQEmax) of 0.54% and 1.03%, respectively. The increase of emissive layer thickness caused the relative variation of recombination area, which led to the widely controlling of EL spectra in the inverted device. These results reveal that tuning EL spectrum utilized by inverted device structure would be a promising method to realize near-infrared emission.
关键词： emissive layer thickness,micro-cavity effects,inverted device structure,Near-infrared polymer light-emitting diodes,external quantum efficiency
更新于2025-09-11 14:15:04
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Organic light-emitting diodes with an electro-deposited copper(I) thiocyanate (CuSCN) hole-injection layer based on aqueous electrolyte
摘要： Copper(I) thiocyanate (CuSCN) has been drawing much attention in optoelectronics due to its exceptional optical and electrical properties, as well as its processing versatility. The first organic light-emitting diodes (OLEDs) integrated with electro-deposited CuSCN crystalline thin films based on aqueous electrolyte were fabricated. With precisely tuned deposition parameters, the CuSCN thin films with satisfactory surface roughness and sufficient grain density were realized. We found that the driving voltage (voltage at a current density of 100 mA/cm2) and turn-on voltage of OLEDs using CuSCN as the hole injection layer (HIL) can be reduced by 1.41 and 1.79 V, respectively, compared with devices using vacuum-deposited hole injecting transition metal oxide molybdenum trioxide (MoO3). Moreover, the fabricated OLEDs also demonstrated considerably mitigated efficiency roll-off. Optical and energetic analyses were conducted to investigate the characteristics and enhancement mechanisms. Efficient hole-injection, electron blocking, improved charge balance, enhanced optical properties and good compatibility of electro-deposited CuSCN with thermally evaporated organic systems were found to be the primary contributors for the performance improvements of the OLEDs.
关键词： Electro-deposition,CuSCN,Hole injection,Organic-inorganic hybrid system,Organic light-emitting diodes,Copper(I) thiocyanate
更新于2025-09-11 14:15:04
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Time controlled growth of CdSe QDs for applications in white light emitting diodes
摘要： Semiconductor nanophosphors have the exceptional resources to demonstrate the quantum phenomenon due to their tailored-size dependent photoluminescence (PL). The work here is focused on the synthesis of highly luminescent Cadmium Selenide (CdSe) Quantum Dots (QDs) by a simple technique. This is a time dependent process where change in the size of CdSe QDs was observed at a reaction temperature of 100 °C without any inert atmosphere. The CdSe QDs were synthesised by using 3-Mercapto propionic acid (MPA) rather than using the typically utilized capping agent. All the samples were characterised for their optical properties. The size of QDs was calculated in a range up to 3 nm by UV–Vis Spectroscopy and con?rmed by High Resolution Transmission Electron Microscopy (HRTEM). It was clear from the UV studies that QDs exhibit size dependent tunable optical absorption. The broad Photoluminescence (PL) emission spectra depicts the presence of surface defects produced along with band edge spectrum. The absorbance and emission spectra were shifted to the red region due to the quantum con?nement e?ect occurred in QDs. The water soluble QDs were economical and easy to fabricate has applications in Light Emitting Diodes (LEDs).
关键词： 3-Mercapto propionic acid,Light Emitting Diodes,Quantum con?nement,Photoluminescence,CdSe Quantum Dots
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE 9th International Nanoelectronics Conferences (INEC) - Kuching, Malaysia (2019.7.3-2019.7.5)] 2019 IEEE 9th International Nanoelectronics Conferences (INEC) - Dependence of operating conditions on lifetime of Phosphor Quantum dots-based white LEDs
摘要： Lifetime of packaged Phosphor- Quantum dot (QDs) based white LEDs is studied. Various stress parameters such as blue light luminance, temperature and moisture are considered and their effect on the performance of the Phosphor- QD based LED is investigated. The lumen degradation rate and degradation trend for LEDs is observed to be different under varying stress conditions. Lumen recovery process is also observed under light stress test.
关键词： down conversion,Light emitting diodes,Quantum dot,lifetime,Phosphor
更新于2025-09-11 14:15:04
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White LEDs With High Optical Consistency Packaged Using 3D Ceramic Substrate
摘要： Packaging efficiency and optical performances are important indexes for white light-emitting diodes (WLEDs) packaging. In this letter, wafer-level WLEDs packaging were presented by printing phosphor on three-dimensional (3D) ceramic substrate to improve packaging efficiency and optical consistency. The 3D ceramic substrate was prepared by repeatedly electroplating copper cups on the planar direct plated copper (DPC) ceramic substrate. The phosphor concentration was adjusted to realize natural white light. The fabrication errors of the 3D ceramic substrate and the optical performances of WLED modules were analyzed to evaluate the optical consistency of the WLED modules packaged by using 3D ceramic substrate. Consequently, the fabrication errors of 3D ceramic substrate are less than 1%. When the phosphor concentration was set at 12.5 wt%, the packaged LEDs achieve a natural white light with luminous efficiency (LE) of 94.55 lm/W, correlated color temperature (CCT) of 5915 K, and chromaticity coordinate of (0.3166, 0.3345). The WLED modules exhibit small standard deviations in LE (1%), color rendering index (1%), correlated color temperature (98 K), and high reliability. The results indicate that the WLEDs packaged using 3D ceramic substrate have excellent optical consistency.
关键词： direct plated copper (DPC) ceramic substrate,optical performance,White light-emitting diodes (WLEDs),LED packaging,reliability
更新于2025-09-11 14:15:04
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[IEEE 2019 54th International Universities Power Engineering Conference (UPEC) - Bucharest, Romania (2019.9.3-2019.9.6)] 2019 54th International Universities Power Engineering Conference (UPEC) - Harmonic Behaviour of RGB WLED
摘要： For the last few years, there has been a decrease in electricity consumption for lighting purposes. The reason for this decrease is the widespread use of energy saving lighting elements that have high efficacy factor. LEDs are one of these lighting elements and have a very important role on energy saving lighting. On the other hand, power quality problems have started to be experienced more frequently and seriously, so it has become an important issue nowadays. Light emitting diodes are a closely related in both subjects. In this study, the harmonic behavior of RGB WLEDs, which has gained importance recently and has become increasingly widespread, has been investigated. RGB WLEDs, which are quite different from monochrome LEDs in terms of package contents and driver circuit, are expected to behave differently in terms of harmonics. In order to observe that, an appropriate test setup has been established and the power quality measurements of an RBG WLED sample have been performed for different operating cases. In the conclusion of the study, the enlightening results about the harmonic behavior of RGB WLEDs were obtained.
关键词： RGB WLED,Light emitting diodes,Distortion measurement,Relative spectral power,Power conversion harmonics
更新于2025-09-11 14:15:04