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Converting an organic light-emitting diode from blue to white with Bragg modes
摘要： Organic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large area surfaces and flexible substrates. In addition, the low fabrication cost of OLEDs renders them particularly attractive as general lighting sources. Current methods for the fabrication of white-light OLEDs rely on the combination of multiple organic emitters and/or the incorporation of multiple cavity modes in a thick active medium. These architectures introduce formidable challenges in both device design and performance improvements, namely the decrease of efficiency with increasing brightness (efficiency roll-off) and short operational lifetime. Here we demonstrate, for the first time, white light generation in an OLED consisting of a sub-100 nm-thick blue single emissive layer coupled to the photonic Bragg modes of a dielectric distributed Bragg reflector (DBR). We show that the Bragg modes, although primarily located inside the DBR stack, can significantly overlap with the emissive layer, thus efficiently enhancing emission and outcoupling of photons at selected wavelengths across the entire visible light spectrum. Moreover, we show that color temperature can be tuned by the DBR parameters, offering great versatility in the optimization of white-light emission spectra.
关键词： distributed Bragg reflector,white organic light-emitting diodes (WOLEDs),Fabry-Pérot modes,electroluminescence color conversion,organic semiconductors
更新于2025-09-19 17:13:59
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Facile, Gram-Scale and Eco-friendly Synthesis of Multi-Color Graphene Quantum Dots by Thermal-Driven Advanced Oxidation Process
摘要： Graphene quantum dots (GQDs) have been demonstrated of great potential and benefits in the fields of bioimaging and white light-emitting-diodes (WLEDs). However, it is still highly demanding at the current level to solve the dilemma of achieving high-yield GQDs of good quality and superior fluorescent property using low-cost sustainable and industrializable production procedure. In this work, we for the first time report the gram-scale synthesis of well-crystalline GQDs with ultra-small size based on thermal-driven Advanced Oxidation Process (AOP) under facile green hydrothermal conditions. The average yield calculated from 20 trials reached up to 60%, and the average size of the dots was measured to be ~3.7 nm. Furtherly, GQDs with the photoluminescence (PL) emission of blue, green, yellow, orange, and red have been prepared by expanding the π-conjugation and introducing graphite nitrogen in the carbon skeleton based on chemical structure engineering. The PL-tunable GQDs have an average size distribution of 2~5 nm and a lamellar structure of 2~6 layers. Structure analysis results have indicated that the red shift of PL emission is attributed to bandgap narrowing. This approach successfully converts the easily available and cheap precursor into high-valued products with great application potentials. The PL-tunable GQDs have been successfully used as fluorescent probes of good biocompatibility for in vitro/ in vivo bio-imaging and to produce highly-photostable white-light-emitting composite film with a quantum yield (QY) of 24%.
关键词： Gram-scale synthesis,White light-emitting-diodes,Photoluminescence,Bioimaging,Advanced Oxidation Process,Graphene quantum dots
更新于2025-09-19 17:13:59
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High-brightness Perovskite Light-emitting Diodes Using a Printable Silver Micro-flake Contact
摘要： Achieving efficient devices while maintaining a high fabrication yield is a key challenge in the fabrication of solution-processed, perovskite-based light-emitting diodes (PeLEDs). In this respect, pinholes in the solution-processed perovskite layers are a major obstacle. These are usually mitigated using organic electron-conducting planarization layers. However, these organic interlayers are unstable under applied bias in air, and suffer from limited charge-carrier mobility. In this work, we present a high brightness p-i-n PeLED based on a novel blade-coated silver micro-flake (SMF) rear electrode, which allows for a low-cost and high performance nanocrystalline ZnO inorganic electron transporting layer to be used. This novel SMF contact is crucial for achieving high performance as it prevents the electrical shorting suffered when standard thermally evaporated silver rear contacts are used. The fabricated PeLEDs exhibit an excellent maximum luminance of 98000 cd/m2, a maximum current efficiency of 22.3 cd/A, and high external quantum efficiency of 4.6% under 5.9 V forward bias. The SMF rear contact can be printed and scaled at low cost to large areas and applied to flexible devices.
关键词： leakage current,light emitting diodes,nanocrystalline ZnO,silver micro-flakes,perovskite materials
更新于2025-09-19 17:13:59
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Effect of anode surface treatment by oblique ion bombardment method on Organic light-emitting diodes performance
摘要： In this work, The influence of oblique ion bombardment treatment of the surface of indium tin oxide (ITO) thin films, on the surface parameters of the film and then the performance of organic light-emitting diodes (OLEDs) has been investigated. Both commercially available and uniquely fabricated ITO substrates which were deposited by electron beam evaporation method have been employed. The ITO surface characteristics have been investigated by atomic force microscopy (AFM), X ray diffraction (XRD) and UV-Vis-NIR spectrophotometer. Then a typical OLED device was fabricated on different ITO surfaces and characterized by Keitley 2450 and JAZ spectrometer. The results show that after anode surface treatment by means of oblique Argon ion bombardment method, surface roughness is extremely decreased, which resulted in increasing current and power efficiencies and also there was no evidence of ohmic junctions before driving voltage. The maximum ohmic resistance, current and power efficiencies were 371 MΩ, 6.4 cd/A and 0.91 cd/w, respectively. Also it is found that local non-emissive area or dark spots creation reduced for treated surface device. These findings provide a simple way to effectively reduce the roughness of the ITO films as anode to be applied in optoelectronic devices such as OLEDs.
关键词： Surface roughness,Organic light emitting diodes,Oblique ion bombardment,ITO,Surface treatment,Dark spot
更新于2025-09-19 17:13:59
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Magneto-electroluminescence response in 2D and 3D hybrid organica??inorganic perovskite light emitting diodes
摘要： We have studied the magneto-electroluminescence (MEL) response in light emitting diodes based on 2D-(PEA)2PbI4 and 3D-MAPbI3 hybrid organic–inorganic perovskites at cryogenic temperatures. We found that the MEL is negative, i.e., the EL decreases with the applied field strength, B. In addition, the MEL(B) response has a Lorentzian line shape whose width depends on the perovskite used. We interpret the MEL(B) response using the “Δg mechanism” in which the spin of the injected electron–hole (e–h) pairs oscillates between singlet and triplet configurations due to different precession frequencies of the electron and hole constituents that originate from the difference, Δg, in the electron and hole gyromagnetic constants, g. In this model, the MEL(B) linewidth is inversely proportional to the spin lifetime and Δg. The model used is validated by directly measuring the spin lifetime of photogenerated e–h pairs using the circularly polarized pump–probe transmission technique with 100 fs resolution.
关键词： hybrid organic–inorganic perovskites,spin lifetime,Δg mechanism,light emitting diodes,magneto-electroluminescence
更新于2025-09-19 17:13:59
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Achievement of Higha??Performance Nondoped Blue OLEDs Based on AIEgens via Construction of Effective Higha??Lying Chargea??Transfer State
摘要： There remains an urgent demand for high-quality blue luminogens that can simultaneously achieve high photoluminescence quantum yield (PLQY) in film and high exciton utilization efficiency (EUE) in the electroluminescence (EL) process. In this study, a referable molecular design strategy is developed for blue luminogens via constructing low-lying locally excited (LE) state with an aggregation-induced emission (AIE) characteristic and high-lying charge-transfer (CT) state for the effective triplet-to-singlet conversion channel. 2TriPE-BPI-MCN with the insertion of p-cyano and o-methyl groups is designed to compare with its matrix framework (2TriPE-BPI). They have analogous properties of the lowest singlet (S1) states with blue emission and free of concentration quenching in film; however, 2TriPE-BPI-MCN exhibits unusual response for hydrostatic pressure owing to its S2 state CT characteristics. Therefore, 2TriPE-BPI-MCN can harness more electrogenerated excitons than 2TriPE-BPI, resulting in a better EL performance in nondoped blue organic light-emitting diodes (OLEDs) (CIEx,y = 0.153, 0.147) with high external quantum efficiency of 4.6% and negligible efficiency roll-off. These findings could open a feasible avenue to develop high-quality blue luminogens for high-performance nondoped blue OLEDs.
关键词： organic light-emitting diodes,blue emission,hydrostatic pressure,aggregation-induced emission,charge-transfer state
更新于2025-09-19 17:13:59
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Highly Efficient Cyan-Green Emission in Self-Activated Rb <sub/>3</sub> RV <sub/>2</sub> O <sub/>8</sub> (R = Y, Lu) Vanadate Phosphors for Full-Spectrum White Light-Emitting Diodes (LEDs)
摘要： Phosphor-converted white-light-emitting diodes (pc-WLEDs) rely on combining a near-ultraviolet (n-UV) or blue chip with trichromatic and yellow-emitting phosphors. It is challenging to discover cyan-green-emitting (480?520 nm) phosphors for compensating the spectral gap and producing full-spectrum white light. In this work, we successfully discovered two unprecedented bright cyan-green emitting Rb3RV2O8 (R = Y, Lu) phosphors that gives emission bands centered at 500 nm upon 362 nm n-UV light excitation. Interestingly, the both self-activated compounds exhibit high internal quantum e?ciencies (IQEs) of 71% for Rb3YV2O8 and 85% for Rb3LuV2O8, respectively. Moreover, controllable emission color can be successfully tuned from cyan-green to orange-red across the warm white light region by design strategy of VO4 3? → Eu3+ energy transfer. The thermal quenching of as-prepared phosphors could be e?ectively mitigated by this design strategy. Finally, the as-fabricated n-UV (λ ex = 370 nm) pumped phosphor-converted (pc) W-LED devices utilizing Rb3RV2O8 (R = Y, Lu) along with commercial phosphors demonstrate well-distributed warm white light with high color-rendering index (CRI) of 91.9 and 93.5, and a low correlated color temperature (CCT) of 5095 and 4946 K. It suggests that the both vanadate phosphors have potential applications in full-spectrum pc-WLEDs.
关键词： cyan-green emission,self-activated,full-spectrum white light-emitting diodes,energy transfer,vanadate phosphors
更新于2025-09-19 17:13:59
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Thermally Activated Delayed Fluorescence Benzyl Cellulose Derivatives for Nondoped Organic Light-Emitting Diodes
摘要： Thermally activated delayed ?uorescence (TADF) benzyl cellulose derivatives (TBC-X), which contained both carbazole (host) and phthalimide-based TADF dye (guest) moieties, were prepared from 2,3-di-O-benzyl cellulose in high yields. The TBC-X samples were soluble in common organic solvents such as CH2Cl2, CHCl3, THF, and toluene. The photoluminescence spectra of TBC-X spin-coated ?lms had a single emission peak derived only from guest moieties, which indicated e?cient energy transfer from the host to guest moieties. The TBC-10 (with a content of host and guest moieties of 93 and 7, respectively) in a spin-coated ?lm had the highest photoluminescence quantum yield of 55.3% and TADF characteristics. A nondoped organic light-emitting diode with TBC-10 as the emitting layer showed green emission (λ EL = 517 nm) and achieved a maximum external quantum e?ciency of 5.9%.
关键词： Thermally activated delayed ?uorescence,TADF,organic light-emitting diodes,benzyl cellulose derivatives,OLEDs
更新于2025-09-19 17:13:59
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Performance analysis of GaN-based micro light-emitting diodes by laser lift-off process
摘要： In this study, a monochromatic GaN-based micro-light-emitting-diode (μLED) array was fabricated using flip-chip technology. The laser lift-off (LLO) process was employed to decrease the light divergence caused by the differing refractive indexes of sapphire (n = 1.77) and GaN (n = 2.4). The LLO-μLEDs considerably improve light collimation, compared with conventional flip-chip μLEDs containing a sapphire substrate. We highlight, in particular, the importance of the optical characteristics before and after LLO. Collimation of light was discovered to be 12% higher after removal of the sapphire substrate. The results are of high importance for understanding the optical properties of μLED arrays after LLO.
关键词： Light-emitting diodes,Micro-LEDs,Laser lift-off,GaN
更新于2025-09-19 17:13:59
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Large-Area Cesium Lead Bromide Perovskite Light-Emitting Diodes Realized by Incorporating a Hybrid Additive
摘要： Encouraging progresses have been made in the development of solution processable perovskite light-emitting diodes (PeLEDs). However, the related fundamental physics of the efficient operation of the large area PeLEDs is still far from adequate. In this work, we report our recent effort in developing a high-performance large area cesium lead bromide (CsPbBr3) PeLEDs through a controlled growth of CsPbBr3 emission layer using a hybrid additive in the CsPbBr3 precursor solution. The hybrid additive comprises a combination of poly(ethylene oxide) (PEO) and cesium carbonate (Cs2CO3). We found that the performance of the CsPbBr3 PeLEDs, prepared using the precursor solution having a hybrid additive of PEO and Cs2CO3, is superior to that of the control PeLEDs, prepared using a pure CsPbBr3 precursor solution in two ways: (1) it helps to suppress both the structural defects and non-radiative recombination-induced leakage current, and (2) it assists in improving the electron-hole current balance. The 1.0×1.5 cm2-sized PeLEDs having a maximum luminance of > 104 cd/m2 has been demonstrated, which is more than three times greater than that of a control PeLED prepared using a pure CsPbBr3 precursor solution (3.0×103 cd/m2).
关键词： hybrid additive,cesium lead bromide,perovskite light-emitting diodes,large area
更新于2025-09-19 17:13:59