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Counter-intuitive junction temperature behavior in AlGaN-based deep-ultraviolet light-emitting diodes
摘要： The junction temperature, one of the major parameters that strongly affect the performance of light-emitting diodes (LEDs), increases during operation because of the power dissipated as heat within an LED device. Therefore, LED devices with poor characteristics are expected to have higher junction temperatures for the same driving conditions. In this study, an observation contrary to this expectation is presented: a deep-ultraviolet LED device with superior electrical characteristics shows a higher junction temperature at the same input electrical power than a device with poor characteristics. A simple equivalent circuit comprising a diode, a series resistor, and shunt components is employed to elucidate this counter-intuitive observation by considering the possible heat sources inside the LED device. It is found that the junction temperature is mainly dominated by the power dissipated at the diode instead of the other possible heat sources including the Joule heating effect of the resistive components.
关键词： junction temperature,Joule heating,AlGaN-based deep-ultraviolet light-emitting diodes,power dissipation,equivalent circuit
更新于2025-09-23 15:21:01
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Rigid Oxygen-Bridged Boron-Based Blue Thermally Activated Delayed Fluorescence Emitter for Organic Light-Emitting Diode: Approach towards Satisfying High Efficiency and Long Lifetime Together
摘要： Thermally activated delayed fluorescence (TADF) materials have emerged as an efficient emitter for achieving high efficiency of blue organic light emitting diodes (OLEDs). However, it is challenging to satisfy both high device efficiency and long operational lifetime together. Here, highly efficient and electrochemically stable blue TADF emitter, 5-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (DBA-DI) is designed and synthesized for high efficiency and long lifetime OLED. This emitter exhibits high photoluminescence quantum yield of 95.3%, small single-triplet energy gap of 0.03 eV, short delayed exciton lifetime of 1.25 μs, and high bond dissociation energy (BDE). Also, phosphine oxide free high triplet energy host systems (single and mixed) and exciton blocking layer materials are analyzed using molecular and optical simulations to find an efficient host system with high BDE and suitable emission zone for high efficiency and stable OLEDs. The fabricated OLED with DBA-DI and high triplet host exhibited a maximum external quantum efficiency (EQE) of 28.1% with blue CIE color coordinates of (0.16, 0.39) and long operational lifetime (LT50) of 329 h at the initial luminance of 1000 cd m?2. Furthermore, the mixed host-based TADF device showed a slightly lower EQE of 26.4% and almost two times longer lifetime (LT50: 540 h) than the single host device.
关键词： stable emitters,organic light emitting diodes,thermally activated delayed fluorescence,long lifetime
更新于2025-09-23 15:21:01
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Performance Improvement of Gate-Tunable Organic Light-Emitting Diodes with Electron-Transport and Hole-Blocking Layers
摘要： The current density and luminance of gate-tunable organic light-emitting diodes (OLEDs) can be modulated by application of an external gate potential. However, existing gate-tunable OLEDs require further optimization to make them suitable for practical use. In this work, the rapid electron conduction of 4,4’-bis(N-carbazolyl)-1,1’biphenyl (CBP) molecules under low operating potential is demonstrated in polymer electrolyte-coated super yellow (SY) polymer light-emitting diodes (PLEDs). This behavior is attributed to the facile electrochemical n-doping of CBP by the polymer electrolyte infiltrated into the SY PLED through the porous aluminum cathode. The field-modulated conductivity of CBP upon applying an external gate potential to electrolyte-gated (EG) PLEDs is demonstrated. These phenomena lead to the improved performance of EG SY PLEDs with a CBP electron-transport layer and 1,3,5-tris[(3-pyridyl)-phen-3-yl]benzene) (TmpypB) hole-blocking layer between the porous aluminum cathode and SY emissive layer, including low turn-on voltage (1.5 V), low current density leakage (0.01 mA/cm2), low off luminance (<0.01 cd/m2), saturated on-current density (2 mA/cm2) and on-luminance (100 cd/m2), and largely suppressed hysteresis. These results pave the path for practical application of EG OLEDs in displays, especially near-to-eye displays.
关键词： facile electrochemical doping,saturated on-current density and on-luminance,low off-current density leakage and off-luminance,suppressed hysteresis,near-to-eye displays,gate-tunable organic light-emitting diodes,grayscale displaying,porous electrodes
更新于2025-09-23 15:21:01
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High efficiency and stability of ink-jet printed quantum dot light emitting diodes
摘要： The low efficiency and fast degradation of devices from ink-jet printing process hinders the application of quantum dot light emitting diodes on next generation displays. Passivating the trap states caused by both anion and cation under-coordinated sites on the quantum dot surface with proper ligands for ink-jet printing processing reminds a problem. Here we show, by adapting the idea of dual ionic passivation of quantum dots, ink-jet printed quantum dot light emitting diodes with an external quantum efficiency over 16% and half lifetime of more than 1,721,000 hours were reported for the first time. The liquid phase exchange of ligands fulfills the requirements of ink-jet printing processing for possible mass production. And the performance from ink-jet printed quantum dot light emitting diodes truly opens the gate of quantum dot light emitting diode application for industry.
关键词： quantum dot light emitting diodes,ink-jet printing,external quantum efficiency,dual ionic passivation,lifetime
更新于2025-09-23 15:21:01
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Testing of Various Monochromatic LED Lights Used in Supplemental Irradiation of Lettuce in Modern Urban Rooftop Polytunnels
摘要： Urban farming could provide both vegetable growers and urban dwellers with more direct access to various fresh vegetables. Nevertheless, certain challenging problems associated with urban farming, including a lack of cultivation space and the effects of urban heat islands, must still be solved. Relatedly, a grower must, in some cases, also know how to utilize various forms of technology, such as lighting systems, as well as factors such as water availability. In this study, an original rooftop polytunnel design for lettuce (Lactuca sativa cv. Lollo Rosso) cultivation equipped with a hydroponic system and light emitting diodes (LEDs) is proposed. Various monochromatic lights were also tested for their effects on different quality parameters of lettuce. Specifically, supplemental red (655 nm), blue (445 nm), green (520 nm), and ultraviolet (380 nm) LED lights were used at night to apply photon fluxes of 150, 150, 150, and 20 μmol·m-2·s-1, respectively. The resulting effects of these different colored LEDs on the pigment concentration and growth response of the lettuce grown inside the roof polytunnel were then investigated. The experiment was then repeated several times with different environmental parameters in order to compare the effects of the different light wavelengths under higher temperatures and higher natural irradiation conditions. The results indicated that supplemental red or blue light at night could be strategically employed to maintain low nitrate levels and enhance the nutritional value and growth of lettuce grown in roof polytunnels.
关键词： Red lettuce,Rooftop polytunnel,Hydroponic,LEDs,Urban agriculture,Light emitting-diodes
更新于2025-09-23 15:21:01
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Mg-Doped ZnO Nanoparticle Films as the Interlayer between the ZnO Electron Transport Layer and InP Quantum Dot Layer for Light-Emitting Diodes
摘要： Because the wide emission spectrum tunability which range from the visible region to the near-infrared, InP based colloidal quantum dots (QDs) show great promise for use in next-generation full-color displays and solid state lighting. The performance-improved InP QD based light-emitting devices (QLEDs) were fabricated by using Mg doped-ZnO nanoparticles (ZnMgO NPs) as an interlayer between ZnO electron transport layer and active InP QD layer. It is found that ZnMgO NPs can reduce electron injection and suppress exciton quenching which is attributed to the improvement of charge balance in the devices. We successfully demonstrated higher maximum current efficiencies of 5.46 and 5.91 cd/A than the references (2.31 and 2.36 cd/A) without the ZnMgO NP layer in highly efficient red and green QLEDs, respectively. These results signify an effective approach to improve heavy-metal-free QLEDs for commercial applications.
关键词： InP quantum dots,Mg doped-ZnO,electron transport layer,light-emitting diodes,charge balance
更新于2025-09-23 15:21:01
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Boosting the Efficiency and Curtailing the Efficiency Roll-off in Green Perovskite Light-Emitting Diodes via Incorporating Ytterbium as Cathode Interface Layer
摘要： Perovskite light-emitting diodes (PeLEDs) exhibit high external quantum efficiencies (EQEs), emerging as a next-generation technology for lighting and display applications. Nevertheless, they suffer from severe efficiency roll-off at high luminance, particularly in case of blue and green emissions, which is one of the major bottlenecks in their industrial applications. Here, we attack this problem using a rare-earth metal, Yb, as cathode interface layer (CIL) for green PeLEDs. By adopting a new device configuration of ITO/TFB/FA-based Quasi-2D Perovskite/TPBi/Yb/Ag, we achieved a peak current efficiency (CE) of 22.3 cd/A with a corresponding EQE of 5.28% and a high maximum luminance of 19,160 cd/m2. Importantly, the maximum CE of 22 cd/A at 2,000 cd/m2 slightly decreased to 16.8 cd/A at 5,000 cd/m2 and maintained a still decent value of 12 cd/A at a very high luminance of 10,000 cd/m2, exhibiting a remarkably low efficiency roll-off. Our Yb-incorporated devices significantly outperformed the PeLEDs containing conventional CILs, including Mg and Liq, in terms of peak efficiency, efficiency roll-off and operational lifetime. We attribute this encouraging performance to barrier-free, efficient electron injection enabled by the low work function of Yb (2.6 eV) which led to a high electron current, nearly approaching the hole current in hole-dominant PeLEDs, as confirmed by the single-carrier device measurements. In addition, we also present Yb-incorporated PeLEDs containing Cs-based Quasi-2D perovskite as the emissive layer which displayed an impressive CE of 51.3 cd/A with a corresponding EQE of 16.4% and a maximum luminance of 14,240 cd/m2, and still demonstrated a reduced efficiency roll-off comparing to that of the Liq-based equivalent. These results unveil the inspiring prospects of Yb as an efficient CIL for PeLEDs towards high efficiency with reduced efficiency roll-off.
关键词： electron injection,ytterbium,quasi-2D,perovskite light-emitting diodes,stability,cathode interface layer,efficiency roll-off
更新于2025-09-23 15:21:01
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High Performances Thermally Activated Delayed Fluorescence Organic Light-emitting Diodes with Wide Gap Phosphorescent Complex as Sensitizer
摘要： In this work, we demonstrated the high performances electroluminescent (EL) devices based on orange-yellow thermally activated delayed fluorescence emitter (TXO-TPA) by utilizing an iridium complex (FK306) as sensitizer. Compared with reference devices without FK306, these co-doped devices displayed significant enhancement of EL performances, which could be attributed to optimized carriers' distribution and efficient energy transfer. In addition, the presence of FK306 molecules helps to broaden the exciton formation zone in EML2, thus suppressing the quenching of triplet excitons. Finally, the optimized co-doped double-EMLs device obtained superior EL performances with maximum current efficiency, power efficiency and external quantum efficiency up to 58.94 cd/A, 61.69 lm/W and 16.5%, respectively. Even at the high brightness of 1000 cd/m2, EL efficiency as high as 12.67 cd/A can still be retained by the same device.
关键词： Organic Light-emitting Diodes,Sensitizer,Wide Gap Phosphorescent Complex,Thermally Activated Delayed Fluorescence
更新于2025-09-23 15:21:01
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Synthesis of Silica-Coated Csa??PbBra?? and Csa??Pb(Br0.4I0.6)a?? Quantum Dots With Long Lifetime and Enhancement in Quantum Efficiency for WLEDs Applications: Lightings With High CRI and Displays With Wide Color Gamut
摘要： To focus on developing white light-emitting diodes (WLEDs) for lightings with high color rendering index (CRI), low correlated color temperature (CCT), and the displays with wide color gamut, inorganic perovskite quantum dots (QDs) such as CsPbX3 (X = Cl, Br, I) were the promising candidate owing to the excellent optoelectronic properties such as high quantum efficiency, narrow emission wavelengths, and tunable emission spectrum. Nevertheless, the CsPbBr3QDs in the form of powders or films had a poor air stability and severe decline of quantum efficiency. Therefore, in this article, a new idea was proposed that 0-D green–red perovskite QDs powders such as Cs4PbBr6 and Cs4Pb(Br0.4I0.6)6 with improved quantum efficiency and long lifetime were first developed by silica-coated method and crystal phase transition in low-temperature synthesis. The quantum efficiency in green Cs4PbBr6 powders could be significantly enhanced from 31.41% to 45.87% and red Cs4Pb(Br0.4I0.6)6 powders was 22.79%. Moreover, the as-prepared perovskite QD powders and commercial YAG phosphors combined with blue chips were applied to high-quality WLEDs for lightings and displays. More importantly, the as-fabricated wide Commission Internationale de l’Eclairage (CIE) color gamut WLEDs for displays possessed 115% National Television System Committee (NTSC) coverage rate and luminous efficiency of 51 lm/W under 20-mA driving current. On the other hand, the constructed WLEDs for high-power lightings would generate a warm white light with a luminous efficiency of 38 lm/W, extremely high CRI of 92.8, and low CCT of 3828 K under 350 mA. Hence, the proposed green–red perovskite QD powders had outstanding potential applications in WLEDs.
关键词： white light-emitting diodes (WLEDs),0-D perovskite quantum dots (QDs),backlights of displays,solid-state lightings
更新于2025-09-23 15:21:01
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A 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) transport layer with high electron mobility for thick organic light-emitting diodes
摘要： In our previous paper [T. Matsushima et al., Nature 572, 502 (2019)], current densities of organic light-emitting diodes (OLEDs) did not decrease significantly when the thicknesses of a 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) transport layer were increased from tens of nanometers to 1 μm. To make this mechanism clear, we carried out several experiments in terms of electron transfer with other organic layers and electron mobility of HAT-CN. Finally, we found that the vacuum-evaporated HAT-CN layers have very high electron mobility and, therefore, using a HAT-CN transport layer can suppress the decrease in current density even in thick OLEDs. The electron mobility of vacuum-deposited HAT-CN layers, which was measured using analysis with a space-charge-limited current model, was 0.1–1 cm2 V?1 s?1. This electron mobility is much higher than those of conventional organic transport layers used in OLEDs (<10?3 cm2 V?1 s?1) even though the HAT-CN layers are amorphous-like. We attributed one of the reasons for this extraordinarily high mobility to be a better overlap of π orbitals in the substrate normal, which is associated with horizontally oriented HAT-CN molecules on a substrate.
关键词： transport layer,thick organic light-emitting diodes,HAT-CN,OLEDs,electron mobility
更新于2025-09-23 15:21:01