- 标题
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A “Positive Incentive” Approach to Enhance Operational Stability of Quantum Dot based Light-Emitting Diode
摘要： Balanced charge injection promises high efficiency of quantum dot based light-emitting diodes (QD-LEDs). Most widely used approach to realize charge injection balance is impeding the injection rate of the dominant charge carrier with energetic barriers. However, these approaches often accompany unwanted outcomes (e.g., the increase in operation voltage) that sacrifice the operation stability of devices. Herein, a “positive incentive” approach is proposed to enhance the efficiency and the operational stability of QD-LEDs. Specifically, the supply of hole, an inferior carrier than its counterpart, is facilitated by adopting a thin fullerene (C60) interlayer at the interface between hole injection layer (MoOX) and hole transport layer (CBP). The C60 interlayer boosts the hole current by eliminating the universal energy barrier, lowers the operation voltage of QD-LEDs, and enhances the charge balance in the QD emissive layer within working device. Consequently, QD-LEDs benefitting from the adoption of C60 interlayer exhibit significantly enhanced device efficiency and operation stability. Grounded on the quantitative assessment of the charge injection imbalance within the QD emissive layer, the impact of electrical parameters of QD-LEDs to their optoelectronic performance and operational stability is also discussed.
关键词： hole injection barrier,operational stability,fullerene,quantum dot based light-emitting diodes,charge injection balance
更新于2025-09-16 10:30:52
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A new strategy for structuring white organic light-emitting diodes by combining complementary emissions in the same interface
摘要： In this work, we proposed a new strategy for structuring white organic light-emitting diodes (WOLEDs) using all exciplex emissions, where the white devices can be fabricated by simply depositing several exciplex acceptor layers on the same exciplex donor layer in a vertical direction, and complementary exciplex emissions can be realized in the same exciplex donor layer interface for forming white emission. Based on this new strategy, a series of WOLEDs with different array arrangements of different exciplex acceptor layers on the same exciplex donor layer were demonstrated. The device with a bisected blue-yellow exciplex acceptor layer on the same exciplex donor layer realizes good two-color white emission with a high color rendering index of 71, and also achieves a high current efficiency of 3.17 cd A?1. Moreover, the emission spectra and device performance of white devices can be adjusted and improved by simply changing the array arrangements of different exciplex acceptor layers on the same exciplex donor layer. More importantly, the proposed new strategy can effectively solve the interface problem induced by employing interface exciplexes to realize multi-color white emission, which provides a new approach to accomplish all exciplex emission WOLEDs.
关键词： exciplex emissions,device performance,color rendering index,white organic light-emitting diodes,current efficiency
更新于2025-09-16 10:30:52
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Direct Synthesis of Quaternary Alkylammonium Capped Perovskite Nanocrystals for Efficient Blue and Green Light-Emitting Diodes
摘要： Cesium lead halide nanocrystals (CsPbX3 NCs) are newcomer inorganic light sources covering the entire visible spectral range and exhibiting near-unity efficiencies. While the last years have seen rapid progress in green- and red-electroluminescence from CsPbX3 NCs, the development of blue counterparts remained rather stagnant. Controlling the surface state of CsPbX3 NCs had proven to be a major factor governing the efficiency of the charge injection and for diminishing the density of traps. Although didodecyldimethylammonium halides (DDAX, X=Br, Cl) had been known to improve the luminescence of CsPbX3 NCs when applied post-synthetically, they had not been used as a sole long-chain ammonium ligand directly in the synthesis of these NCs. Herein we report a facile, direct synthesis of DDAX-stabilized CsPbX3 NCs. We then demonstrate blue and green light-emitting diodes, characterized by the electroluminescence at 463-515 nm and external quantum efficiencies of 9.80% for green, 4.96% for sky-blue and 1.03% for deep-blue spectral regions.
关键词： Cesium lead halide nanocrystals,DDAX-stabilized,external quantum efficiencies,light-emitting diodes,electroluminescence
更新于2025-09-16 10:30:52
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Mixed-Host Systems with a Simple Device Structure for Efficient Solution-Processed Organic Light-Emitting Diodes of a Red-Orange TADF Emitter
摘要： Charge balance, concentration quenching, and exciton con?nement are the most important factors for realizing the use of thermally activated delayed ?uorescence (TADF) emitters for organic light-emitting diodes. Red-orange organic light-emitting diodes of a TADF emitter 2-[4 (diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA) have been reported by doping in a mixed p-type host system of poly(N-vinylcarbazole) (PVK) and 1,3-bis(N-carbazolyl)benzene (mCP) via solution-processed. We have demonstrated the peak external quantum e?ciency of 9.75%, maximum current e?ciency of 19.36 cd/A, and power e?ciency of 12.17 lm/W along with a CIE coordinate of (0.45, 0.51). The devices were compared with di?erent doping concentrations of TXO-TPA, and a comparative investigation on the e?ect of the thickness electron transport layer was studied. The results clearly indicated that this solution-processed TXO-TPA device structure is a promising strategy to develop highly e?cient but simple OLED structures.
关键词： external quantum e?ciency,thermally activated delayed ?uorescence,red-orange,solution-processed,organic light-emitting diodes
更新于2025-09-16 10:30:52
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Cryostat setup for measuring spectral and electrical properties of light-emitting diodes at junction temperatures from 81 K to 297 K
摘要： We introduce a cryostat setup for measuring fundamental optical and electrical properties of light-emitting diodes (LEDs). With the setup, the cryostat pressure and the LED properties of the forward voltage, junction temperature, and electroluminescence spectrum are monitored with temperature steps less than 1.5 K, over the junction temperature range of 81–297 K. We applied the setup to commercial yellow AlGaInP and blue InGaN LEDs. At cryogenic temperatures, the fine structure of the electroluminescence spectra became resolved. For the yellow LED, we observed the phonon replica at 2.094 eV that was located 87 meV below the peak energy at the junction temperature of 81 K. For the blue LED, we observed the cascade phonon replicas at 2.599 eV, 2.510 eV, and 2.422 eV with the energy interval of 89 meV. For both LED types, the forward voltage increased sharply toward the lower temperatures due to the increased resistivity of materials in the LED components. We found significant differences between the temperature dependent behaviors of the forward voltages, spectral peak energies, and bandgap energies of LEDs obtained from the Varshni formula. We also noted a sharp pressure peak at 180–185 K arising from the solid-vapor phase transition of water when the base level of the cryostat pressure was approximately 0.4 mPa.
关键词： spectral properties,light-emitting diodes,electrical properties,junction temperature,phonon replicas,cryostat setup
更新于2025-09-16 10:30:52
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Rapid and green synthesis of fluorescent carbon dots from starch for white light-emitting diodes
摘要： A simple and green synthesis of fluorescent carbon dots (CDs) was achieved by a microwave-assisted hydrothermal method using potato starch as the carbon source. CDs with a maximum quantum yield of 2.46% were prepared by hydrothermal treatment of a 1 mg/mL starch solution at 220 oC for 30 min. Nitrogen doped CDs (N-CDs) were obtained under the same conditions using starch and ethylenediamine as the carbon and nitrogen sources, respectively, and their quantum yield was twice that of the undoped CDs. Both the CDs and N-CDs exhibit excellent water solubility and good thermal stability, emit blue fluorescence under UV light, but the fluorescent intensity of the latter is obviously higher than that of the former. Two white light-emitting diodes using the CD/starch composite and N-CDs as the phosphors emit yellowish white light and white light, respectively with xy coordinates of (0.38, 0.45) and (0.33, 0.35) in the Chromaticity Diagram of the Commission Internationale de L'Eclairage, suggesting that they have great potential application in optoelectronic devices.
关键词： Fluorescent carbon dots,Nitrogen doping,Light-emitting diodes,Microwave-assisted hydrothermal,Starch
更新于2025-09-16 10:30:52
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The role of photon recycling in perovskite light-emitting diodes
摘要： Perovskite light-emitting diodes have recently broken the 20% barrier for external quantum efficiency. These values cannot be explained with classical models for optical outcoupling. Here, we analyse the role of photon recycling (PR) in assisting light extraction from perovskite light-emitting diodes. Spatially-resolved photoluminescence and electroluminescence measurements combined with optical modelling show that repetitive re-absorption and re-emission of photons trapped in substrate and waveguide modes significantly enhance light extraction when the radiation efficiency is sufficiently high. In this manner, PR can contribute more than 70% to the overall emission, in agreement with recently-reported high efficiencies. While an outcoupling efficiency of 100% is theoretically possible with PR, parasitic absorption losses due to absorption from the electrodes are shown to limit practical efficiencies in current device architectures. To overcome the present limits, we propose a future configuration with a reduced injection electrode area to drive the efficiency toward 100%.
关键词： external quantum efficiency,light-emitting diodes,photon recycling,optical outcoupling,perovskite
更新于2025-09-16 10:30:52
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Carbon Dots exhibiting Concentration-Dependent Full-Visible-Spectrum Emission for Light-Emitting Diode Applications
摘要： Carbon dots (CDs) that exhibit emission over the whole visible spectrum are desired for using in light-emitting diodes. Here, CDs displaying tunable fluorescence over the whole visible region are synthesized. Different concentrations of CDs are uniformly dispersed in epoxy resin and coated on 405-nm LED chips to obtain monochrome blue, cyan, green, yellow, red, and deep red LEDs that yield a color gamut covering 99.4% of the National Television Standards Committee (NTSC) standard. These monochrome LEDs display similar stability decay curves. Furthermore, warm and neutral white LEDs are produced by coating cyan- and red-emitting CD layers on 405-nm LED chips, achieving color rendering indexes (CRI) of 96.4 and 96.6, respectively. Two fluorescent conversion layers derived from one material at different concentrations simplifies the preparation of high-CRI white LEDs. The uniform weak changes of the cyan and red PL peaks during operation ensures the high stability of these CD-based white LEDs. This research provides a new avenue to develop low-cost, easy-to-prepare CDs with tunable emission colors as alternative phosphors for LED-based high-performance displays and lighting.
关键词： full-visible-spectrum emission,monochrome light-emitting diodes,concentration-dependent spectrum-tunable carbon dots,high color rendering index,white-light-emitting diodes
更新于2025-09-12 10:27:22
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New Class of Supramolecular Bowl-Shaped Columnar Mesogens Derived from Thiacalix[4]arene Exhibiting Gelation and Organic Light-Emitting Diodes Applications
摘要： A new class of blue light-emitting bowl-shaped mesogens with the thiacalix[4]arene core appended with 1,3,4-thiadiazole derivatives having peripheral alkoxy side chains have been synthesized and well characterized. The liquid crystalline behavior of present synthesized derivatives was examined by optical polarizing microscopy, di?erential scanning calorimetry, and X-ray di?raction studies. It was observed that these thiacalix[4]arene derivatives were capable of stabilizing the observed Colh phase with a higher temperature range. The cone-shaped thiacalix[4]-arene-based liquid crystals with peripheral alkoxy side chains able to pack into the interactions and thermal behavior. All derivatives showed blue luminescence in solution, solid thin-?lm, and gelation state. The hexagonal columnar phase and emissive nature of thiadiazole-based thiacalixarene compounds having xerogel behavior make them favorable in the application of emissive electronic display devices. The electrochemical properties of these thiacalixarene-based compounds demonstrate the e?ect of alkyl side chain on the highest occupied molecular orbital?lowest unoccupied molecular orbital energy levels and also exhibited lower electron band gaps. The electroluminescence behavior of the compound 10c was examined as emissive layers in the fabrication of organic light-emitting diodes.
关键词： thiacalix[4]arene,bowl-shaped mesogens,blue light-emitting,organic light-emitting diodes,1,3,4-thiadiazole derivatives,liquid crystalline behavior
更新于2025-09-12 10:27:22
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The LED Paradox: How Light Pollution Challenges Experts to Reconsider Sustainable Lighting
摘要： In the 21st century, the notion of “sustainable lighting” is closely associated with LED technology. In the past ten years, municipalities and private light users worldwide have installed light-emitting diodes in urban spaces and public streets to save energy. Yet an increasing body of interdisciplinary research suggests that supposedly sustainable LED installations are in fact unsustainable, because they increase light pollution. Paradoxically, blue-rich cool-white LED lighting, which is the most energy-efficient, also appears to be the most ecologically unfriendly. Biologists, physicians and ecologists warn that blue-rich LED light disturbs the circadian day-and-night rhythm of living organisms, including humans, with potential negative health effects on individual species and whole ecosystems. Can the paradox be solved? This paper explores this question based on our transdisciplinary research project Light Pollution—A Global Discussion. It reveals how light pollution experts and lighting professionals see the challenges and potential of LED lighting from their different viewpoints. This expert feedback shows that “sustainable LED lighting” goes far beyond energy efficiency as it raises complex design issues that imply stakeholder negotiation. It also suggests that the LED paradox may be solved in context, but hardly in principle.
关键词： innovation,light pollution,light-emitting diodes (LEDs),artificial light at night (ALAN),sustainable lighting,outdoor lighting
更新于2025-09-12 10:27:22