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Inkjet printing multilayer OLEDs with high efficiency based on the blurred interface
摘要： Inkjet printing technology is considered to be the next generation manufacturing method for organic light-emitting diodes (OLEDs) production because of its simplicity and low cost. However, the dissolution at interfaces in printing process is still one of the great challenges that limits its progress. The present work utilized the dissolution phenomenon innovatively to generate blurred interface during inkjet printing of multi-layer OLEDs, where TAPC and TAPC:TPBi:Ir-complexes were employed as hole transport layer (HTL) and emitting layer (EML) and both of them were dissolvable in butyl benzoate to form the HTL and EML inks. When they were printed sequentially, a blurred interface between HTL and EML was formed because the dissolution phenomenon, which facilitated the exciton formation and charge balance in EML and improved the device performance. With this blurred interface, the maximum current efficiency of 9.8 cd A-1, the maximum power efficiency of 5.0 lm W-1, and the maximum external quantum efficiency of 3.0% were achieved in (fpbt)2Ir(acac) based OLEDs. In contrast, they were only 7.4 cd A-1, 3.9 lm W-1 and 2.2% in devices having a clear interface between HTL and EML.
关键词： organic light emitting diodes (OLEDs),blurred interface,inkjet printing
更新于2025-09-19 17:13:59
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Fabrication of flexible AlGaInP LED
摘要： Flexible light-emitting diodes (LEDs) are highly desired for wearable devices, flexible displays, robotics, biomedicine, etc. Traditionally, the transfer process of an ultrathin wafer of about 10–30 μm to a flexible substrate is utilized. However, the yield is low, and it is not applicable to thick GaN LED chips with a 100 μm sapphire substrate. In this paper, transferable LED chips utilized the mature LED manufacture technique are developed, which possesses the advantage of high yield. The flexible LED array demonstrates good electrical and optical performance.
关键词： light-emitting diodes (LEDs),performance,transfer,flexible
更新于2025-09-19 17:13:59
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Highly Efficient Quantum Dot Light‐Emitting Diodes by Inserting Multiple Poly(methyl methacrylate) as Electron‐Blocking Layers
摘要： This work presents a new device architecture integrating multiple poly(methyl methacrylate) (PMMA) electron-blocking layers (EBL) in quantum dot light-emitting diodes (QD-LEDs). The device utilizes red-emitting CdSe/ZnS QD with a novel structure where multiple PMMA EBLs are sandwiched between a pair of QD layers. A systematic optimization of QD-LED structures has shown that a device including two PMMA and three QD layers performs the best, achieving a current efficiency of 17.8 cd A?1 and a luminance of 194 038 cd m?2. Numerical simulation of a simplified model of the proposed QD-LED structure verifies that the structure consisting of two PMMA and three QD layers provides significant improvement in electroluminescent intensity. The simulation provides further insight into the origin of the effect of the PMMA EBL by showing that the addition of PMMA EBL reduces the electron leakage from the active QD region and enhances electron confinement, leading to an increased electron concentration in the QD active layers and a higher radiative recombination rate. The experimental and theoretical studies presented in this work demonstrate that multiple layers of PMMA can act as efficient EBLs in the fabrication of QD-LEDs of improved performance.
关键词： simulation,device architecture,electron-blocking layer,electron leakage,poly(methyl methacrylate) (PMMA),quantum dot light-emitting diodes (QD-LED)
更新于2025-09-19 17:13:59
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Impact of grain growth of silver reflective electrode by electron bombardment on external quantum efficiency of III-nitride micro-light-emitting diode arrays
摘要： The effect of electron-beam irradiation (EBI) on Ag reflector is investigated in order to improve the efficiency of flip-chip InGaN/GaN multiple-quantum-wells micro light-emitting diode (μ-LED) arrays. After EBI, small size grains are diffused and then become larger grain. Therefore, grain boundaries are reduced which originates the crystal quality and reflectance of Ag reflect to improve. Grain size of Ag reflector is increased with the increase in EBI time that is consistently observed by different kinds of material characterizations. 5 minutes EBI-based Ag reflector shows higher reflectance (~91 %) at 450 nm than without EBI sample (~84 %). Finally, without and with EBI on Ag reflector-based μ-LED arrays are fabricated. After EBI, there is no change in forward bias voltage except optical performances. At driving current, Ag reflector with EBI-based μ-LEDs has higher light-output-power, electroluminescence intensity and electroluminescence distribution over the chip area compared to without EBI-based μ-LEDs. Usually, increased light-extraction-efficiency causes the external-quantum-efficiency of the μ-LEDs to increase. These enhanced optoelectronic performances are consistently described by using microscopic and macroscopic characterizations.
关键词： Ag reflector,Electron-beam irradiation,reflectance,micro light-emitting diodes,grain size
更新于2025-09-19 17:13:59
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Penetration in Biological Tissue Using Light-Emitting Diodes with Highly Efficient Near-Infrared ScBO3:Cr3+ Phosphor
摘要： Recently, infrared (IR) light-emitting diodes (LEDs) have attracted considerable interest in the research field worldwide. IR phosphors, the basic materials utilized in LEDs, have become a research hotspot as well. Here, we introduce the high-quantum-efficiency IR ScBO3:Cr3+ phosphor, which provides a spectral range of emission from 700 nm to 1000 nm with a peak maximum at 800 nm. Electron paramagnetic resonance spectroscopy, with high element selectivity, was used to elucidate the unusual small peak in the photoluminescence spectrum. Phonon structure and electron–lattice interaction were well observed and discussed via temperature-dependent measurements. Moreover, the high quantum efficiency of 72.8% was achieved. To evaluate their potential practical application, phosphor-converted LED packages were designed, which revealed high stability and high output power of 39.11 mW. Furthermore, the fabricated IR LED demonstrated remarkable penetration ability toward biological tissues. This study provides insights into the luminescent properties and the practical applications of IR LEDs.
关键词： infrared,light-emitting diodes,biological tissue penetration,phosphors,quantum efficiency
更新于2025-09-19 17:13:59
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Substitutional effect of different bridging groups on optical and charge transfer properties of small bipolar molecules for OLEDs
摘要： In this work, a series of eight different bipolar molecules were designed and calculated using density functional theory (DFT) and time‐dependent functional theory (TD‐DFT) for organic light emitting diodes (OLEDs) as efficient luminescent and charge transfer materials. The eight donor‐π‐donor type small molecules (D1‐D8) were composed of triphenylamine (TPA) donor (D) unit connected to 1,8‐naphthalimides (NI) acceptor (A) unit though different π‐conjugated or R‐groups (as π‐spacer). The effect of substitutions made in π‐spacer was investigated on optical, electronic, and stability properties. This calculation analysis showed that different substitutions in π‐spacer resulted smaller Eg (range from 1.63 to 2.00 eV), broader absorption with the lowest excitation energy covering both visible and near infrared regions of solar spectrum, especially D3, D4, D5, and D6 molecules. The analyses of local densities of states, frontier molecular orbitals, and natural population analysis of orbitals revealed that studied molecules exhibited π‐π* electronic transitions of absorption in singlet excited states, but D5 and D6 also show intramolecular charge transfer (ICT) characteristics. The study of chemical indices, molecular electrostatic potential (MEP) surfaces, and charge transfer properties turned out that D4, D5, and D6 are expected to show good potential for luminescent and hole transport materials in the favor of OLEDs.
关键词： DFT,organic light emitting diodes (OLEDs),optical properties,absorption spectra,electronic structures
更新于2025-09-19 17:13:59
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One‐Pot Exfoliation of Graphitic C <sub/>3</sub> N <sub/>4</sub> Quantum Dots for Blue QLEDs by Methylamine Intercalation
摘要： Here, a simplified synthesis of graphitic carbon nitride quantum dots (g-C3N4-QDs) with improved solution and electroluminescent properties using a one-pot methylamine intercalation–stripping method (OMIM) to hydrothermally exfoliate QDs from bulk graphitic carbon nitride (g-C3N4) is presented. The quantum dots synthesized by this method retain the blue photoluminescence with extremely high fluorescent quantum yield (47.0%). As compared to previously reported quantum dots, the g-C3N4-QDs synthesized herein have lower polydispersity and improved solution stability due to high absolute zeta-potential (?41.23 mV), which combine to create a much more tractable material for solution processed thin film fabrication. Spin coating of these QDs yields uniform films with full coverage and low surface roughness ideal for quantum dot light-emitting diode (QLED) fabrication. When incorporated into a functional QLED with OMIM g-C3N4-QDs as the emitting layer, the LED demonstrates ≈60× higher luminance (605 vs 11 Cd m?2) at lower operating voltage (9 vs 21 V), as compared to the previously reported first generation g-C3N4 QLEDs, though further work is needed to improve device stability.
关键词： graphitic carbon nitride,quantum dot light-emitting diodes,metal-free semiconductors,hydrothermal exfoliation
更新于2025-09-19 17:13:59
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Temperature Sensing Characteristics and Long Term Stability of Power LEDs Used for Voltage vs. Junction Temperature Measurements and Related Procedure
摘要： A detailed study about the direct measurement of junction temperature TJ of off-the-shelf power light emitting diodes (LED) is presented. The linear dependence on temperature of the voltage drop across the device terminals at a constant current is in particular exploited and fully characterized, in the temperature range from T = 35 ?C to 135 ?C, with tests repeated at one thousand different probe currents. The accurate experimental data, obtained on several LED samples bearing two different part numbers, are reported, showing that they exhibit a high degree of linearity in wide current ranges, a circumstance that allows for a fast and reliable calibration as sensors. The measurement error is also fully characterized in terms of repeatability and stability over time, with measurements repeated after 600, 900, 1200 and 1800 hours of applied electro-thermal stress, demonstrating that the relevant sensor parameters stabilize after a few hundred hours of operation. A full set of parameters is provided for the two device models, allowing the direct use of each LED for the self-monitoring of the junction temperature and ensure compliance with their safe operating area over time. Moreover, a procedure and a simple circuit for the real time measurement of TJ , while the LED is on, are presented. The procedure does not require a stable current source, and relies instead on the application of a sub-threshold current ramp for such a short time that the change in the output light is not perceived by human eyes.
关键词： junction temperature,diode sensors,light emitting diodes,temperature sensors,LED
更新于2025-09-19 17:13:59
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5H-Benzo[d]Benzo[4,5]Imidazo[2,1-b][1,3]Thiazine as a Novel Electron-Acceptor Cored High Triplet Energy Bipolar Host Material for Efficient Solution-Processable Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes
摘要： Organic entities that can transport electrons are seldom available to develop adequate bipolar host materials applicable for solution-processable thermally activated delayed ?uorescence (TADF)-organic light-emitting diodes (OLEDs). Therefore, the introduction of new electron-af?ne entities that plausibly demonstrate high triplet energy (ET) is of urgent need. In this contribution, we introduced benzimidazo[1,2-a][3,1]benzothiazine (BBIT) as a novel electron-af?ne entity and developed two new bipolar host materials, CzBBIT and 2CzBBIT. Both host materials exhibit high ET of 3.0 eV, superior thermal robustness with the thermal decomposition temperature of up to 392?C, a glass transition temperature of up to 161?C, and high solubility in common organic solvents. Consequently, the solution-processable OLEDs fabricated using a recognized IAcTr-out as the green TADF emitter doped into CzBBIT as the host, realized a maximum external quantum ef?ciency (EQE) of 23.3%, while the 2CzBBIT:IAcTr-out blend ?lm-based device displayed an EQE of 18.7%. These outcomes corroborated that this work could shed light on the scienti?c community on the design of new electron-af?ne entities to establish the effective use of bipolar host materials toward pro?cient solution-processable TADF-OLEDs.
关键词： bipolar hosts,new electron-acceptor core,thermally activated delayed ?uorescence,organic light emitting diodes,solution process
更新于2025-09-19 17:13:59
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Theoretical Studies of Photophysical Properties of Da????a??Aa????a??D-Type Diketopyrrolopyrrole-Based Molecules for Organic Light-Emitting Diodes and Organic Solar Cells
摘要： A series of D–π–A diketopyrrolopyrrole(DPP)-based small molecules were designed for organic light-emitting diode(OLEDs) and organic solar cell(OSCs) applications. Applying the PBE0/6-31G(d,p) method, the ground state geometry and relevant electronic properties were investigated. The first excited singlet state geometry and the absorption and fluorescent spectra were simulated at the TD-PBE0/6-31G(d,p) level. The calculated results revealed that the photophysical properties were affected through the introduction of different end groups. Furthermore, the electronic transitions corresponding to absorption and emission exhibited an intramolecular charge transfer feature. Our results suggest that the designed molecules acted not only as luminescent for OLEDs, but also as donor materials in OSCs. Moreover, they can also be used as potential electron transfer materials for OLEDs and OSCs.
关键词： photophysical properties,organic solar cells(OSCs),organic light-emitting diodes(OLEDs),diketopyrrolopyrrole(DPP)-based molecules,Charge transporting property
更新于2025-09-19 17:13:59