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Thermal Impact of LED Chips on Quantum Dots in Remote-Chip and On-Chip Packaging Structures
摘要： Light-emitting diode (LED) chips in quantum dot (QD)-converted LEDs serve simultaneously as a heat source and a heat sink, but it remains unclear which of these is the major factor that affects the operating temperature of QDs. Here, we investigated the thermal and optical performances of QD-converted LEDs using QD-on-chip and QD-remote-chip packaging structures, to better understand the thermal effect of LED chips on QDs. Our results indicated that the QD-on-chip structure achieved the same optical performance as the QD-remote-chip structure, while the former can save QD usage up to 75.9% owing to the higher absorption probability of QDs closer to the blue source. Most importantly, the QD-on-chip structure largely reduced the maximal surface temperature from 82.7 ?C to 60.2 ?C at 250 mA, and had a longer operating lifetime compared with the QD-remote-chip structure. Simulations revealed that the QD-remote-chip structure could suppress the heat transfer from chips to QDs; however, the hot spot remained in QDs, owing to the heavy conversion loss and low thermal conductivity of the silicone matrix; consequently, the QD-on-chip structure had better heat dissipation (lower temperature) for QDs closer to the chip that served as heat sinks. Therefore, it is suggested to place QDs near the heat sink with high thermal conductivity, such as the LED chip, for heat dissipation; this is better than removing QDs for blocking the heat generated by the LED chip.
关键词： Light-emitting diodes (LEDs),quantum dot (QD),packaging structure,thermal and optical performance
更新于2025-09-16 10:30:52
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High-performance hybrid white organic light-emitting diodes with bipolar host material and thermally activated delayed fluorescent emitter
摘要： Bipolar host material and thermally activated delayed fluorescent (TADF) emitter were used in hybrid white organic light-emitting diodes (OLEDs) with the aim to achieve high performance. First of all, the single color OLEDs was optimized by changing the thickness of hole transporting layer, electron transporting layer and the doping concentration of emission material. Then, white organic light-emitting diodes (WOLEDs) were fabricated on the basis of the former single color OLEDs by modifying the doping concentration of TADF emitter. Finally, an optimized white device shows the best results of 43.67 cd/A, 45.73 lm/W and 18.52% for current efficiency, power efficiency and external quantum efficiency, respectively. This research may supply a theoretical basis for the development of WOLEDs.
关键词： Thermally activated delayed fluorescent (TADF),Energy transfer,Hybrid white organic light-emitting diodes (WOLEDs),Bipolar host material,High performance
更新于2025-09-16 10:30:52
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Low Rolla??Off Perovskite Quantum Dot Lighta??Emitting Diodes Achieved by Augmenting Hole Mobility
摘要： The external quantum efficiencies (EQEs) of perovskite quantum dot light-emitting diodes (QD-LEDs) are close to the out-coupling efficiency limitation. However, these high-performance QD-LEDs still suffer from a serious issue of efficiency roll-off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non-radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll-off of 11% at 500 mA cm?2 (the lowest roll-off known so far) where the EQE is still over 11%.
关键词： perovskites,quantum dots,light-emitting diodes,Auger processes
更新于2025-09-16 10:30:52
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Efficient CsPbBr3 Inorganic Perovskite Light-Emitting Diodes via Lewis Acid-Base Reaction with Organic Small Molecule mCP
摘要： CsPbBr3 all-inorganic perovskite light-emitting diodes (PeLEDs) have received increasing attention in recent years due to their unique luminescent property and superior thermal stability. However, the low solubility of bromide precursors and the fast crystallization of perovskites usually cause the formation of discontinuous CsPbBr3 films with rough grains and large pin-holes. This would increase the defects and non-radiative recombination and severely degrade the device electroluminescence (EL) performance. To tackle this issue, herein, the 1,3-bis9H-carbazol-9-ylbenzene (mCP) small molecule was elaborately selected as an effective additive to enhance the film-forming ability of CsPbBr3 emissive layers. With the addition of mCP, the submicron-sized CsPbBr3 grains were reduced to nanometer range, and the resulting perovskite films became uniform and continuous. It was found that the electron pairs of N2- in mCP would donate to metal Pb2+ in CsPbBr3. Thus the so-called Lewis acid-base reaction occurred, which could retard the fast crystallization process and contribute to the connection of perovskite grains. As such, the film roughness was decreased from 8.28 nm to 1.62 nm, and the carrier lifetime was increased from 2.49 ns to 68.39 ns. The CsPbBr3:mCP device with an optimized mass ratio of 1:0.10 exhibited a maximum luminance (L) of 21008 cd/m2, a maximum current efficiency (CE) of 3.74 cd/A, and the corresponding maximum external quantum efficiency (EQE) of 1.21%, far surpassing the EL performance of the pristine CsPbBr3 PeLEDs.
关键词： Organic small molecule mCP,Effective additive,CsPbBr3 inorganic perovskite,Lewis acid-base reaction,Light-emitting diodes
更新于2025-09-16 10:30:52
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Recent advances in circularly polarized electroluminescence based on organic light-emitting diodes
摘要： Since the first attempt that was made to obtain direct circularly polarized (CP) light from OLEDs by Meijer et al. in 1997, considerable efforts have been devoted to the development of circularly polarized organic light-emitting diodes (CP-OLEDs), particularly in the recent years. Circularly polarized electroluminescence (CPEL) based on OLEDs has attracted increasing interest for its efficient ability to generate CP light directly and wide potential applications in 3D displays, optical data storage, and optical spintronics. In this review, we systematically summarize the recent progress in chiral emitter based OLEDs with CPEL properties including CPEL based on chiral conjugated polymers, CPEL based on chiral metal complexes, and CPEL based on chiral simple organic molecules, especially chiral thermally activated delayed fluorescence (TADF) molecules. We believe that this review will provide a promising perspective of chiral emitter based OLEDs with CPEL properties for a broad range of scientists in different disciplinary areas and attract a growing number of researchers to this fast-growing research field.
关键词： chiral simple organic molecules,circularly polarized electroluminescence,thermally activated delayed fluorescence,chiral conjugated polymers,organic light-emitting diodes,chiral metal complexes
更新于2025-09-16 10:30:52
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Temporal Luminescence of Broadband Light-Emitting Diodes and Their Use for Generating Customizable White Light
摘要： Broadband visible light-emitting diodes (LEDs) are now being used for applications where high-quality tunable light is needed. These LEDs are based on phosphors with wide emission bands (full width at half maximum, FWHM, of 70 nm or more). We describe the time-dependent characteristics of light emission from such devices. We found time lags in both luminescence buildup and decay as the broadband red, green and white LEDs are pumped by square pump photon flux. The reasons for such delays are photon percolation in phosphor/light scatterer blends and luminescence persistence due to defects in phosphors. The latter part of the paper describes a setup for combining light from phosphor-based red and green broadband LEDs with that of a band-edge emission blue LED to produce white light. It is shown that the chromaticity of white light can be changed stably by changing the frequency/duty cycle of PWM waveforms that are used for controlling red, green and blue LEDs. We also introduce a new LED drive scheme where PWM signals are converted to steady DC levels before driving LEDs. The setup described here enables the generation of full-spectrum white light with electrically controllable chromaticity.
关键词： light-emitting diodes,pulse width modulation,phosphors,color mixing,Chromaticity
更新于2025-09-16 10:30:52
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High-efficient, spherical and thermal-stable carbon dots@silica fluorescent composite as rare earth-free phosphors for white LED
摘要： This paper reported a facile synthesis path to realize high-luminescent rare-earth-free composite powder, by embedding blue/green-emitting N-doped carbon dots into silica nano-spheres (CD@SiO2). Carbon dots were evenly dispersed in CD@SiO2 composites and eventually the aggregation-induced luminescence quenching is eliminated. Compared to the naked CDs, CD@SiO2 composites exhibit perfectly spherical morphology with average size of ~200 nm, signi?cantly enhanced emission intensity (> 4 times) and better thermal stability (T50 > 150 °C). As-synthesized CD@SiO2 own strong blue/green emission with high quantum e?ciency (QE) over 60%. White LEDs prototypes with promising properties, i.e. CRI = 89.1, CCT = 4850 K and CIE coordinates = (0.3514, 0.3715), were fabricated by combining blue/green CD@SiO2 and red CdTe@CaCO3 composites with NUV chip. All results indicate that these rare-earth-free, mono-dispersed spherical, and thermal-stable composite materials with e?cient blue/green emission could be an exceptional choice as phosphors for LED application.
关键词： Composite phosphors,Silica nano-sphere,Carbon dots,Luminescence,Light-emitting diodes
更新于2025-09-16 10:30:52
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Temperature Dependence of Raman and Photoluminescence Spectra of Ternary Alloyed CdSe0.3Te0.7 Quantum Dots
摘要： The Raman and photoluminescence spectra of ternary alloyed CdSe0.3Te0.7 quantum dots (QDs) have been studied at temperatures between 84 K and 293 K. The average diameter of QDs is about 5.1 nm. The temperature dependence of the longitudinal optical (LO) phonon frequencies and the phonon band width was analyzed and the anharmonic constants relating to various high-order phonon processes was determined. While the three-phonon processes plays a dominant role in the temperature-dependent shift of the LO-phonon frequencies, the four-phonon processes contribute to the increase of the phonon linewidth with increasing temperature. The photoluminescence (PL) spectra were used to study the temperature dependence of the bandgap, the linewidth and the integrated PL intensity. At low temperatures below about 120 K, the PL linewidth decreases and the PL intensity increases as temperature increases. This temperature behavior can be ascribed to the exciton ?ne structure.
关键词： light-emitting diodes,anharmonicity,exciton ?ne structure,photoluminescence,Raman scattering,phonon
更新于2025-09-16 10:30:52
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Modulation of Ligands Conjugation for Efficient FAPbBr3 based Green Light-Emitting Diodes
摘要： Organic ligands capped on surface of perovskite nanocrystals (PeNCs) strongly influence the optical and electrical properties of the obtained PeNCs films, which are fundamental for efficient perovskite light-emitting diodes (PeLEDs). Here, we investigate the ligands effect through introduction of ligands with strong π conjugation, 1-(1-naphthyl)ethylamine bromide (NEABr), for the fabrication of FAPbBr3 PeNCs. Compared to the widely applied ligands of phenylethylamine bromide (PEABr), NEABr molecules containing naphthalene ring possess more delocalized electrons and better conductivity, which is beneficial for charge injection and transportation between interfaces. By varying the ligands ratio, high quality three dimensional FAPbBr3 PeNCs films with photoluminescence quantum yields up to 80% are fabricated. Based on the optimized PeNCs films, electroluminescent (EL) devices achieve a maximum external quantum efficiency of 8.6%, which is about three times higher than that of EL devices based on PEABr. Importantly, through understanding into the ligands effect, we demonstrate that the enhanced device efficiency is attributed to lower defect densities and decreased interfacial resistance in NEABr derived EL devices. Our findings about ligands conjugation on device performance may benefit other perovskites based optoelectronic devices.
关键词： ligands conjugation,perovskite nanocrystals,light-emitting diodes,charge injection,FAPbBr3
更新于2025-09-16 10:30:52
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Performance Enhancement of All-Inorganic Quantum Dot Light-Emitting Diodes via Surface Modification of Nickel Oxide Nanoparticles Hole Transport Layer
摘要： All-inorganic quantum dot light-emitting diodes (QLEDs) show promise for advanced lighting and display due to their superior advantage in stability. However, all-inorganic QLEDs suffer from the low efficiency because of the exciton quenching and inefficient hole transport from inorganic hole transport layer (HTL) to QDs. Herein, we demonstrate an efficient all-inorganic QLED with NiO nanoparticals (NPs) HTL modified by 11-mercaptoundecanoic acid (MUA). The MUA can passivate the defects of NiO and suppress the exciton quenching. Moreover, the declined valance band level of modified NiO could facilitate the hole transport, promoting the charge balance. In addition, the surface engineering improves the quality of NiO film, leading to the decrease of current leakage. As a result, the maximum current efficiency and external quantum efficiency (EQE) of our QLEDs achieve 5.50 cd/A and 1.28%, respectively, exhibiting the enhancement of 4.5 and 1.72 folds, respectively. Meanwhile, the stability of the device is drastically improved by more than 20 folds after modifying the NiO with MUA. The strategy offers a pathway to enhance the efficiency and the operation lifetime of all-inorganic QLEDs.
关键词： exciton quenching,nickel oxide nanoparticles,performance enhancement,surface modification,all-inorganic quantum dot light-emitting diodes
更新于2025-09-16 10:30:52