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Boosting Efficiency of Near‐Infrared Organic Light‐Emitting Diodes with Os(II)‐Based Pyrazinyl Azolate Emitters
摘要： Tremendous effort has been devoted to developing novel near-infrared (NIR) emitters and to improving the performance of NIR organic light-emitting diodes (OLEDs). Os(II) complexes are known to be an important class of NIR electroluminescent materials. However, the highest external quantum efficiency achieved so far for Os(II)-based NIR OLEDs with an emission peak wavelength exceeding 700 nm is still lower than 3%. A new series of Os(II) complexes (1–4) based on functional pyrazinyl azolate chelates and dimethyl(phenyl)phosphane ancillaries is presented. The reduced metal-to-ligand charge transfer (MLCT) transition energy gap of pyrazinyl units in the excited states results in efficient NIR emission for this class of metal complexes. Consequently, NIR OLEDs based on 1–4 show excellent device performance, among which complex 4 with a triazolate fragment gives superior performance with maximum external quantum efficiency of 11.5% at peak wavelength of 710 nm, which represent the best Os(II)-based NIR-emitting OLEDs with peak maxima exceeding 700 nm.
关键词： N-donor,phosphorescence,osmium,near-infrared emission,organic light-emitting diodes
更新于2025-09-11 14:15:04
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Improving the charge balance and performance of CdSe/ZnS quantum-dot light-emitting diodes with a sputtered zinc-tin-oxide electron-transport layer and a thermally evaporated tungsten-oxide charge-restricting layer
摘要： The charge carrier balance and performance of CdSe/ZnS quantum-dot light-emitting diodes (QD-LEDs) with a vacuum-deposited electron-transport layer (ETL) and carrier-restricting layer (CRL) were successfully improved. Optimizing the fabrication process of the reactively sputtered zinc-tin-oxide (ZTO) ETL and adopting a thermally evaporated tungsten-oxide (WOx) CRL improved the electron-hole balance, thus leading to QD-LEDs with improved performance. Impedance spectroscopy analysis was successfully exploited in investigating charge carrier injection into each layer of the QD-LED and electron-hole recombination behaviors. The QD-LED with optimized ZTO ETL and without WOx CRL exhibited 2600 cd m?2 luminance and 3.2 cd A?1 current efficiency, and the QD-LED with both optimized ZTO ETL and a WOx CRL exhibited 3900 cd m?2 luminance and 5.1 cd A?1 current efficiency. These results imply a practical method for improving the electron-hole balance and performance of QD-LEDs, and provide a reliable technique for analyzing the carrier behavior of QD-LEDs.
关键词： CdSe/ZnS quantum-dot,light-emitting diodes,tungsten-oxide,charge balance,zinc-tin-oxide,impedance spectroscopy
更新于2025-09-11 14:15:04
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Divalent europium-doped near-infrared-emitting phosphor for light-emitting diodes
摘要： Near-infrared luminescent materials exhibit unique photophysical properties that make them crucial components in photonic, optoelectronic and biological applications. As broadband near infrared phosphors activated by transition metal elements are already widely reported, there is a challenge for next-generation materials discovery by introducing rare earth activators with 4f-5d transition. Here, we report an unprecedented phosphor K3LuSi2O7:Eu2+ that gives an emission band centered at 740 nm with a full-width at half maximum of 160 nm upon 460 nm blue light excitation. Combined structural and spectral characterizations reveal a selective site occupation of divalent europium in LuO6 and K2O6 polyhedrons with small coordination numbers, leading to the unexpected near infrared emission. The fabricated phosphor-converted light-emitting diodes have great potential as a non-visible light source. Our work provides the design principle of near infrared emission in divalent europium-doped inorganic solid-state materials and could inspire future studies to further explore near-infrared light-emitting diodes.
关键词： divalent europium,Near-infrared luminescent materials,4f-5d transition,light-emitting diodes,phosphor
更新于2025-09-11 14:15:04
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Highly Efficient and Stable White Light‐Emitting Diodes Using Perovskite Quantum Dot Paper
摘要： Perovskite quantum dots (PQDs) are a competitive candidate for next-generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD-based white light-emitting diodes (LEDs) show only modest luminous efficiency of ≈50 lm W?1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4+ phosphor and blue GaN LED chips to fabricate a high-performance white LED demonstrating ultrahigh luminous efficiency (124 lm W?1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.
关键词： light-emitting diodes,stability,paper,quantum dots,perovskites
更新于2025-09-11 14:15:04
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Dipolar and Quadrupolar Luminophores Based on 1,8‐Dimethylcarbazole?Triazine Conjugates for High‐Efficiency Blue Thermally Activated Delayed Fluorescence OLEDs
摘要： Highly efficient blue thermally activated delayed fluorescence emitters combining 1,8-dimethylcarbazoles as a donor (D) unit with a triazine acceptor (A) core are designed and synthesized. A D-A-D-type emitter exhibits superior photo- and electroluminescence (EL) properties compared to a D-A-type counterpart and displays a brilliant blue EL emission with a maximum external EL quantum efficiency as high as 21.2 %.
关键词： organic light-emitting diodes,optoelectronics,donor-acceptor systems,electroluminescence,delayed fluorescence
更新于2025-09-11 14:15:04
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Surface-modification of Cu2O nanoparticles towards band-optimized hole-injection layers in CsPbBr3 perovskite light-emitting diodes
摘要： Herein, we have proposed a strategy to grow surface-modified cuprous oxide (Cu2O) nanoparticles as an efficient hole-injecting layer (HIL) in all-inorganic cesium lead bromide (CsPbBr3) perovskite light-emitting diodes (PeLEDs). Surface of the oxide nanoparticles was modified by different ligands (thiols or silane) which in turn tailored its conduction and valence band-edge energies. As evidenced from the density of states (DOS) spectra, such modification of band-edge energies tuned the band-alignment at the perovskite-HIL interface influencing the efficiency of the PeLEDs thereby. The device performance has been correlated with the band-diagram of the heterojunctions. The report hence provides a strategy to achieve a favorable band-alignment in perovskite-based heterojunctions for optoelectronic applications.
关键词： scanning tunneling spectroscopy,Cu2O nanoparticles,band-engineering,surface-modification,perovskite light-emitting diodes.
更新于2025-09-11 14:15:04
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Human-eyes-friendly white electroluminescence from solution-processable hybrid OLEDs exploiting new iridium (III) complex containing benzoimidazophenanthridine ligand
摘要： This paper primarily deals with the development of highly efficient phosphorescent iridium (III) complex based on benzoimidazophenanthridine as main ligand. The potential of this complex, as phosphorescent emitter for optoelectronic applications, was screened by different methods, including luminescence spectrometry, cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry as well as photoelectron emission spectrometry. The possible application of the developed complex in single-colour vacuum-deposited organic light emitting diodes (OLEDs) exhibiting warm orange electrophosphorescence was demonstrated. The device was characterized with CIE1931 colour coordinates of (0.539, 0.459), colour temperature of 2088 K and maximum external quantum efficiency of 17.5 %. Good performance in OLEDs can be partly explained by efficient orange phosphorescence with quantum yield of 60 % at room temperature. This paper also deals with the development of white hybrid solution-processable organic light-emitting devices, exploiting ultralow concentration of newly synthesized iridium (III) complex as phosphorescent dopant in combination with blue fluorescencent emitter(host), and green emitter exhibiting thermally activated delayed fluorescence emitter. It was designed and fabricated by spin coating white hybrid devices, and was characterized by high quality (human-eyes-friendly) electroluminescence achieving CIE1931 coordinates of (0.335, 0.392), colour temperature of 2910K and colour rendering index of 72 as well as high maximum external quantum efficiency of 8.7 %.
关键词： external quantum efficiency,electrophosphorescence,phosphorescent iridium (III) complex,benzoimidazophenanthridine,white hybrid OLEDs,solution-processable,organic light emitting diodes (OLEDs)
更新于2025-09-11 14:15:04
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Decrease of intermolecular interactions for less-doped efficient deep blue monomer light-emitting diodes
摘要： Intermolecular interactions arise from molecular aggregation and cause concentration quenching and excimer emission. Although aggregation or excimer induced emission are sometimes favored, for example for color tuning, intermolecular interactions should usually be minimized because concentration quenching and excimer emission usually result in poor efficiency and color instability. In this paper, two novel tert-butyl modified naphthyl derivates, 4,5'-di-{[N,N,N',N'- tetrakis-(4-tert-butyl-phenyl)]phenyl-1'',4'''-diamine}-1,1'-binaphthalenyl (BN5) and 1,5-di-{[N,N,N', N'-tetrakis-(4-tert-butyl-phenyl)]phenyl-1'',4'''-diamine}-3,7-bi-tertbutylnaphthalenyl (BN6), have been synthesized and their intriguing photophysical properties and high-efficiency deep-blue electroluminescence (EL) in less-concentrated condensed phase investigated. Electroluminescent devices based on BN5 in 50% matrix achieved a high external quantum efficiency (EQE) of 3.7% and the Commission Internationale de L’Eclairage (CIE) coordinates of (0.160, 0.081) which is very close to the National Television Standards Committee’s (NTSC of USA) pure blue standard. Meanwhile, the non-doped device based on BN5 demonstrated a much higher EQE of 4.5%. Neat BN6-based device presented a pure monomer emission (λpeak = 420 nm) with an extremely high EQE of 5.1% and a satisfactory CIE coordinate of (0.171, 0.076). Such values are the best ever reported for 420 nm EL emission with an un-doped layer. We attributed the enhanced performance of deep blue monomer light-emitting diodes to tert-butyl groups of BNs due to a reduction of intermolecular interaction, especially the tert-butyl substituents on the molecular backbone of BN6 play a major role in inhibiting dimer and crystallization-induced emission.
关键词： excimer emission,organic light-emitting diodes,deep blue,intermolecular interactions
更新于2025-09-11 14:15:04
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Triplet–triplet upconversion enhanced by spin–orbit coupling in organic light-emitting diodes
摘要： Triplet–triplet upconversion, in which two triplet excitons are converted to one singlet exciton, is a well-known approach to exceed the limit of electroluminescence quantum efficiency in conventional fluorescence-based organic light-emitting diodes. Considering the spin multiplicity of triplet pairs, upconversion efficiency is usually limited to 20%. Although this limit can be exceeded when the energy of a triplet pair is lower than that of a second triplet excited state, such as for rubrene, it is generally difficult to engineer the energy levels of higher triplet excited states. Here, we investigate the upconversion efficiency of a series of new anthracene derivatives with different substituents. Some of these derivatives show upconversion efficiencies close to 50% even though the calculated energy levels of the second triplet excited states are lower than twice the lowest triplet energy. A possible upconversion mechanism is proposed based on the molecular structures and quantum chemical calculations.
关键词： Triplet–triplet upconversion,spin–orbit coupling,anthracene derivatives,quantum chemical calculations,organic light-emitting diodes
更新于2025-09-11 14:15:04
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Ultrapure Green Light-Emitting Diodes Based on CdSe/CdS Core/Crown Nanoplatelets
摘要： Colloidal nanoplatelets is a kind of two-dimensional nano-materials with an atomically flat surface, leading to an ultra-narrow emission linewidth of 8~12 nm. In this paper, we fabricated a green light-emitting diodes (LEDs) based on CdSe/CdS core/crown NPLs. This device exhibited an electroluminescence (EL) at 521 nm with a full-width at half maximum (FWHM) of 15 nm and a maximum luminance of 4684 cd/m2. Such narrow EL FWHM indicates that the core/crown NPLs can achieve an ultrapure green LED with a 124.7% of NTSC (National Televison System Committee), realizing a high color saturation and wide color gamut display.
关键词： Colloidal nanoplatelets,light-emitting diodes,color purity,wide color gamut display
更新于2025-09-11 14:15:04