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Oligo(ethylene glycol)/alkyl-modified chromophore assemblies for photon upconversion in water
摘要： Molecular self-assembly is a powerful means to construct nanoscale materials with advanced photophysical properties. Although the protection of the photo-excited states from oxygen quenching is a critical issue, it still has been in an early phase of development. In this work, we demonstrate that a simple and typical molecular design for aqueous supramolecular assembly, modification of chromophoric unit with hydrophilic oligo(ethylene glycol) chains and hydrophobic alkyl chains, is effective to avoid oxygen quenching of triplet-triplet annihilation-based photon upconversion (TTA-UC). While a TTA-UC emission is completely quenched when the donor and acceptor are molecularly dispersed in chloroform, their aqueous co-assemblies exhibit a clear upconverted emission in air-saturated water even under extremely low chromophore concentrations down to 40 μM. The generalization of this nano-encapsulation approach offers new functions and applications using oxygen-sensitive species for supramolecular chemistry.
关键词： photon upconversion,photochemistry,oxygen quenching,self-assembly,triplet-triplet annihilation
更新于2025-09-23 15:23:52
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Effect of exciton diffusion on the triplet-triplet annihilation rate in organic semiconductor host-guest systems
摘要： We study the contribution of triplet exciton diffusion to the efficiency loss resulting from F?rster-type triplet-triplet annihilation (TTA) in organic phosphorescent semiconductor host-guest systems, using kinetic Monte Carlo (KMC) simulations. Our study focusses on diffusion due to F?rster-type guest-guest transfer, but includes also a comparison with simulation results for the case of Dexter-type guest-guest transfer. The simulations are carried out for a wide range of F?rster radii, and for guest concentrations up to 100 mol%, with the purpose to support analyses of time-resolved photoluminescence experiments probing TTA. We find that the relative contribution of diffusion to the TTA-induced efficiency loss may be deduced quite accurately from a quantitative experimental measure for the shape of the time-dependent photoluminescence intensity, the so-called r ratio. For small guest concentrations and F?rster radii that are most relevant to organic light-emitting diodes (OLEDs), the diffusion contribution is in general quite small. Under these weak-diffusion conditions, the absolute diffusion contribution to the TTA-induced efficiency loss can be understood quantitatively using a capture radius formalism. The effective guest-guest diffusion coefficient that follows from the TTA simulations, using the capture radius formalism, agrees well with the diffusion coefficient that follows from direct KMC diffusion simulations. The simulations reveal that the diffusion coefficient is strongly affected by the randomness of the distribution of guest molecule locations.
关键词： OLEDs,photoluminescence,kinetic Monte Carlo simulations,Dexter transfer,organic semiconductors,triplet-triplet annihilation,exciton diffusion,host-guest systems,F?rster transfer
更新于2025-09-23 15:23:52
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Understanding degradation of organic light-emitting diodes from magnetic field effects
摘要： The impact of magnetic field effects on the electroluminescence of organic light-emitting diodes is commonly used to characterize exciton dynamics such as generation, annihilation, and performance degradation. However, interpreting these effects is challenging. Here, we show that magnetic field effects in organic light-emitting diodes can be understood in terms of the magnetic response of device characteristics derived from polaron-pair and triplet exciton quenching processes, such as triplet-polaron interactions and triplet-triplet annihilation. Device degradation shows a clear relationship with the amplitude of the magnetic field effects, enabling non-destructive measurement of the degradation. The results and proposed mechanism provide a better understanding of magnetic field effects on organic light-emitting diodes and device degradation phenomena.
关键词： magnetic field effects,device degradation,organic light-emitting diodes,triplet-polaron interactions,triplet-triplet annihilation,exciton dynamics
更新于2025-09-23 15:21:01
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Novel strategy to improve the efficiency roll-off at high luminance and operational lifetime of hybrid white OLEDs via employing an assistant layer with triplet-triplet annihilation up-conversion characteristics
摘要： The efficiency roll-off at high luminance and operational lifetime remain a major challenge before the wide applications of white organic light-emitting diodes (WOLEDs) technology. Here we present a novel strategy to improve the efficiency roll-off at high luminance and operational lifetime by employing an assistant layer with triplet-triplet annihilation (TTA) up-conversion characteristics in emitters. It can be seen that at high luminance, the partial triplet energies in emitters will transfer to the TTA assistant layer and finally lead to the TTA emission, which reduces the exciton quenching at high luminance. Therefore, not only the efficiency roll-off, but also the operational lifetime are greatly improved. The resulting hybrid WOLEDs exhibited the maximum forward-viewing external quantum efficiency and power efficiency of 23.6% and 68.8 lm W?1, and they only dropped to 18.3% and 38.1 lm W?1 at 1000 cd m?2 and 17.1% and 25.9 lm W?1 at 5000 cd m?2, which are significantly higher than 10.5% and 17.9 lm W?1 at 5000 cd m?2 of WOLEDs without TTA assistant layer. Furthermore, the operational half-lifetime of the resulting hybrid WOLEDs also reached 600 hours at the luminance of 1000 cd m?2, which is nearly two-fold longer than that of the reference WOLEDs.
关键词： exciton diffusion,triplet-triplet annihilation up-conversion,Efficiency roll-off,white organic light-emitting diodes,lifetime
更新于2025-09-23 15:21:01
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High efficiency???low efficiency roll-off and long lifetime fluorescent white organic light-emitting diodes based on strategic management of triplet excitons via triplet-triplet annihilation up-conversion and phosphor sensitization
摘要： The simultaneous realization of high efficiency, low efficiency roll-off, long lifetime and stable electroluminescence (EL) spectra in fluorescent white organic light-emitting diodes (WOLEDs) is still a huge challenge. Here, we used a triplet-triplet annihilation up-conversion (TTA-UC) material as blue emission layer and phosphor sensitized fluorescent emitter as red emission layer and introduced a bipolar interlayer between them to fabricate high efficiency, low efficiency roll-off and long lifetime fluorescent WOLEDs. It is clearly seen that the bipolar interlayer not only efficiently distributed the singlet and triplet excitons, but also significantly stabilized the EL spectra. Thus, the resulting two-color fluorescent WOLEDs exhibited the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) of 26.9 cd A-1, 22.3 lm W-1 and 12.8%, and remained 25.9 cd A-1, 16.9 lm W-1 and 12.1% at the luminance of 1000 cd m-2 and 23.1 cd A-1, 10.6 lm W-1 and 10.7% at the luminance of 10000 cd m-2, respectively, and the operational lifetime LT50 (50% decay, initial luminance of 1000 cd m-2) was also up to 984 h. It can be seen that these devices also showed stable EL spectra with Commission Internationale de I’Eclairage (CIE) of (0.51, 0.41) from 1000 cd m-2 to 5000 cd m-2 luminance. Furthermore, the fabricated three-color fluorescent WOLEDs by further introducing a green fluorescent emitter, also showed high efficiencies of 15.5 cd A-1, 13.0 lm W-1 and 8.1% and stable EL spectra with CIE of (0.43, 0.36) form 1000 cd m-2 to 5000 cd m-2 luminance. More importantly, their CE and EQE exhibited an increasing tendency with the luminance, a fully negligible efficiency roll-off. This design strategy provides a potential route towards high performance fluorescent WOLEDs.
关键词： fluorescent WOLEDs,bipolar interlayer,high efficiency,triplet-triplet annihilation up-conversion,phosphor sensitization,long lifetime,low efficiency roll-off
更新于2025-09-23 15:21:01
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Neara??Infrareda??toa??Visible Photon Upconversion by Introducing an Sa??T Absorption Sensitizer into a Metala??Organic Framework
摘要： Triplet-triplet annihilation-based photon upconversion (TTA-UC) of near-infrared (NIR) light to visible light in the solid-state remains as a great challenge due to the sensitizer aggregation that impedes the efficient triplet energy transfer. Herein, we successfully introduce a molecular sensitizer exhibiting direct singlet-to-triplet (S–T) absorption into a new emitter-based metal-organic framework (MOF) to achieve an efficient triplet sensitization and a NIR-to-visible TTA-UC in the solid-state.
关键词： photon upconversion,near-infrared light,metal-organic framework,singlet-to-triplet absorption,triplet-triplet annihilation
更新于2025-09-23 15:19:57
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The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters
摘要： The electroluminescence quantum e?ciency roll-o? in iridium(III)-based complexes, namely Ir(iqbt)2(dpm) and Ir(iqbt)3 (iqbt = 1 (benzo[b]thiophen-2-yl)-isoquinolinate, dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) utilized as near-infrared emitters in organic light emitting diodes with remarkable external quantum e?ciencies, up to circa 3%, 1.5% and 1%, are measured and analyzed. With a 5–6 weight% of emitters embedded in a host matrix, the double-layer solution-processed structure as well as analogous three-layer one extended by a hole-conducting ?lm are investigated. The triplet-polaron, the Onsager electron-hole pair dissociation and the triplet-triplet annihilation approaches were used to reproduce the experimental data. The mutual annihilation of triplets in iridium emitters was identi?ed as prevailingly controlling the moderate roll-o?, with the interaction between those of iridium emitters and host matrixes found as being less probable. Following the ?tting procedure, the relevant rate constant was estimated to be (0.5 ? 12) × 10?12 cm3/s, values considered to be rather too high for disordered organic systems, which was assigned to the simplicity of the applied model. A coexistence of some other mechanisms is therefore inferred, ones, however, with a less signi?cant contribution to the overall emission quenching.
关键词： infrared emitters,iridium complex,quantum e?ciency roll-o?,triplet-triplet annihilation,OLEDs
更新于2025-09-23 15:19:57
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Multiscale Simulation of Photoluminescence Quenching in Phosphorescent OLED Materials
摘要： A multiscale simulation protocol to treat triplet–triplet annihilation (TTA) in phosphorescent organic light-emitting diodes (PhOLEDs), in which microscopic parameters are computed with ab initio electronic structure methods, is presented. Virtual photoluminescence experiments are performed on a prototypical PhOLED emission material consisting of 4,4?,4?-tris(N-carbazolyl)triphenylamine and fac-tris(2-phenylpyridine)iridium. The obtained TTA quenching rate is comparable to experimental results in the low-intensity limit.
关键词： multiscale modeling,organic light-emitting diodes,exciton quenching,triplet–triplet annihilation
更新于2025-09-23 15:19:57
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Triplet-triplet annihilation effects in rubrene/C60 OLEDs with electroluminescence turn-on breaking the thermodynamic limit
摘要： Recently, Engmann et al. experimentally and theoretically examined the higher-order effects in rubrene/C60 organic light-emitting diodes (OLEDs), claiming that triplet-triplet annihilation (TTA) is not responsible for the electroluminescence (EL) with extremely-low turn-on voltage (Voc). Instead, the evidence from the equivalent circuit fitting suggest that the direct band-to-band recombination can interpret the low voltage phenomena. However, at applied bias of about 1.0 V, the excitons prefer to form on the charge-transfer state between rubrene/C60 interface. Direct singlet formation on rubrene and direct band-to-band recombination seems impossible to be accountable for such low Voc.
关键词： thermodynamic limit,electroluminescence,rubrene/C60 OLEDs,triplet-triplet annihilation
更新于2025-09-19 17:13:59
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Routes for Efficiency Enhancement in Fluorescent TADF Exciplex Host OLEDs Gained from an Electro‐Optical Device Model
摘要： Fluorescence-based organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) have increasingly attracted attention in research and industry. One method to implement TADF is based on an emitter layer composed of an exciplex host and a fluorescent dopant. Even though the experimental realization of this concept has demonstrated promising external quantum efficiencies, the full potential of this approach has not yet been assessed. To this end, a comprehensive electro-optical device model accounting for the full exciton dynamics including triplet harvesting and exciton quenching is presented. The model parameters are fitted to multiple output characteristics of an OLED comprising a TADF exciplex host with a fluorescent emitter, showing an external quantum efficiency of >10%. With the model at hand, an emission zone analysis and a parameter study are performed, and possible routes for further efficiency enhancement are presented.
关键词： exciton dynamics,triplet–triplet annihilation,triplet harvesting,split emission zones,electro-optical simulations
更新于2025-09-16 10:30:52