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High Efficiency Non‐Doped White Organic Light Emitting Diodes Based on a Bilayer Interface‐Exciplex Structure
摘要： High efficiency non-doped blue and white organic light emitting diodes (OLEDs) are realized by using a bilayer interface-exciplex (i-Exc) structure. Since the neutral exciplex are formed at the interface, the interface charge accumulation is reduced, thereby suppressing exciton quenching in the device. With the i-Exc structure, a maximum external quantum efficiency (EQE) of 23.1% is achieved in the non-doped blue phosphorescent OLED. Moreover, the white emission can be obtained by inserting an ultrathin orange-red phosphorescent emitter into the blue devices. The charge trapping in the orange-red emitter can be suppressed by adjusting the position of the ultrathin orange-red emitting layer in the device, contributing to superior spectral stability. The WOLED achieves an EQE of 20.0% and exhibits a stable warm white emission. The Commission Internationale de l’Eclairage (CIE) coordinates of WOLED are (0.41, 0.40) at 5 V and slightly change to (0.40, 0.41) at 9 V.
关键词： interface-exciplex,PHOLED,WOLED,bilayer structure,ultrathin non-doped emitting layers
更新于2025-11-14 15:26:12
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Non-doped phosphorescent organic light-emitting devices with an exciplex forming planar structure for efficiency enhancement
摘要： Organic light-emitting devices (OLEDs) consisting of a non-doped phosphorescent dye that inserted in an exciplex forming planar structure have been fabricated, and the thickness of ultrathin phosphor layer is optimized to achieve high efficiency. The results showed that OLEDs based on the exciplex interface and a 0.5 nm thick phosphorescent dye have a power efficiency, a current efficiency, and an external quantum efficiency of 37.4 lm/W, 40.5 cd/A, and 14.3%, respectively, which are almost two-folds higher than those with non-exciplex interface devices. Meanwhile, the efficiency roll-off is significantly suppressed. These improved device performances are attributed to the elimination of triplet energy leakage from exciplexes to constituting molecules, efficient energy up conversion of triplet exciplexes and complete host-guest F?rster energy transfer. These results will provide an easily-fabricated and time-saving approach for high-performance OLEDs.
关键词： non-doped,planar structure,Organic light-emitting device (OLED),exciplex,phosphorescent dye
更新于2025-09-23 15:22:29
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Nature of the excited states of layered systems and molecular excimers: Exciplex states and their dependence on structure
摘要： Weakly bound systems, like noble-gas dimers or two-dimensional layered materials (graphite, hexagonal boron nitride, or transition-metal dichalcogenides), exhibit excited electronic states of a particular nature. These so-called exciplex states combine on-site (or intralayer) and charge-transfer (or interlayer) configurations in a well-balanced way. We show by ab initio many-body perturbation theory that the energy and composition of the exciplex states depend sensitively on the bond length or interlayer distance of the material. When the constituents approach each other, the charge-transfer contribution increases and the excitation is redshifted to lower energy. If the system is excited into the exciplex state, then a covalent-like bond results. In consequence, noble-gas dimers form excimer complexes, while layered materials exhibit interlayer contraction.
关键词： charge-transfer excitations,many-body perturbation theory,interlayer contraction,exciplex states,layered systems
更新于2025-09-23 15:22:29
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A Comparative Study via Photophysical and Electrical Characterizations on The Interfacial and Bulk Exciplex-Forming Systems for Efficient Organic Light-Emitting Diodes
摘要： An efficient organic light-emitting diode (OLED) based on BCzPh:CN-T2T exciplex as emitting layer (EML) has been fabricated by exploiting the charge balance and favorable molecular orientations. To further understand the details of the exciplex-forming mechanism, time-resolved photoluminescence (TRPL), capacitance-voltage (CV), impedance spectroscopy (IS), and transient electroluminescence (EL) measurements were used to probe the photophysical and electrical characteristics of EL devices incorporating interfacial- (BCzPh/CN-T2T) and bulk- (BCzPh:CN-T2T) exciplex as emitting layer. The interfacial- and bulk-exciplex devices reveal maximum external quantum efficiency (EQE) of 7.7% and 26.4%, respectively. The reason for different device performance was rationalized by comparing the amount of charge density accumulated at the EML’s interface responsible to exciplex emission. In addition, the TRPL measurement monitored from short to long wavelength was used to explore the harvest of non-radiative triplet back to singlet via reverse intersystem crossing as well as to examine the efficiency of delayed fluorescence. The bulk-exciplex system showed a distinct delayed fluorescence as compared to that of the interfacial one, which was also corroborated by the observation in the transient EL. The result indicates that bulk-exciplex can reduce the accumulated charge in EML rapidly, resulting in the improvement of EL efficiency. This assumption was further verified by the CV and IS measurements. Our results reveal that the accumulated charge density as well as the bulk resistance of the bulk-exciplex device are much lower as compared to those of the interfacial counterpart device.
关键词： transient photoluminescence,impedance spectroscopy,Interfacial exciplex,transient electroluminescence,bulk exciplex
更新于2025-09-23 15:19:57
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High External Quantum Efficiency in Fluorescent OLED by Cascade Singlet Harvesting Mechanism
摘要： The cascade singlet harvesting (CSH) organic light-emitting diodes (OLEDs) are devised to resolve the low quantum efficiency issue of fluorescent OLEDs by efficient singlet exciton harvesting of the fluorescent emitters. The CSH mechanism is realized by doping a fluorescent emitter in the singlet exciton harvesting matrix consisted of high energy exciplex and low energy exciplex. The high energy exciplex serves as the main component of the emitting layer and the low energy exciplex is a medium harvesting the singlet excitons of the fluorescent emitter. Both exciplexes are thermally activated delayed fluorescence type exciplexes to effectively harvest singlet excitons by reverse intersystem crossing process. The singlet excitons of the low energy exciplex are harvested by the high energy exciplex through F?rster energy transfer and then the singlet excitons of the fluorescent emitter are harvested by the low energy exciplex through the second F?rster energy transfer process. The CSH mechanism maximizes the singlet exciton formation in the fluorescent emitter, which significantly enhances the external quantum efficiency (EQE) of the fluorescent OLEDs. The optimization of the emitting layer structure provides high EQE of 19.9% in the fluorescent OLEDs compared with 10.4% of a conventional singlet harvesting fluorescent OLED.
关键词： energy transfer,external quantum efficiency,fluorescent OLEDs,thermally activated delayed fluorescence,cascade singlet harvesting,exciplex
更新于2025-09-23 15:19:57
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All-fluorescent white organic light-emitting diodes with EQE exceeding theoretical limit of 5% by incorporating a novel yellow fluorophor in co-doping forming blue exciplex
摘要： For all-fluorescent white organic light-emitting diodes (WOLEDs), it is a current challenge to achieve comparable device efficiency to phosphorescent devices. A novel yellow fluorophor (Y), synthesized by our group, realizes ultra-high electroluminescence performance with maximum luminance and external quantum efficiency (EQE) reaching 74820 cd/m2 and 5.65%, respectively, indicating a huge potential applications in developing high-performance all-fluorescent WOLEDs. Herein, we employ above yellow emitter Y to demonstrate a series of all-fluorescent WOLEDs, where the devices are fabricated by doping yellow emitter Y in blue-emitting thermally activated delayed fluorescent (TADF) host of mCP:PO-T2T-forming exciplex. And white emission are realized by the combination of blue and yellow emissions from mCP:PO-T2T host and yellow emitter Y through the incomplete energy transfer. By simply adjusting the doping ratio of yellow emitter Y in mCP:PO-T2T host, the optimized all-fluorescent white device achieves high device performance with maximum current efficiency, power efficiency, and EQE reaching 20.78 cd/A , 24.25 lm/W, and 8.22%, respectively. The EQE obviously exceed the theoretical limit value of 5% for all-fluorescent WOLEDs, and is comparable to some fluorescent/phosphorescent or all-phosphorescent WOLEDs in reported literatures. The achievement of such high performance is mainly ascribed to the highly efficient exciton utilization derived from excellent yellow fluorescent emitter Y and effective reverse intersystem crossing (RISC) from triplet level to singlet level in mCP:PO-T2T exciplex host.
关键词： white emission,exciplex host,all-fluorescent emission,organic light-emitting diodes,external quantum efficiency
更新于2025-09-23 15:19:57
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High-performance white organic light-emitting diodes with doping-free device architecture based on the exciton adjusting interfacial exciplex
摘要： White organic light-emitting diodes (WOLEDs) with doping-free device architecture have aroused more attention due to their attractive merits such as simplified fabrication procedures and reduced costs. However, the electroluminescence performance of that is still manifestly unsatisfactory and needs to be further improved. Here, high-performance doping-free two-color and three-color WOLEDs with the accurate manipulation of excitons have been successfully fabricated by optimizing the interfacial exciplex. As a result, two-color WOLEDs exhibit the controllable electroluminescence spectra with a wide correlated color temperature (CCT) spanning from 2878 to 9895 K at the voltage of 4 V, as well as the maximum forward-viewing power and current efficiencies of 83.2 lm W?1 and 63.3 cd A?1, respectively. The three-color WOLED not only realizes the maximum efficiencies of 50.1 lm W?1 and 44.7 cd A?1, but also exhibits superior color stability with a color rendering index of 86, a CCT of 2679 K, and a Commission International de I’Eclairage coordinates of (0.49, 0.46) at the voltage of 5 V. Such surprising efficiencies obtained in our WOLEDs indicate that the reasonable application of interfacial exciplex should be a helpful way to develop high-performance and low cost WOLEDs with a simple technology.
关键词： high-performance,color stability,White organic light-emitting diodes,doping-free,interfacial exciplex
更新于2025-09-23 15:19:57
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4s to 5s and 4p photoexcitation dynamics of K atoms from the surface of helium nanodroplets: a theoretical study
摘要： We study the photodissociation of the potassium atom from a superfluid helium nanodroplet upon 5s 2S or 4p 2P excitation using the time-dependent helium density functional method (He-TDDFT). The importance of quantum effects is assessed by comparing the absorption spectrum obtained for a classical or a quantum description of the K atom. In the case of the 5s 2S ' 4s 2S excitation the difference is rather large, and we use a quantum description for the ensuing direct dissociation dynamics. In the case of the 4p 2P ' 4s 2S absorption spectrum, the difference is much smaller, hence a classical description of K is used to describe 4p 2P excitation dynamics. Excitation to the 4p 2S1/2 state leads to the direct dissociation of the K atom, while the 4p 2P3/2 state initially leads to the formation of an exciplex and the 4p 2P1/2 state to a bouncing atom above the droplet surface. Remarkably, electronic relaxation can be observed for the latter two states, leading to spin–orbit relaxation and the binding of the initially departing one-atom excimer as a ring excimer for the 2P3/2 state and to the formation of a bound, ring excimer for the 2P1/2 state.
关键词： potassium,spin-orbit relaxation,quantum effects,helium nanodroplets,exciplex formation,photodissociation
更新于2025-09-19 17:15:36
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High triplet energy materials for efficient exciplex-based and full-TADF-based white OLEDs
摘要： Materials with high triplet energies have attracted great attention for their application in exciplex-based or thermally activated delayed fluorescence-based organic light-emitting diodes. To study the correlation between triplet energy and chemical structure, six compounds with typical donor-acceptor-donor structures were designed, synthesized, and characterized. Through the adjustment of molecular configuration by weakening the strengths of donors and increasing the angles between donors and acceptors, the triplet energies of the materials were gradually increased from 2.5 to 3.0 eV. Three exciplex-based organic light-emitting diodes containing one of the synthesized compounds were fabricated, which exhibited efficient blue, green-yellow, and white thermally activated delayed fluorescence. Blue and green-yellow organic light-emitting diodes exhibited the maximum external quantum efficiencies of 9.1% and 8.3%, respectively. White organic light-emitting diodes showed turn-on voltage of 4.8 V, high maximum luminance of 18474 cdm-2, and maximum external quantum efficiency of 10.6%. Maximum external quantum efficiencies of blue and white organic light-emitting diodes were close to the record values observed for all-exciplex-based blue and white organic light-emitting diodes.
关键词： full-TADF-based,exciplex-based,High triplet energy materials,white OLEDs
更新于2025-09-19 17:13:59
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Recent advances in thermally activated delayed fluorescence for white OLEDs applications
摘要： Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons without utilizing any noble metals to emit light, are becoming the key cornerstone for developing the next generation of organic light-emitting diode (OLED) devices. In recent years, TADF materials are attracting numerous attentions as a new surge of research focuses on both science and industry owing to their high efficiency, low power consumption, and low production cost attributes when applied to white OLEDs. The design and application of TADF in WOLED devices have also experienced the rapid development in fundamental science and industrial technology perspectives. In the present review, the specific reverse intersystem crossing mechanism and evolution of TADF is outlined firstly, and then the latest research progress of TADF-WOLEDs is summarized and discussed. TADF/conventional fluorescence, TADF/phosphorescence, all TADF and TADF exciplex-based WOLEDs are categorized and elaborated in terms of the device structure, working mechanism, efficiency, color-rendering index, etc. Finally, we conclude with the future challenges and opportunities in high-quality TADF devices and application area.
关键词： Thermally activated delayed fluorescence,exciplex,OLED,TADF,RISC,white OLEDs,organic light-emitting diode,reverse intersystem crossing
更新于2025-09-19 17:13:59