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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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Versatile Phosphole Derivatives with Photovoltaic, Light-Emitting, and Resistive Memory Properties
摘要： A series of dithienophosphole compounds has been successfully synthesized and characterized by photophysical, electrochemical, and thermal studies. Possessing the electron-deficient dithienophosphole oxide moiety, these compounds are found to display strong intramolecular charge transfer character and exhibit high photoluminescence quantum yields of up to 0.68. Taking advantage of these phosphole-based the properties, compounds have been applied as active materials in the fabrication of organic photovoltaics (OPVs), organic light-emitting devices (OLEDs) and organic resistive memory devices. Satisfactory performances with power conversion efficiencies of up to 4.23% for OPV devices, external quantum efficiencies of up to 3.0% for OLEDs, and binary resistive memories with retention time of over 10000 s and distinctive OFF/ON current ratio of 1:107 have been realized based on these dithienophosphole compounds. These findings revealed the multifunctional behavior of these dithienophosphole compounds and represent for the first time the use of phosphole-based small molecules as donor materials for the vacuum-deposited OPV devices.
关键词： OPVs,dithienophosphole derivatives,multifunctional materials,resistive memory devices,fluorescent OLEDs,intramolecular charge transfer
更新于2025-09-23 15:19:57
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Asymmetric anthracene derivatives as multifunctional electronic materials for constructing simplified and efficient non-doped homogeneous deep blue fluorescent OLEDs
摘要： Herein, large π-conjugated core anthracene with an innate bipolar property was employed to construct multifunctional organic electronic materials. Delicate manipulating molecules via combining anthracene core and large periphery groups, two asymmetric anthracene derivatives namely (4-(10-(4-(9H-1,5-diazacarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide (p-PO15NCzDPA) and (3-(10-(3-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide (m-PO15NCzDPA) were firstly designed and developed. The large periphery groups 1,5-diazarcarbazole (15NCz) and diphenylphosphine oxide (PO) efficiently interrupt the intramolecular π-conjugation, presenting an asymmetric bulky periphery enveloping strategy achieving highly twisted structures, which help to realize deep-blue emission. Meanwhile, due to the high PLQY and well-balanced bipolar transport characteristics, desired device addressing the contradiction of efficiency, color gamut and structure complexity is within reach. Detailed device engineering study was carried out, in which p-PO15NCzDPA and m-PO15NCzDPA were functioned as multifunction layers. As expected, p-PO15NCzDPA-based homogenous and unilateral homogenous OLEDs exhibited outstanding performance with impressive EQEmax of 4.55% and 6.40%, deep blue CIE coordinates of (0.152, 0.075) and (0.151, 0.066) at the voltage of 6 V, narrow FWHM of 46 nm and 50 nm, respectively. More importantly, the simplified homogenous device achieved extremely low efficiency roll-offs of 1.3% and 4.8% at 1000 and 5000 cd m-2, respectively. These results are among the most outstanding performance, which provided a guide for further improving the performance of deep blue fluorescent OLEDs and simplifying the structure of OLEDs.
关键词： asymmetric anthracene derivatives,homogenous device structure,multifunctional materials,deep-blue emission,fluorescent OLEDs
更新于2025-09-19 17:13:59
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Unveiling the Root Cause of the Efficiency-Lifetime Trade-Off in Blue Fluorescent Organic Light-Emitting Diodes
摘要： The origin of efficiency-lifetime trade-off in triplet–triplet fusion (TTF) type blue fluorescent organic light-emitting diodes (OLEDs) was investigated and the device structure to resolve the issue was developed. The efficiency and lifetime were simultaneously improved in the blue OLEDs by developing a multilayer hole transport stack which can adjust carrier densities and recombination zone in the emitting layer (EML). It was found that electron leakage from EML and high spatial density of excitons in the vicinity of the electron blocking layer for high TTF rates by narrow recombination zone are the detrimental factors for efficiency-lifetime trade-off. A multilayer hole transport stack employing a deep highest occupied molecular orbital hole transport layer and an electron blocking layer combined with an appropriate hole blocking layer simultaneously improved the power efficiency by 16% at 500 cd/m2 and lifetime by almost 100% (from 73 h up to 145 h). In addition, the low efficiency in the low luminance region was also completely controlled, resulting in negligible efficiency variation in the entire luminance range.
关键词： Efficiency-lifetime trade off,Blue fluorescent OLEDs,Triplet–triplet fusion
更新于2025-09-11 14:15:04