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 Förster energy transfer and then the singlet excitons of the fluorescent emitter are harvested by the low energy exciplex through the second Förster 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.

中文翻译：

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级联单重态收获机制在荧光OLED中的高外部量子效率

级联单重态收获（CSH）有机发光二极管（OLED）旨在通过有效地激发荧光体的单重态激子来解决荧光OLED的低量子效率问题。通过在由高能激基复合物和低能激基复合物组成的单重态激子收获基质中掺入荧光发射体来实现CSH机制。高能激基复合物充当发射层的主要成分，而低能激基复合物是收集荧光发射体的单重态激子的介质。两个激基复合物都是热激活的延迟荧光型激基复合物，以通过逆系统间交叉过程有效地收获单重态激子。低能激子的单重态激子通过Förster能量转移被高能激子捕获，然后低能激基通过第二次Förster能量转移过程捕获荧光发射体的单重态激子。CSH机制使荧光发射体中的单线态激子形成最大化，从而显着增强了荧光OLED的外部量子效率（EQE）。发光层结构的优化可在荧光OLED中提供19.9％的高EQE，相比之下，传统的单重态收获荧光OLED的10.4％。这大大提高了荧光OLED的外部量子效率（EQE）。发光层结构的优化可在荧光OLED中提供19.9％的高EQE，相比之下，传统的单重态收获荧光OLED的10.4％。这大大提高了荧光OLED的外部量子效率（EQE）。发光层结构的优化可在荧光OLED中提供19.9％的高EQE，相比之下，传统的单重态收获荧光OLED的10.4％。