Fluorescent organic light-emitting diodes (OLEDs) have aroused a lot of attention due to the advantages of lost cost, good operational stability and low efficiency roll-off. However, how to realize high efficiency and long lifetime fluorescent OLEDs simultaneously is still a huge challenge. The use of exciplex and thermally activated delayed fluorescence (TADF) materials as sensitizers for conventional fluorescent emitters is a promising route to improve the efficiency and operational stability of fluorescent OLEDs. Herein, we demonstrate a novel strategy by using a TADF material as sensitizer in exciplex host to realize high efficiency and long lifetime fluorescent OLEDs. The key in our design is the further formation of additional exciplex between TADF sensitizer and electron-acceptor, thus three RISC processes to efficiently convert triplet excitons into singlet excitons by cascaded energy transfer processes. Based on this design strategy, the resulting fluorescent OLEDs achieve the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) of 22.6 cd A⁻¹, 29.5 lm W⁻¹ and 13.0%, and the operational lifetime LT₅₀ (decay to 50% of the initial luminance of 1000 cd m⁻²) reaches 415 h, which are significantly higher than those based on the conventional sensitized methods, fully demonstrating the effectiveness of our design concept to realize higher efficiency and longer lifetime fluorescent OLEDs.

荧光有机发光二极管（OLED）由于具有成本损失，良好的操作稳定性和低效率滚降的优势而引起了很多关注。然而，如何同时实现高效率和长寿命的荧光OLED仍然是一个巨大的挑战。使用激基复合物和热活化延迟荧光（TADF）材料作为常规荧光发射器的敏化剂是提高荧光OLED效率和操作稳定性的有前途的途径。在这里，我们演示了通过使用TADF材料作为激基复合物基质中的敏化剂来实现高效和长寿命荧光OLED的新策略。我们设计的关键是在TADF敏化剂和电子受体之间进一步形成附加的激基复合物，因此，通过级联的能量转移过程可以通过三个RISC过程将三重态激子有效地转化为单重态激子。基于此设计策略，所得荧光OLED达到22.6 cd A的最大电流效率（CE），功率效率（PE）和外部量子效率（EQE）^-1，29.5流明w ^ ^-1和13.0％，而工作寿命LT ₅₀（的为1000cd米的初始亮度衰减到50％^-2）达到415小时，其是显著基于常规方法致敏比更高，充分证明了我们设计理念的有效性，以实现更高的效率和更长的使用寿命的荧光OLED。