Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property

Two new blue emitters, i.e., bis-­[2-(9,9-dimethyl-9,10-dihydroacridine)-­phenyl]-­sulfone
(o-ACSO2) and bis-­[3-(9,9-dimethyl-9,10-dihydroacridine)-­phenyl]-­sulfone
(m-ACSO2), with reserved
fine thermally activated delayed fluorescent (TADF) nature and simply
tuned thermal and optoelectronic properties, were synthesized by isomer
engineering. The meta-linking compound, i.e., m-ACSO2, obtains the highest photoluminescence
quantum yield with a small singlet–triplet energy gap, a moderate
delayed fluorescent lifetime, excellent solubility, and neat film
homogeneity. Due to its unique aggregation-induced emission (AIE)
character, neat film-based heterojunction-like organic light-emitting
diodes (OLEDs) are achievable. By inserting an excitonic inert exciton-blocking
layer, the PN heterojunction-like emission accompanied by intefacial
exciplex was shifted to a homojunction-like channel mainly from the
AIE emitter itself, providing a new tactic to generate efficient blue
color from neat films. The solution-processed nondoped sky-blue OLED
employing m-ACSO2 as emitter
with homojunction-like emission achieved a maximum external quantum
efficiency of 17.2%. The design strategies presented herein provide
practical methods to construct efficient blue TADF dyes and realize
high-performance blue TADF devices.

合成两种新型的蓝色发射体，即双-(2-(9,9-二甲基-9,10-二氢蒽)-苯基)-磺酮(o-ACSO2)和双-(3-(9,9-二甲基-9,10-二氢蒽)-苯基)-磺酮(m-ACSO2)，这两种发射体保留了优异的热激活延迟荧光(TADF)特性，并具有易于调节的热学和光电子性质。通过同分异构工程合成的方法，m-ACSO2这种元连接化合物达到了最高的光致发光量子产率，其单重态-三重态能隙较小，延迟荧光寿命适中，溶解度优异，且薄膜均匀性良好。由于其独特的聚集诱导发光(AIE)特性，可制备基于纯净薄膜的异质结类似有机发光二极管(OLED)。通过插入一种激子惰性激子阻隔层，PN异质结类似的发射伴随界面激基复合物被转移到主要由AIE发射体本身主导的同质结类似通道，从而提供了一种从纯净薄膜中生成高效蓝色光的新策略。采用m-ACSO2作为发射体，并具有同质结类似发射的溶液处理非掺杂天蓝色OLED实现了17.2%的最大外部量子效率。本文提出的设计策略为构建高效蓝色TADF染料和实现高性能蓝色TADF器件提供了实用的方法。