三合一：基于荧光敏化原理构筑的高激子利用率三元共混发光层及器件应用研究

The design of the light-emitting layer and the utilization of excitons are two of the key fundamental issues in improving the electroluminescent performances of organic light-emitting devices (OLEDs). The developments of fluorescence, phosphorescence, and the very recently reported thermally activated delayed fluorescence (TADF) materials and the related OLEDs are basically referred to the above-mentioned topics. In order to develop highly efficient, easy-processed, bright and novel OLEDs and make them feasible for mass production, it is essential to construct the highly cost-effective light-emitting layers (EMLs). In this regard, we propose to introduce the principle of fluorescence sensitization to improve the exciton utilization efficiency (EUE) by means of the combination of high quantum yield TADF molecule as the sensitizer, excellent charge carrier transporting host to confine the excitons, and the chemically stable emitters to harvest all of the electrically generated excitons. To further unveil the mechanism of TADF molecules as the fluorescence sensitizers, we dedicate to figure out the relationships among the sensitizer, the host and the emitter. Consequently, it is feasible to demonstrate efficient EMLs with nearly 100% quantum yield and nearly 100% EUE in simplified OLEDs respectively with fluorescence, phosphorescence, and TADF emitters. By refraining the non-radiative channels, triplet-triplet annihilation, and triplet-polaron quenching effects investigated via the electric field induced fluorescence quenching experiments, it is promising to achieve minimal efficiency roll-offs of TADF sensitized OLEDs at high brightness. Eventually, this investigation should provide theoretical and experimental guidelines for developing novel organic light-emitting materials and devices.

发光层的设计及激子的利用是提高有机电致发光器件（OLED）性能的关键的科学问题。从荧光、磷光到热激活延迟荧光（TADF）材料和器件的发展都是围绕这一科学问题展开的，本项目旨在利用荧光敏化原理，围绕提高发光层的激子利用率的基本点，以高荧光量子效率的TADF材料作为敏化剂、结合电学传输性能优良的主体和结构稳定的发光分子来高效利用单线态和三线态激子，构筑结构和工艺简化、发光效率高的的器件。通过研究敏化剂对发光层光电性能的影响，摸索材料配伍的一般规律，实现发光层接近100%的内量子效率；通过抑制非辐射复合通道、三线态-三线态湮灭、三线态-极化子淬灭等机制，可以分别提高荧光、磷光、TADF等发光分子的辐射复合几率，实现近100%的激子利用率；研究电场诱导荧光淬灭和激子损耗途径，辅助各个功能材料的优选，实现基于TADF敏化剂的器件在高亮度下较低的效率滚降，为开发新型的发光材料和器件奠定理论和实验基础。

发光层的设计及激子的利用是提高OLED性能的关键科学问题，目前已知的大部分有机发光材料和器件的发展都是围绕这一科学问题展开的。本项目利用荧光敏化原理，围绕提高发光层的激子利用率，以高荧光量子效率的热激活延迟荧光（TADF）材料作为敏化剂、能级匹配的主体、新型发光分子来高效利用单线态和三线态激子，构筑三元共混的简化结构，实现了一系列发光效率高、激子利用率甚至接近100%的器件。通过研究TADF敏化剂对发光层光电性能改善的协同作用，摸索出一系列材料配伍的一般规律，通过抑制非辐射复合通道分别提高荧光、磷光、TADF等发光分子的辐射复合几率；另外，从改善色纯度的角度出发，同时兼顾能量传递效率，阐明高效的TADF敏化剂的发光光谱不仅要与发光分子的吸收光谱有较好的重叠，而且敏化剂的发光光谱须跟客体分子发光光谱有一定交叠，以抑制敏化剂的残余发光。另外，选用激子寿命短的敏化剂，可有效提高发光亮度和改善效率滚降。综上，藉由本研究开展，解释了TADF敏化剂具有多重协同作用机制，为高性能OLED材料设计和器件构筑提供了重要参考依据。