基于激基复合物的超高效稳定白光器件及界面机理研究

Organic light-emitting diodes (OLEDs) based on exciplex hosts or emitters have aroused much attention recently due to their superior electroluminescence performance. Our preliminary results unveil that OLEDs based on exciplex-forming co-host showed remarkable charge transport properties, lower driving voltage and much higher device efficiency than those of using conventional host materials. Benefiting from the intermolecular donor-acceptor (D-A) construction and sufficiently small singlet-triplet (S1-T1) splitting ΔEST (< 0.1 eV) in the exciplex system, the exciplex based OLEDs exhibit thermally activated delayed fluorescent (TADF) characteristics which would result in an internal quantum efficiency of 100%. However, their working mechanisms are still unclear and rarely reported. In this project, we will deeply investigate the mechanisms of exciplex-based OLEDs and then make use of these findings to design more D-A pairs with the ultimate targets to achieve high-efficiency and color-stable white OLEDs with a power efficiency of greater than 100 lm/W, C.I.E. (x,y) of (0.35-0.40, 0.38-0.43) and extremely reduced efficiency roll-off of less than15% when the brightness is increased from 100 to 5000 cd/m2. With further optimization of the device structures, we will also explore highly stable exciplex-based white OLEDs with a T50 lifetime of longer than 2500 hours (at an initial luminance of 1000 cd/m2).

近年来，使用激基复合物作为主体或者发光体引起了OLED领域专家们的关注，掀起了一阵研究的热潮。据我们调查研究表明，基于激基复合物主体的OLED器件可以获得比传统主体更好的器件性能，他具有优秀的空穴传输能力和电子传输能力，可以拥有超低的工作电压，达到节约能源的效果。在拥有超低电压的同时，它能够依旧保持、甚至达到更高的器件效率。与传统主体相比，激基复合物主体作为新型的OLED器件结构，本身就具备了热激活延迟荧光的效应，可以有效的同时利用单线态激子与三线态激子，实现100%的内量子效率。本项目将致力于深入探究激基复合物形成的机理与条件，进一步设计和选择优秀的激基复合物组合，制备出功效超过100 lm/W的白光器件。同时，对激基复合物做主体的器件结构进行优化和改进，力求控制单色光的器件效率滚降在10%以内（亮度从100 cd/m2-5000 cd/m2），提高基于激基复合物的OLED器件的效率。

本项目首先设计并优化了两种新型激基复合物组合：Trz-PhCz：B4PyMPM和mCBP：B4PyMPM，对比传统激基复合物，在开启电压、功效、稳定性等多个方面，这两者均体现出优秀的性能，在探索过程中，我们获得了大量激基复合物机理，可用于指导高效激基复合物主体设计与应用。我们首先制备了蓝、绿、黄、橙和红光等单色光OLED，器件EQE分别达到了26.3%，25.0%，30.7%，32.5%和26.2%，器件开启电压均在2.2-2.5 V之间，验证了理论的可行性。基于此，我们以双发光层结构制备了WOLED，通过调控发光层之间的间隔层探索了发光单元之间的能量传递机制，最终获得了36.9%的最大EQE、137.4 lm/W的最大PE，且器件的滚降仅5.4%（@1000 cd/m2），展现出超高的稳定性。随后，我们配合叠层结构、自主研发的内外光提取手段、封装技术，在大面积（10*10 cm2）的基板上获得了足够满足照明需要的器件，拥有高达126.2%的EQE和150.7 lm/W的PE，器件T50寿命高达12,600小时（@15,000 cd/m2）。同样结构的小型器件，功效为173.7 lm/W（@1000 cd/m2），滚降小于15%，C.I.E.坐标（0.36，0.43），显色指数88。