Wang Jingyu, Yin Jiaxuan, Li Xiaofang, Wang Zhe, Wu Ruixia, Zhou Liang
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei 230027, China.
Molecules. 2022 Oct 14;27(20):6882. doi: 10.3390/molecules27206882.
The low-lying HOMO level of the blue emitter and the interfacial miscibility of organic materials result in inferior hole injection, and long exciton lifetime leads to triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), so the efficiencies of blue phosphorescent organic light-emitting diodes (PhOLEDs) are still unsatisfactory. Herein, we design co-host and co-dopant structures to improve the efficiency of blue PhOLEDs by means of solution processing. TcTa acts as hole transport ladder due to its high-lying HOMO level, and bipolar mCPPO1 helps to balance carriers' distribution and weaken TPA. Besides the efficient FIr6, which acts as the dominant blue dopant, FCNIrPic was introduced as the second dopant, whose higher HOMO level accelerates hole injection and high triplet energy facilitates energy transfer. An interesting phenomenon caused by microcavity effect between anode and cathode was observed. With increasing thickness of ETL, peak position of electroluminescence (EL) spectrum red shifts gradually. Once the thickness of ETL exceeded 140 nm, emission peak blue-shifts went back to its original position. Finally, the maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of blue phosphorescent organic light-emitting diode (PhOLED) went up to 20.47 cd/A, 11.96 lm/W, and 11.62%, respectively.
蓝色发光体较低的最高占据分子轨道（HOMO）能级以及有机材料的界面混溶性导致空穴注入较差，并且激子寿命较长会导致三重态-三重态湮灭（TTA）和三重态-极化子湮灭（TPA），因此蓝色磷光有机发光二极管（PhOLED）的效率仍然不尽人意。在此，我们设计了共主体和共掺杂结构，通过溶液处理来提高蓝色PhOLED的效率。由于其较高的HOMO能级，TcTa充当空穴传输阶梯，双极性的mCPPO1有助于平衡载流子分布并减弱TPA。除了作为主要蓝色掺杂剂的高效FIr6之外，还引入了FCNIrPic作为第二种掺杂剂，其较高的HOMO能级加速空穴注入，并且高三重态能量促进能量转移。观察到阳极和阴极之间的微腔效应引起的一个有趣现象。随着电子传输层（ETL）厚度的增加，电致发光（EL）光谱的峰值位置逐渐红移。一旦ETL的厚度超过140 nm，发射峰蓝移回到其原始位置。最终，蓝色磷光有机发光二极管（PhOLED）的最大电流效率（CE）、功率效率（PE）和外量子效率（EQE）分别提高到20.47 cd/A、11.96 lm/W和11.62%。
