Unraveling the Important Role of High-Lying Triplet-Lowest Excited Singlet Transitions in Achieving Highly Efficient Deep-Blue AIE-Based OLEDs

作者：Guo, Xiaomin; Yuan, Peisen; Fan, Jianzhong; Qiao, Xianfeng^*; Yang, Dezhi; Dai, Yanfeng; Sun, Qian; Qin, Anjun; Tang, Ben Zhong^*; Ma, Dongge^*

来源：Advanced Materials, 2021, 33(11): 2006953.

DOI：10.1002/adma.202006953

• aggregation&#8208
• induced emission
• deep&#8208
• blue organic light&#8208
• emitting diodes
• high&#8208
• lying triplet excitons
• magnetic field effect

Aggregation-induced emission (AIE) materials are attractive for achieving highly efficient nondoped organic light-emitting diodes (OLEDs) owing to their strong luminescence in the solid state. However, the electroluminescence efficiency of most AIE-based OLEDs remains low owing to the waste of triplet excitons. Here, using theoretical calculations, photophysical dynamics, and magnetoluminescence measurements, the spin conversion process is demonstrated between the high-lying triplet state (T-n) and the lowest excited singlet state (S-1) in AIE materials. Moreover, the relative positions of T-n (n < 4) and S-1 are shown to have a significant impact on the spin-conversion efficiency, thus influencing the harvesting of triplet excitons and the device efficiency. Finally, by selecting an upconversion material with an appropriate energy level for further utilizing the triplet excitons, a deep-blue fluorescent OLED with CIE coordinates of (0.15, 0.08), a maximum external quantum efficiency of 10.2%, low efficiency roll-off, and a high brightness of 16817 cd m(-2) is developed. This is one of the most efficient deep-blue OLEDs based on AIE materials reported so far. These findings also provide new insights into the design of more efficient AIE molecules and corresponding OLEDs by managing high-lying triplet excitons.