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

Abstract 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 (S₁) in AIE materials. Moreover, the relative positions of T_n (n < 4) and S₁ 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.