Understanding of Degradation Mechanism by Exciton Dynamics and Enhancement of Operational Lifetime by Exciton Management in Blue Fluorescent OLEDs Based on Hybridized Local and Charge‐Transfer Molecule

Abstract The operational lifetime of blue organic light‐emitting diodes (OLEDs) is still insufficient for practical applications in lighting and display. One type of blue organic emitting materials with hybridized local and charge‐transfer (HLCT) process are beneficial in achieving high‐efficiency OLEDs through “hot exciton” channel by harnessing high‐lying triplet (T_n) excitons. However, the operational lifetime of the resulting blue OLEDs is rarely studied and understood. In this article, the aging properties of blue fluorescent OLEDs based on an HLCT material (2‐(4‐(10‐(3‐(9H‐carbazol‐9‐yl)phenyl)anthracen‐9‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole) (PAC) are systematically investigated by exciton dynamics calculation and transient EL experiments. It is experimentally and theoretically revealed that whether the reverse intersystem crossing (hRISC) process from high‐lying excited triplet to singlet in HLCT materials is completely effective determines the device degradation. A fluorescent emitter is doped into PAC host to accelerate the hRISC process, thus enhancing device operational lifetime to reach T₇₅ = 110 ± 2 h (time to 75% of initial luminance) under 1000 cd m⁻². This work provides inspirations to investigate the stability of blue fluorescent OLEDs based on HCLT materials and further enhance the operational lifetime.