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

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 T-75 = 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.