Anthracene-based fluorescent emitters toward superior-efficiency nondoped TTA-OLEDs with deep blue emission and low efficiency roll-off

Three new anthracene-based emitters, 4-(10-(9,9 '-spirobi[fluoren]-2-yl)anthracen-9-yl)benzonitrile (SBFAnCN), 4-(10-(9,9-diphenyl-9H-fluoren-2-yl)anthracen-9-yl)benzonitrile (DPF-AnCN) and 4-(10-(9,9-dimethyl9H-fluoren-2-yl)anthracen-9-yl)benzonitrile (DMF-AnCN) are developed for deep blue organic light-emitting diodes (OLEDs). Their photophysical properties, thermal properties, molecular configurations and device performances have been systematically investigated. As verified by crystallographic study, these anthracene derivatives possess highly twisted configuration, leading to deep-blue light emission by restraining pi-conjugation extension. Furthermore, the difference in the molecular packing manner may influence the photoluminescence quantum yields (PLQYs) in solid state and the proportion of singlet exciton harvested by triplet-triplet annihilation (TTA) process. A nondoped device fabricated using DPF-AnCN as emitter exhibits a maximum external quantum efficiency (EQE) of 7.1% with insignificant efficiency roll-off (6.6%@1000 nit) and Commission Internationale de L'Eclairage (CIE) index of (0.149, 0.104), approaching the standard blue index of the National Television System Committee (NTSC) of (0.14, 0.08). It is demonstrated that TTA is responsible for the excellent electroluminescence (EL) performance. In comparison with doped OLEDs, transient EL decay measurements demonstrate that TTA process is more efficient in the nondoped device. This work would provide an efficient method for designing deep-blue nondoped EL materials.