Effective Energy Transfer for Green, Orange, and Red Phosphorescent Organic Light‐Emitting Diodes Based on a Bipolar Deep‐Blue Emitter with Low Efficiency Roll‐Off at High Brightness

Of paramount significance in phosphorescent organic light-emitting diodes (PHOLEDs) are the facts that Forster resonance energy transfer (FRET) must be sufficient and back energy transfer should be prohibited. Herein, the FRET efficiencies for high-performance PHOLEDs based on a simple bipolar luminogen 1-phenyl-2-(5 '-phenyl-[1,1 ':3 ',1 ''-terphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (PHT-PPI) with high triplet energy of 2.44eV are systematically investigated. As a result, with PO-01 as dopant, the high-performance orange PHOLED is achieved with maximum external quantum efficiency (EQE(max)) of 26.14% and ultrahigh brightness of 152000cdm(-2), which are the highest reported efficiencies for orange OLEDs with such high brightness. In addition, the green and red PHOLEDs are also fabricated with EQE(max) of 15.38% and 16.12%, respectively. Furthermore, the nondoped device based on PHT-PPI as a deep-blue emitter is also obtained with an EQE(max) of 5.12% and the Commission Internationale de L'Eclairage (CIE) index of (0.15, 0.08). More importantly, the blue, green, orange, and red devices exhibit low efficiency roll-off, particularly, of which the orange PHOLED is extremely small (<9%) even at the brightness of 10000cdm(-2).