Highly efficient and low efficiency roll-off white organic light-emitting diodes based on ultrathin phosphorescent emitters with a deep-blue exciplex host

Achieving high-efficiency white organic light-emitting diodes (WOLEDs) based on simplified architecture with low efficiency roll-off at high luminance remains a challenge. Herein, we manufacture high-efficiency phosphorescent WOLEDs with extremely low roll-off by strategically combining an ultrathin emitting layer (UEML) with a novel deep-blue exciplex host. This architecture significantly suppresses exciton annihilation owing to the expansion of the exciton diffusion region. Meanwhile, the bipolar transport properties of the exciplex host and the UEML design help reduce triplet exciton accumulation by expanding the recombination zone and facilitating free exciton diffusion. The resulting WOLED exhibits the maximum current efficiency (CE) and power efficiency (PE) of 59.5 cd/A and 61.1 lm/W with the Commission Internationale de L’Eclairage (CIE) coordinates variation of (0.002, 0.002) over a wide luminance range. Notably, the CE still retains 57.6 cd/A at 1000 cd/m 2 , corresponding to a roll-off of only 3.2%, which is one of the best performances in phosphorescent WOLEDs based on ultrathin-layer architecture. These results provide an effective approach to construct high-performance WOLEDs.