Extremely Low Roll-Off and High Efficiency Achieved by Strategic Exciton Management in Organic Light-Emitting Diodes with Simple Ultrathin Emitting Layer Structure.

Phosphorescent organic light-emitting diodes (OLEDs) possess the property of high efficiency but have serious efficiency roll-off at high luminance. Herein, we manufactured high-efficiency phosphorescent OLEDs with extremely low roll-off by effectively locating the ultrathin emitting layer (UEML) away from the high-concentration exciton formation region. The strategic exciton management in this simple UEML architecture greatly suppressed the exciton annihilation due to the expansion of the exciton diffusion region; thus, this efficiency roll-off at high luminance was significantly improved. The resulting green phosphorescent OLEDs exhibited the maximum external quantum efficiency of 25.5%, current efficiency of 98.0 cd A-1, and power efficiency of 85.4 lm W-1 and still had 25.1%, 94.9 cd A-1, and 55.5 lm W-1 at 5000 cd m-2 luminance, and retained 24.3%, 92.7 cd A-1, and 49.3 lm W-1 at 10 000 cd m-2 luminance, respectively. Compared with the usual structures, the improvement demonstrated in this work displays potential value in applications.