High performance doping-free hybrid WOLED utilizing bipolar TADF material as emitters with an ultra-low efficiency roll-off

Abstract

The efficiency roll-off under high brightness is still crucial work for manufacturing high performance white organic light-emitting diodes (WOLEDs). Herein, by inserting ultrathin orange phosphorescent layers in an advisable location between blue bipolar TADF layers, high-efficiency nondoped WOLEDs can be achieved. The device structure is simple, and the efficiency roll-off is reduced. The optimal WOLED showed high power efficiency (PE), external quantum efficiency (EQE), and current efficiency (CE) of 47.4 lm/W, 15.0%, and 46.2 cd/A. At the same time, WOLEDs retained 14.7%, 41.7 lm/W, and 45.8 cd/A at a practical brightness of 1000 cd/m2. WOLEDs show excellent electrical stability, only decreased by 2% from the maximum EQE. In addition, the turn-on voltage is only 2.5 V, and the maximum brightness is 39810 cd/m2. The results demonstrated that the slight efficiency roll-off was attributed to the suppression of exciton quenching and triplet-triplet annihilation (TTA) effect, TADF effect, and bipolar transport characteristics. An actual method was provided to simplify the preparation process and alleviate efficiency roll-off at high brightness.