Highly efficient orange and white organic light-emitting devices based on exciplex-assisted multilayer thermally activated delayed fluorescence sensitization strategy

Achieving highly efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off at high current densities still faces severe challenges. Herein, by employing a new sensitization strategy that cleverly arranges thermally activated delayed fluorescence (TADF) sensitized layers and phosphorescent layers alternately, high-performance orange and white OLEDs are fabricated based on a novel exciplex host. The resulting orange phosphorescent OLED achieves a maximum current efficiency (CE) of 90.6 cd/A, and still maintains at 87.3 cd/A at a luminance of 1000 cd/m². Meanwhile, by further changing the thickness of blue TADF sensitizer, the hybrid white OLED exhibits extremely stable spectrum with a total CIE variation of only (0.003, 0.001) from 1105 cd/m² to 9988 cd/m². Notably, the CE retains 65.6 cd/A at 1000 cd/m², corresponding to only a 2.5 % decrease in CE. These outstanding performances are attributed to the enhanced Förster energy transfer between sensitizer and emitter, thereby effectively alleviating exciton aggregation and annihilation. These results demonstrate that our strategy shows great potential in achieving high-efficiency OLEDs with low efficiency roll-off.