Interfacial exciplex has recently been adopted as an effective host to achieve phosphorescent organic light-emitting diodes (OLEDs) with high efficiencies and low driving voltages. However, a systematic understanding of exciton recombination behavior in either host of interfacial exciplex is still deficient. Herein, the strategic design rule of interfacial exciplex host is proposed to overcome the negative effects of direct trapping recombination by systematically investigating exciton recombination behavior in interfacial exciplex hosts. As a result, blue and orange phosphorescent devices acquire peak external quantum efficiencies of 23.5% and 29.2% with low turn-on voltages. These results provide a simple method to realize highly efficient OLEDs aiming for general lighting and display applications.
Keywords: exciplex; high efficiency; organic light-emitting diodes; phosphorescence.