Mimicked Host-Dopant System Using Exciplexes in the Organic Light-Emitting Diodes

The host-dopant system in the conventional light-emitting layer of organic light-emitting diodes (OLEDs) was mimicked using exciplexes made up of a bipolar material and a p-type material for high-efficiency exciplex OLEDs. The ratio of the p-type material was kept between 5 and 50% to mimic the host-dopant system. The bipolar material played the role of a host and the exciplex between the bipolar material and p-type material acted like a dopant dispersed in the host. A series of bipolar materials and p-type materials were combined to study the key factors for efficient exciplex emission in the mimicked host-dopant exciplex system. The changes in the photoluminescence quantum yield (PLQY) and external quantum efficiency (EQE) according to the p-type material content relied on the energy level offset of the two components in the exciplexes. The exciplexes with large energy level offset showed the highest PLQY and EQE at 5% p-type material content, while the exciplexes with small energy level offset offered the best PLQY and EQE at 10 or 20% p-type material content. Although the optimum exciplex composition depended on the energy level offset of the exciplexes, the EQE was dramatically enhanced in the exciplex with low p-type material contents by mimicking the host-dopant system in the exciplex. A schematic model was proposed to explain the enhanced EQE and different optimum p-type material contents depending on the energy level offset.