Fully utilizing exciton for high performance organic light emitting diodes based on exciplex hosts and emitters (Conference Presentation)

Exciplexes formed by intermolecular charge transfer between electron-donating and electron-accepting molecules have attracted much attention because of their triplet harvesting characteristics for highly efficient OLEDs. Similar to thermally activated delayed fluorescence (TADF), exciplex exhibit an extremely small singlet-triplet energy splitting, and allow upconversion from triplet states to singlet states. Here, we will show our recent results on high performance OLEDs based on exciplex hosts and emitters. Phosphorescent white OLEDs with simple structure were successfully fabricated by doping a blue emitter in the exciplex host and then inserting an ultrathin nondoped orange layer within the blue emissive zone. By optimizing the location of the orange emitter, a high power efficiency of 75.3 lm/W was achieved in the phosphorescent white OLED with reduced efficiency roll-off. Hybrid white OLEDs were fabricated by using exciplex as both of the blue fluorescent emitter and the host for phosphorescent emitters. An exciplex-sandwich emissive architecture was designed to precisely manipulate the exciton allocation. And a high external quantum efficiency of 28.3% and a high power efficiency of 102.9 lm/W were realized in the hybrid white OLEDs, which remain as high as 25.8% and 63.5 lm/W at 1000 cd/m2. Most recently, we proposed a method by exciplex engineering to fabricate fluorescent OLEDs with high efficiency and low efficiency roll-off, which could open a useful avenue to design all-fluorescent white OLEDs without TADF emitters for high performance lighting.