Blocking exciton-quenching pathways in host and guest interfaces for high performance solution-processed TADF OLEDs with external quantum efficiency approaching 25%

摘要

Although doping system can effectively reduce the concentration quenching of thermally activated delayed fluorescence emitter, the inevitable collision between host and guest may be other energy leakage pathways, which are usually ignored in the previous studies. Here, a new encapsulated molecule Cz-4CzIPN with TADF emissive core and steric shield is conveniently synthesized and fully characterized. The TADF property ensures the efficient triplet exciton utilization, while the encapsulated feature endows the adjacent molecules a big steric bulk to reduce exciton quenching. By using the encapsulated TADF materials as both host and guest, solution-processed TADF OLEDs achieved the maximum external quantum efficiency (EQE) as high as 24.3%, which is among the best results for solution-processed TADF OLEDs reported so far. However, removing any protection of host or guest, the device efficiency will be accordingly reduced. Particularly, when the host and guest are both unencapsulated, the device can only exhibits the EQE_(max) of 8.0%, which indicates the existence of severe exciton quenching process. This research demonstrates the molecular interface engineering is a promising strategy for blocking the exciton quenching pathways of the solution-processed doping system by suppressing the intermo-lecular interaction.