Spatial separation of a TADF sensitizer and fluorescent emitter with a core-dendron system to block the energy loss in deep blue organic light-emitting diodes

An optimized, thermally activated delayed fluorescence-(TADF)-sensitized fluorescence (TSF) strategy is proposed to boost the electroluminescence efficiency of solution-processed deep blue organic light-emitting diodes (OLED). The TADF sensitizer and the fluorescent emitter with a core-dendron structure emit mostly by a Forster energy transfer process while the Dexter energy transfer is suppressed by spatial separation. In addition, the high-bandgap carbazole terminal substituents are introduced to protect the hyper-fluorescent core by a cascade energy transfer channel. Fluorescent OLEDs based on a core-dendron system achieved a deep-blue emission with Commission Internationale de L’Eclairage (CIE) coordinates of (0.15,0.14) and a high external quantum efficiency of 10.16%. This new TSF system can be used in high efficiency fluorescent OLEDs with 100% exciton utilization, thereby promoting the development of solution-processed blue OLEDs.