Hybrid Multi-Resonance Thermally Activated Delayed Fluorescent Emitters with High Efficiency and High Color Purity

Highly efficient blue organic light-emitting diodes (OLEDs) generally exhibit inferior color purity or large full width at half maximum (FWHM). Therefore, emitting materials with simultaneously high efficiency and small FWHM in the deep-blue region are challenging to construct. To address this, hybrid multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters are designed by combining boron-based MR-TADF materials, which exhibit small FWHM and high efficiency, with indolo[3,2,1-jk]carbazole (ICz)-based MR-TADF materials, which exhibit high color purity. Two hybrid MR-TADF emitters are synthesized by hybridizing ICz with a boron-based MR-TADF core to prepare deep-blue OLEDs with high efficiency and high color purity. The hybrid MR-TADF emitter exhibits a maximum external quantum efficiency of 28.7% and deep-blue emission at 454 nm with an FWHM of 25 nm, and CIEy of 0.053, nearly satisfying the BT 2020 color standard. The device efficiency achieved in this work is one of the highest values reported for the blue OLEDs with the CIEy close to 0.05.