Enhancing the stereo structure via bulky peripheral groups to improve resistance to concentration quenching in OLEDs

Abstract

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have attracted widespread attention from researchers in the field of organic light-emitting diodes (OLEDs). However, there remains significant room for improvement regarding the concentration quenching issue in OLEDs. Herein, we report two MR-TADF emitters, DtCzB-mDPA and DtCzB-mDS, based on the boron–nitrogen MR core, which were connected to bulky groups on the periphery of the framework. This strategy successfully enhanced the stereo structure in the molecule. For DtCzB-mDS, the introduction of the methyl(phenyl)sulfane group resulted in a larger dihedral angle and thus stronger concentration quenching resistance, as well as stronger spin–orbit coupling (SOC) compared to DtCzB-mDPA. Finally, OLEDs using DtCzB-mDS as a dopant achieved a 25.4% maximum external quantum efficiency (EQE_max) and a full width at half maximum (FWHM) of 27 nm, while the EQE_max of the DtCzB-mDPA-based device was 23.4%. As the doping concentration increased, the EQE_max of the DtCzB-mDS-based device remained around 24%, while the DtCzB-mDPA-based device saw a significant decrease in EQE_max. This work broadened the MR-TADF material design strategy and provided new ideas for the development of high-performance OLEDs.