Steric groups fusion strategy for green multi-resonance emitters toward efficient OLEDs with narrowband emission

Multi-resonance induced thermally activated delayed fluorescence (MR-TADF) emitters have demonstrated significant advantages in high-efficient organic light-emitting diodes (OLEDs) with wide color gamut due to their high photoluminescence quantum yields (ΦPL) and narrow spectra. Herein, two novel green MR-TADF emitters, MFCzBN and SFCzBN, were designed and synthesized by integrating steric groups into the classic framework of BNCz. These emitters exhibited narrowband green emission both in solution and films, fast radiative decay rates of approximately 108 s−1, as well as high ΦPL values of up to 90%. The fabricated vacuum-deposited OLEDs displayed bright green emission at 508 nm, achieving remarkable maximum external quantum efficiencies (EQEmax) of 24.3% and 24.7% for MFCzBN and SFCzBN, respectively. Notably, the MFCzBN-based device demonstrated low efficiency roll-off values of 1.6% and 2.5% at practical luminance of 100 cd m−2 and 1000 cd m−2. This work presents an effective strategy for attaining high-efficiency MR-OLEDs through the fusion of steric groups.