Stable Pure-Green Hyperfluorescent Organic Light-Emitting Diodes with Ultimate Efficiency at High Brightness Toward...

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters represent a promising platform for high-efficiency, wide-color-gamut OLEDs. However, current green MR-TADF emitters face challenges in simultaneously achieving high color purity, high efficiency at high brightness, and high device stability. In this study, we report the synthesis and device integration of a novel MR-TADF emitter, DBF-v-DABNA. Designed with a rigid meta-dibenzofuran framework and meta-phenyl related two boron units, the molecule exhibits narrowband pure-green emission (FWHM = 16-19 nm) and a high horizontal dipole ratio (94%). Moreover, sufficient steric shielding of the MR core suppresses exciton loss from Dexter energy transfer (DET). When incorporated into hyperfluorescent (HF) bottom-emitting OLED architectures, DBF-v-DABNA achieved high external quantum efficiencies (EQE) exceeding 35 % with negligible roll-off, CIEy ≥ 0.73, superior brightness stability up to 7.2 × 10⁵ cd m^-2, and device lifetimes exceeding 600 h at 5000 cd m^-2. The top-emitting configuration reached BT.2020 green coordinates with record-setting current efficiency (233 cd A^{- 1}). These results highlight DBF-v-DABNA as a promising pure-green emitter for next-generation UHD OLED displays requiring high efficiency and color purity.