Stable Pure‐Green Hyperfluorescent Organic Light‐Emitting Diodes with Ultimate Efficiency at High Brightness Toward Rec 2020 Standard

ABSTRACT 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 × 10 5 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.