Dibenzofuran‐Modulated Narrowband Red MR‐TADF Emitters for BT.2020 OLEDs With Ultralow Roll‐Off and Long Lifetime

Achieving high efficiency, long operational stability, and narrowband pure‐red emission through rational molecular design remains a critical challenge for next‐generation ultrahigh‐definition displays. Here, we present an integrated materials‐to‐device strategy enabling narrowband, high‐efficiency red multi‐resonance thermally activated delayed fluorescence (MR‐TADF) organic light‐emitting diodes (OLEDs) with suppressed roll‐off and extended operational lifetime. Three boron–nitrogen–oxygen (BNO)‐fused emitters—4BPBNO, 3DBFBNO, and 2DBFBNO—were rationally designed by modulating multi‐resonance pathways and incorporating dibenzofuran (DBF) units. The rigidified π‐framework suppresses vibronically active C–C stretching modes, enabling precise color tuning while preserving MR character and high photoluminescence quantum yield (PLQY). As a result, 3DBFBNO exhibits red emission with a peak wavelength of 613 nm and a narrow full width at half maximum (FWHM) of 32 nm. To overcome the intrinsic roll‐off of MR‐TADF systems, an exciplex‐assisted phosphorescent‐sensitized fluorescence (Ex‐PSF) architecture was employed. The 3DBFBNO optimized device achieved a peak external quantum efficiency of 31.6%, <1% roll‐off at 5000 cd m −2 , and LT 90 of 571 h @ 5000 cd m −2 , representing a 13‐fold lifetime enhancement over single‐host devices. Additionally, an optical‐cavity‐engineered top‐emission OLED incorporating 3DBFBNO further achieved 619 nm emission, 23 nm FWHM, along with CIE coordinates of (0.68, 0.32), approaching BT.2020 requirements.