Spiro-Fluorene Locked Multi-Resonance Emitters Enabling High-Performance Pure-Green OLEDs With CIEy Coordinate of...

Pure-green organic emitters compliant with the Broadcast Television 2020 (BT.2020) green standard are critical for ultra-high-definition (UHD) organic light-emitting diodes (OLEDs). Herein, we propose a simple yet effective spiro-fluorene locking strategy to develop two pure-green multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, namely DBN-MS and DBN-TMS. The introduction of the spiro-fluorene units not only extend π-conjugation to redshift emission to 512-513 nm but also enhance molecular planarity and rigidity, suppressing vibrational relaxation and enabling ultra-narrow full-width at half-maximum (FWHM = 16 nm) in toluene. Notably, DBN-MS maintains stable emission profile (λ_em = 518-520 nm, FWHM = 19-20 nm) across a broad doping concentration range (1-10 wt%), effectively mitigating spectral broadening and aggregation-caused quenching. Non-sensitized OLEDs exhibit a maximum external quantum efficiency (EQE) of 35.5%, low efficiency roll-off with an EQE value of 26.9% at 1000 cd m^-2, and remarkable operational stability with lifetime (LT₉₀) of 167 h in a stable device structure. More importantly, the state-of-the-art CIEy coordinates of 0.76-0.77 are demonstrated over 1-10 wt% broad doping range, representing the first bottom-emitting green OLED with a CIEy value reaching 0.77, and the closest to the BT.2020 green standard reported to date.