Spiro‐Fluorene Locked Multi‐Resonance Emitters Enabling High‐Performance Pure‐Green OLEDs With CIEy Coordinate of 0.77

Abstract

ABSTRACT 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 (LT 90 ) 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.