Color‐Fidelity Stepwise Charge‐Transfer Modulation Enables Highly Efficient BT.2020‐Compliant Deep‐Blue OLEDs

ABSTRACT Achieving deep‐blue organic emitters that combine high efficiency with the strict color purity required for the BT.2020 display standard remains one of the most persistent challenges in organic electronics. A key limitation arises from the difficulty of reconciling narrow emission with efficient harvesting of both singlet and triplet excitons. Here, we introduce a color‐fidelity stepwise charge‐transfer modulation strategy sequentially strengthens short‐range and long‐range charge‐transfer pathways, suppresses vibrational coupling to narrow the emission spectrum, and simultaneously reduces the singlet–triplet energy gap while enhancing spin–orbit interactions to accelerate the spin‐flip process. Guided by this design principle, the optimized emitter ( BOCz‐CzPO ) achieves a markedly increased reverse intersystem crossing rate (12.5 × 10 3 s −1 ) and a near unity photoluminescence quantum yield. When incorporated into organic light‐emitting diodes, BOCz‐CzPO delivers one of the highest external quantum efficiencies (28.0%) among deep‐blue OLEDs based on mono‐boron MR frameworks with CIE y values close to the BT.2020 target, exhibiting Commission Internationale de l’Éclairage chromaticity coordinates of (0.146, 0.052) and approaching the BT.2020 deep‐blue specification.