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

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 × 10³ 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.