Deep-blue organic light-emitting diodes for ultrahigh-definition displays

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have emerged as promising candidates for next-generation ultra-high definition displays due to their narrowband emission and triplet-harvesting capability. However, achieving optimal color purity and device efficiency for blue MR-TADF emitters has presented challenges. Here we demonstrate an effective approach to attain superior deep-blue molecules by constructing twisted boron/nitrogen/oxygen embedded higher-order fused-ring frameworks with fully resonating structures. The optimized emitter exhibits high rigidity and minimized bonding/anti-bonding character for ultra-sharp emission, along with near-degenerate singlet and triplet states and large spin-orbit couplings for rapid spin-flip. This combination of features allows our emitter to produce deep-blue emission at 458 nm with an exceptionally narrow full-width at half-maximum (FWHM) of 12 nm in solution, and a reverse intersystem crossing rate constant (kRISC) of 2.60 × 106 s−1, on par with those of heavy-atom-based MR-TADF molecules. The related single unit organic light-emitting diode (OLED) achieves an external quantum efficiency (EQE) of 31.5% at color coordinates of (0.130, 0.050), and sets a new benchmark with its 13 nm FWHM, outperforming conventional light-emitting diodes, perovskite, and quantum-dot devices. Furthermore, the two-unit stacked tandem hyperfluorescence OLED realizes an ultra-high EQE of 74.5% and demonstrates low efficiency roll-off at high luminance. This exceptional performance represents a significant advancement in the quest to balance efficiency and color purity in the deep-blue region, marking an important step toward power-efficient ultrawide color gamut displays.