Multiple Fusion Strategy for High‐Performance Yellow OLEDs with Full Width at Half Maximums Down to 23 nm and External Quantum Efficiencies up to 37.4%

Abstract The pursuit of ideal narrowband yellow multiple resonance (MR) emitters is hampered by the mutual constraints of effective spectral redshift and maintaining a small full width at half maximum (FWHM) value. Here, a novel multiple fusion molecular design strategy is reported to break this trade‐off. Compared with the selected narrowband parent core, the specific multiple MR effects in target molecules can simultaneously extend the π‐conjugation length, increase the rigidity of the structure, and reduce the vibrational frequency. Proof‐of‐the‐concept emitters BN‐DICz and DBN‐ICz show bright yellowish green to yellow emissions in dilute toluene solutions with peaks at 533–542 nm and extremely small FWHMs of ≤20 nm. Notably, BN‐DICz‐based electroluminescent device exhibits excellent efficiencies of 37.4%, 136.6 cd A −1 , and 119.2 lm W −1 with an FWHM of merely 23 nm, representing the best performance for yellow MR organic light‐emitting diodes.