High‐Performance Narrowband Pure‐Red OLEDs with External Quantum Efficiencies up to 36.1% and Ultralow Efficiency Roll‐Off

Abstract High‐color‐purity blue and green organic light‐emitting diodes (OLEDs) have been resolved thanks to the development of B/N‐based polycyclic multiple resonance (MR) emitters. However, due to the derivatization limit of B/N polycyclic structures, the design of red MR emitters remains challenging. Herein, a series of novel red MR emitters is reported by para ‐positioning N–π–N, O–π–O, B–π–B pairs onto a benzene ring to construct an MR central core. These emitters can be facilely and modularly synthesized, allowing for easy fine‐tuning of emission spectra by peripheral groups. Moreover, these red MR emitters display excellent photophysical properties such as near‐unity photoluminescence quantum yield (PLQY), fast radiative decay rate ( k r ) up to 7.4 × 10 7 s −1 , and most importantly, narrowband emission with full‐width at half‐maximum (FWHM) of 32 nm. Incorporating these MR emitters, pure red OLEDs sensitized by phosphor realize state‐of‐the‐art device performances with external quantum efficiency (EQE) exceeding 36%, ultralow efficiency roll‐off (EQE remains as high as 25.1% at the brightness of 50 000 cd m −2 ), ultrahigh brightness over 130 000 cd m −2 , together with good device lifetime.