High‐Efficiency Narrowband Multi‐Resonance Emitter Fusing Indolocarbazole Donors for BT. 2020 Red Electroluminescence and Ultralong Operation Lifetime

Polycyclic heteroaromatics with multi-resonance (MR) characteristics are attractive materials for narrowband emitters in wide-color-gamut organic light-emitting diodes. However, MR emitters with pure-red colors are still rare and usually exhibit problematic spectral broadening when redshifting emission. Here, a narrowband pure-red MR emitter is reported by fusing indolocarbazole segments into a boron/oxygen-embedded skeleton, realizing BT.2020 red electroluminescence for the first time together with a high efficiency and an ultralong lifetime. The rigid indolocarbazole segment possesses a strong electron-donating ability due to its para-positioned nitrogen-π-nitrogen backbone and also enlarges the π-extension of the MR skeleton to suppress structural displacement during radiation, achieving concurrently redshifted and narrowed emission spectrum. An emission maximum at 637 nm with a full width at half-maxima of merely 32 nm (0.097 eV) is recorded in toluene. The corresponding device simultaneously exhibits CIE coordinates of (0.708, 0.292) precisely matching the BT.2020 red point, a high external quantum efficiency of 34.4% with low roll-off and an ultralong LT95 (time to 95% of the initial luminance) of >10 000 h at 1000 cd m-2 . These performance characteristics are superior even to those of state-of-the-art perovskite and quantum-dot-based devices for this specific color, paving the way toward practical applications.