Sterically shielded multi-resonance emitter via peripheral engineering for narrowband blue OLEDs with high efficiency and high color purity

Abstract

Indolo[3,2,1-jk]carbazole (ICz) based multi-resonance (MR) emitters hold great promise in the blue organic light-emitting diodes (OLEDs) for their superb narrowband emission, but the device performance is till limited by the severe aggregation-caused issues and excessively large energy gap. In this work, the peripheral engineering strategy is introduced to modulate the emission color and suppress molecular aggregation in ICz-MR emitters. The proof-of-concept emitters display a blue narrowband emission with red-shifted peak, extremely small full-width-at-half-maximum (FWHM) and near-unity photoluminescent quantum yield. Benefiting from the steric hindrance imparted by peripheral substituents, both target ICz-MR emitters exhibit enhanced aggregation resistance in the doped films, leading to basically consistent emissive properties over the practical mass-production concentration range (1 wt%–4 wt%). Consequently, the resulting OLEDs achieve ultra-narrowband blue electroluminescence with a peak of 457 nm and a small FWHM of 14 nm, corresponding to the CIE coordinates of (0.137, 0.078). Of particular note, high external quantum efficiencies (EQEs) of up to 10.4% and 17.8% are demonstrated for the target ICz-MR emitters in single- and two-stack devices, representing state-of-the-art performance for blue OLED based on the triplet-triplet annihilation host.