High-Performance Nondoped Blue Delayed Fluorescence Organic Light-Emitting Diodes Featuring Low Driving Voltage and High Brightness

Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light-emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile-based TADF emitters (namely 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile (2PhCz2CzBn) and 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert-butyl group can weaken the intermolecular π–π stacking in the nondoped TADF emitter, and thus significantly suppress self-aggregation-caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn-based nondoped device with an extremely low turn-on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m⁻², a narrow full-width at half-maximum of 70 nm, and CIE color coordinates of (0.167, 0.248).