Simultaneous and Significant Improvements in Efficiency and Stability of Deep-Blue Organic Light Emitting Diodes through Friedel-Crafts Arylmethylation of a Fluorophore

The molecular design of purely organic fluorophores for highly efficient and stable deep-blue organic light-emitting diodes (OLEDs) is still a challenge. Excellent performances in terms of Commission Internationale de l'Eclairage (CIE) coordinates, external quantum efficiency (EQE), brightness and lifespan, often cannot be achieved simultaneously in one deep-blue OLED. Herein, a novel carbazole-based thermally activated delayed fluorescence emitter DPFCz-TRZ is designed and synthesized through Friedel-Crafts arylmethylation of Cz-TRZ. Compared with the parent compound Cz-TRZ, the OLED based on DPFCz-TRZ exhibits significantly improved performances with a maximum EQE of 15.5 % and brightness beyond 16000 cd m⁻², while retaining similar deep-blue emission with a CIE coordinate of (0.15, 0.10), an electroluminescence (EL) maximum of λ=445 nm and full width at half maximum (FWHM) of 65 nm. Additionally, the device also shows a respectable lifetime (LT50, time to 50 % of initial luminance) of 78 h at 500 cd m⁻², corresponding to a LT50 of 1304 h at 100 cd m⁻². Impressively, a record high EQE of 5.2 % can be obtained at a very high luminance of 10000 cd m⁻². This work demonstrates the first report of simultaneous achievement over 15 % EQE and 1000 h LT50 (100 cd m⁻²) in deep-blue purely organic electroluminescence devices with a coordinate of (≤0.15, ≤0.10) and maximum brightness beyond 16000 cd m⁻².