High performance pure blue organic fluorescent electroluminescent devices by utilizing a traditional electron transport material as the emitter
In this work, we demonstrated a novel device design strategy to obtain efficient pure blue organic fluorescent electroluminescent (EL) devices by doping a traditional electron transport material, 9,10-bis[4-(6-methylbenzothiazol-2-yl)phenyl]anthracene (DBzA), into a hole transporting host material, 4,4′,4′′-tris(carbazol-9-yl)-triphenylamine (TcTa), as the light-emitting layer (EML). Here, DBzA functions not only as a blue emitter but also as an electron transport material. Due to the well matched energy levels of DBzA and TcTa, the obtained devices displayed a broadened recombination zone, improved trapping of carriers, and balanced distribution of holes and electrons on emitter molecules. Interestingly, a single-EML device displayed higher EL efficiencies and lower operation voltage than those of a double-EML device. Finally, a pure blue EL device (Commission Internationale de l'Eclairage (CIE) coordinates of (0.141, 0.165)) with maximum brightness, current efficiency, power efficiency and external quantum efficiency (EQE) of up to 10384 cd m−2, 6.41 cd A−1, 6.71 lm W−1, and 4.3%, respectively, was realized by optimizing the doping concentration. Even at a certain brightness of 1000 cd m−2, current efficiency as high as 4.1 cd A−1 (EQE = 2.8%) can be retained by the same device.