Dibenzo[,]furan and dibenzo[,]thiophene molecular dimers as hole blocking materials for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes

Novel hole blocking materials (HBMs) based on dibenzo[ b , d ]furan and dibenzo[ b , d ]thiophene molecular dimers have been rationally designed and synthesized for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes (PhOLEDs). Thermal, optical, and electrochemical analyses show that [2,2′-bidibenzo[ b , d ]furan]-6,6′-diylbis(diphenylphosphine oxide) ( DBF-d-PO ), [2,2′-bidibenzo[ b , d ]thiophene]-6,6′-diylbis(diphenylphosphine oxide) ( DBT-d-PO ), 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[ b , d ]furan ( DBF-d-Py ), and 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[ b , d ]thiophene ( DBT-d-Py ) possess high thermal stability, deep highest occupied molecular orbital energy levels (−6.61 to −6.95 eV), and high triplet energy ( E T ) (2.68-2.95 eV). Blue PhOLEDs with DBF-d-PO , DBT-d-PO , DBF-d-Py , and DBT-d-Py exhibit low turn-on and operating voltages, excellent external quantum efficiency, and high current and power efficiencies. A blue PhOLED with DBF-d-Py shows the best efficiency with a maximum external quantum efficiency of 24.3%, a maximum current efficiency of 44.3 cd A −1 , and a maximum power efficiency of 46.4 lm W −1 . In addition, it exhibits an outstanding external quantum efficiency of 22.4% at a practical luminance of 1000 cd m −2 and a very high maximum luminance of 88 953 cd m −2 at 12 V. Furthermore, blue PhOLEDs with DBF-d-Py and DBT-d-Py exhibit highly improved lifetimes compared with the conventional HBM, BmPyPB , because of the efficient hole blocking by the deep HOMO energy level and the high thermal stability stabilizing hole blocking layer morphology. Novel hole blocking materials based on dibenzo[ b , d ]furan and dibenzo[ b , d ]thiophene molecular dimers are synthesized for high-efficiency and long-lived blue phosphorescent OLEDs.