High efficiency blue PhOLEDs using spiro-annulated triphenylamine/fluorene hybrids as host materials with high triplet energy, high HOMO level and high Tg

Abstract

Two spiro-annulated triphenylamine/fluorene oligomers, namely 4′-(9,9′-spirobifluoren-4-yl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (NSF-SF), and 4,4′-di(spiro(triphenylamine-9,9′-fluorene)-2-yl)-spiro(triphenylamine-9,9′-fluorene) (NSF-NSF), are designed and synthesized. Their thermal, electrochemical and photophysical properties were investigated. The introduction of spiro-annulated triphenylamine moieties assurances the high HOMO energy levels of NSF-NSF and NSF-SF at −5.31eV and −5.33eV, respectively, which accordingly facilitates the hole injection from nearby hole-transporting layer. Meanwhile, the perpendicular arrangement of the spiro-conformation and the full ortho-linkage effectively prevents the extension of the π-conjugation and consequently guarantees their high triplet energies of 2.83eV. Phosphorescent organic light-emitting devices (PhOLEDs) with the configurations of ITO/MoO3/TAPC/EML/TmPyPB/LiF/Al were fabricated by using the two compounds as host materials and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) picolate (FIrpic) as the dopant. The turn-on voltage of the device B based on NSF-NSF was 2.8V. Simultaneously, the device exhibited excellent performance with the maximum current efficiency of 41cdA−1, the maximum power efficiency of 42lmW−1 and the maximum external quantum efficiency (EQE) of 19.1%. At a high brightness of 1000cdm−2, the device remained EQE of 16.2% and the roll-off value of external quantum efficiency is 15%.