Highly efficient yellow phosphorescent organic light-emitting diodes with novel phosphine oxide-based bipolar host materials

Two bipolar host materials, (4-((4-(naphthalen-1-yl(phenyl) amino) naphthalen-1-yl)(phenyl) amino) phenyl)diphenylphosphine oxide (POpN) and (3-((4-(naphthalen-1-yl(phenyl) amino) naphthalen-1-yl)(phenyl) amino)phenyl) diphenylphosphine oxide (POmN), comprising a hole-transporting N-1-(naphthalen-1-yl)-N-1, N-4-diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting phosphine oxide (PO) acceptor at different positions of the phenyl bridge have been synthesized. POpN (glass transition temperature T-g = 119 degrees C) and POmN (T-g = 115 degrees C) exhibit high morphological stability. Two yellow phosphorescent organic light-emitting diodes (PhOLEDs, ITO (indium tin oxide)/TAPC (1,1-bis[4-(dip-tolylamino)phenyl]cyclohexane, 40 nm)/POpN or POmN: Ir(bt)(2)(acac)(bis(2-phenylbenzothiozolato-N,C2')iridium(acetylacetonate), 15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm)) exhibit maximum luminances (Lmax) of 82 057 and 78 385 cd m(-2), maximum current efficiencies (eta(c,max)) of 68.28 and 44.95 cd A(-1), respectively, with low efficiency roll-off.