Highly efficient yellow phosphorescent OLEDs based on two novel bipolar host materials?

New Journal of Chemistry Pub Date: 2015-07-28 DOI: 10.1039/C5NJ00939A

Abstract

Two bipolar host materials, N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONP) and N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(3-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONM), comprising a hole-transporting N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting 1,3,4-oxadiazole (OXD) acceptor at different phenyl bridge positions, have been synthesized. NONP (glass transition temperature Tg = 127 °C) and NONM (Tg = 105 °C) exhibit high morphological stability. The theoretical calculations on both hosts show that the HOMOs (highest occupied molecular orbitals) are mainly dispersed on the electron-donating groups, and the LUMOs (lowest unoccupied molecular orbitals) are predominantly dispersed on the electron-accepting units, suggesting bipolar charge transporting property. Two yellow phosphorescent organic light-emitting diodes (PHOLEDs, ITO (indium tin oxide)/TAPC (1,1-bis[4-(di-p-tolylamino) phenyl]cyclohexane, 40 nm)/host: 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)) fabricated using NONP and NONM as the host and Ir(bt)2(acac) as the emitter exhibit maximum current efficiencies (ηc,max) of 43.2 and 44.4 cd A?1, respectively, with low current efficiency roll-off. The values of 40.4 and 43.6 cd A?1 can still be achieved at the luminance of 3000 cd m?2, respectively.

Graphical abstract: Highly efficient yellow phosphorescent OLEDs based on two novel bipolar host materials
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