High performance semitransparent phosphorescent white organic light emitting diodes with bi-directional and symmetrical illumination

Abstract

A semitransparent white organic light-emitting diode (WOLED) is produced based on a blue phosphorescence from iridium(III)[bis(4,6-difuorophenyl)-pyridinato-N,C2] picolinate and an orange phosphorescence from bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3) iridium(acetylacetonate). In this work, a hole-transporting layer of N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPB) and an electron-transporting layer of 3,5,3″,5″-tetra-3-pyridyl-[1,1′;3′,1″] terphenyl (B3PyPB) were used. B3PyPB has high electron mobility and a high triplet energy level. The use of B3PyPB helps to reduce the triplet quenching and also to confine the charge recombination in the emissive region of a single-host two-color WOLED. A bi-layer Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and a cathode of Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) were employed. The semitransparent WOLEDs thus developed have perfect symmetrical, bi-directional illumination characteristics, and the weak angular dependent EL emission spectra, which are beneficial for application in planar diffused lighting.