Organic electroluminescent devices using organosilicon polymers containing phenylene or diethynylanthracene units

Abstract

Double-layer electroluminescent (EL) devices composed of an alternating polymer with mono-, di-, or tri-silanylene and phenylene units, [(Si R) m (C 6 H 4 )] n (R = alkyl, m = 1-3) as a hole-transporting layer, and tris(8-quinolinolato) aluminium(III) complex (Alq) as an electron-transporting-emitting layer were fabricated. The longer silanylene chain lengths in the polymer, on going from m = 1 to m = 2 and 3, result in better electrical properties for the EL devices, implying that the σ-π conjugation in the polymers plays an important role in the hole-transporting properties, including the hole-injection efficiency from an anode. This is in marked contrast to the improved hole-transporting properties that occur in response to reducing the silanylene chain length of silanylene-diethynylanthracene polymers previously reported. The UV absorption maxima of silanylene-phenylene polymers shift to longer wavelengths with increasing m, and their oxidation peak potentials in cyclic voltammograms shift to lower potential with increasing m, in accordance with the improved electrical properties of the device that are observed with the polymers containing the longer silanylene chain. A triple-layer EL device with a hole-transporting layer of monosilanylene-diethynylanthracene polymer, an electron-transporting-emitting layer of Alq, and an electron-blocking layer of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) exhibited a maximum efficiency of 1.0 lm W -1 and a maximum luminance of 14750 cd m -2 , both of which are much higher than the values obtained from a conventional EL device with TPD/Alq.