Molecular oreintation of host mateirals for high-efficiency phosphorescent organic light-emiting diodes

Abstract

We investigated the vacuum-processed phosphorescent organic light-emitting diodes (PHOLEDs) characteristics using the diphenylbis(3-(pyridine-2-yl)phenyl)silane (2PTPS), diphenylbis(3-(pyridine-3-yl)phenyl)silane (3PTPS), and diphenylbis(3-(pyridine-4-yl)phenyl)silane (4PTPS) host materials. The 4PTPS-based PHOLEDs with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant with homoleptic-structure showed highest current efficiency of 53.54 cd/A compared to those of 2PTPS (40.75 cd/A) and 3PTPS (29.35 cd/A). This result has caused by the well-aligned structure with preferential horizontal orientation of the emitting materials by two-dimensional grazing incidence X-ray diffraction (2D-GIXD) analysis. We found that the molecular orientation of 4PTPS-based co-host and co-host:dopant showed better priority to the horizontal direction than the 2PTPS and 3PTPTS host materials, which implies the importance of preferential orientation of the host molecule.