High-Efficient Tetrahedral Silicon-Based Organic Light-Emitting Diodes

Abstract

The co-host materials composed with hole transporting and electron transporting materials have been investigating, due to their advantages for high efficiency by balanced charge carriers in organic light-emitting diodes (OLEDs). Tetrahedral silicon-based hosts of 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) have been used as electron-transporting host materials in phosphorescent OLEDs (PHOLEDs). The 4PTPS-based OLEDs with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant showed highest current efficiency and external quantum efficiency of 53.54 cd/A and 15.61 %, compared to those of 2PTPS (40.75 cd/A, 11.84 %) and 3PTPS (29.35 cd/A, 8.54 %). These results are attributed to the well-aligned structure with preferential horizontal orientation of the emitting material layer by the diffraction intensity distribution as a function of azimuthal angle in two-dimensional grazing incidence X-ray diffraction analysis. The Ir(ppy)3 and Firpic-doped 4PTPS devices with preferential horizontal orientation showed high efficiency due to balanced hole and electron recombination in the emitting material layer with the well-aligned stacking structure to the horizontal direction, which can contribute to the useful molecule design of emitting materials.