Highly efficient organic electrophosphorescent light-emitting diodes with a reduced quantum efficiency roll off at large current densities

High efficiency electrophosphorescence (EPH) in organic light-emitting devices was achieved employing a cyclometallated platinum [Pt(II)]-complexes-doped blend of N,N-'-diphenyl-N,N-'-bis(3-methylphenyl)-1,1'-biphenyl-4,4' diamine and bisphenol-A-polycarbonate as the emitting layer. Using bis-[2-(5-trimethylsilanyl-thiophen-2-yl)-pyridine] Pt(II) [Pt(thpy-SiMe3)] as a phosphorescent dopant, a maximum EPH external quantum efficiency of 11.5+/-0.5% photons/carrier was achieved with a three-fold lower roll-off factor at increasing current density, compared with commonly used Pt-based dye 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum (II) (PtOEP). The emission spectrum of the device peaking at congruent to590 nm shifts the chromaticity coordinates toward the orange relative to the PtOEP-based devices. (C) 2004 American Institute of Physics.