Optimization of emitting efficiency in organic LED cells using Ir complex

Multilayer organic light-emitting devices (C,LED) with phosphorescent guest emitter, tris(2-phenylpyridine) iridium doped in a host 4,4 ' -N,N ' -dicarbazol-biphenyl layer, were prepared. We optimized the cell structure paying special attention to the multiple reflection at the multilayers' interfaces and succeeded in improving the luminance efficiency. Our method consists of adjusting optical distances between emission sites and dominant reflective surfaces, organic/cathode and ITO/glass interfaces. The device with the 8.7 wt.% guest emitter exhibited external quantum efficiency and power luminous efficiency of 14.9% and 43.4 lm/W: respectively at the luminance of 100 cd/m(2) driven at the voltage of 4.2 V. In addition, we investigated the emission site in the electrophosphorescent cells and recalculated the external quantum efficiency by the actual emission pattern. (C) 2001 Elsevier Science B.V. All rights reserved.