Employing exciton transfer molecules to increase the lifetime of phosphorescent red organic light emitting diodes

The lifetime of phosphorescent red organic light emitting diodes (OLEDs) is investigated employing either N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), TMM117, or 4,4',4 ''-tris(N-carbazolyl)-triphenylamine (TCTA) as hole-conducting host material (mixed with an electron conductor). All OLED (organic vapor phase deposition-processed) show similar efficiencies around 30 lm/W but strongly different lifetimes. Quickly degrading OLED based on TCTA can be stabilized by doping exciton transfer molecules [tris-(phenyl-pyridyl)-Ir (Ir(ppy)(3))] to the emission layer. At a current density of 50 mA/cm(2) (12 800 cd/m(2)), a lifetime of 387 h can be achieved. Employing exciton transfer molecules is suggested to prevent the degradation of the red emission layer in phosphorescent white OLED. (C) 2011 American Institute of Physics. [doi:10.1063/1.3584033]