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/cm2 (12 800 cd/m2), 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.

Articles you may be interested inDistinguishing triplet energy transfer and trap-assisted recombination in multi-color organic light-emitting diode with an ultrathin phosphorescent emissive layer

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Abstract. Organic light-emitting diodes (OLEDs) are a key technology in solid state lighting. Without a long-lived phosphorescent blue emitter, a hybrid concept based on phosphorescent red and green emitters and a fluorescent blue emitter in a white OLED stack is a promising approach for pure-white emission. Several challenges such as exciton recombination on all emitters and triplet diffusion, as well as quenching, have to be overcome. To address these issues, a mixed-host phosphorescent emission layer is employed. The mixture ratio is locally varied in the emission layer. An interlayer separates the phosphorescent and fluorescent emission layer.

White OLED consisting of a fluorescent blue emissive layer combined with a phosphorescent green and a phosphorescent red emissive layer were processed by means of Organic Vapor Phase Deposition (OVPD). Different concepts to tune the color coordinates of the device are discussed with respect to the luminous efficiency. Furthermore, the influence of device aging on the emitted spectrum is being investigated by means of spectrally resolved lifetime measurements.