Highly efficient white organic light-emitting diodes based on fluorescent blue emitters

Beside inorganic LEDs and fluorescent lamps, organic light-emitting diodes (OLEDs) are evolving into a serious alternative to incandescent lamps. Up to now, it was assumed that all-phosphorescent OLEDs are required for reaching sufficiently high efficiencies. However, the stability of phosphorescent blue emitters is a major challenge. We present a novel approach to achieve highly efficient (up to 90 lm/W at 1000 cd/m(2) using a macroextractor) white light emission from OLEDs. The here presented combination of a fluorescent blue and a phosphorescent red emitter simultaneously allows for a strong blue emission and efficient triplet transfer to the phosphor. The spectrum is extended in the green and yellow region by a full phosphorescent unit stacked on top of the triplet harvesting device. This superposition of four different emitters results in color coordinates close to illuminant A and a color rendering index of 80. Furthermore, color stability is given with respect to varying driving conditions and estimations of the electrical and optical efficiencies are provided. (C) 2010 American Institute of Physics. [doi:10.1063/1.3516481]