Triplet harvesting for efficient white organic light emitting diodes

A novel hybrid device structure for efficient white organic light emitting diodes has been developed, which has a high hole injection barrier between a fluorescence blue emission layer and a electron transporting layer, and therefore excitons could be confined in the emission layer close to the electron transporting layer. A phosphorescent red dopant has been introduced into the electron transporting layer to harvest triplet states of the fluorescent blue emission layer and we have succeeded in obtaining the balanced white emission from blue singlet excitons and red triplet excitons with high efficiency. The optimized device showed the maximum external quantum efficiency of about 25% at 100 cd/m2.