ABSTRACTOrganic light-emitting diodes (OLEDs) are developing into a competitive
alternative to conventional light sources. Nevertheless, OLEDs need further
improvement in terms of efficiency and color rendering for lighting
applications. Fluorescent blue emitters allow deep blue emission and high
stability, while phosphorescent blue emitter still suffer from insufficient
stability. The concept of triplet harvesting is the key for achieving
internal quantum efficiencies up to 100 % and simultaneously benefiting from
the advantages of fluorescent blue emitters. Here, we present a stacked OLED
consisting of two units comprising four different emitters in total. The
first unit takes advantage of the concept of triplet harvesting and combines
the light emission of a fluorescent blue and a phosphorescent red emitter.
The second unit emits light from a single emission layer consisting of a
matrix doped with phosphorescent green and yellow emitters. With this
approach, we reach white color coordinates close to the standard illuminant
A and a color rendering index of above 75. The presented devices are
characterized by high luminous efficacies of above 30 lm/W on standard glass
substrates without outcoupling enhancement.
