We focus on the determination of the internal luminescence quantum efficiency of a green-emitting organic light-emitting diode (OLED). By considering different geometrical configurations of OLED thin-film stacks, we elucidate the role of the internal luminescence quantum efficiency of the emitter in the thin-film microcavity. Combining optical simulations with experimental results, a comprehensive efficiency analysis is performed. Here the electroluminescence of a set of OLEDs is characterized. Additionally, the devices are characterized using time-resolved photoluminescence measurements. The experimental data are analyzed using optical simulations. This analysis leads to a quantification of internal luminescence quantum efficiency and allows conclusions about competing mechanisms resulting in nonradiative recombination of charge carriers.
Phosphor down-conversion of blue organic light-emitting diodes (OLEDs) is one approach to generate white light, which offers the possibility of easy color tuning, a simple device architecture and color stability over lifetime. In this article previous work on down-conversion devices in the field of organic solid state lighting is briefly reviewed. Further, bottom emitting down-conversion OLEDs are studied from an optical point of view. Therefore the physical processes occurring in the down-conversion layer are translated into a model which is implemented in a ray tracing simulation. By comparing its predictions to experimental results the model is confirmed. For the experiments a blue-emitting polymer OLED (PLED) panel optically coupled to a series of down-conversion layers is used. Based on results obtained from ray tracing simulation some of the implications of the model for the performance of down-conversion OLEDs are discussed. In particular it is analysed how the effective reflectance of the underlying blue OLED and the particle size distribution of the phosphor powder embedded in the matrix of the down-conversion layer influence extraction efficiency.
"Optical Technologies have conquered the world" - their economic key data showed an impressive growth in the past
couple of years, and the predictions for the up-coming years keep the expectations high<sup>1, 2</sup>. In the case of OLED (Organic
Light Emitting Diode) lighting, e.g. IDTechEx is predicting a worldwide market growth from 50 million USD in 2009 to
3.3 billion USD in 2012<sup>3</sup>.
LED and OLED technology, although both being referred to as solid state lighting, are rather complementary in their
characteristics. Whereas LEDs are high efficient point light sources, OLEDs cover large area, diffuse lighting applications
which can follow the increased awareness for creation of personalized atmosphere. Ambience and mood lighting
can be perfectly realized by the means of OLED large area illumination which will pave the way for applications that up
to now could not have been realized.
OLED lighting technology rests on three pillars at the same time, the basic performance like efficiency and lifetime, the
unique features, and costs. These key challenges and their impact on various applications will be discussed.