Micro-Cavity in Organic Light-Emitting Diode

The study on micro-cavity in organic light-emitting diode(OLED) demands understanding the theory of multi-layer films. It is because OLED is basically an optical device and its structure consists of organic or inorganic layers of sub-wavelength thickness with different refractive indices. When the electron and holes are injected through the electrodes, they combine in the emission layers emitting the photons. These photons will experience the reflection and transmission at each interface and the interference will determine the intensity profile. The light reflected at the interfaces or the metallic electrode returns to the emission layer and affects the radiation efficiency. In optical terminology, OLED belongs to a micro-cavity being comprised of multi-layers. Therefore, before studying the cavity effect of OLED, we better begin with the theory of multi-layer film theory in optics. This theory is well explained in most of textbook dealing with optics since it relates to optical coatings and lasers(Fowles, 1975; Born & Wolf, 1989). In this section, a brief review will be given for the purpose of self-containment, which will be especially helpful for the beginners.