Reliability aspects of organic light emitting diodes

Various functional elements in organic optoelectronics devices are sensitive to oxygen an moisture. Thus, without an encapsulation the lifetime of organic light emitting diodes or organic solar cells does not meet the requirements of a serious application. We will discuss the particular challenges to form reliable, dense, pin-hole free thin-film barriers on top of organic devices. Specifically, atomic layer deposition (ALD) will be shown to be a highly attractive technique, that allows to operate at temperatures below 100°C. Particularly, the use of nanolaminates - multilayer structures of two alternating oxide materials - have evolved as a promising candidate to seal organic devices with a powerful moisture barrier. We will discuss the preparation technology of these barrier layers, the characterization of their gas permeation rate as well as their performance in real OLED devices. With a proper ALD barrier, the lifetime of an OLED operated at 1 000 cd/m2 can be increased to be well in excess of 20 000 h. For top-emitting or transparent OLEDs, the optical properties of the thin-film encapsulation layer can be used to concomitantly tune the light extraction efficiency of the devices.