Organic Light Emitting Diodes: materials, device structures and light extraction

Organic Light Emitting Devices (OLEDs) are presented with particular emphasis on materials, device structures and strategies to improve light extraction. For the fabrication of efficient OLEDs, two types of electroluminescent materials are used (small molecules and polymers) with efficiencies and lifetimes which are now acceptable for small size or low content information displays. Two main approaches are described to enhance external efficiency, one is based on direct modification of the species emission and the other on modification of emitted guided modes propagation within the device. The features of the different approaches are evidenced through examples of devices reported in the literature.