Organic Microcavities and OLEDs

Abstract
The merging fields of photonics and organic electronics into organic optoelectronics has created a surge of enthusiasm over the possibility of developing low-cost and large-area advanced optoelectronic systems. These applications can combine the best functionalities of both fields, such as tailoring the organic semiconductors by chemical means, engineering the structure in which organic materials are embedded in, are to name a few. These advances have stimulated the excitement over the next generation of optoelectronic systems with enhanced capabilities and low-cost manufacturing processes compared to their inorganic counterparts. Such technology direction is mainly reflected by the high investments towards the aim of developing flexible, and roll-to-roll organic light-emitting diodes and organic solar cells.
Interestingly, more sophisticated applications require a deeper understanding of the underlying mechanisms at play that merge concepts from the fields of photonics and organic electronics. Particularly, organic light-emitting diodes (OLEDs) under certain constraints (such as cavity light confinement, strong exciton-photon interaction) exhibit modified spectral emission compared to OLED devices that are not bounded by the same conditions. The introduction of the polariton concept as a quasi-particle, which is part-light and part-matter, has emerged to describe such new physical phenomena caused by this photon-exciton intricate interaction. Polariton physics is well established in inorganic semiconductors were a plethora of physical phenomena have been demonstrated, such as the appearance of Bose-Einstein Condensation or low-threshold laser devices. The later is what has as yet to be demonstrated from the field of solid state physics utilising organic semiconductors.
This thesis is focused on the study of the physics and the engineering of organic light-emitting diodes that will aid in the realization of efficient organic polariton LEDs. The main body of work examines various organic semiconductor materials in their ability to reach the strong light and matter interaction regime and, subsequently, to be used in OLEDs as the emissive component. Furthermore, a degradation investigation highlights the issues that affect small-molecule based OLEDs, and finally, the possible pathways for achieving efficient polariton OLEDs are discussed.