Interfacial reliability and failure mechanisms in organic light emitting diodes.

摘要

Adhesion and its origins have been widely studied in biological, chemical and mechanical systems in many aspects of science. Apart from the knowledge gained from an understanding of the mechanisms of adhesion, engineering functional layers of increased and decreased adhesion into various systems has led to the development of amphibian robots, localized drug treatment, parallel printing processes and many other technological advancements. This thesis presents a combined theoretical and experimental investigation into the role of adhesion as regards the processing, failure and reliability of polymer light emitting diodes. In addition, since failure is, in a manner of speaking, the reverse of adhesion, this thesis also considers aspects of interfacial failure in polymer light emitting diodes.;By considering the interfaces that are relevant to novel deposition techniques which are relevant to roll-to-roll processing this thesis presents evidence for the role of interfacial contaminants in void formation and subsequent ramifications for the yield and reliability of cold-welded junctions that are relevant to the electrode patterning of organic light emitting diodes. In a similar fashion, the role of processing conditions on the interfacial properties of pressure-transferred and temperature-laminated organic semiconductor junctions is studied. A model to describe and predict the formation of thermally induced spiral blisters is also developed and shown to provide insight into the effects of joule heating and its attendant stresses that are generated due to bias currents. Finally, by considering adhesive interactions between poly-dimethylsiloxane (PDMS) and suitably patterned stamps, a scalable and low-cost encapsulation technique is presented which has shown promise for protecting fabricated polymer light emitting diodes from harsh environments.