Photoelectron spectroscopy studies of conjugated polymer surfaces and interfaces for organic-based light emitting devices

Sammanfattning: Since the initial discovery of metallic conductivity in doped polyacetylene in 1977, which lead to the Nobel Prize in Chemistry year 2000, the field of conducting polymers has expanded tremendously. Today, research developments in this area cover transistors, photodiodes and light emitting diodes (LEDs). The latter one was initiated by the first report on electroluminescence in conjugated polymer that appeared in 1990 by the group of Prof. R. H. Friend in Cambridge. After a decade from this discovery the first polymer-based LEDs are approaching the stage of commercial manufacturing. The low-cost processing and attractive device characteristics make them strong competitors for the inorganic LED-industry.The focus of the work presented in the papers in this thesis is the characterization of the electronic structure of some conjugated polymers used in polymer-LED, as well as different types of interfaces often occurring in real structures (metal-polymer, polymer-metal, metal-insulator-polymer, etc.) and interface materials. The analysis technique that was used for these investigations was almost exclusively photoelectron spectroscopy with both X-ray photons (XPS) and ultraviolet light (UPS), occasionally some measurements were also done employing synchrotron radiation. These two methods XPS and UPS are the complementary techniques and enormous amount of information concerning the valence band electronic structure and electronic core levels can be obtained at the same time. This combination has proven to be especially powerful when applied to the investigations of interfaces formed between conjugated polymers and various metals where the undergoing changes can be mapped step by step in situ while building the metal contact under ultra high vacuum (UHV). The later issue is of great importance for applications in LEDs, where the device characteristic depends strongly on the character of interfaces between emissive polymer layer and injecting electrodes.