Photodynamics of Organic Thin Film Multilayer Struvtures with Optical Functions

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This research was carried out aimed at developing a new material structure with novel optical functions, i.e., organic thin film multilayer structures, through critical characterization of their photodynamics. The results are summarized as follows ;1. Organic materials for electroluminescence (EL) applications were chosen as target for this reserach. Well-defined multilayer structures with aluminumquinoline (Alq3), diamine (TPD), oxadiazole (PBD), and cyclopentadiene (PPCP) were fabricated by molecular beam deposition technique with the controllability of smaller than 20Å, which was proven by x-ray diffraction and non-contact mode atomic force microscopy.2. Techniques for elucidating energy structures of organic materials were developed by using UPS, excitation PL, and photoabsorption characteristics. The results revealed type-II energy lineup with respect to HOMO and LUMO levels for Alq/TPD and Alq/PPCP and type-I for Alq/PBD.3. Photodynamics characterization conditions with time-resolved PL were established and with this technique fast (within few ps) energy transfer of photoexcited carriers to Alq followed by effective radiative recombination in type-I structures and separation of electrons and holes in different layers in type-II structures were evidenced.4. Doping of C60 into electron transport layers enhanced electron mobility and this successfully improved the efficiency of EL devices where electron mobility dominated the total efficiency.5. Based on the photodynamics revealed in this study, novel structures for EL devices were newly proposed and actually contributed to improvement of efficiency of green EL devices and visibility of white EL devices.