Photodynamics of Organic Thin Film Multilayer Struvtures with Optical Functions

本研究旨在通过对其光动力学的关键表征，开发一种具有新型光学功能的新材料结构，即有机薄膜多层结构。结果总结如下：1。本文选择电致发光用有机材料作为研究对象。通过x射线衍射和非接触模式原子力显微镜证实，采用分子束沉积技术制备了具有良好定义的铝喹啉（Alq3）、二胺（TPD）、恶二唑（PBD）和环戊二烯（PPCP）的多层结构，其可控性小于20Å。利用UPS、激发PL和光吸收特性研究了有机材料的能量结构。结果显示，Alq/TPD和Alq/PPCP的HOMO和LUMO水平为ii型，Alq/PBD.3为i型。建立了时间分辨PL的光动力学表征条件，并利用该技术证明了光激发载流子向Alq的快速（在几ps内）能量转移，随后在i型结构中有效的辐射复合以及在ii型结构中不同层的电子和空穴分离。在电子传输层中掺杂C60，提高了电子迁移率，从而成功地提高了电子迁移率占总效率主导的EL器件的效率。基于本研究所揭示的光动力学，提出了新的光致发光器件结构，并实际有助于提高绿色光致发光器件的效率和白色光致发光器件的可见性。

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.