Electronic Structures and Interfacial Chemistry of Oligofluorene-based Organic Light Emitting Devices

• Main Authors: Guan-Ru Lee, 李冠儒
• Other Authors: 吳志毅
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/94069737415358175093

博士 === 國立臺灣大學 === 光電工程學研究所 === 97 === The electronic structures, interfacial chemistry, and temperature dependences of oligofluorenes are investigated via high resolution synchrotron radiation photoemission. The energy structures and physical properties of pristine oligofluorenes are reported and their regular tendencies are observed. Substitutions of the pristine oligofluorenes will significantly influence the electronic and optical characteristics and the operation of oligofluorene-based devices are also substitution dependent. In order to lower the electron injection barrier and enhance the electron injection efficiency at the cathode, the alkali metal fluorides as LiF and CsF are used as n-type dopants for the oligofluorenes. Both of them react with oligofluorenes without the existence of Al and offer us more choices for cathode metals. Our results indicate that to obtain an effective cathode structure, not only n-type doping effect, but also gap state appearance is crucial. In addition, Cs2CO3 as n-type dopant and transition metal oxide, such as MoOx, and F4-TCNQ as p-type dopants are verified. Influences of temperature and inter-unit angle to the electronic structures of oligofluorenes are also studied. Deposition at different temperatures alters the electronic structures due to the inter-unit angles in oligofluorenes molecules. To be specific, the fluorene-units at low temperature are nearly perpendicular to each other and the inter unit angle becomes 41° in the stable state at room temperature. In addition, the low temperature will soften the n-type doping reaction between alkali metal fluoride and oligofluorenes, since the thermal energy is too low to drive this reaction. Upon the sample warming back to the room temperature, however the reaction between these two layers is completed.