| In the last decade, the continued development of phosphorescent organic light-emitting diodes (OLEDs) has permitted great progress in the efficiencies that can be achieved for a variety of colors. Typically, the organic materials used in these highly efficient multilayer devices have been processed by vacuum sublimation. Although sublimation offers many advantages, it has some disadvantages, such as potentially high cost and deposition area limitations. As an alternative, solution-processable polymers such as poly(N-vinylcarbazole) and others have been explored in recent years. Despite the potential ease of fabrication of layers (from solution) that can be achieved using polymers, these materials also come with their own disadvantages including difficulty in purification and issues with the fabrication of multilayers. Despite these issues, the limited amount of research has yet to clearly show whether polymers are viable alternatives to vacuum-processed layers for achieving efficient OLEDs.;In this thesis, a series of charge transport moieties were synthesized and converted to side-chain homopolymers. These moieties were specifically incorporated as side groups onto a norbornene polymer backbone with the intention to impart ease of solution processing without resulting in major changes to the properties of the core transport group. In Chapter 3, several types of carbazole containing groups were explored as hole-transport and as host polymers for phosphorescent emitters. In Chapter 4, ambipolar charge-transport molecules containing both hole- (carbazole) and electron-transport moieties (including oxadiazole and triazole) were designed and converted to side-chain polymers, as well. In addition, the design of these ambipolar molecules was undertaken in such a way as to avoid strong charge-transfer effects that could narrow the optical gap and lower the triplet energy; therefore, these molecules might be candidates for blue phosphorescent OLEDs. Finally, some of these charge transport materials were studied in OLED devices in collaboration with the Kippelen group (School of Electrical and Computer Engineering) and shown to give promising results.;Multilayers fabricated from solution-processed materials can be complicated by issues of layer damage/destruction (upon subsequent processing of additional layers). This issue was addressed in the thesis through the development and evaluation of crosslinkable side-chain copolymers containing both a carbazole-based hole transport group and one of several different crosslinkable co-monomers. In addition, a crosslinkable carbazole-based small-molecule was also synthesized and evaluated. For these materials, the crosslinkable groups chosen for study included thermally and/or photochemically initiated moieties such as benzocyclobutenes, trifluorovinyl ethers, oxetanes, or bis(styrene). Although crosslinking was achieved, for several of these materials the processing times could take several hours. In order to reduce the times needed to crosslink these materials, a study of rapid thermal processing (RTP) in collaboration with Dr. Jassem Abdallah was pursued to further reduce the time required to insolubilize the films from hours to thirty minutes or less; which could be beneficial from a device manufacturing point of view. |
