Synthesis and Characterization of Hole-Transporting and Electroluminescent Polymers

Citation

Bellmann, Erika (2000) Synthesis and Characterization of Hole-Transporting and Electroluminescent Polymers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/580c-6t05. https://resolver.caltech.edu/CaltechTHESIS:11012023-173457731

Abstract

This thesis describes research on synthesis and characterization of electroluminescent and hole-transporting polymers for applications in organic light-emitting diodes (OLEDs). The first part of the project focuses on the synthesis of derivatives of the electroluminescent polymer poly(para-phenylenevinylene) (PPV) using ring-opening metathesis polymerization (ROMP) of substituted barrelenes. Barrelenes (a certain kind of bicyclic olefins) have been prepared through multi-step synthetic procedures, and the existing synthetic route was extended to barrelenes without electron-withdrawing groups. ROMP of barrelenes was explored because this polymerization can be living, which allows the preparation of well-defined polymeric products. A new version of a soluble PPV derivative was prepared via this route.

The second part of the project focuses on hole-transporting (HT) polymers. A range of HT polymers were prepared via ROMP and anionic polymerization to explore the influence of different hole mobility and different ionization potential on the performance of a two-layer OLED. OLED devices were fabricated using spin-casting and vacuum vapor deposition, and were characterized in terms of current-voltage behavior and light output. A photo-crosslinkable hole transport layer was demonstrated. The HT polymers have been found to yield improved OLEDs by comparison to analogous small-molecule materials due to better film coverage and better film morphology. The device performance has been found to improve with increasing ionization potential of the hole transport polymer. An optimized device was fabricated, which showed 20 Lm/W efficiency. The best HT polymer was modified further to improve the operational stability of the device by improving the interfacial contact to the anode. A better adhesion to the conducting glass was achieved by preparing trimethoxysilane-containing copolymers via radical polymerization, and developing a procedure to cross-link these copolymers to the anode surface.

The appendix describes a project unrelated to the general topic of materials for OLEDs. It presents a study on four chiral molybdenum-based ROMP-initiators with regard to their ability to yield highly stereoregular polymers.

Thesis Files