Fabrication of Organic Electrodes Using Conducting Polymers and Graphene and Their Organic Electronic Device Applications

Abstract

Organic electronic devices will significantly improve and revolutionize several aspects of our daily life. The most envisaged applications are the displays, lighting modules, and organic photovoltaic cells. Organic electronic devices have considerable advantages in contrast to current devices, such as lightweight, thin, robust, conformable, and flexibility. The performance, efficiency and lifetime of organic electronic devices are greatly affected by the optical, electrical, and structural properties of the organic electrodes. These should meet specific and advanced requirements, such as high optical transparency, ultra low atmospheric gas permeability, electrical conductivity, structural stability, film–substrate adhesion, etc. Electrodes consisted of transparent conductive oxides have attracted a considerable amount of interest and have been extensively investigated. Traditionally, the most common material is indium tin oxide, which has retained its dominance due to superior combination of high optical transparency and low resistance. However, indium tin oxide is also prone to several major problems. The supply of indium is constrained by both mining and geo-political issues

therefore, indium is relatively expensive. Adding to the cost of indium tin oxide is the expense of setting up and maintaining a sputter deposition line, as well as the low deposition yields. In addition to cost, indium tin oxide suffers from being quite brittle, showing cracks at relatively low strains. This is already a problem in many of todays devices, and promises to be an even bigger issue in future flexible electronics. To make light, unbreakable, flexible, rollable, and fully transparent devices, eventually, it is indispensable that the metal-based components should be replaced with organic materials. This dissertation presents a potential solution of the materials for the electrode of organic electronic devices focusing on conducting polymers and graphene. Solution-processable polyaniline is fabricated by secondary doping with camphorsulfonic acid. The polyaniline solution can be spin-coated onto various substrates including glass, indium tin oxide and flexible polymeric film, which process yields highly conductive polyaniline electrodes successfully. Inkjet printing-mediated vapor deposition polymerization is emerging as a useful method for printing an electrode pattern of nondispersive conducting polymers. An exquisitely patterned polypyrrole electrodes is formed by the technique in top-contact thin film transistor instead of metal electrodes. A novel and reliable approach for the preparation of reduced graphene oxide transparent electrodes is conducted through the combination of chemical and subsequent pressure-assisted thermal reduction at 180°C on a flexible plastic substrate. This reduction process produces reduced graphene oxide electrodes without the transferring or imprinting processes used in conventional synthetic approaches for graphene thin film production. These results strongly suggest that these organic electrodes should be potentially very useful in many new types of applications related to organic electronic devices.