Structural investigations and processing of electronically and protonically conducting polymers

Abstract

Various conducting polymers form a special class of materials with the potential for many applications in organic electronics and functional materials. These polymers can be electronically conducting or semiconducting due to a conjugated polymer backbone, or alternatively possess conductivity due to mobile protons or other ions. This thesis discusses such conducting polymers and shows ways how they can be processed by printing and how the nanostructure allows controlling their electrical properties. The printability of conducting polymers, studied in paper I, has opened up new fields for their use in electronics. We showed that conducting polymers like polyaniline can be printed with industrial printers and high speed (up to 100 m/min) on paper achieving 60 µm resolution. One of the most promising fields for conducting polymers is sensor applications. Papers II and III show how polyaniline can be utilised to detect changes in temperature and moisture by selecting suitable counter-ions. Melting of the counter-ion side chains was found to induce a reversible change in conductivity. On the other hand, humidity triggered an irreversible change in conductivity due to crystallisation and phase-separation of the counter-ion. Paper IV studies the effect of polymer microstructure in resistive memory devices. Even though the structure of polymers often has a significant effect on the electrical properties, in this case the polymer-electrode interface was found to be dominating. Finally, paper V shows that highly self-assembled polymer complexes may be achieved by utilising ionic liquids. The polymer-ionic liquid complex forms a surprisingly well organised nanophase-separated structure that provides pathways for proton conduction. This thesis takes a step from the laboratory towards applications of conducting polymers and gives insight into utilisation and processing of functional materials to be used in organic electronics components and devices.