Collections > Electronic Theses and Dissertations > Conjugated Polymer Brushes as Molecular Wires in Electronic Devices: Synthesis, Device Design, and Characterization
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Lack of efficient charge transport is a major factor holding back performance of organic electronic devices. For polymer semiconductors, some of the best performing devices have significant contributions from intramolecular transport mechanism on the process of charge transport as a whole. This is because charge transport along conjugated polymer backbones is much faster than transport between polymers, but measurements of intramolecular charge transport have only ever been done using technique that measure local properties, not device properties. Few devices have measured properties like charge carrier mobility as a function of polymer chain orientation, but in every case charges are required to hop between chains to transport through the film. This work endeavors to make charge transport devices from monolayers of poly(3-methylthiophene) (P3MT) in brush conformation grown from an ITO surface via Palladium catalyzed surface initiated Kumada catalyst-transfer polycondensation and to characterize the charge transport through the polymer brush films. Though the polymer synthesis is not new, it was thoroughly characterized in order to grow films with the maximum level of control possible. The polymer growth was found to be linear with respect to time and concentration of monomer, suggesting that the polymerization follows first order kinetics. The P3MT films were characterized to determine film morphology. As grown, films exhibited some degree of vertical orientation, which could be increased with thermal annealing. Besides increasing orientation, annealing also increased film thickness and chain rigidity making structures ideal for measuring intramolecular charge transport. In order to make devices, a new transfer printing method was adapted for called kinetically controlled transfer printing (KTP). Gold electrodes were deposited on the P3MT brush surface by KTP, and devices were measured by conducting atomic force microscopy. The data were modelled with a cubic fit to compare transport between films. Before annealing, P3MT films were found to be quite conductive as evidenced by their charge transport decay coefficient (β), and SCLC charge carrier (hole) mobilities were measured to be similar to other poly(3-alkylthiophene) materials. After annealing, the SCLC charge carrier mobility increased in every film measured. The enhancement of charge transport properties is likely due to the change in the structure of the film.