Collections > Electronic Theses and Dissertations > Design, Fabrication, and Characterization of Organic Electronic Devices for Thermoelectric Applications
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Thermoelectric devices are an emerging application for conducting organic materials. Translating between heat and electricity, these materials could help to meet the energy needs of the future. Organic materials are advantageous because of their flexibility, processability, low toxicity, and cost. However, organic thermoelectric devices are presently lower efficiency than their inorganic counterparts, due to their lower electrical conductivities. This work seeks to progress towards higher-efficiency organic thermoelectric devices using several different approaches. First, poly(3,4-ethylenedioxythiophene) (PEDOT) thin-films were polymerized electrochemically onto a surface using galvanostatic, potentiostatic, and potentiodynamic techniques. It was determined that the surface morphologies of the potentiostatic and galvanostatic films are quite similar, but the potentiodynamic morphology is markedly different. An electrochemical dedoping process was developed for these films, and the degree of dedoping was monitored with UV-Vis and XPS. The oxidation levels in the films were found to vary between 11.7 and 33%. The electrical conductivity, Seebeck coefficient, and thermoelectric power factor of the PEDOT films were measured, and a maximum value of 13.6 µW m-1 K-2 was obtained. Second, two analogous polymers, HTAZ and FTAZ, were studied for future thermoelectric use. The polymers were chemically doped with FeCl3, the degree of doping was monitored with UV-Vis, and the doping stabilities of both polymers were recorded. The electrical conductivity was also measured and related to the doping level. Despite the space-charge limited current (SCLC) mobility of FTAZ being nearly an order of magnitude higher than HTAZ, the conductivities were nearly identical. Finally, as a way to increase mobility and conductivity in future organic thermoelectric devices, a novel metal-molecule-metal junction was designed and fabricated using an adapted transfer-printing technique. Patterned gold contacts were transferred onto poly(3-methylthiophene) (P3MT) brushes anchored to an ITO electrode. The junctions were electrically characterized via conducting AFM to determine charge transport behavior, and the SCLC mobility was extracted from the current-voltage curves. The polymer brush devices could be improved by annealing before transfer of the top gold contacts, and this led to a maximum increase of two orders of magnitude in device mobility.