An Investigation of Electroactive, Conducting, Thiophene-Based Oligomers: Electronic Structure, Synthesis, Characterization, and Device AnalysisPublic Deposited
Theoretical studies on electronic structure governing charge transport properties are investigated to understand and improve the prediction of electron charge carrier organic semiconductors used in field-effect transistors. Perfluorinated oligothiophene semiconductors have shown experimental n-type behavior, but placement of fluorinated aryl groups changes charge polarities. Models were developed to investigate how geometric, electronic, and energetic properties of these systems allowed for the promotion of electron carriers. Density functional theory (DFT) is utilized in the analysis of simple tight-binding dimer and band structure models allowing for the evaluation of transport properties in these materials. In addition, investigations of reorganization energies, ionization potentials, and electron affinities, elucidate further chemical and electrical properties resulting in observed transport behavior. Results from these analyses indicate that most organic semiconductors should exhibit ambipolar behavior under favorable fabrication conditions. To improve further transport properties in organic semiconductors, the design of self-assembling organic conductors through the utilization of hydrogen-bonds is investigated. The unique architecture obtained by self-assembly is believed to be a tool for overcoming fabrication defects such as grain-boundaries in crystalline materials that lead to poorer conduction. Quadruple hydrogen-bonding ureidopyrimidone groups have been selected to be tethered synthetically to oligothiophene semiconducting cores. DFT methods were used to model geometrically planar structures, with solubilizing alkyl groups on the oligothiophene core. Synthesis and characterization of final hexathiophene structures were optically, thermally, and structurally investigated. Unique thermal properties gave promising results for a thermoplastic semiconductor. Electrochemical supercapacitors with n-dopable electroactive polymer electrodes are investigated for improving future instantaneous power density devices. Two polythiophene-based polymers are used to fabricate asymmetric polymer-only based devices. Ionic liquids used in these devices have been varied for optimum performance, and a new device configuration for electrochemical supercapacitors is reported.