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Polymer/Nanoparticle Nanocomposite Thin Films for Optoelectronics: Experiment and Theory
- Author / Creator
- McClure, Sean
Third-generation optoelectronics, which utilize nanoscale materials, have received a considerable amount of attention in the chemical sciences and are poised to make a large impact in both fundamental research and real-world application. In order to make a contribution to the field, this thesis describes a route towards highly stable, water-soluble semiconductor nanorods and their incorporation into nanoparticle/polymer composite thin films. To characterize the photoelectrical properties of these multilayers, and to provide a proof-of-concept for a functional optoelectronic device, the films were integrated into an excitonic solar cell. To gain further insight into the physical properties of the thin films, computational modeling of the carrier transport in thiophenes was conducted, and the limits to device performance were described in the context of their charge transport characteristics.
Electrostatic layer-by-layer (ELBL) assembly was used for the synthesis of multilayer nanorod/polymer composite films. CdSe nanorods (NRs) were synthesized and made cationic and water-soluble using ligand exchange chemistry. The NRs were partnered with anionic polymers including poly(sodium 4-styrenesulfonate) (PSS) and the two polythiophene-based photoactive polymers, sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate (PTEBS) and poly3-(potassium-6-hexanoate)thiophene-2,5-diyl.
Multilayer growth, with nanoscale control, is shown through UV-vis spectroscopy, cross-sectional scanning electron microscopy (SEM) and surface
analytical techniques including atomic force microscopy (AFM). The formation of an intimate nanorod/conducting polymer bulk heterojunction is confirmed through cross-sectional SEM, transmission electron microscopy (TEM), and scanning Auger analysis. A series of photovoltaic devices was fabricated on ITO electrodes using CdSe NRs in combination with PTEBS or P3KHT. A thorough device analysis showed that performance was limited by carrier transport throughout the films.
Computational modeling of the thiophene component in polymer-based third-generation devices was done using density functional theory (DFT) with core potentials added to account for long range dispersion interactions inherent to optoelectronic thin films. Binding energies and orbital splittings in dimers composed of monomers up to six rings were investigated. The combination of experimental and computational studies elucidates some of the underlying mechanisms behind the production of third-generation solar energy.
- Graduation date
- Spring 2011
- Type of Item
- Doctor of Philosophy
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