Conjugated polymers, Energy transfer, Nanoparticles, Spectrum analysis, Time resolved spectroscopy
As the global economy searches for reliable, inexpensive and environmentally friendly renewable energy resources, energy conservation by means of photovoltaics has seen near exponential growth in the last decade. Compared to state-of-the-art inorganic solar cells, organic photovoltaics (OPVs) composed of conjugated polymers are particularly interesting because of their processability, flexibility and the potential for large area devices at a reduced fabrication cost. It has been extensively documented that the interchain and intrachain interactions of conjugated polymers complicate the fundamental understanding of the optical and electronic properties in the solid-state (i.e. thin film active layer). These interactions are highly dependent on the nanoscale morphology of the solid-state material, leading to a heterogeneous morphology where individual conjugated polymer molecules obtain a variety of different optoelectronic properties. Therefore, it is of the utmost importance to fundamentally study conjugated polymer systems at the single molecule or nanoparticle level instead of the complex macroscopic bulk level. This dissertation research aims to develop simplified nanoparticle models that are representation of the nanodomains found in the solid-state material, while fundamentally addressing light harvesting, energy transfer and interfacial charge transfer mechanisms and their relationship to the electronic structure, material composition and morphology of the nanoparticle system. In preceding work, monofunctional doped nanoparticles (polymer-polymer) were fabricated with enhanced light harvesting and Fӧrster energy transfer properties by blending Poly[(o-phenylenevinylene)-alt-(2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene)] (BPPV) and Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) at various MEHPPV doping ratios. While single particle spectroscopy (SPS) reveals a broad distribution of v optoelectronic and photophysical properties, time-correlated single photon counting (TC-SPC) spectroscopy displays multiple fluorescence lifetime components for each nanoparticle composition, resulting from changing polymer chain morphologies and polymer-polymer aggregation. In addition, difunctional doped nanoparticles were fabricated by doping the monofunctional doped nanoparticles with PC60BM ([6,6]-phenyl-C61-butyric acid methyl ester) to investigate competition between intermolecular energy transfer and interfacial charge transfer. Specifically, the difunctional SPS data illustrated enhanced and reduced energy transfer mechanisms that are dependent on the material composition of MEH-PPV and PC60BM. These data are indicative of changes in inter- and intrachain interactions of BPPV and MEH-PPV and their respective nanoscale morphologies. Together, these fundamental studies provide a thorough understanding of monofunctional and difunctional doped nanoparticle photophysics, necessary for understanding the morphological, optoelectronic and photophysical processes that can limit the efficiency of OPVs and provide insight for strategies aimed at improving device efficiencies.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Dissertations, Academic -- Sciences, Sciences -- Dissertations, Academic;
Bonner, Maxwell Scotland, "Characterization Of Composite Broad Band Absorbing Conjugated Polymer Nanoparticles Using Steady-state, Time-resolve And Single Particle Spectroscopy" (2011). Electronic Theses and Dissertations, 2004-2019. 1828.