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Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Paul M. Lahti
Materials Chemistry | Organic Chemistry | Physical Chemistry | Polymer and Organic Materials | Semiconductor and Optical Materials
Dramatic improvements in organic photovoltaic device efficiency can be obtained by optimizing spectral absorbance and frontier molecular orbital (FMO) energies, increasing solid state exciton/charge mobility, and utilizing p-/n-type nanoarchitecture. Combining all of these properties into a new material presents a considerable synthetic challenge because potential commercial applications require materials that are high-performance and inexpensive. Thus, it is advantageous to design new materials using a versatile, modular synthetic approach that allows each design criterion to be engineered individually, in a synthetically efficient manner.
Several strategies were successfully pursued using simple interchangeable electron donor and acceptor components as functional modules, which provided various donor-acceptor chromophores in a synthetically straightforward manner. This approach provided broad functional tunability to the range of materials produced and, as a result, various molecular engineering requirements were systematically addressed. In some cases, these materials were utilized in photovoltaic devices as p-type active layers or redox enhancement additives. In these cases, competitive power conversion efficiencies were obtained or test device performance was considerably enhanced by comparison to control devices.
Fluorenone, fluorenylidene-malononitrile, and squaric acid were utilized as electron acceptor modules, and electron donor module strength was varied using a styrene-based and several di- and triarylamine-based components.
One strategy, published in Phys. Chem. Chem. Phys., (Chapter 2, DOI-10.1039/C2CP41813D) is to fix the donor-acceptor lowest unoccupied molecular orbital energy using the synthetically versatile fluorenone module. Fluorenone was chosen because of its ready availability and synthetic versatility, and its multiple functionalization sites allow for selective FMO engineering. Extrapolation of this approach was published in J. Phys. Chem. A. (Chapter 3, DOI-10.1021/jp407854r), describing various fluorenylidene-malononitrile derivatives. Chemical oxidation of fluorenone-based triarylamines to produce stable radicals was published in Tetrahedron Letters (Chapter 4, DOI-10.1016/j.tetlet.2012.10.060).
Fluorenone derivatives applied as dye sensitized solar cell redox system enhancement additives was described in RSC Advances (Chapter 5, DOI-10.1039/C3RA40986D). Development of new, functionalized, squaraine-based materials was described in J. Phys. Chem. C. (Chapter 6, DOI-10.1021/jp410362d) and was extrapolated for use in single-heterojunction photovoltaic cells having 4.8% maximum power conversion efficiency.
The fundamental insights provided by these findings will be valuable for developing new high-performance photovoltaic materials in the future.
Homnick, Paul J., "Molecular Engineering Strategies for the Design and Synthesis of New Organic Photovoltaic Materials" (2014). Doctoral Dissertations. 95.