Date of Award

June 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Michael B. Sponsler

Keywords

dye-sensitized solar cells, electron reservoir, photovoltaics, polypyridine, ruthenium, up-conversion

Subject Categories

Physical Sciences and Mathematics

Abstract

Increasing the usable portion of solar spectrum is a key factor in increasing the efficiency of modern solar cells. The near-IR region of the solar spectrum is often underutilized as a means of energy production, as the photons in this region do not contain enough energy to promote electrons to the conducting band of common semiconductors used in photovoltaics. To help achieve this goal, the creation of an electron reservoir was attempted. The electron reservoir would be a holding place for an electron that is excited by a sub-bandgap photon until another photon excites it to the conduction band.

The first chapter of this dissertation describes the basics of dye-sensitized solar cell technology and the requirements and characteristics of an electron reservoir. It also discusses characteristics that molecules would need to have in order to act as electron reservoirs. The electron reservoirs envisioned consist of multi-metal complexes with at least three metal centers and the presence of a near-IR absorption in the mixed-valence state.

The second chapter describes the synthesis of a number mono- and diruthenium of building blocks that were used to create larger triruthenium molecules. Most notable of these was bis(4,4’-dicarboxy-2,2’-bipyridine)(2,2’-bipyrimidine)ruthenium(II) hexafluorophosphate. The two 4,4’-dicarboxy-2,2’-bipyridine ligands allow strong attachment of the complex to TiO2 and the 2,2’-bipyrimidine ligand allows for additional ruthenium centers to be attached.

The third chapter describes the creation of a series of triruthenium complexes. Initially, an unsuccessful combinatorial synthesis was attempted using TiO2 as a stationary phase. Afterwards, a series of triruthenium complexes were made using the mono- and diruthenium building blocks previously made. None of the complexes synthesized had a near-IR absorption in their mixed-valence state.

The fourth chapter describes the synthesis of a cyclometalated diruthenium complex made using 2,3,5,6-tetra-(2-pyridyl)pyridine as a bridging ligand. A strong mixed-valence near-IR absorbance was seen at 1370 nm.

The fifth chapter describes the fabrication of dye-sensitized solar cells and the photovoltaic results obtained using the dyes from chapters two through four. The solar cells tested had efficiencies of 0.3% to 0.7%. However, no current was generated from photons in the near-IR region.

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Open Access

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