Document Type

Thesis - University Access Only

Award Date

2010

Degree Name

Master of Science (MS)

Department / School

Electrical Engineering and Computer Science

Abstract

Photovoltaic solar cell technology may fulfill the need for a nonpolluting and sustainable energy future. Organic materials may be a better choice than inorganic materials like silicon as they are less expensive to fabricate, flexible, lightweight, disposable and nontoxic. They can also be customized at the molecular level to possess favorable properties for high efficiency organic solar cells. One way to improve solar cell efficiency is to absorb a larger portion of the solar spectrum by finding up-converter materials. The concept of frequency up-conversion, which is the conversion of low energy photons to higher energy photons, can allow an efficient use of the solar spectrum. This can be accomplished by two-photon absorption. In this work, novel molecular structures were designed by grafting of two elongated conjugated linkers on a conjugated core and then adding donor group at both ends. Fluorene derivatives were used as core acceptors, phenylethynl as conjugated linkers and diphenylamino or methyl-9Hcarbozole as the donor end groups. Gaussian03W software was used for modeling and simulation of molecular electronic structure and properties, and to study one-photon absorption properties of these molecules. It was found that donor-acceptor combination on organic n -conjugated molecules can improve charge transfer and large transition dipole moments between energy states due to charge transfer contribute to the enhancement of two-photon absorption cross section in an -conjugated molecular system. Molecules without the central acceptor core have a negligible two-photon absorption cross section and therefore need to have both donor and acceptor groups to be a good two-photon absorbers. Molecules with 9H-fluoren-9-one as the acceptor core and methyl-9H-carbazole as the donor end group can be suitable as up-converters in aluminum gallium arsenide and copper gallium selenide solar cells because of the small band gap. Molecules with fluorene as an acceptor core, phenylethynyl as conjugated linker and diphenylamino or methyl-9H-carbazole as the donor end group can be suitable as up-converters in high band gap solar cells like silicon carbide. Future work should address further simulation of these up-converters to achieve lower band gap and higher two-photon absorption cross section, and fabricate it to be used in a solar cell.

Library of Congress Subject Headings

Photovoltaic cells
Two-photon absorbing materials
Solar cells
Organic compounds
Photovoltaic power generation

Format

application/pdf

Number of Pages

104

Publisher

South Dakota State University

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