Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Arthur J. Nozik

Second Advisor

David M. Jonas

Third Advisor

Garry Rumbles

Fourth Advisor

Gordana Dukovic

Fifth Advisor

Ivan Smalyukh

Abstract

Semiconductor quantum dots (QDs) are an interesting class of materials in that they exhibit unique physical properties when compared to their bulk counterparts. These unique properties and the breadth of tunability which they possess have made QD research a major field of study for more than 20 years for technologies such as catalysis, bio-imaging, solid-state lighting, and solar energy conversion. The primary concern for the application of semiconductor QDs in any field is not only to be able to precisely control physical properties (i.e., optical, electrical, magnetic) but also to understand how to achieve increased stability in these materials. A greater understanding of the chemistry of QD growth, surface construction, and composition are necessary to realize these goals. This thesis explores each of these areas of QD chemistry and the subsequent effects on their photophysical properties. Through manipulation of QD morphology, we have prepared PbSe QD dimers, which has allowed for a better understanding of electronic structure in quantum confined systems. Specifically we have observed a new absorption feature in the 1st exciton QD-dimer spectra, which we assign to a splitting of the 8-fold degenerate 1S level upon fusion of two monomer species. Surface treatment of PbSe QDs with a newly synthesized alkylselenide ligand has led to higher air stability, unique temperature dependent PL properties and the observation of a new surface-related trap level. Alongside producing more stable QDs, the nature of the strong Pbsurface to Se-R bond may also have implications for affecting kinetic processes like carrier relaxation, which could facilitate production of materials that show enhanced multiple exciton generation (MEG) yields. Finally, substitutional doping of PbSe QDs has allowed for modulation of QD compositions and in turn tuning of the dominant carrier type in both solution and in QD films. Although just a small contribution to the larger reservoir of work in this area, these results provide promise for improving stability and efficiency of QD devices for solar energy conversion.

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