Modification of silicon quantum dot band gaps for energy applications

Abstract

Photovoltaic materials are increasing in importance as the world's energy needs are constantly increasing and available resources are shrinking. An overview of renewable energy and of photovoltaic materials is given. For a variety of reasons, quantum dot materials in general, and silicon quantum dots in particular, are the subject of a great deal of research interest in the area of photovoltaics and other applications. However, silicon quantum dots have several current limitations, including instability in ambient conditions and band gaps and absorption spectra that are poorly matched to the solar spectrum. This thesis seeks to begin to address these limitations by functionalizing silicon quantum dots with two types of ligands (conjugated molecules and silanols) in an effort to modify their band gaps, increase their absorption profiles, and enhance their stability. Characterization data are provided, showing the successful production of hydride-terminated silicon quantum dots, the successful attachment of ligands, and the physical, optical, and electronic properties of the resulting products. The band gaps are successfully red shifted (with the conjugated ligand) and blue shifted (with the silanol ligands). Possible experimental and computational explanations for the observed band gap shifts, energy transfer, and size-dependent behavior are presented. In addition, new, milder, and less-toxic reaction conditions for the direct conversion of hydride to siloxane terminated silicon quantum dots (SiQDs) are presented and shown to be viable.