Photophysical and Redox Properties of Degenerately Doped Nanocrystals

Abstract

For the past few decades, semiconductor nanocrystals (NCs) have been the subject of intense interdisciplinary research in both fundamental science and device engineering. Their size-tunable electronic and optical properties, solution processability, and diverse synthetic chemistries make them attractive candidates for applications such as photovoltaics, photocatalysis, and lighting technologies. Besides the well-known quantum confinement effect, the introduction of dopants introduces many more opportunities to tune the electronic, optical, and magnetic properties of NCs. This thesis focuses on NCs containing excess band-like electrons, their photophysical properties, and the redox chemistries associated with these dopants in relation to their charge-compensation mechanisms. Chapter 1 outlines the basic properties of degenerately doped NCs. Methods for preparing degenerately doped NCs are discussed, along with spectroscopic and electrochemical techniques for studying their optical and electronic properties. Chapter 2 describes a new method for preparing photodoped PbSe quantum dots with high electron densities. These high doping densities allow for a careful analysis of the changes in electronic absorption, which reveal conclusive evidence for the assignment of the electronic transitions in their absorption spectra. Chapter 3 employs spectroelectrochemical potentiometry to study the redox properties of excess electrons in Sn4+:In2O3 NCs. An important difference is observed between the redox properties of electrons added by photodoping compared to aliovalent doping. These differences reflect the impact of the charge-compensation motif on determining the stability of charges in degenerately doped NCs.