Author's School

School of Engineering & Applied Science

Author's Department/Program

Energy, Environmental and Chemical Engineering

Language

English (en)

Date of Award

January 2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Pratim Biswas

Abstract

The correlation between energy consumption and human development illustrates the importance of this societal resource. We will consume more energy in the future. In light of issues with the status quo, such as climate change, long-term supply and security, solar energy is an attractive source. It is plentiful, virtually inexhaustible, and can provide more than enough energy to power society. However, the issue with producing electricity and fuels from solar energy is that it is expensive, primarily from the materials: silicon) used in building the cells. Metal oxide semiconductors are an attractive class of materials that are extremely low cost and can be produced at the scale needed to meet widespread demand. An industrially attractive thin film synthesis process based on aerosol deposition was developed that relies on self-assembly to afford rational control over critical materials parameters such as film morphology and nanostructure. The film morphology and nanostructure were found to have dramatic effects on the performance of TiO2-based photovoltaic dye-sensitized solar cells. Taking a cue from nature, to overcome the spatial and temporal mismatch between the supply of sunlight and demand for energy consumption, it is desirable to produce solar fuels such as hydrogen from photoelectrochemical water splitting. The source of water is important -- seawater is attractive. The fundamental reaction mechanism for TiO2-based cells is discussed in the context of seawater splitting. There are two primary issues with producing hydrogen by photoelectrochemical water splitting using metal-oxide semiconductors: visible light activity and spontaneous activity. To address the light absorption issue, a combined theory-experiment approach was taken to understand the fundamental role of chemical composition in determining the visible light absorption properties of mixed metal-oxide semiconductors. To address the spontaneous activity issue, self-biasing all oxide p/n bulk-heterojunctions were synthesized and the nanostructure was systematically varied to understand the fundamental role of various characteristic length scales in the nanostructured region of the device on performance. The conclusion of this work is that solar energy harvesting by metal oxide semiconductors is highly promising. All of the scientific concepts have been proven, and steady gains in efficiency are being achieved as researchers continue to tackle the problem.

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Permanent URL: http://dx.doi.org/10.7936/K7GM85D8

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