Thomas Hamann
Assistant Professor Office: 411 Chemistry
Phone: 517-355-9715 146 /
Websites: Research Group - Area
Awards & Honors
Inorganic Materials / Electrochemistry
(Research Description PDF - 1242 kb)The increasing societal demands for clean energy in conjunction with recent advances in nanotechnology make this a very exciting time for solar energy research. The ability to control material composition and architecture at the nanometer length scale, understand the surface/interface properties, and tune the heterogeneous electron-transfer reaction kinetics will allow for rapid advances of the capture, conversion, and storage of this massive resource. Our research thus revolves around the theme of developing and thoroughly characterizing nanostructured materials, coupled with detailed investigations of interfacial electron-transfer processes for solar energy conversion applications.
The efficiency of conventional planer photovoltaic devices is generally limited by the lifetime of charge carriers; efficient devices therefore require very pure and expensive materials. The development of nanostructured semiconductor materials with controlled composition and geometry, however, offers the potential for obtaining high energy-conversion efficiencies from more defective (inexpensive) semiconducting materials. The generic concept of nanostructured photoelectrochemical cells will be extended to a wide range of materials, configurations, and contacting phases. Advancement in this area will rely upon increased understanding of interfacial electron- transfer reactions, interface stability, and material structure and properties.
Dye-sensitized solar cells (DSSCs) are a potentially very inexpensive system for converting sunlight into electrical energy, with reported devices having up to 11% energy conversion efficiency. Despite over 17 years of intense research, however, the configuration of the best cells is essentially unchanged since Gratzel's initial report. In addition, there are processes in this system that remain poorly understood - specifically, what controls recombination of injected electrons with oxidized redox species in solution. Further significant improvements in efficiency of DSSCs will almost certainly rely on identifying redox couples to replace I3-/I-. Our goal is thus to understand in microscopic detail what controls the rate of recombination in order to guide a rational design of alternate redox couples, as well as the photoanode composition, to increase the efficiency of DSSCs.
Organic photovoltaics, OPVs, are a relatively new and very promising technology. The most efficient polymer-based photovoltaic cells fabricated to date consist of disordered blends of a polythiophene polymer (P3HT) and a C60 derivative (PCBM). There are several disadvantages of the blend configuration, however, including a lack of material variability and controllable dimensions. We will develop more ordered organic/inorganic hybrid systems which will allow for systematic studies to address outstanding questions - such as what controls open-circuit voltage and how much energy is necessary to split the excitons - and improve device performance.
Selected Publications
Aerogel templated ZnO Dye-Sensitized Solar Cells, Hamann, T.W., Martinson, A.B.F., Pellin, M., Hupp, J.T., Adv. Mater. 2008, accepted.Alternative Photoanode Architectures for Dye-Sensitized Solar Cells, Martinson, A.B.F., Hamann, T.W.; Pellin, M., Hupp, J.T., Chem.-Eur. J. 2008, accepted.
Control of the Stability, Electron-Transfer Kinetics, and pH-Dependent Energetics of Si/H2O Interfaces Through Methyl Termination of Si(111) Surfaces, Hamann, T.W., and Lewis, N. S., J. Phys. Chem. B. 2006, 110, 22291-22294.
Measurement of the Dependence of Interfacial Charge-Transfer Rate Constants on the Reorganization Energy of Redox Species at n-ZnO/H2O Interfaces, Hamann, T.W., Gstrein, F., Brunschwig, B. S., Lewis, N. S., J. Am. Chem. Soc. 2005, 127, 13949-13954.
Measurement of the Free Energy Dependence of Interfacial Charge-Transfer Rate Constants Using ZnO/H2O Semiconductor/Liquid Contacts, Hamann, T.W., Gstrein, F., Brunschwig, B. S., Lewis, N. S., J. Am. Chem. Soc. 2005, 127, 7815-7824.
