Research: Semiconductor Photoelectrochemistry

The electrochemistry of semiconductors is important for device fabrication and processing, photovoltaic cells, photoelectrochemical solar energy conversion devices, and other properties of semiconductor surfaces. Work in the Lewis lab focuses primarily on the chemistry of semiconductors that are technologically important and that have band gaps appropriate for efficient capture of solar energy for use in energy conversion systems. These materials include primarily Si, InP, and GaAs.

Rate Constants

A primary interest of this research is the use of these materials in solid/liquid junctions to convert sunlight into stored electrical energy and/or chemical fuels. Semiconductor/liquid junctions comprise the most efficient wet chemical means for storing solar energy known to date, with efficiencies in excess of 16% in the most efficient systems. A brief introduction to the principles of photoelectrochemistry is available on these pages, with a more extensive primer available in Progress in Inorganic Chemistry.

Current research projects are devoted to elucidating the fundamental energetic and kinetic properties of charge carrier generation, transport, and recombination at semiconductor/liquid interfaces. Questions of interest include:

  1. What processes control the charge separation yield at such interfaces?
  2. What processes control the charge recombination at such interfaces?
  3. How does one describe interfacial charge transfer from delocalized charge carriers in a semiconductor electrode to redox-active ions in the electrolyte solution?
  4. What changes in the solid and in the liquid can be performed in order to obtain improved energy conversion efficiencies from such systems?

Control of Si Surface Properties Through Surface Modification Reactions:

  1. Exploiting Surface Alkylation Reactions to Enhance the Stability of Si Toward Passivation/Oxidation Processes
    1. Fluorocarbon monolayers
    2. Acetylide derivatization and subsequent modification
    3. Functionalization of Si Nanoclusters via the Halogenation/Alkylation Procedure
  2. Exploiting the Alkylated Surface to Obtain Information on the Distance Dependence of Electron Transfer at Semiconductor Electrodes
  3. Surface Functionalization and Scanning Electrochemical Microscopy Measurements
  4. A Comparative Study of the Surface Recombination Velocity of Various Differently Functionalized Si Surfaces
  5. Fabrication and Study of Metal-Insulator-InP Structures
  6. Experimental and Theoretical Investigations of Outer-Sphere Electron Transfer Rate Constants at Semimetal Electrodes
  7. Electrochemistry on the Nanometer Scale: An Electrochemical Study of Electron Tunneling Through Solvents at Various Temperatures
  8. A Quantitative Evaluation of Minority vs. Majority Carrier Charge Transfer Rate Constants at InP/Liquid Contacts
  9. Effect of the Reorganization Energy on the Rate Constant of Electron Transfer Reactions at n-ZnO/Liquid Contacts