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The need for renewable energy that emits no CO2 is perhaps society's most important
and pressing problem. Solar energy is the largest potential source of this renewable
energy however a method for storing the energy for night and transportation uses is
needed. We have a project that involves a combinatorial search for metal oxide materials
that are capable of either one or two photon photoelectrolysis of water to produce
a stored fuel, hydrogen. We are ink jet printing patterns of metal oxide precursors
onto conductive substrates that are then pyrolyzed to produce gradients of metal oxide
compositions. We then scan a laser over the patterned substrates to measure regions
of high photocurrent that indicate promising compositions. The library is then expanded
about the promising compositions and the physical and structural properties of these
compositions are investigated in detail.
We are also involved in an outreach program where many undergraduate students will be enlisted to use our simple preparation and screening techniques to help prepare screen some of the millions of possible ternary and quaternary metal oxide compositions and test them for water splitting activity.
We are studying the structure of the interface between sensitizing dyes and semiconducting oxide surfaces. The low index single crystal metal oxide surfaces are used to model the surfaces in the promising nanocrystalline anatase dye sensitized solar cell. We are using photoelectrochemical, scanning probe and ultrahigh vacuum (UHV) techniques to investigate sensitizing dyes with multiple attachments to the single crystal metal oxide surfaces. Other high surface area substrates, such as single crystal and porous GaP are also being used to study the fundamental aspects of the dye sensitization process.
Photovoltaic solar cells can convert solar energy directly into electricity. Currently the price of energy from these solar converters is not competitive with fossil fuel derived electricity. In addition many of the promising technologies to lower the price of solar cells use materials that are not abundant (In, Te) or are toxic (Cd, Te, Se). We are investigating copper zinc tin sulfide (Cu2ZnSnS4), a potentially inexpensive thin film solar cell material that contains only earth-abundant elements, as a solar cell material. To prepare thin films of this material we use nanoparticle precursors dispersed on a substrate and then anneal them into a continuous film. Photoelectrochemical techniques are then used to measure the photovoltaic properties of the thin films.
We have been investigating the interfaces between organic molecules, of interest for applications in organic electronic devices, with metal surfaces. We look at both the structural and electronic properties of this interface. The electronic structure, or band line up, of the interface is investigated by photoemission spectroscopies where the valence band states and core levels of the surface and adsorbate are monitored as a function of coverage of the organic molecule. Temperature programmed desorption is also used to measure the strength of the interaction of the molecule with the substrate. The structure of the interface is followed with scanning tunneling microscopy (STM). A surprising number of ordered structures can be observed. Trends in the electronic and structural properties of the interface are measured by variation of the structure of the molecules and the metal substrate and we are working with theoreticians to understand these trends.