International Research Fellowship Program: Fabrication and Characterization of Inexpensive Solar Cells Based on Dye-Sensitized TiO2 Nanoparticles

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0402129AgriosThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-two-month research fellowship by Dr. Alexander G. Agrios to work with Dr. Michael Graetzel at Ecole Polytechnique Federale de Lausanne in Switzerland and with Dr. Anders Hagfeldt at Uppsala University of Sweden.Energy production from the combustion of fossil fuels releases carbon dioxide, nitrogen and sulfur oxides, mercury, and other pollutants, resulting in global climate change, acid rain, and photochemical smog, among other problems. Silicon-based solar energy technology has existed for decades but has been too costly to compete with fossil fuel use. Clearly, if the cost of solar energy production can be reduced to a level at which the displacement of fossil fuel consumption by solar energy conversion becomes practical, the environmental benefit would be enormous. In 1991, a novel type of solar cell was invented in the laboratory of Dr. Michael Gratzel at Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland. Unlike silicon solar cells, the so-called dye-sensitized solar cell (DSSC), or Gratzel cell, uses a different semiconductor, titanium dioxide (TiO2), small (10 nm) particles of which are coated with a light-absorbing molecule (dye), which injects electrons into the TiO2 upon light absorption. In a silicon cell, any impurities or defects in the silicon crystals cripple the efficiency of solar energy conversion, requiring high materials processing costs to achieve the necessary silicon purity. In contrast, the fundamentally different mechanism of the Gratzel cell places much less stringent requirements on the TiO2 nanocrystals, resulting in a far less expensive technology. Dr. Agrios is working on the fabrication of a new generation of dye-sensitized solar cells with Dr. Gratzel at EPFL. An electrostatic layer-by-layer technique for film production, developed in the past decade, is being used to produce two new types of DSSC. The new cells are expected to exhibit better harvesting of the full spectrum of solar light and improved energy conversion efficiency. Dr. Anders Hagfeldt, at Uppsala University in Sweden, has been in close collaboration with Dr. Gratzel for a decade. His laboratory group has developed a suite of advanced characterization techniques for dye-sensitized solar cells known as the "toolbox". The second phase of the project will be spent at Dr. Hagfeldt's laboratory, using his techniques to understand electronic processes occurring in the layered TiO2 films produced at EPFL. In addition, Dr. Hagfeldt has developed a process for producing DSSCs without a high-temperature step, which allows the cells to be continuously fabricated on cheap, flexible plastic substrates. This process will be applied to the layer-by-layer Gratzel cells to determine whether the method of layer-by-layer film deposition is compatible with a low-temperature production technique.