ABSTRACT
One of the most exciting and technologically promising areas of application of contemporary photochemistry is the liquid-junction solar cell. Perhaps the most compelling version of the cell is the “Grätzel cell”—a photovoltaic cell that converts sunlight into electricity with nearly 100% quantum efficiency and greater than 10% overall energy efficiency [1-3]. The cell uses a broadly absorbing coordination compound to sensitize a wide-bandgap semiconductor-a high-area nanocrystalline form of TiO2-to visible light. As shown schematically in Fig. 1, sensitization involves molecular photoexcited-state formation, followed by transfer of an electron (“injection”) from the excited molecule into the conduction band of the semiconductor. The oxidized dye is restored to its chromophoric form by reduction with iodide ions present in the surrounding solution. The electrochemical circuit is completed at a dark electrode, which supplies the electrons needed to regenerate iodide from triiodide.
