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Pure Appl. Chem., 2001, Vol. 73, No. 3, pp. 459-467

Molecular photovoltaics that mimic photosynthesis

Michael Grätzel

Ecole Polytechnique Fédéral, CH-1015 Lausanne, Switzerland

Abstract: Learning from the concepts used by green plants, we have developed a photovoltaic cell based on molecular light absorbers and mesoporous electrodes. The sensitized nanocrystalline injection solar cell employs organic dyes or transition-metal complexes for spectral sensitization of oxide semiconductors, such as TiO2, ZnO, SnO2, and Nb2O5. Mesoporous films of these materials are contacted with redox electrolytes, amorphous organic hole conductors, or conducting polymers, as well as inorganic semiconductors. Light harvesting occurs efficiently over the whole visible and near-IR range due to the very large internal surface area of the films. Judicious molecular engineering allows the photoinduced charge separation to occur quantitatively within femtoseconds. The certified overall power conversion efficiency of the new solar cell for standard air mass 1.5 solar radiation stands presently between 10 and 11. The lecture will highlight recent progress in the development of solar cells for practical use. Advancement in the understanding of the factors that govern photovoltaic performance, as well as improvement of cell components to increase further its conversion efficiency will be discussed.