Biomimetic Nanocrystalline Solar Cells

Michael Grätzel

École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland


Learning from the concepts used by green plants we have developed a molecular photovoltaic device which achieves very efficient light harvesting by a molecular absorber grafted onto a nanocrystalline oxide semiconductor film of very high internal surface area. The pores of the film are filled with a redox electrolyte or an organic hole conductor. The cell employs transition metal complexes for spectral sensitization having a broad absorption band throughout the visible region and being characterized by a high stability. 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 photo-induced charge separation to occur quantitatively within a few femtoseconds. The quantum yield for electron injection from the sensitizer into the conduction band of the oxide is practically unity. The certified overall power conversion efficiency of the new solar cell for AM 1.5 solar radiation stands presently at 10.4 %. By virtue of their wide range of possible applications, their environmental compatibility, as well as the simplicity and low cost of production, these devices are credible alternatives to conventional p-n junction solar cells.


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