09 August 2010
A tailored porphyrin dye has allowed researchers to achieve 11% solar-to-electric power conversion efficiency with dye-sensitized solar cells. The researchers, who are from École Polytechnique Fédérale de Lausanne, National Chiao Tung University and National Chung Hsing University believe that this is the first time such a high efficiency has been obtained with a sensitizer that did not contain ruthenium.
Dye-sensitized solar cells are promising because they can offer high light-to-electricity conversion efficiencies, are not difficult to fabricate, and have low production costs. The cells have a porous layer of titanium dioxide nanoparticles covered with a molecular sensitizer, or dye, that absorbs sunlight. Sunlight passes through the transparent electrode into the dye layer and excites electrons that then flow into the titanium dioxide. The electrons flow toward the transparent electrode where they are collected for powering a load.
Dye-sensitized solar cell research has been focused on finding sensitizers that are efficient and practical. For example, ruthenium sensitizers have attained efficiencies of more than 11%. Porphyrin chromophores are also being studied as sensitizers. These chromophores, which harvest light in photosynthetic bacteria and plants, have strong absorption and emission in the visible region and a tunable redox potential.
Thus far the best reported conversion efficiencies in dye-sensitized solar cells using porphyrin dyes have been in the range of 5 to 7%. The researchers, led by Michael Grätzel, used a porphyrin chromophore as a bridge in a donor-acceptor dye. Using this conjugated porphyrin dye as a photosensitizer on a double layer TiO2 film under standard illumination test conditions achieved an efficiency of 11%. They also showed that the dye enhanced photovoltaic performance when co-sensitized on a thin TiO2 film (2.4 mm) with a metal-free dye that has a complementary spectral response.
The researchers conclude that this study shows the possibility of improving photovoltaic performance of dye-sensitized cells with judicious design of donor–acceptor porphyrin dye conjugates. They would like to next test co-sensitization for various TiO2 film designs.
Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on Donor–Acceptor-Substituted Porphyrins, Angew. Chem. Int. Ed., DOI: 10.1002/anie.201002118
Read these other stories on dye-sensitized solar cells:
Grätzel receives Millennium Technology Prize for work on dye-sensitized solar cells
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Learning from Nature: Dye-sensitized solar cells