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This issue of the Green Indicator will reveal some new insight in dye-sensitized solar cells and the CatScan section will have a closer look at how to use photons to fix carbon dioxide. Perhaps this could be a way of creating the carbon-chains much needed in a future, non-oil based economy? We would also like to congratulate BASF who recently announced that they have already met their 2020 goal with respect to carbon dioxide emissions, almost a decade early. Hopefully this can be an inspiration both within BASF, setting new targets for 2020, and for other players in the business.

/ Christian Hulteberg

Cost efficient solar cells?

Over the last couple of years there has been a significant improvement in the efficiency of direct electrical solar cells. The best research cell efficiencies reported are above 40% for three-junction cells with concentrators, however there is a significant discrepancy between the research results and what may be produced in larger cells; with respect to both efficiency and cost effectiveness.

Lately, one type of cells has however gained interest and that is the dye-sensitized solar cells. The principle of this cell is that when solar radiation comes in contact with the cell, energy is transferred to the dye and excites it. The positively charged dye must then be regenerated, which is done by a Co-complex acting as a redox mediator and picking up a positive charge before diffusing to the other side of the cell to the counter electrode.

The efficiency of this type of cell, with the advantage of being transparent and versatile in color and design, saw a rapid increase from 5% to about 10% during the 1990-ies. However, little improvement has been seen since until very recently when researchers at École Polytechnique Féderal de Lausanne reported efficiencies in the 12%-range. The researchers predict reaching their 15% efficiency target within a not too distant future. However, the increase in efficiency is not the major breakthrough in the research, instead the ability of achieving this without the expensive ruthenium complexes earlier used. This achievement is of major importance and may bring this type of cell into commercial production, with high efficiencies soon.