Sensitised cells

An international group of researchers reported last month that it has developed and tested a new generation of photovoltaic cells in Lausanne, Switzerland.

For the first time, the team at Ecole Polytechnique Federale de Lausanne (EPFL) used two different dyes to make dye-sensitised solar cells, making them capable of reacting to a larger range of the light spectrum and thus more efficient.

Dye-sensitised solar cells date to the 1990s. But the phthalocyanine dyes used in them are only sensitive to a restricted range of the solar spectrum.

The new cells, developed by a team led by EPFL's Prof Michael Grätzel, allows that spectral sensitivity to extend to the red, green and blue ranges of visible light, by incorporating a second, perylene dye. With a larger range of light sensitivity, the cells' efficiency is thus improved.

Although the perylenes do not directly generate an electric charge, they react to the blue and green parts of the visible light spectrum. They transfer their energy to the phthalocyanines, which in turn transmit the electric charge. Without the new dyes, the phthalocyanines can react only to the red part of the spectrum.