In nature, plants operate for billions years with solar radiation converting it into energy through photosynthesis.
The dye solar cells operate on a similar principle: in the cells called “Grätzel” in reference to its designer, organic dyes called phthalocyanines are stimulated by the red spectrum of sunlight and thereby generate an electrical charge.

A team researchers, under the leadership of Michael Grätzel at École Polytechnique Fédérale de Lausanne (EPFL) and Brian Hardin of Stanford University, has now succeeded in increasing the efficiency of cells by adding new colors called perylene. The sensitivity of these new cells has been expanded to include green and blue spectra of sunlight and energy intake increased by one quarter.

Compared with other conventional semiconductor solar cells, these “Grätzel cells” are also effective in low light and their production is cheaper. However, their efficiency remains relatively low, around 11% while that of silicon cells is about 15%.

The perylene alone do not directly generate electric charges, but it transfers the energy to the phthalocyanine, which in turn induces the current. This technique increases the efficiency for over 25%.

But to go from lab scale to industrial applications, a barrier must still be overcome: the problem of long-term stability of their vitrification. For the development of dye-sensitized photovoltaic cells, chemistry professor Michael Graetzel has received last year the Prize from the International Balzan Foundation.

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