Friday, November 7, 2008

Here Comes the Sun, continued

Maybe it's because I'm looking, but it seems there's a new advance in solar energy daily. Here is more on improved efficiency in dye-sensitized solar cells (known as Gratzel cells). These easier-to-make, cheaper cells are now reaching the 10% efficiency necessary to compete with conventional solar cells. Some background from the Australia-based solar company Dyesol:
Leaves of plants are tiny factories in which sunlight converts carbon dioxide gas and water into carbohydrates and oxygen. They are not very efficient however but are very effective over a wide range of sunlight conditions. In spite of the low efficiency and the fact that the leaves must be replaced, the process has worked for hundreds of millions of years, and forms the primary energy source for all life on earth.

Since the 1970's, attempts have been made to create a better solar cell based on this principle. There were early attempts to cover crystals of semiconductor titanium dioxide with a layer of chlorophyll. However, the electrons were reluctant to move through the layer of pigment, so the efficiency of the first solar cells sensitised in this way was about 0.01%.

Then in 1988 at EPFL in Switzerland, Michael Graetzel discovered that nanotechnology could overcome the problem. Instead of using a single large titanium dioxide (titania) semiconductor, he worked with a sponge of small particles, each about twenty nanometres in diameter, coated with an extremely thin layer of pigment. This method increased the effective surface area available for absorbing the light by 'many times'- now the sunlight was efficiently converted into an electric current.

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