Conventional solar cells consist of silicon wafers. They convert light into energy by making use of the photovoltaic effect that takes place at the junction of p-type and n-type semiconductors. The absorption of light in these solar cells causes electrons to excite: to 'jump' out of their positions and leave behind electron holes. The electric field in the p-n junction then causes charge separation. The movement of the electrons and holes causes the solar cell to work. In order to avoid the premature recombination of electrons and holes however, the silicon must be extremely pure and free of defects. This makes production of silicon solar cells very expensive.

The dye sensitized solar cell works on a different principle, where the absorption of light and the separation of charge carriers do not take place in the same material. The cell consists of two conducting glass electrodes (usually in the shape of small plates) in a sandwich configuration with a redox electrolyte separating the two. On one of the electrodes a compact but very porous layer of TiO2 is constructed. On the particles of TiO2 a dye is adsorbed.
When light falls onto the dye sensitized solar cell it is absorbed by the dye. The electrons that are excited due to the extra energy the light provides can escape from the dye and into the TiO2 and diffuse through the TiO2 to the electrode. They are eventually returned to the dye through the electrolyte.

The dye sensitized cell is made from much cheaper materials than the conventional type with silicon wafers. TiO2 is a very common material (also used in toothpaste and sun lotion) and the dye can be an organic type like the colouring you find in blackberries. The efficiency of the cell is not very high yet, but this will improve with continued research.

The dye sensitized solar cell was developed by the group of professor Graetzel at the Swiss Federal Institute of Technology. You can find more detailed information and also some diagrams on how the cell works at their site:

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