A photovoltaic cell is a device that turns light into electric energy.
There are three main types of photovoltaic cells.
- monocrystalline cells
- polycrystalline cells
- amorphous cells
Monocrystalline cells are the most expensive to make because they require very pure silicon and involve a complicated crystal growth process. They also have the highest energy efficiency of the three: around 16%.
Polycrystalline cells are less expensive because the cells are not grown in single crystals but in a large block that is then sawn into cells. Their energy efficiency is around 15%.
Amorphous cells are not crystals, but a thin layer of silicon vaporised on a cheap base such as glass. They are relatively cheap, but their energy efficiency is only around 8%. When light is diffuse, the difference in efficiency compared to the other types becomes smaller. This type of cell is typically used as a coating for windows, and on facades.
Development
Much research is currently going into photovoltaic cells. The main focus is making them cheaper and more efficient, so they can replace fossil energy better. This mostly means development of cheaper methods of obtaining silicon that is sufficiently pure. Silicon is a very common element, but is normally bound in glass sand.
The invention of conductive plastics that Alan Heeger got a Nobel prize for might lead to cells that can make do without silicon and might be much cheaper than current ones.
In 2004, the Fraunhofer Institute reported they had created a particularly small cell with an energy efficiency of over 20%.