Crystals in a Solar Energy CellThis page deals with the original solar energy cell design that uses silicon atoms arranged in a covalently bonded 3-dimensional lattice. Other types of photovoltaic solar cells are dealt with on other pages. Let's start with the definition of a CRYSTAL. According to the Wikipedia, "a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions." We are dealing with atoms, so that is the word I will use in this discussion. In terms of the solar cell as we have been discussing it, a crystal of silicon atoms would look like this:
Monocrystalline solar cells
That's what ONE silicon crystal would look like. It goes on like that until you reach the edge of the crystal. There is no break in the structure, it is continuous. Growing large, continuous crystals like this is difficult and expensive. Solar cells that are made from a single unbroken crystal are called monocrystalline, meaning "ONE crystal". These are the most efficient and also the most expensive solar cells. Note the uniform colour of the cell.
Multicrystalline solar cells
These are simply cells that are made of more than one crystal. The crystals are smaller than the ones used to make monocrystalline cells. Because they are smaller they are quicker and easier to grow. This then brings down the manufacturing cost for multicrystalline solar cells. You can see the different crystal regions in this image; because of their slightly different orientations they reflect light slightly differently, giving the patchy appearance of the cell.
What difference does this make?Have a look at the two versions of the silicon lattice below. The one on the left represents a single crystal, the one on the right shows multiple crystals.
Each boundary between one crystal and the next has a tiny negative effect on the flow of electrons through the cell. The more boundaries there are, the poorer the electron flow. Return from Crystals in a Solar Energy Cell to Photovoltaic FAQ OR return to the Green Planet home page for more Solar Power Facts.
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