Inside an amorphous silicon solar cell

July 12, 2007
Thin-film solar cells often use amorphous silicon as the basic photosensitive material, or amorphous silicon in combination with microcrystalline silicon (that is,amorphous silicon containing small grains of crystalline silicon).

An example of such a cell is that from United Solar Ovonic LLC. It uses three layers of amorphous silicon created so that each has a different bandgap energy. The different bandgaps let each layer react to a different part of the sun’s energy spectrum as a way to boost conversion efficiency. The cells absorb blue, green,and red light in layered thin films of amorphous silicon and germanium alloys containing hydrogen and fluorine.

The microcrystalline silicon has a high electron mobility and is relatively stable. The amorphous materials don’t have prolems with grain boundaries in the crystal lattice of crystalline silicon used in coventional solar cells. The imperfections can cause a lot of charge carriers to be asorbed in the silicon material rather than generate electrical current,and thus forces conventional cells to be relatively thick (50 to 100 microns) in order to generate a usful amount of electrical current. In contrast, the triple-layer amorphous cell used by United Solar is less than 1 micron thick.

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