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Types of PV cells |
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Crystalline Silicon PV Cells: 88% market share |
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Mono-crystalline: Mono-crystalline cells are the most common type of PV cell on the market. These cells are produced by slicing wafers of crystalline silicon from a large rod of silicon known as a boule. This rod is grown in a furnace which fuses vaporized silicon onto a crystal seed. Once these crystals are sliced into wafers, they are etched or cut with a laser to insert wires into the front of the cell to act as the anode or positive terminal. The back of the cell is coated with a carbon film or foil which acts as the cathode or negative terminal. |
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Multi-crystalline: Multi-crystalline cells are made in a similar manner to mono-crystalline cells, but they are not cut from a boule. Silicon is first cast into bricks, which are then cut into wafers. The advantage to this process is the speed! Growing a boule in a silicon furnace takes a long time, but if liquid silicon is poured into a form and then cut, the process time is drastically reduced, along with the price! |
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Thin Film PV Cells: 12% market share |
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| Amorphous thin film PV cells are a rather interesting! Some of them are flexible, and by flexible we mean they can be rolled up! Amorphous films are generally made of Silicon, just as the other cells, but the silicon is in a different state which allows it to flex and bend. Amorphous PV cells are less |
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| efficient than their comparable mono-crystalline or multi-crystalline counterparts, but scientists are finding unique ways around this. The Staebler-Wronski Effect causes the degradation in amorphous silicon, producing a decrease in total output over time until a relative state is reached where the output stabilizes. The solar roofing materials above have produce more power then their comparable crystalline counterparts because they have multiple layers of amorphous film. | ||||
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Scientists
are layering the amorphous silicon films and stacking the equivalent of
three amorphous silicon cells on top of each other in what is called a
"triple junction cell". By layering cells, the light that passes through the previous layer is collected in the next. This does not reverse the Staebler-Wronski Effect, but it does increase the output of the PV panels without increasing their size. Click the image to the left for a larger view of the layering. |
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Other materials used to manufacture thin film PV cells are Cadmium Telluride
(CdTe), Copper Indium Diselenide (CIS), and Copper Indium Gallium Diselenide
(CIGS). Some forms are flexible and others are not, depending on the
manufacturing process and intended use.
Ribbon Silicon: Solar cells using silicon ribbons are similar to others in their components, though the silicon is manufactured quite differently. Silicon is grown for these cells in ribbons. The molecules of silicon are lined up end-to-end which yields a lower resistance and higher output. Though the manufacturing costs are rather high at present, as the process is improved the price will come down. |
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