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A "solar cell" is a device which converts light energy from the sun into electricity. Solar cells are currently used in a wide range of applications, such as calculators, watches, road signs, streetlights, and marine and alpine observation equipment. Recently solar power generating systems using solar cells have also become more widespread in general housing.
Solar cells do not generate carbon dioxide (CO2) which contributes to global warming, or sulfur oxide (SOx) or nitrogen oxide (NOx) which cause acid rain. Not only that, but in contrast to fossil fuels (oil, coal, natural gas) and uranium of which there are finite deposits, the solar energy which reaches the earth's surface is vast and unfailing. Greater expectations are being placed on solar cells as an environmentally-friendly energy source free of concerns for depletion. |
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Solar cells use the property of semiconductors, which generate an internal charge when they receive light. Currently the mainstream "silicon solar cells" comprise two types of semiconductors with different electrical properties - n-type and p-type - connected to one another (see diagram). When the surface where p-type and n-type semiconductors are joined receives light energy, free electrons (negative) and holes (positive) are generated, and the internal electrical field at the pn junction causes the electrons to move to the n-type semiconductor, and the holes to move to the P-type semiconductor. If the electrodes on the two types of semiconductor are connected by an external wire (see diagram), electrons move along the wire, i.e. current is generated. |
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There are two types of silicon solar cells - "crystalline" and "amorphous (non-crystalline)." Crystalline solar cells can be further classified into single crystal type, which have high conversion efficiency, and polycrystalline type, which are inexpensive to produce.
Amorphous solar cells are fabricated by vapor-depositing silane gas directly onto a glass substrate, so a significant feature of this type is that only a small quantity of raw material silicon is required. Recently crystalline/amorphous hybrid types have started to appear in a bid to improve conversion efficiency.
There are also "organic" solar cells which do not use silicon at all. The foremost of these is the "dye-sensitized solar cell." As the principle of power generation is similar to photosynthesis which occurs in plants, this type of cell is also referred to as a photosynthetic solar cell. The materials required are inexpensive, and production does not require large-scale facilities, so this type of solar cell is attracting attention as a low-cost solar cell. |
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