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Principle of Solar Cell |
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| How do we make electricity from sunlight? |
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Solar cell
(polycrystalline silicon)
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Solar modules are vital in order to convert sunlight directly into electricity. Solar modules are made of semiconductors which are very similar to those used in the manufacturing of integrated circuits for electronic equipment. The most popular type of semiconductor currently in use is silicon crystal. Silicon crystals are laminated into n-type and p-type. When light is applied, a photoelectric effect is induced which generates power. The electricity produced is called direct current and can be immediately stored in typical acid batteries. For systems installed on homes served by the utility grid, a device called an "inverter" (power converter) changes the electricity to alternating current in order to use it as a standard power supply. |
| Power generation using the p-n gate |
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High purity silicon crystals are used in solar cells. The crystals are processed into solar cells using a melt and 'cast' method. The cast 'cube' is then cut into 'ingots', and then sliced into very thin wafers.
The processing of these wafers is as follows:
Silicon atoms have four "arms". Under stable conditions, they become perfect insulators. By combining a small number of five-armed atoms (with a surplus electron), it will have a negative charge when sunlight(photons) hit the surplus electron. The electron is then discharged from the arm and moves around freely. Silicon with these impurities will conduct electricity. This is called a n (negative)-type semiconductor, and is usually caused by having the silicon 'doped' with a boron film.
On the other hand, combining three-armed atoms would lack one electron, which will result in a hole with an electron missing.The semiconductor will then carry a positive charge. This is called a p (positive)-type semiconductor, and is usually obtained when phosphorous is doped into the silicon.
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A p-n junction is formed by placing p-type and n-type semiconductors next to one other. The p-type, with one less electron attracts the surplus electron from n-type to stabilize itself. Thus the electricity is displaced and generates an electric flow.
When the sunlight hits the semiconductor, an electron springs up and is attracted toward the n-type semiconductor. This will cause more negatives in the n-type and more positives in the p-type semiconductors, generating a higher flow of electricity. This is the photovoltaic effect. |
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