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How do semiconductor layers create an electric current in a solar cell?
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energy conversion
Before the Industrial Revolution, power came from three main sources: humans, draft animals, and water.
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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In a solar cell, semiconductor layers create an electric current through the photovoltaic effect, a process driven by the interaction between light and the material's electronic structure.31
The process functions as follows:
- Excitation: When light strikes the semiconductor absorber layer, photons transfer energy to electrons. This energy excites electrons, causing them to jump from the lower-energy valence band to the higher-energy conduction band.31
- Charge Carriers: This transition leaves behind a vacancy in the valence band known as a hole. Both the free electrons in the conduction band and the holes in the valence band are mobile charge carriers.21
- Built-in Electric Field: To prevent these carriers from simply recombining, the cell uses a junction between two dissimilar materials—typically a p-type and an n-type semiconductor. This contact creates a built-in [electric field].31
- Current Generation: The electric field exerts a force on the free electrons and holes, forcing them to move in specific directions. This collective, oriented motion constitutes an electric current that flows through electrical contacts into an external circuit to perform work.341