Photo Voltaic Effect
When light falls on a PN junction, a voltage difference builds up as a consequence of the absorption of photon energy parallel to it. The generation of parallel voltage difference due to the effect of light on the PN junction is called Photo Voltaic Effect. In other words, the production of voltage due to the influence of parallel light energy on some semiconductors is called Photo Voltaic Effect. Remember, when light falls on some semiconductor, voltage differences generate (due to absorption of light energy) due to the mutually inverse flow of electrons and holes within it. Further, voltage difference depends on the intensity of light, size and nature of the semiconductor, and generation quantity of electrons-holes pairs. Electricity is also produced using solar light through the photovoltaic effect. Such a system is called solar power generation.
The best example of a photovoltaic effect is a solar cell or photovoltaic cell (a cell resistance that changes with light). This cell functions on a principle of photovoltaic effect.
Solar Cell or Photo Voltaic Cell
A cell, which converts solar energy directly into electrical energy, is called a solar cell. It is also called a solar energy converter.
Working Principle of the Photovoltaic Cell:
We know that when the light casts on some photo-sensitive material (a material too sensitive to light), it emits electrons from its surface by means of absorbing photon energy derived from light. Thus, deficiency of negative charge occurs in this material (as electrons have a negative charge) and from an electric point of view, the material gets positive. On the contrary, material that absorbs electrons becomes negative from an electric point of view (as a positive charge of material declines). There are two different layers of two varied materials in a solar cell(one material emits electrons due to the reflection of light while the second one absorbs it) and it works on the same principle.
Construction of the Photovoltaic Cell
A solar cell basically consists of two layers of semiconductor materials (through recombining which a junction is manufactured) or a silicon PN junction. There is a narrow glass above the cell, through which light permeates into the junction. A layer of P material is relatively thin so that light reflecting on it or photon energy could reach the junction easily (so that the photovoltaic effect occurs easily). When suitable frequency light falls on the junction’s upper layer, its electrons, shatter its parent atoms by absorbing photon energy and start crossing the junction. Thus, free electrons and holes produce on both sides of the junction (remember holes move in the opposite directions of electrons) This process goes on until a potential difference produces parallel to the cell due to the collection of negative ions on one side of the junction and positive ions on another side. There are those maximum voltages, which generate a photovoltaic cell. For example, a silicon photovoltaic cell (in the case of the open circuit) provides 0.6 volts and gallium arsenide about 0.9 volts when placed directly into sunlight. Maximum voltage can be obtained through joining several solar cells in a series or a required current through connecting cells parallel. Remember, solar cell’s current is directly proportionate to illumination. Further, it also depends on the surface size of a cell. Moreover, the power output of the cell depends on the level of sunlight. The cells are made in the form of flat disks or flat strips in order to increase their surface area.
Germanium and silicon are mostly used as semiconductor materials in solar cells. However, gallium arsenide, indium arsenide, and cadmium arsenide are also used nowadays. The construction of a basic solar cell has been elaborated in figure1
Uses of the Photovoltaic Cell
The cells working on principles of photovoltaic effect are used for charging satellite batteries directly from sunlight. As they are small in size and also have low output, therefore this objective is achieved by fitting hundreds of cells on a series or parallel. Moreover, these cells are also used in observatories, laboratories, battery charging units, calculators, electronic instruments, solar energy projects, space ships, and all those places where direct electrical energy is required through sunlight.
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