Solar Cell

The photovoltaic effect was experimentally demonstrated first by French physicist Edmond Becquerel

Q.What is a solar cell?

A.A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by thephotovoltaic effect.

Q.Explain the operation of photovoltaic cell.

A. The operation of a photovoltaic (PV) cell requires 3 basic attributes:

  • The absorption of light, generating either electronhole pairs or excitons.
  • The separation of charge carriers of opposite types.
  • The separate extraction of those carriers to an external circuit.

Q.What are the different layers of a solar cell?

A.The different layers are:

A. Encapsulate – The encapsulate, made of glass or other clear material such clear plastic, seals the cell from the external environment.

 

B. Contact Grid– The contact grid is made of a good conductor, such as a metal, and it serves as a collector of electrons.

 

C. The Antireflective Coating (AR Coating)– Through a combination of a favorable refractive index, and thickness, this layer serves to guide light into the solar cell. Without this layer, much of the light would simply bounce off the surface.

 

D. N-Type Silicon – N-type silicon is created by doping (contaminating) the Si with compounds that contain one morevalence electrons* than Si does, such as with either Phosphorus or Arsenic. Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth valence electron is available for conduction.

 

E. P-Type Silicon– P-type silicon is created by doping with compounds containing one less valence electrons* than Si does, such as with Boron. When silicon (four valence electrons) is doped with atoms that have one less valence electrons (three valence electrons), only three electrons are available for bonding with four adjacent silicon atoms, therefore an incomplete bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates another hole in a different Si atom. This movement of holes is available for conduction.

 

F. Back Contact – The back contact, made out of a metal, covers the entire back surface of the solar cell and acts as a conductor.

Q.how does the photon proceed in a solar cell?

A. After a photon makes its way through the encapsulate it encounters the antireflective layer. The antireflective layer channels the photon into the lower layers of the solar cell.Once the photon passes the anti reflective layer, it will either hit the silicon surface of the solar cell or the contact grid metallization. The metallization, being opaque, lowers the number of photons reaching the Si surface. The contact grid must be large enough to collect electrons yet cover as little of the solar cell’s surface, allowing more photons to penetrate.

Q.Does the presence of photon result in photoelectric effect?

A.Yes it does the photon’s energy transfers to the valence electron of an atom in the n-type Si layer. That energy allows the valence electron to escape its orbit leaving behind a hole. In the n-type silicon layer, the free electrons are called majority carriers whereas the holes are called minority carriers. As the term “carrier” implies, both are able to move throughout the silicon layer of the solar cell, and so are said to be mobile. Inversely, in the p-type silicon layer, electrons are termed minority carriers and holes are termed majority carriers, and of course are also mobile.

Q.Define Potentiometer.

A. An instrument for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance.

solar cell

 

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