Introduction to Solar Cell

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Introduction to Solar Cell

A solar cell is also known as photovoltaic cell or a photoelectric cell which is made of solid state electrical device that converts light energy directly into a electrical energy by the photovoltaic effect.

The term "photovoltaic" derived from the Greek meaning "light", and "voltaic", from the name of the Italian physicist Volta, after whom a unit of electro-motive force, the volt, is named.  The photovoltaic effect was first recognized in 1839 by French physicist A. E. Becquerel and the first photovoltaic cell was built, by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions.

The solar cell works in three steps:

1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.

2. Electrons (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.

3. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.

How are Solar Cells made?

Silicon solar cells are made using either

· single crystal wafers

· polycrystalline wafers

· Amorphous silicon

Single crystal wafers-

Single crystal wafers are sliced, from a large single crystal brick which has been grown at around 1400oC, which is a very expensive process. The silicon must be of a very high purity and have a near perfect crystal structure and a single crystal solar cell is made.

Polycrystalline wafers-

Polycrystalline wafers are made by a casting process in which molten silicon is poured into a mould and allowed to set. Then it is sliced into wafers. As polycrystalline wafers are made by casting they are significantly cheaper to produce, but not as efficient as mono-crystalline cells. The lower efficiency is due to imperfections in the crystal structure resulting from the casting process. After that a polycrystalline wafers solar cell is made.

Amorphous silicon-

Amorphous silicon, one of the thin film technologies, is made by depositing silicon onto a glass substrate from a reactive gas such as silane (SiH4) Amorphous silicon is one of a number of thin film technologies. This type of solar cell can be applied as a film to low cost substrates such as glass or plastic. Other thin film technologies include thin multicrystalline silicon, copper indium diselenide/cadmium sulphide cells, cadmium telluride/cadmium sulphide cells and gallium arsenide cells.

In solar cell production the silicon has dopant atoms introduced to create a p-type and an n-type region and thereby producing a p-n junction. This doping can be done by high temperature diffusion, where the wafers are placed in a furnace with the dopant introduced as a vapour. There are many other methods of doping silicon. In the manufacture of some thin film devices the introduction of dopants can occur during the deposition of the films or layers. After this process  a Amorphous silicon solar cell is made.

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Introduction to Solar Cell

This article was published on 2012/01/13