Solar Panels

Photovoltaic (PV or solar) cells are made of semiconducting material which directly convert sunlight into electricity. The simplest system of photovoltaic cells power small devices such as watches and calculators. More complex systems can light houses and provide power to the electrical grid.

Crystalline silicon (c-Si) is the leading commercial material used for solar panels. The forms it is used in are:

• Monocrystalline
• Polycrystalline
• Ribbon
• Sheet
• Thin-layer silicon

How Solar Panel Works:

When light is absorbed by a semiconductor such as silicon, the electrons within the material increase in energy. This increase in energy causes the electrons to move within the material. However, there must be charge carriers in order for the electrons to move in a preferred direction to generate an electrical current. Charge carriers are created by doping the semiconductor, which is to say adding small amounts of impurities to change the material's electrical properties.

Silicon is an element with four valence electrons. This means that when a silicon atom bonds with other silicon atoms, they complete their valence shells by sharing all four electrons. Doping silicon involves adding small amounts of a material with three valence electrons or a material with five valence electrons. By adding a small amount of aluminum, for example, an atom with three valence electrons, covalent bonding of the aluminum to silicon creates 'holes'. A 'hole' is the absence of an electron where there would normally be one if there was no impurity bonded to silicon, which results in a p (positive) -type silicon semiconductor. Adding a small amount of an atom with five valence electrons, such as antimony, causes an opposite effect. Once antimony is bonded to other silicon atoms, there will be an extra electron that is loosely bound to antimony, which will result in a n (negative) -type silicon semiconductor. Introduction of a voltage to either type of semiconductor causes current to move in a preferred direction.

A solar panel uses a layer of p-type silicon and a layer of n-type silicon. This way, when light is absorbed and the electrons in the n-type layer increase in energy, the electrons will be able to travel from the n-type layer to the 'holes' in the p-type layer. This electrical current is what allows solar panel technology to convert light energy into electricity.

Production techniques of solar cells include the Czochralski process, float-zone method, and thin film deposition. The removal of surface impurities and defects in the silicon is of critical importance, and is addressed with techniques such as surface passivation and gettering.

Silicon based solar panels are not the only type of solar cells. Other types include solar panels that use conductive polymers or light absorbing dyes.