Solar or photovoltaic (photo = light, voltaic = voltage or electricity) cells are created from special materials such as Silicon (Si) mixed with other elements, which when exposed to sunlight will generate an electrical current.
Basically sunlight is absorbed into the photovoltaic material, which in turn knocks electrons within the material loose.
This allows the electrons to flow freely within the material structure, creating an electrical current.
Silicon is a common choice for solar cells because of its inherent physical qualities.
Silicon has 4 outer shell electrons from a possible 8 ‘holes’.
It will always try to fill the other 4 ‘holes’, and does this by sharing electrons with neighbouring silicon atoms.
This creates a lattice type structure, where every atom in the structure bonds with four other atoms in the structure.
When energy is added to the silicon, in the form of sunlight, it can knock electrons free of the lattice structure, but this requires a lot of energy and generates very few free electrons.
With few free electrons, there is very little current flow, so impurities are added to the silicon to increase its current carrying properties.
This process is called ‘doping’.
The silicon is ‘doped’ with atoms which contain more electrons to create negatively charged silicon or with atoms which contain less electrons to create positively charged silicon.
These compounds are referred to as n-type and p-type respectively.
When energy is added to n-type silicon there are a lot more free electrons present within the structure.
This n-type silicon is placed next to the p-type silicon, causing the free electrons in the n-type silicon to rush towards the holes in the p-type silicon, which creates a current flow.