There are three main types of PV cells in the mainstream market today: Monocrystalline, polycrystalline and amorphous. This nomeclature refers to the crystal structure of the silicon wafers, and monocrystalline cells (cut from single crystal) are the most efficient but most expensive, while amorphous cells (formed from a blend of very small crystals) are the least efficient and cheapest, but are more flexible.

Basic Construction and Operation

The basic PV cell consists of two different silicon semiconductors sandwiched together between very thin transparent wires. To make the semiconductors, crystals of silicon (similar to those used in microchips and computers) are sliced into thin wafers. These wafers are then 'doped' with additives, such as boron and phosphorous. This doping process disrupts the rigid, regular structure of the silicon and either leaves spare, unbonded electrons (n-type silicon) or creates 'holes' where electrons should be (p-type silicon).

When the boundary between the two silicon layers (the p-n junction) is exposed to certain wavelengths of light, including those found in sunlight, the 'spare' electrons in the n-type layer become excited. This gives them sufficient energy to move across the p-n junction to 'fill' the 'holes' in the p-type layer (they are attracted to the holes as they are opposite charges).

The net effect of this is that there are more electrons in the p-silicon than there should be, so it becomes negatively charged, while the n-silicon has become deficient in electrons, making it positively charged. This creates a voltage potential between the two silicon layers.