In this article I will discuss the Physics and the Science behind Solar cells.
The Physics behind the Solar cells is called photo electric effect. It was this explanation wan the Nobel Prize for Einstein. This photo electric effect was discovered by th experiments done in which light frequency and intensity wer varied. It was observed if frequency is beolw certain charecteristics which is different for different materials nothing happened even the intensity of light is fairly high. In addition, it was observed if frequency of light is above the threshold more electrons were found on the surface of materials. In addition if the intensity of light increased more electrons were found on the surface of the material. If frequency was increased electrons move away from the material with greater kinetic energy. Einstein argued that is due to the particle nature of light called photons. These bundles of light carry energy proportional to the frequency in these photon packages. It takes a certain minimum quantum of energy to kick an electron from an atom which is called the ionization energy. If the energy is too lower than the minimum energy then no electron will be kicked off from an atom. However, if the energy is high compared to the minimum energy then eelectrons will be kicked off from the atom. Coupled with this if intensity is increased then more electrons will be kicked off from the atom.
If a negatively charged electroscope and if a Zinc metal a top of electroscope and if ultrviolet light is shed on this then one see the leaves of the electroscope come gradually down due to loss of electrons.
Semiconductors of bands, and band gap
Photo electric effect can generate electrons on the surface of materials on the proviso that the electrons do not leave the surface. In may materials the recombination of electrons with ions are immediate. Materials which prevent recombination are the materials suited to build Solar cells.In this respect semiconductors are the candidates to be useful in constructing Solar cells.
When atoms are in a solid they often being separated from one another in regular spacing in three dimensions and from a lattice. Such an array of lattices are called a crystal structure. Because the atoms influence one another, the electrons energy levels combined in such a way that the possible energy levels of the electrons are spread out in to bands. Some are partially full or full or empty. In metals the existence of bands allow electrons to wander about where ever they are pushed within the material. Such materials are conductors. In insulators some band have higher energy levels than others. In these materials some are filled some are unfilled, In these materials electrons are not free to move. Energy to move electrons from one band to the next is called band gap.
In semi conductors the filled band ( valence band) and the band where electrons are free to move is separated by 1 volt. Hence the light can push the electrons from valance band to conduction band. If it is kept recombine again then it can give up its energy in an external circuit before coming back to the material.
Doping of Semiconductors