Photovoltaics converts photons into electrons
Photovoltaic (PV) cells are magical objects that convert light energy, usually from the sun, into electrical energy.photovoltaic cellsor PV for short, are magical objects that convert light energy, usually from the sun, into electrical energy. Solar cells are made from semiconductor materials such as silicon (Si), the second most abundant material in the world after oxygen, which is used to convert sunlight into electricity, as photovoltaics turns photons into electrons.
This conversion process, however efficient, does not produce any harmful waste or emissions to the environment, making it a clean, green and efficient source of energy. Secondly, a photovoltaic cell, also known as a "solar cell", is a semiconductor device that generates direct current electricity when light falls on it.
Photovoltaics transforms photons into electrons through the so-called "photovoltaic" effect, (photo meaning light, and voltaic meaning electricity). In the photovoltaic effect, photons from sunlight strike the surface of the silicon semiconductor material, releasing free electrons from the atoms of the material. There are a variety of different materials from which a solar cell can be made and all convert solar radiation into direct current (DC) electricity.
The photovoltaic solar cell is usually made from modified silicon crystals such as silicon crystallin and amorphous, or other semiconductor materials, which absorb and convert sunlight into electricity.
Certain "doping" chemicals are added to the silicon composition to help establish a path for the passage of the released electrons. This creates a flow of electrons called direct current.
Semiconductors are non-metallic materials, such as germanium and silicon, whose solar cell characteristics are somewhere between those of a conductor, which offers very little resistance to the passage of electric current, and an insulator, which blocks the passage of electric current almost completely. Hence the term "semiconductor".
The silicon-based material is called a semiconductor because the device only conducts electrons in one direction, from negative to positive.
Crystalline silicon has been the main material used to manufacture solar photovoltaic cells over the past few decades, with polycrystalline silicon and amorphous silicon leading the way. The recent increase in interest in domestic solar energy and photovoltaic cells has led to significant advances in thin film solar technology, with cadmium telluride and copper indium sulphide now being used in domestic renewable energy applications.
Photovoltaic cells essentially consist of a junction between two thin layers of dissimilar semiconductor materials. One layer of silicon is treated with a substance to create an excess of electrons. This becomes the negative or "N" type semiconductor layer. The other layer is treated to create a deficit of electrons and becomes the positive or "P" type semiconductor layer.
N-type semiconductors are made from crystalline silicon that has been "doped" with tiny amounts of an impurity atom (usually phosphorus) so that the doped material has a surplus of free electrons, hence the term negative-type semiconductor. P-type semiconductors are also made from crystalline silicon, but are doped with very small amounts of a different impurity atom (usually boron), resulting in a deficit of free electrons in the material.
These 'missing' electrons in the semiconductor lattice are affectionately called 'holes' and since the absence of a negatively charged electron can be considered equivalent to a positively charged particle, silicon doped in this way is known as a positive type semiconductor.
When these dissimilar semiconductor materials are assembled with conductors, the arrangement becomes a light-sensitive PN junction semiconductor that establishes an electric field in the junction region and is commonly referred to as a photovoltaic solar cell. Thus, when similar solar or PV cells are combined in solar panels, the result is a much higher electricity generation capacity.
So how does a photovoltaic cell turn photons into electrons?
Sunlight acting as a fuel carries energy into the photovoltaic cell. When a photon particle of sunlight strikes the surface of the silicon solar cell or doped structures made of silicon-phosphorus or silicon-boron, the photons of absorbed sunlight break away and dislodge electrons from the energy-transferring silicon atoms of the cell and excite them. This excitation of the electrons causes them to break free from their parent atom and move to a valence level valence level. As billions of photons strike the cell every second, many electrons are released.
Eventually, the excited electron is expelled from the atom, allowing it to move freely around the semiconductor material. As one side of the PN junction has a "lack of electrons" (holes) while the other side of the junction has an "excess of electrons", these free electrons move across the junction, creating and filling holes in the cell. It is this movement of electrons and holes that generates electricity and as long as there is light hitting the cell, there will be electrons leaving the cell. The physical process by which a PV cell converts sunlight into electricity is known as the photovoltaic effect.
The electrons released by the interaction of sunlight with the semiconductor material create a flow of electrons as the free electrons move together around an external circuit. The production of electrical energy requires both voltage and current. Thus, to produce energy, the PV cell must generate a voltage as well as the current provided by the flow of electrons.
The cell voltage is provided by the internal electric field created by the PN junction, which can be thought of as a small battery producing a fixed output voltage of about 0.5 to 0.6 volts.
A single silicon PV cell typically produces an electrical current of about 3 amps, with a single photovoltaic solar cell producing up to 1.5 watts of power. Depending on the semiconductor materials used, some PV cells can produce more power than this, and others less. So 36 cells connected together in series have enough voltage and power to charge 12-volt batteries or run pumps and motors.
Sunlight is clean, easy to harness and available worldwide, and because it comes from the sun, it will continue to be freely available for millions of years to come. Solar energy is clean, green and efficient and with today's efficient solar panels or photovoltaic cells readily available on the market, homeowners can have free, clean energy for many years with the only cost involved being the cost of a solar panel itself, making solar energy an ideal choice as part of a home renewable energy system.
Photovoltaic cells convert one type of energy (sunlight) into another (electron flow).
Converting sunlight into electricity is also very environmentally friendly, as it produces no pollution or waste, making it ideal for a greener future.
Photovoltaics is very modular: You can install a PV system as small or as large as you like. The simplest PV cells power watches and calculators, while larger, more complex solar panels and arrays can be used to lighting houses and feed into the electricity grid.