In electronics, a photoelectric cell or a photovoltaic cell is an electrical / electronic device that converts the incident energy of solar radiation into electricity through the photovoltaic effect. Photovoltaic cells are the basic components of photovoltaic modules, which are solar panels capable of generating electrical energy from solar radiation. It is therefore the essential basic element for this type of renewable energy.
Compounds of a material that has a photoelectric effect absorb photons of light and emit electrons. When these free electrons are captured, the result is an electric current that can be used as electricity. A photovoltaic panel is composed of a group of photoelectric cells forming. This group of photovoltaic cells form a network of solar cells connected in series circuit to increase the output voltage while connecting several networks in parallel circuit to increase the electrical current that is capable of providing the device. The type of electric current it provides is direct current.
The average conversion efficiency obtained by commercially available photovoltaic cells produced from monocrystalline silicon is lower than that of multilayer cells, usually gallium arsenide. Currently there are also new technologies in the production of solar panels that do not use silicon, for example, with cadmium telluride semiconductors, gallium arsenide and indium copper diseleniur.
Description of the photovoltaic cell
The most common photovoltaic solar cell is a crystalline silicon sheet with a thickness of approximately 0.3 mm. The elaboration process is of a sophisticated and delicate level to be able to achieve a homogeneity of the material.
The electric field is generated from the different polarization of two zones of the photovoltaic cell. Generally, the upper part has a negative character and the positive side to create the p-n junction.
It is achieved, thus, that one of its zones has:
- Electron defect, called p or positive zone, or anode or receiver. Generally, it is achieved by adding to the pure silicon a small part of boron that only has 3 valence electrons.
- Excess of electrons, called n or negative, or cathode or emitter. Generally formed by the diffusion of phosphorus that has 5 electrons in the last orbit.
Due to this difference in electrical charge in the material, the electric field responsible for pushing the electrons out of the cell is produced by the surface of the N layer, which implies the establishment of an electric current.
The solar cell is equipped with electrical contacts to channel the energy it produces when it is illuminated. These contacts are designed in a branched way (on the sunny side). There are two main ones and, in addition, there are the branches that join them to collect better the electrons in the whole surface of the cell. The objective is to combine a good electrical contact, low resistivity and make the minimum shade so that the photons reach the active material of the cell.
On the back side, the contacts usually form a tight frame or even a continuous sheet that allows the reduction of the value of the internal resistance.
Principle of operation of the photovoltaic cell
When a photovoltaic solar cell is connected to a load or consumption and, at the same time, illuminated by the Sun, it generates a potential difference between its contacts that causes the circulation of the electrons through the charge.
Under these conditions, the cell functions as a current generator. Next, we will describe with a little more detail the different processes that make it possible:
- Photons that reach the interior of the cell and have a kinetic energy equal to or higher than the valence energy impact on the material and generate pairs of carriers (electro-hole).
- The electric field, or potential difference, produced by the p-n junction separates the carriers before recombinations can occur.
We can say that the current generated by a photovoltaic solar cell illuminated and connected to a charge is the rest between its gross production capacity and the losses by recombination between electrons and photons.
Applications of the photoelectric cell
Photovoltaic cells are sometimes used alone (garden lighting, calculators, ...) or grouped in photovoltaic solar panels.
They are used to replace the batteries (the energy is by far the most expensive for the user), the cells have invaded the calculators, clocks, devices, etc.
It is possible to increase its usage range by storing it with a (condenser or electric battery). When used with a device for storing energy, a diode must be placed in series to prevent discharge of the system during the night.
They are used to produce electricity for many applications (satellites, parking meters, ...), and for powering homes or in a public network in the case of a photovoltaic solar power station.
Last review: May 25, 2018