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 . Therefore, the essential basic element for this type of renewable energy .
The 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 consists 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 the device is capable of providing. The type of electrical 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 semiconductors cadmium telluride, gallium arsenide and copper diseleniur in indium.
Description of the photovoltaic cell
The most common photovoltaic solar cell is a crystalline silicon sheet with an approximate thickness of 0.3 mm. The manufacturing process is of a sophisticated and delicate level in order to achieve a homogeneity of the material.
The electric field is generated from the different polarization of two areas of the photovoltaic cell . Generally, the upper part has a negative character and the rest positive to create the pn junction.
It is achieved, thus, that one of its areas has:
- Electron defect, called po 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, non-negative call, 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 through the surface of the N layer is produced, 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 face). There are two of the main ones and, in addition, there are the ramifications that unite them to better collect the electrons in the entire 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 weft or even a continuous sheet that allows the reduction of the internal resistance value.
Working principle of the photovoltaic cell
When a photovoltaic solar cell is connected to a load or consumption and, at the same time, is illuminated by the Sun , it generates a potential difference between its contacts that causes the circulation of electrons through the charge.
Under these conditions, the cell functions as a current generator. Next, we will describe in a little more detail the different processes that make it possible:
- The photons that reach inside the cell and have a kinetic energy equal to or greater than the energy of Valencia impact the material and generate pairs of carriers (electro-hole).
- The electric field, or potential difference, produced by the pn 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 load is the rest between its gross production capacity and the losses by recombination between electrons and photons .
Photoelectric cell applications
Photovoltaic cells are sometimes used alone (garden lighting, calculators, …) or grouped in photovoltaic solar panels .
They are used to replace batteries (energy is by far the most expensive for the user), cells have invaded calculators, clocks, devices, etc.
It is possible to increase its range of use by storing by means of a (capacitor or electric battery ). When used with a device to store energy, a diode must be placed in series to prevent system discharge during the night.
They are used to produce elec t ricidad for many applications (satellites, parking meters, …) and for powering homes or public network in case of a photovoltaic solar plant.