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What is a Solar Cell? How does it work?

What is a Solar Cell? How does it work ?

Solar cells are electronic systems that can convert sunlight directly into electricity. However, in order to understand the definition of solar cell well, you need to know the definition of photovoltaic. The word photovoltaic is a combination of the Greek words photo, meaning light, and voltaic, meaning voltage. Other names of solar cells are the words photovoltaic cells, photovoltaic cells and solar cells. Solar cells can be made in square, rectangular, pyramid or circle shape. The areas of solar cells are generally 100 cm2. Their thickness varies between 0.2-0.4 mm. The solar cell has an efficiency between 5% and 20% depending on the materials used in its construction. Solar cells are connected in series and parallel to each other and form a solar panel or photovoltaic module. Solar panels are connected to each other in series and parallel to form large energy facilities called solar power plants or solar fields.

The materials used in solar cell production are as follows;

Crystalline silicon,

Amorphous silicon,

Gallium arsenic,

Cadmium telluride,

Copper indium diseleneide,

Optical condenser cells.

Solar Cell Working Principle

Solar cell cell generates electricity with photovoltaic effect. Photovoltaic effect is the physical event in which the sun’s rays are converted into electricity. Photons are formed when the sunlight hits the semiconductor surface and the electrons inside the atom are released. Photons contain different amounts of energy for each wavelength in the solar radiation spectrum. When the photons come to the solar cell, some of it is reflected exactly, some of it is absorbed by the solar cell and some of it passes through the solar cell. Photons absorbed by the solar cell generate electricity.


How Is Electric Current Formed In Solar Cells?

Sunlight is formed in different colors by combining low-energy infrared photons with high-energy ultraviolet photons and visible light photons in between. Any photovoltaic material responds to a narrow range of these energies, depending on its specific bandwidth. Bandwidth is the amount of energy required to send an electron from the atom-bound and electrons-filled valence band to the empty conduction band where electrons move freely. Its unit is electron volt and is represented by the eV symbol. If the semiconductor n-type binds to the dopant atoms to form an electrically negative material, it already has several electrons in the conduction band. Conversely, a p-type positive material binds to leave electrons or spaces in the valence band. The connection between N and P type creates a voltage supply. When the incident photons are absorbed, the electrons move towards the positive side of the joint and the voids towards the negative side. As a result of this movement, electric current occurs. Free electrons directed towards the positive side of the joint formed by photons coming to a photovoltaic cell create an electric current.

What Are The Usage Areas Of Solar Cells?

The usage areas of solar cells are very common. Their main usage areas are as follows;

Communication systems,

In oil pipelines,

In electricity distribution systems,

In water distribution systems,

At meteorology stations,

In lighting,

In forest watchtowers,

In the lighthouses,

In security cameras,

In alarm systems,

In agricultural irrigation systems,

In garden or hobby homes without electricity.


What Are The Types Of Solar Cells?

Solar cell types consist of 4 main technologies. These can be listed as crystal structure technology, thin film technology, unified technology and nanotechnology. All solar cell types are listed below. 1 Inorganic Solar Cells

A single layer inorganic solar cell consists of an inorganic semiconductor such as silicon placed between 2 metal electrodes, one of which is semiconductor and has different electrochemical potential. The efficiency of single layer inorganic solar cells is very low.

2 Two Layer Inorganic Solar Cells

A 2-layer inorganic solar cell is made using 2 semiconductors, n-type and p-type. In these cells, charge separation takes place near the boundary between n-type and p-type semiconductors. Inorganic cells are chemically and heat-stable solar cells. Today, these solar cells can provide up to 30% efficiency

3 Single Crystal Silicon Solar Cells

Single crystal silicon solar cell is frequently used in solar panel production. The cost of single crystal silicon material is quite high. Therefore, polycrystalline solar cell is used more intensively. There are many reasons why silicon material is widely used in solar cell production. These are because silicon can preserve its electrical, optical and structural properties for a long time. Pure single crystal silicon technology is quite expensive and difficult. There is the most silicon element in the world after oxygen. Sand and quartz forms of this element are the most common. Sand is not preferred because of its low purity structure. But about 90% of quartz material consists of silicon. Quartz is obtained by many processes and 99% purity silica. Later, silicon is also obtained from silica. After these stages, silicon is purified to obtain semi-conductive polycrystalline silicon. The processes up to the stage of obtaining polycrystalline silicon are quite costly. Polycrystalline silicon is melted again and grown in order to obtain semiconductor pure polycrystalline silicon. The cores are drawn from the molten silicon bath at very low speed. Thus, the growth of thin single crystal layers is achieved. Most commercially used silicon (Si) solar cells are manufactured from boron-doped single crystal slices (400 micron thick) by the Czochralski (CZ) process. Cage defects do not occur in solar cells produced by the CZ process. Crystalline silicon batteries make up about 80% of the solar cell market. The efficiency of this solar cell variety ranges from 15% to 23%.

4 Polycrystalline Silicon Solar Cells

Polycrystalline silicon solar cell material is electrically, optically and structurally identical. The size of the veins is directly proportional to their quality. The discontinuity between the veins plays a preventive role in the transfer of electrical charge carriers. Polycrystalline silicon cells are easier to manufacture and less costly. Casting method is used in the production of polycrystalline silicon material. The production phase is briefly as follows. First of all, most of the processes to obtain single crystalline silicon are done exactly. Molten semiconductor silicon is poured into molds and waited for cooling. Blocks obtained from molds are cut in a square shape. The solar cell produced by this method is less efficient. But its cost is very low. Polycrystalline silicon (pc-Si) solar cell efficiency varies between 12-15%.

5 Thin Film Solar Cells

A thin film solar cell consists of extremely thin semiconductor layers placed one on top of the other. Thin film solar cell can be made from a wide variety of materials. Commercially used thin-film solar cells are made from amorphous silicon. Apart from that, very crystalline copper indium diseleneide and cadmium telluride are also used in its production. Different precipitation methods are used in thin film cell technology. These methods are quite inexpensive. In addition, with this method, 2 × 2 inch sized solar cells can be obtained. Layers are deposited on low cost glass or plastic-based material. While normally single crystal silicon is designed individually interconnected within the solar module, thin film devices can be made as a single unit. Non-reflective coating and conductive oxide layers are added to the semiconductor material and back electrical contacts. Thin film solar cells have an efficiency of 8-12%.

6 Amorphous Silicon Solar Cells

The atoms of amorphous solid materials such as glass are not arranged in a certain order. Such materials do not form a fully crystalline structure. It also contains a large number of structural and connection errors. In the past, the electrical properties of amorphous silicon were described as insulating. However, in the following years, it was thought that amorphous silicon could also be used in photovoltaic cells. Today, amorphous silicon is widely used in low power devices. Carbon, germanium, nitrogen and tin and amorphous silicon alloys are used to develop multi-functional devices. Amorphous silicon solar cell shows more than 13% efficiency in the laboratory environment. Thin film solar cells made with gallium arsenide show efficiency more than 24%.

7 Polycrystalline Thin Film Solar Cells

Polycrystalline thin film solar cell consists of very small crystalline particles of semiconductor materials. The materials used in this type of solar cells have different properties than silicon. In these cells, the electric field is created more easily with the interface between 2 different semiconductor materials. The polycrystalline thin solar cell has a top layer that is thinner than 0.1 micron, which is called a window. The function of the window layer is to absorb high-energy radiation energy. This layer must be thin enough to have sufficient band gap.

8 Thin Film Kalgonite Solar Cells

In 1960, CuxS-CdS, CuxSe-CdSe and CuxTe-CdTe thin film solar cell cells were developed. These solar cells are quite simple to manufacture. CdS, CdSe and CdTe films are produced by chemical precipitation process. CuxS, CuxSe and CuxTe layers are produced together with CdS, CdSe and CdTe films by immersion in CuCl solution for 1-2 minutes. These 3 types of solar cell cells can also give more than 10% efficiency. However, R&D studies have been terminated due to the deterioration of copper calgonite layers by copper diffusion. These solar cell types are no longer produced.

9 Cadmium Telluride Solar Cells (CdTe)

Cadmium telluride (CdTe) has a high solar absorption coefficient and ideal bandwidth. Cadmium telluride is one of the most promising photovoltaic materials in thin film solar cell technology. Cadmium telluride solar cell efficiency is more than 15%. And the solar panel modules made with these cells have more than 9% efficiency. Cadmium telluride is more suitable for easier storage and larger-scale production compared to other thin-film solar cell technologies. Cadmium telluride (CdTe) is a semiconductor formed by the combination of the second group element cadmium (Cd) and the 6th group tellurium (Te) element of the periodic table. CdTe has 1.45 eV bandwidth. This value is a very suitable value for generating electricity with solar cells. The optical absorption level of CdTe is 10 ^ 5 / cm and it is a very high value. Due to this feature, it is a very suitable material for photovoltaic applications to provide p-type conductivity. The compound can be easily developed in stoichiometric form at a temperature of 400 C (centigrade).

10 Copper Indium Diseleneide Solar Cells

It is a semiconductor formed by the combination of three or more elements of the 1st, 3rd and 6th group of the periodic table. The absorption coefficient of this semiconductor is quite high. Copper indium diseleneide solar cell is produced from composite semiconductor material made with copper, indium and selenium. The advantages of this thin film solar cell technology are as follows; Optical absorption coefficient is high, Its conductivity and resistivity can be changed, High-efficiency cells can also be produced in a factory environment. CIS solar cell has very high absorptivity. The first 1 micron thick layer of this material can absorb 99% of the incoming rays. Its stability in outdoor tests is very good. Therefore, CIS photovoltaic solar cell is widely used commercially. Also, if Ga (gallium) element is added to CIS solar cell cells, higher efficiency can be obtained.

11 Copper Indium Gallium Diceleneide Solar Cells (CIGS)

Another type of thin film solar cell is Copper indium gallium diseleneide. It is called CIGS for short. This solar cell is built on a semiconductor flexible base. CIGS solar cells have a higher efficiency than other thin film solar cells. While many thin film solar cells have an efficiency of 8%, CIGS solar cells have an efficiency of around 10%. While CIGS and CdTe solar cells theoretically have 30% efficiency, they reach a maximum efficiency of 25% under application conditions.

12 Flexible CIGS Solar Cells

The most important advantage in thin film solar cell technology is the cheap production method. These solar modules are electrically interconnected. And it can be produced in one piece. In recent years, flexible solar cells in roll form are very popular. In fact, flexible CIGS solar cell type is used especially for solar roof systems. These lightweight and roll-shaped CIGS solar cells have a very high potential in terms of space technology.

13 Multi-Articulated Solar Cells

Solar cells made with a single type of material can provide 30% theoretical efficiency and 25% efficiency in practice. Therefore, research on multi-joint solar cells has increased considerably. Multi-joint solar cell is made of 2 or more than 2 semiconductor layers. While one of these layers absorbs blue light very well, the other absorbs red light better. Therefore, multi-joint solar cell is more efficient than cells made of uniform material. Theoretically, the ideal solar cell can consist of hundreds of layers tuned to different wavelengths found between ultraviolet and infrared. In such a case, it can reach an unbelievable efficiency of 70%. However, this ideal solar cell cannot be done in terms of application. Because of this, scientists have concentrated on solar cells that are several layers. Today, multi-joint solar cell efficiency has been increased to 35-40% levels.

14 Nanophotovoltaic Solar Cells (NanoPV)

Nanophotovoltaic technology is the solar cell technology of the future. It includes nano-micro crystalline high efficiency solar cells. NanoPV (nano photovoltaic) batteries provide efficiency over 8-10% compared to other solar cells with nano crystal a-Si: H (hydrogen amorphous silicon) and permeable conductor (TCLO) technology in their structure. Nanomaterials are very good in terms of optical, electrical and chemical properties. Therefore, cell efficiency can be increased. 3 types of materials are used in nanophotovoltaic technology; crystal semiconductor 3-5 materials, polymeric materials, carbon-based nanostructures. Different solutions can be produced in terms of cost and application in solar cells made using these materials. Zinc (ZnO) and titanium (TiO2) nanowires can be used as conductors in solar cell production. Each of these nanowires can be 1000 times thinner than hair. Advantages of Nano Solar Cell Technology With NanoPv technology, architects will be able to use flexible solar cells. It will allow different designs, It will be able to regenerate and clean itself. Thus, maintenance-operating costs will be eliminated, Thanks to NanoPV technology, solar cell efficiency will increase by at least 8-10%, Since the solar panels produced with nanotechnology will be very light, the static load on the building will be almost negligible, It will reduce unemployment and open up new jobs. Disadvantages of Nano Solar Cell Technology Special manufacturing methods will be required, since it is very difficult to manufacture in nanometric dimensions and to observe this scale, The initial investment cost of solar panels produced with this technology is much higher than other solar panels, It will take many years to train technical staff who can work in this field.

15 Quantum Dot Solar Cells

Quantum dots are crystal semiconductors of nanometer size that can be produced by different methods. The advantages of quantum dots are that they allow the absorption threshold to be adjusted by simply selecting the dot diameter. Quantum dots are often called artificial atoms. These points allow control of energy carriers by adjusting 3-dimensional constraints. The quantum dot is the nanometer-sized granule of semiconductor material. These nanocrystals function as 3-dimensional channels for electrons. The solar cell in the p-i-n design can theoretically achieve 63% efficiency by placing a single-dimensional point in the sequential arrays inside. Quantum dot materials are at the nanometer level and the bandwidth is adjustable. The reason for the increase in the efficiency of the quantum dot solar cell is the fusion of the dots to absorb the lower space energies. With this method, higher efficiency can be obtained than the efficiency of an ordinary multi-joint cell when current is drawn. The efficiency value is limited by the host band gap, not by the energy of the photons.

16 Dye Sensitive Solar Cells

Dye sensitive solar cell cells contain semiconductors such as silicon and electrolyte liquid, which is a conduction solution formed with salt dissolved in solvent liquid such as water. The semiconductor and electrolyte try to separate the closely linked electron-space pairs produced when solar radiation reaches the cell. The source of the charge carriers induced by the radiation is the photosensitive dyes that give solar cell cells their name. The dye commonly used is iodide. Also, nanomaterials such as titanium dioxide (TiO2) are used to keep the dye molecules in a skeletal structure. The use of dye sensitive cells in solar cell applications dates back to the beginning of studies to imitate chlorophyll movement in plants. This method is the same as the photosynthesis method in plants. The most important development of these cells is the study in 1991. In this study, TiO2 nanoparticle is made by using a complex dye that is detected by ruthenium (ru), which is more efficient and stable, and a light-absorbing dye is developed.



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