How Solar Cells Work

Solar cells are a kind of technology that may be used to transform the energy that is gained from the sun into forms that can be used. This may be accomplished by first using a substance that is able to absorb sunlight, and then employing a mechanism that is able to convert the absorbed energy into an electric current. After the current has been produced, it may either be utilized to power equipment or used to generate energy for use elsewhere. As a result, solar cells may be used in a wide variety of contexts. This is because of their adaptability and the ease with which they can be transformed from forms of solar energy into forms that may be used. Solar cells are used for a wide range of purposes and may be found in a number of different gadgets. As an example, you’ll find them in things like autos, home appliances, and even portable electronic devices. Solar cells are also becoming increasingly prevalent in the industrial sector because of their cheap cost and great efficiency. This is mostly due to the fact that solar cells are getting more common. This is due to the fact that solar panels may be utilized to create electricity even in regions where access to other sources of energy is difficult to come by. For instance, solar panels may be used to produce electricity even in places that are inaccessible or when it is nighttime. As a result of this, solar cells are gaining an ever-increasing amount of significance in the industrial sector.

How They Carry It Out

The solar cell provides a source of power that is both non-polluting and inexhaustible. The solar cell has the ability to generate energy from photons in their natural state. One way to think of a photon is as a bundle of light, and the amount of energy contained in a photon is proportional to the length of the wavelength of the light it contains. Solar Cell Structure:  Encapsulate – The encapsulate, which may be composed of glass or another transparent material like clear plastic, serves the purpose of isolating the cell from its surrounding environment. For example, the cell may be shielded from the outside world by a window frame or a piece of metal that has the ability to be sealed shut at night. This would serve as a kind of environmental control.

 Active Material – Photons have interactions with this active material, which causes the material’s electrons to get excited. These excited electrons are driven towards an electrode by the energy of the photon, which results in the generation of an electrical current. It is necessary for the active material to be effective at converting photons into electrons in order for this current to continue flowing for a significant amount of time (Cuevas et al., 2018). In addition, solar cells made of mercury-cadmium-gallium-arsenide feature a polymer housing that encloses the cells, a silver electrode, and connectors for connecting to the external electrical system. Reflective coating: Both the front and the back of the encapsulation will have a coating that is reflective put to it. This coating has the ability to transform light into an electrical current and helps to improve the quantity of light that is absorbed by the cell as a result. 

Brewster angle – A Brewster angle is a crucial angle at which light is able to traverse the cell and form an electric current. Brewster angles are named after Brewster, who discovered them. Both the refractive index of the material and the wavelength of the light have an effect on the angle. It is possible for light to generate an electrical current inside the cell if it strikes the cell at this angle. When light strikes the cell at any other angle, however, it is considered a reflection and does not cause a current to be produced. Because it is the angle at which light is able to generate an electrical current, the Brewster angle is considered to be a crucial angle in physics. It is possible for light to generate an electrical current inside the cell if it strikes the cell at this angle. However, reflection occurs if light strikes the cell at any other angle, and this does not cause a current to be produced. This indicates that when the solar cell is positioned at the Brewster angle, it is able to convert a greater amount of light into an electrical current. This is due to the fact that light that strikes the cell at the Brewster angle is able to travel across the cell and produce an electric current (Mora-Seró, 2018). If light enters the cell at any other angle outside normal incidence, it is reflected and does not cause a current to be produced. This indicates that when the solar cell is positioned at the Brewster angle, it is able to convert a greater amount of light into an electrical current. It is essential to have a suitable Brewster angle in order to maximize the efficiency with which solar cells convert light into usable energy. The Brewster angle is a crucial angle that must be reached for light to generate an electric current. It is possible for light to generate an electrical current inside the cell if it strikes the cell at this angle.

Solar Cell Structure

A. Encapsulate – The encapsulate, which may be composed of glass or another transparent material like clear plastic, serves the purpose of isolating the cell from its surrounding environment. These components are essential for the solar cells to be able to carry out their duty. The cells are what take in and make use of the solar energy that comes in via the top. The electrons in the cell are then stimulated to the point where they reach excited levels and release energy in the form of photons after being excited by the photons (light). This energy is sent into the collector, which is then responsible for transforming it into electricity. In this area as well, the process of encapsulation is taking place in order to protect the cells from being harmed by the environment outside of the body (Lei et al., 2018). Rear surface field (BSF) is an abbreviation for back surface field, which refers to a substance that is attached to the back of a solar cell in order to absorb light that is not absorbed by the solar cell itself. Additionally, the BSF contributes to the process of reflecting light that is not absorbed back into the cell where it may then be absorbed. The front surface field (FSF) is a substance that is put on the front of the solar cell in order to reflect light that is not absorbed by the solar cell back into the cell so that it may be absorbed. This is done in order to maximize the amount of light that is absorbed by the solar cell. Because of this, the solar cell is able to absorb more light, which eventually results in the generation of more power.

B. Contact Grid — The contact grid is a collector of electrons; it is constructed of a material that is a good conductor, such as a metal, and it is formed of that material. This section is where the energy is converted into electricity, hence it is an important one. When light is shone onto the contact grid, it triggers the movement of electrons toward the metal and results in the creation of a current. The rear surface field and the front surface field come together at the contact grid, which is another function of this structure. This is the part of the solar cell where the light is first absorbed and then reflected back into it. This gives the solar cell the ability to collect additional light. 

C. The AR Coating, also known as the Antireflective Coating– This layer acts as a light guide for the solar cell by having a favorable refractive index and sufficient thickness. This allows more light to enter the solar cell. If this layer were absent, a significant portion of the light would simply reflect off of the surface. Because of the process that is taking place here, the solar cell is able to absorb more light, which eventually results in the production of more energy. The sunlight that is gathered by the solar cell would not be able to be converted into usable power by the cell. This layer may also be referred to as the antireflective coating in other contexts. Because it is constructed out of a substance that has a favorable refractive index, it allows light to enter the solar cell and be absorbed by it (Upama et al., 2018). This is how it generates energy. Additionally, the antireflective coating serves to direct the light into the solar cell, where it may be absorbed and turned into power. This is an important function of the solar cell. It is necessary for the solar cell to have both a contact grid and an anti-reflective coating in order for it to be able to gather more light, which will eventually result in the production of more energy. As a result, these two layers play an important role in directing the light towards the solar cell, which ultimately enables the light to be absorbed and turned into energy. The contact grid, which acts as a collector of electrons, is constructed out of a material that is an excellent conductor, such as a metal. This section is where the energy is converted into electricity, hence it is an important one. When light is shone onto the contact grid, it triggers the movement of electrons toward the metal and results in the creation of a current.

N-Type Silicon, Exhibit D – Doping, also known as contaminating, Si with elements or compounds that have one more valence electron than Si itself does results in the formation of N-type silicon. Examples of such elements or compounds include phosphorus and arsenic. Because only four electrons are needed to form bonds with the four atoms of silicon that are immediately close to one another, the fifth valence electron is free to participate in conduction. When the material is in this form, it is referred to as being in an n-type state. This indicates that the silicon has been doped with a chemical such as phosphorus or arsenic, both of which contain one more valence electron than silicon does on its own. When light is shone upon the substance, it induces the fifth electron in the material to migrate toward the light, which in turn creates a current. Following that, the current is sent via the solar cell, where it is turned into energy. In addition to that, the solar cell is constructed out of p-type silicon as well (Wang et al., 2020). Doping, also known as contaminating, Si with elements like boron, which possess one less valence electron than Si does, produces P-type silicon. Boron is one example of such an element. This indicates that the silicon was doped with a chemical such as boron, which has one less valence electron than silicon does on its own. Boron is an example of such a substance. When light is shone upon the substance, just four of the material’s five valence electrons are caused to migrate toward the light, rather than all five. Because of this, there are charge carriers that have been used up, which indicates that there is no current. Solar cells do not make use of p-type silicon because of this reason. It is essential for the solar cell to be constructed out of n-type silicon in order for it to be operational. The only sort of silicon that can be used in solar cells is this particular variety, and it only functions properly when light is shone on it. When light is shone upon n-type silicon, it induces the fifth electron to migrate towards the light and creates a current as a result. Following that, the current is sent via the solar cell, where it is turned into energy.

E. P-Type Silicon P-type silicon may be produced by doping silicon with chemicals, such as boron, that have a valence electron count that is one lower than that of silicon itself. Only three electrons are available for bonding with four adjacent silicon atoms when silicon is doped with atoms that have one fewer valence electron than silicon (three valence electrons). As a result, there is a hole in the bond, which can attract an electron from an adjacent atom. This occurs when silicon, which normally has four valence electrons, is doped with atoms that have only three valence electrons. When one hole is filled, it results in the formation of another hole in a different Si atom. Electrical current may be conducted through the material thanks to the movement of the perforations. When an external voltage is provided, the holes are attracted to the anode, and the electrons are coerced into traveling to the cathode through the external circuit. This process results in the production of an electric current, which may then be tapped into for many beneficial uses. In the last step, an additional layer that serves as an outside contact grid is laminated on top of the backsheet. This layer is constructed of a good conductor, such as metal. This second layer acts as a guide for the light as it enters the solar cell, which increases the likelihood that the light will be absorbed and turned into power. When light is shone onto the contact grid, it triggers the movement of electrons toward the metal and results in the creation of a current. Following that, the current is sent via the solar cell, where it is turned into energy.

F. Back Contact: The rear contact, which is a conductor and is formed out of a metal, covers the whole of the back surface of the solar cell and extends all the way to the edges. When the light is shone onto the contact, the electrons are coerced into flowing to the cathode through the external circuit. The photovoltaic effect is the process through which light is converted into energy by solar cells. At this point, the solar cell has been subjected to light, and it is now attempting to transform the light into something that can be used by humans (Calabrò et al., 2018). It is referred to as “incident light,” and it is the light that has been shone onto the solar cell. After the light has been transformed into photons by the solar cell, we may say that the incident light has occurred. Because of this, the next step is to make an effort to catch these photons and convert them into electricity. The absorber is responsible for carrying this out. An absorber is a piece of metal that has been coated on one side with a substance that is capable of absorbing photons. After that, the photons are transformed into electric current by this substance.

A photon’s path through the solar cell

When a photon has successfully navigated its way through the enclose, it arrives at the antireflective layer. The photon is guided downward through the solar cell by the antireflective layer, which is the topmost layer. Please follow the link below if you are interested in learning more about the revolutionary room temperature wet chemical growth antireflective layer that SPECMAT has developed. After the photon has traveled through the antireflective layer, it will either make contact with the silicon surface of the solar cell or with the contact grid metallization. Due to the opaque nature of the metallization, a reduced amount of photons are able to reach the Si surface. The contact grid has to be big enough to gather electrons, but it also needs to cover as little of the solar cell’s surface as possible so that more photons may get through.

The Photoelectric Effect is brought about by a Photon. In the n-type Si layer, the energy from the photon is transferred to the valence electron of an atom. This energy makes it possible for the electron configuration to leave its orbit, creating a hole in its wake. When referring to the n-type silicon layer, the valence electrons are referred to as the majority carriers, while the holes are referred to as the minority carriers. Both electrons and ions are considered to be mobile because, as the word “carrier” suggests, they are able to travel freely across the silicon layer of the solar cell (Aslam et al., 2018). In the p-type silicon layer, however, electrons are referred to as minority carriers, while holes are referred to as majority carriers. Both types of carriers are mobile, by the way.

The p-n intersection, if you will. The p-n junction is the part of the solar cell that is named after the intersection of the n-type Si layer and the p-type Si layer. As you may have already suspected, the p-type silicon layer has a higher concentration of positive charges, also known as holes, while the n-type silicon layer has a higher concentration of negative charges, also known as electrons. When p-type and n-type elements are brought into close proximity with one another, current will flow easily in one side (forward biased), but it will not flow in the other direction (reverse biased). In a solar cell with its p-n junction covered by darkness, an intriguing interaction takes place. The formation of a depletion zone is the result of extra valence electrons from the n-type layer moving into the p-type layer and filling the holes in the p-type layer (Schmager et al., 2019). Within the depletion zone, there are no mobile favorable or negative charges of any kind. Additionally, additional charges from the p-type and n-type layers are prevented from travelling across this zone because it acts as a barrier. So, to summarize, there is a zone surrounding the junction that is devoid of carriers, and there is also a little electrical imbalance inside the solar cell itself. This imbalance in the electrical current amounts to around 0.6 to 0.7 volts. Therefore, as a result of the p-n junction, an electric field is constantly present all the way throughout the solar cell. P = V × I

When photons collide with a solar cell, unbound electrons (-) in the p-type layer make an effort to combine with holes there. Because it is a road with just one lane of traffic, the p-n junction only permits the electrons to go in one direction. If we make available an external conductor channel, electrons will use it to return to the p-type side of the material where they originated and combine with holes there. The electron flow generates the current (I), while the electric field of the cell is responsible for the voltage (V). When we have both voltage and current, we get power (P), which is just the product of the two quantities. Therefore, when an external load (like an electric lamp) is connected between the front and rear contacts, electricity flows in the cell, working for us along the way.

The Limitations of Solar Power

When considering the use of solar power to generate energy, it is necessary to take into account certain constraints. A high starting price is one of the drawbacks to consider. This is because solar panels need to be both bought and installed before they can be used (Datta et al., 2008). There is a large initial cost, and then there is also the cost of upkeep to take into consideration. This may be a major investment for people as well as companies, particularly if solar power is to be utilized as an alternative source of energy in case of an emergency.

Another drawback of solar energy is that it requires a significant amount of area, particularly when contrasted with other types of energy generation. This is because solar panels have to be installed on the top of the building or in another location that gets enough of sunlight. This indicates that room will be required not just for them, but also for the wiring that will be required to link them to the power grid. Therefore, solar power is not as efficient as other forms of energy in terms of the quantity of area that it needs. Other forms of energy include wind power and nuclear power.

Solar power has a number of drawbacks, one of which is that it is not as dependable as other forms of energy. This is due to the fact that solar power is reliant on their being sun throughout the day. In the event that it is a cloudy day, the solar panels’ ability to generate power will be reduced. For instance, if there are clouds in the sky and the sun is not shining, the solar panels will not generate as much power as they would if the weather was clear and bright (Shin et al., 2018). In addition to this, if the solar panels are broken in any way, they will be unable to generate any power at all. Solar power is not completely dependable, which might provide a challenge in situations when it is required to serve as an alternative source of energy in case of an emergency.

Solar power also has another drawback in that it does not generate a significant amount of pollution throughout the manufacturing, transportation, and installation processes. This is particularly true when compared to other types of energy sources. The reason for this is because the production, transportation, and installation of solar panels all involve the usage of components that might contribute to environmental pollution. For example, the production of solar panels requires the use of several components that are potentially hazardous. This indicates that the manufacturing process for solar panels may result in the discharge of contaminants into the surrounding environment. In addition, the installation procedure might result in pollution, which is another potential issue. For instance, if the solar panels are positioned on the incorrect kind of surface, they may cause pollution to be released into the environment. This may lead to a variety of environmental issues, one of which being rendering the region in which the solar panels are situated uninhabitable. In addition to this, the transportation of solar panels may also result in the emission of pollutants into the atmosphere. Because of this, transporting solar panels has to be done in a manner that does not result in pollution. As an example, solar panels are not allowed to be carried in a vehicle that is also carrying other types of pollution. Transporting solar panels in a manner that does not make a lot of noise is another need. This is due to the fact that the noise produced by the transportation might cause damage to the panels in addition to contributing to pollution.

References

Aslam, Z., Shahid, H., & Mehmood, Z. (2018). Ageing effects of perovskite solar cells under different environmental factors and electrical load conditions (Retraction of Vol 185, Pg 471, 2018).

Calabrò, E., Matteocci, F., Palma, A. L., Vesce, L., Taheri, B., Carlini, L., … & Di Carlo, A. (2018). Low temperature, solution-processed perovskite solar cells and modules with an aperture area efficiency of 11%. Solar Energy Materials and Solar Cells, 185, 136-144.

Cuevas, A., Wan, Y., Yan, D., Samundsett, C., Allen, T., Zhang, X., … & Bullock, J. (2018). Carrier population control and surface passivation in solar cells. Solar energy materials and solar cells, 184, 38-47.

Datta, A., Damon-Lacoste, J., i Cabarrocas, P. R., & Chatterjee, P. (2008). Defect states on the surfaces of a P-type c-Si wafer and how they control the performance of a double heterojunction solar cell. Solar Energy Materials and Solar Cells, 92(11), 1500-1507.

Lei, J., Gao, F., Wang, H., Li, J., Jiang, J., Wu, X., … & Liu, S. F. (2018). Efficient planar CsPbBr3 perovskite solar cells by dual-source vacuum evaporation. Solar energy materials and solar cells, 187, 1-8.

Mora-Seró, I. (2018). How do perovskite solar cells work?. Joule, 2(4), 585-587.

Schmager, R., Gomard, G., Richards, B. S., & Paetzold, U. W. (2019). Nanophotonic perovskite layers for enhanced current generation and mitigation of lead in perovskite solar cells. Solar Energy Materials and Solar Cells, 192, 65-71.

Shin, D. Y., Chung, H. W., Song, H. J., Lee, J. I., Kim, K. H., & Kang, G. H. (2018). Thermomechanical-stress-free interconnection of solar cells using a liquid metal. Solar Energy Materials and Solar Cells, 180, 10-18.

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