How solar cells work

You may have seen a calculator that uses a solar cell—a calculator that doesn't require a battery, and sometimes it doesn't even have a close button. As long as there is enough light, these calculators seem to work all the time. You may have seen larger solar panels – such panels can be seen in emergency traffic signs, public kiosks, buoys and even in parking lots and on power indicators. Although these large panels are not as common as solar calculators, they do exist, and if you know the location, it's easy to spot them. Solar cells are also mounted on artificial satellites to power them.

In the past 20 years, you may continue to hear the "solar revolution" - that is, one day we will all use the free energy from the sun. This is an enticing promise: in sunny, sunny days, the sun radiates about 1,000 watts per square metre of energy to the Earth's surface. If we can collect all of this energy, it can easily be used for homes and The office provides free electricity.

Photovoltaic cells: converting photons into electrons

The calculators and satellite solar cells you see are also known as photovoltaic (PV) cells, as the name suggests (photos, meaning "light" and photovoltaic, meaning "electric"), which convert sunlight directly into electricity. One module is an electrically connected battery pack that is packaged into a single frame (commonly known as a solar panel) so that it can be combined into a larger array of solar cells, like an operating system at Nellis Air Force Base, Nevada.

Photovoltaic cells made of special materials, called semiconductors such as silicon, are currently the most commonly used. Basically, when the light is irradiated inside the semiconductor material, some parts of it are absorbed. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocking on the door is loose, allowing them to flow freely.
Photovoltaic cells also have one or more electric fields that force the light to absorb the electrons released to flow in a certain direction. This electron flow is a current, and by placing the metal contacts on the top and bottom of the PV cell, we can draw it for external use, that is, a calculator supply current cutoff. This current, along with the cell's voltage (which is a result of its built-in electric field or field) defines the power (or power) of the solar cell that can be fabricated.
This is the basic process, but it is really more. In the next page, let's take a deeper look at a photovoltaic cell: a monocrystalline silicon cell is an example.

How silicon makes solar cells

Silicon has some special chemical properties, especially in its crystalline form. The silicon atom has 14 electrons arranged in three different shells. The first two rounds - 2 to 8 electrons held separately - are fully filled. The outer shell, however, is only four electrons only half full. Silicon atoms always look for ways to fill their final shell, and to do this, they will share electrons with four atoms nearby. It's like each atom holds its hands in a neighboring country, except in this case, each atom has four neighbors with four hands joined. This is the crystalline structure formed, the result of which is important for this type of photovoltaic cell.
The problem with ** is that pure crystalline silicon is a poor conductor of electricity because electrons without it can move freely, unlike more optimized ones, such as electrons in copper conductors. To solve this problem, the silicon impurity in the solar cell - the silicon atoms of other atoms are intentionally mixed - it changes the working position. We usually think that impurities are not desirable, but in this case, our cells are not working without them. Consider the phosphorus atoms of silicon here and there, perhaps one of every million silicon atoms. Phosphorus has five electrons in its outer casing, not four. It still bonds, its silicon neighboring atoms, but in a sense, phosphorus, no one holds the hand, there is an electron. It does not form part of a bond, but it keeps a positive proton in the phosphorous nucleus.
When energy is added to pure silicon, such as hot forms, it can cause some electrons to break free of their bonds and leave their atoms. Leave a hole in each case. These electrons, the so-called free carriers, then randomly look for another hole in the surrounding crystalline lattice to fall in to carry the current. However, there are few such pure silicon, they are very useful.
However, our pure silicon and phosphorus atoms are a different story. A lot less energy is lost because they don't have much "extra" phosphorous electrons in one of the bonds of any adjacent atom. So these electrons break free and we have more free carriers than we are in pure silicon. The method of adding impurities, called doping, and doping with phosphorus, the resulting silicon is called N-type (negative "n") because of the prevalence of free electrons. N-type doped silicon is a better conductor than pure silicon.
The other part of a typical solar cell is doped with elemental boron, with only three electrons in its outer casing, instead of four, becoming P-type silicon. There is a free opening, rather than having free electrons, P-type ("p" means a positive number), and the opposite (positive) charge is applied.
In the next page, let's take a closer look at what happens when the two substances begin to interact.

Anatomical solar cell

Prior to this, our two separate silicon were electrically neutral, and the most interesting parts started when you put them together. This is because without an electric field, the cells will not function properly; when forming N-type and P-type silicon, this field is touched. Suddenly, the N-end of the free electron saw all the openings on the P side, and there was a rush to fill them. All free electrons fill all free holes? If they do this, then the whole arrangement will not be very useful. However, they do so at the junction, the structure and the form of obstacles make it increasingly difficult to cross the electrons on the N-side of the P-side. In the end, the balance is reached and we have an electric field separating both sides.
This electric field acts as a diode, causing (continuously pushing) electrons from the N side of the P side, but not other methods around it. It's like a hill - the electrons are easy to go down (N side), but can't climb up (P side).
When the light is shining, the form of the photon hits our solar cell, whose energy decomposes the electron-hole pair. Each photon with sufficient energy is usually released, resulting in a free hole, and an electron if this happens to an electric field close enough, or if free electrons and free holes drift to its extent, this field The N- and P-side holes of the electrons will be transmitted. This will lead to further damage to the electrical neutrality, if we provide an external current path, the electrons flow through the path P side to unite the hole, the electric field is sent there, along the way for us to do the work. The flow of electrons provides the current, and the voltage caused by the electric field of the cell. With current and voltage, power, this is the two of the product.
We can really use our cells before there are a few components left. Silicon happens to be a very shiny material that can send photons to bounce off before they have finished their work, so anti-reflective coatings are applied to reduce these losses. The final step is to install something that will protect the cells from the elements - usually the glass cover. Photovoltaic modules are typically combined by connecting several separate cells to achieve useful voltages and currents, and place them in a rugged frame, complete front and negative terminals.
How much solar energy does our photovoltaic cells absorb? Unfortunately, it may not be a terrible lot. For example, in 2006, most solar panels could only achieve an efficiency level of about 12% to 18%. The cutting-edge solar panel system, which is finally muscled this year, has an efficiency barrier of 40% for the long-term 40% of the industry's solar cells. So why is such a challenge to make a sunny day?

Energy loss in solar cells

Visible light is only part of the electromagnetic spectrum. Electromagnetic radiation is not monochromatic - it is made up of different wavelengths and, therefore, energy levels. (See the light principle for a discussion of a good electromagnetic spectrum.)
Light can be divided into different wavelengths, and we can see a rainbow form. Since light hits our cells with a wide range of photons, it turns out that some people don't have enough energy to change an electron-hole pair. They will simply pass through the cells as if they were transparent. There are other photons that have too much energy. Only a certain amount of energy in electron volts (eV) and measurement is defined by our grid material (crystal silicon about 1.1eV), which requires a knock on an electron. We put the band gap energy of this material. If a photon has more energy than the required amount, then additional energy is lost. (That is, unless a photon is twice as much energy as needed and can create more than one electron-hole pair, the effect is not significant). Both effects can explain the loss of about 70% of our radiant energy events in our cells.
Why can't we choose a very low bandgap material, so we can use more photons? Unfortunately, our bandgap also determines our electric field strength (voltage). If it is too low, then we do extra current (by absorbing more photons) and we lose a small voltage. Remember that power is the voltage multiplied by the current. The band gap that balances these two effects is about 1.4 eV for cells made from a single material.
We have other losses. Our electrons flow through the external circuit from the other side of the cell. We can use metal to cover the bottom to make good electrical conductivity, but if we completely cover it, then photons can't get through the opaque conductor, we lose all our current (in some cells, the top surface is used on transparent conductors, but Not at all). If we take our contacts and then have electrons on either side of our cells, go to a very long distance to reach the contact. Keep in mind that silicon is a kind of semiconductor - this is not the metal that carries current. Its internal resistance (called series resistance) is quite high, and the high resistance of high resistance devices. In order to minimize these losses, cells usually cover a shortened distance of metal contact, electrons have travel, and only a small portion of the cell surface covers the mesh. Even so, some of the photons blocked by the grid should not be too small, otherwise their own resistance will be too high.