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Solar power generation principle
- Jun 06, 2018 -

What's the process the solar power generation ? 

Solar cells, solar planes, solar cars, these are all converted to electricity through the sun, but what is the specific process? If you are not at a glance, it is easy to understand. It is related to semiconductors.Silicon is a good thing. Computers and IT can't live without it, and solar power can't do without it.


Semiconductors principle

The outermost layer of silicon atoms has four electrons, it's an imperfect structure. To reach the 8th level, the outermost layer of silicon atoms urgently needs to reach 8 electrons. When many silicon atoms are together, each silicon atom shares 4 electrons of the adjacent 4 silicon atoms, and also shares the 4 outermost electrons own has, so that they form a stable silicon crystal.

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The crystal chemistry of silicon is very stable. At room temperature, it is difficult to react with other substances except hydrogen fluoride.
The silicon crystal is a poor conductor because it does not have free electrons. Now we will reform it. The outermost layer of phosphorous atoms (P) has five electrons. When phosphorus atoms are doped into silicon crystals, there is obviously one free electron in silicon crystals. After the phosphorus atom takes out 4 electrons and shares it with 4 silicon atoms, it still has one electron left. It is free.

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The innumerable silicon atoms in silicon crystals are replaced by phosphorous atoms, and there is a lot free electrons. Therefore, it conducts electricity. At this point, we have made a semiconductor, called "N-type semiconductor." 

Then, if there is an aluminum (AI) with only three electrons in the outermost layer, what will happen?

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After mixing with aluminum atoms, apparently, there is a missing electron. It is like an unfilled hole. We call it a "hole."

After the silicon crystal is mixed with trivalent atoms such as aluminum and boron, another semiconductor is formed, called a "P-type semiconductor." 

P-type semiconductors are also conductive , because after the external electric field is applied, the electrons in the P-type semiconductor fill the holes in sequence against the direction of the electric field, and at the same time, the holes also move in the direction of the electric field. Thus, the current is generated.


PN junction

What's N-type semiconductors and P-type semiconductors can do? Very useful if you joint them together.

If one side of a semiconductor crystal is an N-type semiconductor and the other side is a P-type semiconductor, then the middle connected contact surface is called a PN junction.

The PN junction is the material basis of many electronic components such as diodes and various transistors. The transistor is considered to be one of the greatest inventions in modern history. It can be compared with printing, automobiles and telephones in terms of importance.

We now know that in N-type semiconductors, the concentration of free electrons is high, whereas in P-type semiconductors, the concentration of holes is high. According to the principle of diffusion, substances are always diffused from places with high concentration into low concentrations.

Therefore, in the PN junction, there will be many free electrons diffused from the N-type semiconductor into the P-type semiconductor. As a result, the original N-type semiconductor is electrically neutral and uncharged, but after losing some of the electrons, it takes positive electricity.

In P-type semiconductors, because a lot of free electrons come over and fill a lot of holes, which leads to a decrease in the hole concentration. Originally, P-type semiconductors were also electrically neutral, and now there are a lot electrons, it’s negative.

In the PN junction, one side is positively charged and the other side is negatively charged, thus forming an internal electric field at the contact surface.

 

How does the sun generate electricity ?

Having said the PN junction, and the internal electric field in the PN junction, now we can finally get to the point - how does the sun become current?

In the photoelectric effect, we know that light above a certain frequency can emit electrons from metals. This tells us that the energy of light can act on electrons.

When sunlight strikes a general semiconductor, it will generates a free electron in a semiconductor, a hole is generated at the same time, because the electrons leave the sunlight under the influence of sunlight energy. When the position is to become free electrons, that position will inevitably lack an electron, and holes will be created.

However, in general semiconductors, the free electrons and holes generated by sunlight quickly combine together, and the life cycle of free electrons and holes is short.

But in a PN junction semiconductor, it is different.

Because there is an internal electric field in the PN junction, when sunlight generates electron and hole pairs in the PN junction, the electrons move to the N-type semiconductor under the action of the internal electric field. Similarly, holes move to the P-type semiconductor.

At this point, if the PN junction is wired at both ends, current can be generated.

Above, it is the principle of solar power generation. The following schematic diagram shows below:


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