In my previous posts, I gave an overview about the composition of a solar cell, what it is made of and how it is used to transform sunlight into electric energy. In this article, I will illustrate the inside anatomy of a cell and how it really works.

In the last post, I explained the concept of a solar cell with two separate pieces of silicon, that were electrically neutral. However, it becomes much more interesting when you put them together. This is because without an electric field, the cell wouldn’t work; the field is formed when the N-type and P-type silicon come into contact. This makes the free electrons on the N side to rush to the openings on the P side.

But do all the free electrons rush to fill all the free holes? The answer is no. They do mix and form a barrier at the junction, making it more harder for further electrons on the N side to cross over to the P side. Eventually, equilibrium is reached and an electric field is created separating the two sides.

This electric field now acts as a diode, allowing the electrons to flow from the P side to the N side, but not the other way around. It’s just like a hill, where the electrons can go down to the N side, but can’t climb to the P side.

When sunlight falls on the solar cell in the form of photons, its energy is used to break apart electron-hole pairs. Each photon having enough energy will usually free exactly one electron, resulting in a free hole as well. The electron flow provides the current, and the cell’s electric field causes a voltage. Together with both current and voltage, we get power, which is the product of the two.

Silicon, which is commonly used to make solar cells, is a very shiny material, and thus reflects photons, causing them to bounce away before they’ve done their job. To counter this, an antireflective coating is applied to reduce the loss.

At the end, a glass cover case may be applied to keep the solar cell safe, and several solar cells may be combined together to form an array of solar panels, absorbing more sunlight and thus creating more electricity.

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