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The working principle of solar cells is based on the photovoltaic effect of semiconductor PN junctions. The so-called photovoltaic effect is an effect that generates an electromotive force and an electric current when the charge distribution state in the object changes when the object is illuminated. When sunlight or other light illuminates the semiconductor PN junction, a voltage appears on both sides of the PN junction, which is called photogenerated voltage.

How solar cells work

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The working principle of solar cells is based on the photovoltaic effect of semiconductor PN junctions. The so-called photovoltaic effect is an effect that generates an electromotive force and an electric current when the charge distribution state in the object changes when the object is illuminated. When sunlight or other light illuminates the semiconductor PN junction, a voltage appears on both sides of the PN junction, which is called photogenerated voltage.

When light strikes the pn junction, an electron-hole pair is generated. The carriers generated near the internal PN junction of the semiconductor are not recombined and reach the space charge region. They are attracted by the internal electric field and the electrons flow into the n region. Flowing into the p-region results in excess electrons being stored in the n-region and excess holes in the p-region. They form a photogenerated electric field near the pn junction in the opposite direction of the barrier. In addition to partially offsetting the effect of the barrier electric field, the photogenerated electric field also makes the p region positively charged and the N region negatively charged. The thin layer between the N and P regions generates electromotive force, which is the photovoltaic effect.

When energy is added to pure silicon (such as in the form of heat), it causes several electrons to leave their covalent bonds and leave the atom. Every time an electron leaves, a hole is left. These electrons then wander around the lattice, looking for another hole to settle in. These electrons are called free carriers and they can carry electric current. By mixing pure silicon with phosphorus atoms, it takes very little energy to escape a certain "excess" electron of the phosphorus atom (the outermost five electrons). It is called N-type ("n" means negative charge), and only a part of the solar cell is N-type. The other part of silicon is doped with boron. The outermost electron layer of boron only has three instead of four electrons, so that P-type silicon can be obtained. No free electrons in P-type silicon