![]() As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. It takes a lot less energy to knock loose one of our "extra" phosphorus electrons because they aren't tied up in a bond with any neighboring atoms. However, there are so few of them in pure silicon, that they aren't very useful.īut our impure silicon with phosphorus atoms mixed in is a different story. These electrons, called free carriers, then wander randomly around the crystalline lattice looking for another hole to fall into and carrying an electrical current. When energy is added to pure silicon, in the form of heat for example, it can cause a few electrons to break free of their bonds and leave their atoms. It doesn't form part of a bond, but there is a positive proton in the phosphorus nucleus holding it in place. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorus has one electron that doesn't have anyone to hold hands with. Phosphorus has five electrons in its outer shell, not four. Consider silicon with an atom of phosphorus here and there, maybe one for every million silicon atoms. We usually think of impurities as something undesirable, but in this case, our cell wouldn't work without them. To address this issue, the silicon in a solar cell has impurities - other atoms purposefully mixed in with the silicon atoms - which changes the way things work a bit. ![]() The only problem is that pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move about, unlike the electrons in more optimum conductors like copper. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. The outer shell, however, is only half full with just four electrons. The first two shells - which hold two and eight electrons respectively - are completely full. An atom of silicon has 14 electrons, arranged in three different shells. 8.Silicon has some special chemical properties, especially in its crystalline form.Mismatch for Cells Connected in Parallel.Impact of Both Series and Shunt Resistance. ![]() Applying the Basic Equations to a PN Junction.Solar Radiation Outside the Earth's Atmosphere.the dissipation of power in the load and in parasitic resistances.the generation of a large voltage across the solar cell and. ![]()
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