Solar cells are made from silicon, which, in the case of the cell developed by Calvin Fuller, Daryl Chapin, and Gerald Pearson, is doped with arsenic. Silicon is an atom that has four outer electrons that bind with four other silicon atoms to make a lattice in which each silicon atom shares an electron with another atom. Each silicon atom in the lattice has eight electrons surrounding it: four of its own and the other four from the surrounding four silicon atoms. In this form, the lattice has a neutral charge. However, arsenic has five outer electrons, so when an arsenic atom replaces a silicon atom in the lattice, the arsenic has four bonded electrons and one extra, unbonded electron. The extra electron gives the semiconductor a negative charge, making it an N-type semiconductor. When the semiconductor is bathed in boron, the opposite situation occurs. Boron has only three electrons in its outer shell, and when it enters the silicon lattice, it creates a "hole," because one bond between the boron and silicon atom has only half of a bond. Thus, a boron-doped semiconductor is a P-type semiconductor because it has a positive charge. When a solar cell is constructed, an N-type chemical is added to one side of a P-type strip, or a P-type chemical onto an N-type strip.

When a section of P-type silicon is next to an N-type silicon, it forms a PN junction. When the silicon is exposed to sunlight, electrons are freed from the N-area to flow through the silicon, producing electricity. The freed electrons leave positively charged holes that flow in the opposite direction of the electrons. If 100 percent of the electrons that are freed flowed out of the cell into the electrical wires, then the cell would have 100 percent efficiency, but many of the electrons go back into the lattice to fill in the holes in the P-area and thus do not contribute to electricity generation.

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