Solar cells are converters. They take the energy from sunlight and convert that energy into another form of energy, electricity. Solar cells convert sunlight to electricity without any moving parts, noise, pollution, radiation, or maintenance. The conversion of sunlight into electricity is made possible with the special properties of semiconducting materials.
Most solar cells are made from silicon, the 14th element. Silicon is a “semi-conductor” or a “semi-metal,” and has properties of both a metal and an insulator. Atoms in a metal have loosely bound electrons that easily flow when electrical pressure is applied, whereas atoms in an insulator have tightly bound electrons that cannot flow when electric voltage is applied. Atoms in a semi conducting material bind their electrons tighter than metals, but they may be manipulated to have conductive properties.
Solar cells are made by joining two types of semiconducting material: P-type and N-type. P-type semiconductors are manufactured to contain negative ions, and N-type semiconductors to manufactured to contain positive ions. The positive and negative ions within the semiconductor provide the environment necessary for an electrical current to move through a solar cell.
At the atomic level, light is made of a stream of pure energy particles, called “photons.” This pure energy flows from the sun and shines on the solar cell. The photons actually penetrate into the silicon and randomly strike silicon atoms. When a photon strikes a silicon atom, it ionizes the atom, giving all its energy to an outer electron and allowing the outer electron to break free of the atom. The photon disappears from the universe and all its energy is now in the form of electron movement energy. It is the movement of electrons with energy that we call “electric current.”
Sunlight to Electricity
A typical solar cell consists of a glass cover to seal the cell, an anti-reflective layer to maximize incoming sunlight, a front and back contact or electrode, and the semiconductor layers where the electrons begin and complete their voyages. The electric current stimulated by sunlight is collected on the front electrode and travels through a circuit back to the solar cell via the back electrode.