The Peltier effect occurs when two dissimilar conductors form an electric junction, causing electrons to flow in a specific direction that generates heat on one side of the junction and cold on the other side. The junction uses two types of conductors, one rich in electrons (n-type) and one that can accept electrons (p-type).
Jean Peltier discovered the effect in 1834, but it remained a laboratory curiosity until the discovery of semiconductors. A typical Peltier device sandwiches a thin array of p-type and n-type semiconductors between two metal plates along with conductors for direct current. One metal plate absorbs heat while the opposite plate loses heat and provides the cooling effect. The “hot side” can reach 200 degrees Celsius, while the “cold side” will reach minus 100 degrees Celsius. The temperature range depends on the size of the device and the materials used.
Most manufacturers use either bismuth telluride or lead telluride for the semiconductors. Commercial Peltier devices range in size from one-half inch square up to 3 inches square, and they can be wired in series to cover a large area. Peltier devices can cool computer chips when used with heat sinks, and many portable coolers use battery-powered Peltier devices.