In this equation ΔV is the voltage difference between the hot and cold sides, ΔT is the temperature difference between the hot and cold sides. The negative sign comes from the negative charge of the electron, and the conventions of current flow. A negative Seebeck coefficient results in electrons being the dominant charge carriers (n-type), whereas holes are the dominant carrier (p-type) in materials with a positive Seebeck coefficient. The majority charge carriers are said to move away from the heated side toward the cooler side. Minority charge carriers move in the opposite direction, but at a slower rate due to phonon drag and charge carrier diffusion rates. Thus, both n-type and p-type materials are required to realize current flow in a device.
Things to remember about the Seebeck effect:
- Solids have charge carriers that facilitate the flow of electrical power
- The charge carriers come in two flavors negative electrons "n-type" and positive "holes" that we use to keep track of mobile positive charge in "p-type" solids
- Heating one end of a conducting solid pushes on the charge carriers concentration and the distribution of charge creates voltage that can be measured this is called the Seebeck effect
The Peltier effect was first discovered in 1834 by Jean C.A. Peltier, for whom it was named. Peltier discovered that whenever a circuit of two dissimilar materials passes current, heat is absorbed at one end of the junction and released at the other. This is a linearly dependent and thermodynamically reversible process, unlike Joule heating which is irreversible and quadratic in nature mean. This process forms the basis for thermoelectric cooling and temperature control, these are currently the widest applications of thermoelectric devices.
However, applying a temperature differential the reverse process occurs, and current is caused to flow, thereby generating power. The figure below shows a TEP device in both cooling and power generation configurations.