This effect can be used to generate electricity, measure temperature or change the temperature of objects. Because the direction of heating and cooling is determined by the polarity of the applied voltage, thermoelectric devices are efficient temperature controllers.
The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect, Peltier effect and Thomson effect. Textbooks may refer to it as the Peltier–Seebeck effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is related though it is not generally termed a thermoelectric effect. The Peltier–Seebeck and Thomson effects are thermodynamically reversible,[1] whereas Joule heating is not.
Reference: WIKIPEDIA
Seebeck investigated the thermoelectric properties of a large number of metals and arranged them in a thermoelectric series. When a circuit is formed of two metals in the series, the thermal electromotive force (emf) is greater the further the metals are apart in the series. Also, the direction of the current, at the hot junction, is from the metal occurring earlier in the series to the metal occurring later in it.