Thermoelectric Figure Of Merit Essay

Thermoelectric figure of merit has a very important role in determining the efficiency of thermoelectric operation and thus a high value of thermoelectric figure of merit would help in achieving a greater efficiency in thermoelectric conversion. The thermoelectric figure of merit can be expressed as follows:

ZT= (S^2 σT)/k

Here, S = Seebeck coefficient, σ = Electrical conductivity, T = Temperature,

 Thermal conductivity

For having a high thermoelectric figure of merit value and in turn having a high thermoelectric efficiency, a thermoelectric material needs to have a large Seebeck coefficient (found in low carrier concentration semiconductors or insulators) to obtain high voltage output, a large value of electrical

The values of the Seebeck coefficient and that of the electrical conductivity are inversely proportional to each other. As the carrier concentration increases the value of Seebeck coefficient (S) decreases accordingly while the value of electrical conductivity (σ) decreases. Due this the value of thermoelectric power factor (S2σ) increases with carrier concentration to a maximum and then again decreases. As the Seebeck coefficient is present in quadratic form in the equation for figure of merit, hence it is preferred to have a higher value of S at the cost of σ to obtain an optimum value of thermoelectric power factor. The thermoelectric power factor is maximum somewhere in the region between a metals and semiconductors. Good thermoelectric materials are typically heavily doped semiconductors with carrier concentration of 1019 to 1021carriers/cm3. For ensuring a large net Seebeck effect, there should only be a single type of carrier that is either they should be n-type or p-type. Mixed n-type and p-type conduction will lead to opposing Seebeck effect and thus a low thermoelectric power as the two opposing type of carriers will eventually nullify each other. The n-type and p-type carriers can be separated by having a large enough band