Cooling Enhancement Using Inhomogeneous Thermoelectric Materials

The maximum cooling temperature of a thermoelectric refrigerator made of uniform bulk material is limited by its dimensionless figure-of-merit ZT. Cascaded stages are typically needed in order to obtain a higher cooling temperature. Multiple stage configurations have disadvantages of device complexity, and reduced efficiency due to the non-ideal heat spreading between different stages. In this paper, we prove that the maximum cooling temperature can be increased by using a single stage made of inhomogeneous material. This optimization is different from conventional graded materials where there is a large temperature gradient and local material properties are optimized in order to achieve the highest ZT at the local temperature under operation. The new optimization is attributed to the redistribution of the Joule heating and Peltier cooling profiles along the current and heat flow directions. The cooling efficiency can also be increased by a moderate amount. Numerical simulations are used to optimize the doping profile for a thermoelectric cooler based on single crystal silicon