Thermoelectric power factor in nano- to microscale porous composites

The peculiarities of the Seebeck coefficient and power factor are studied in porous thermoelectric materials with spherical hollow pores of varying diameter from nanometer to micrometer length scales. The pores are assumed to be randomly dispersed throughout the matrix material. The influence of trap centers situated at pore interfaces on the power factor is investigated. Using the model based on gamma distribution of the pore sizes, the analytical expression is obtained for the power factor at the arbitrary level of the Fermi energy. Limiting cases of nondegenerate and degenerately doped porous semiconductors are examined as well. The results are compared with calculations for a multilayer composite in which each layer contains pores of a single length-scale. It is shown that the presence of hollow pores with multiscale hierarchical disorder leads to more considerable enhancement in the thermopower over its value in the bulk. Necessary conditions for the enhancement of the power factor are found.