The effects of interface scattering on thermoelectric properties of film thermoelectric materials

A theoretical model taking into consideration the interface effects is established to predict the Seebeck coefficient and the electrical conductivity for a polycrystalline thermoelectric (TE) thin film. The interface scattering mechanisms (including the film-surface scattering and grain-boundary scattering) of the transport electrons in the film materials are revealed. The relations between the Seebeck coefficient, the electrical conductivity and the interface parameters (the film-surface reflection coefficient and the grain-boundary transmission coefficient) are then discussed with respect to the proposed model. The differences in the TE properties between the films and bulk materials caused by size restriction are investigated. The results indicate that the higher grain number leads to stronger grain-boundary scattering and more distinct size effects of the TE properties. In contrast to the surface effect, the grain-boundary effect plays a main role in the TE properties of TE films with polycrystalline structures.