Theoretical studies on the thermopower of semiconductors and low-band-gap crystalline polymers

A numerical procedure has been used for the prediction of the Seebeck coefficient of a crystalline material based on its electronic band structure with the goal of testing this approach on the simple polymers polythiophene and polyaminosquaraine. The investigation of several representative materials, including the crystalline solids $\beta \text{−}{\mathrm{Zn}}_4{\mathrm{Sb}}_3$ and $\mathrm{Au}{\mathrm{In}}_2$ and these polymers, under ambient or external pressure conditions, indicates that Seebeck coefficients can be calculated within the rigid-band and constant-relaxation-time approximations. The results are in semiquantitative agreement with experiment and provide a basic understanding of the mechanisms for thermopower. These theoretical results together with previous similar studies show that band-structure calculations can be used to guide the rational design of high-performance thermoelectric materials. We also suggest that appropriate and specially engineered doped low-band-gap polymers may be promising candidate materials for thermoelectric applications.