Model of the thermoelectric properties of anisotropic organic semiconductors

TL;DR

This paper presents a model for the thermoelectric properties of anisotropic organic semiconductors, highlighting how anisotropy and Coulomb interactions influence conductivity and Seebeck coefficients, explaining recent experimental observations.

Contribution

It introduces a charge hopping transport model that incorporates anisotropy and Coulomb interactions, revealing distinct mechanisms affecting thermoelectric properties.

Findings

Anisotropic localized states cause exponential changes in conductivity ratios.

Seebeck coefficient ratios remain nearly unaffected by anisotropy.

Stronger Coulomb screening increases Seebeck coefficient ratios in certain directions.

Abstract

A model of charge hopping transport that accounts for anisotropy of localized states and Coulomb interaction between charges is proposed. For the anisotropic localized states the degree of orientation relates exponentially to the ratio of conductivities in parallel and perpendicular directions, while the ratio of Seebeck coefficients stays nearly unaffected. However, the ratio of Seebeck coefficients increases if Coulomb interaction is screened stronger in a direction parallel to the predominant orientation of the localized states. This implies two different physical mechanisms responsible for the anisotropy of thermoelectric properties in the hopping regime: electronic state localization for conductivities, and screening for Seebeck coefficients. This provides explanation for recent experimental findings on tensile drawn and ribbed polymer films.