Enhancement of the Seebeck Coefficient of Organic Thermoelectric Materials via Energy Filtering of Charge Carriers

Abstract

Recently, organic materials have emerged as next-generation thermoelectric (TE) materials because of their unique advantages including low cost, high mechanical flexibility, low or no toxicity, and low intrinsic thermal conductivity over inorganic TE materials. However, the Seebeck coefficient of organic materials with high TE properties is remarkably lower than that of its inorganic counterparts. Therefore, it is important to improve their Seebeck coefficient and thus, overall TE properties. A high-performance TE material should have high Seebeck coefficient and high conductivity, but there is a trade-off relationship between these two parameters. Lowering the charge carrier concentration can increase the Seebeck coefficient while decreasing the conductivity. A solution is to adopt energy filtering that can remarkably increase the Seebeck coefficient while only slightly lowering the conductivity. In this article, we review energy filtering methods to enhance the Seebeck coefficient and power factor of organic TE materials, including the composite formation with inorganic TE nanomaterials or carbon nanomaterials, composition formation of p- and n-type materials, and surface energy filtering induced by the dipole moment or ionic accumulations. Finally, a prospect is provided for the development of high-performance organic TE materials by energy filtering.