AnisoTEP · Anisotropic thermoelectric polymers

Conducting polymer (CP) based thermoelectric materials (TE) gained significant interest from the scientific community due to their natural advantages such as low cost, high flexibility, lightweight and low toxicity over inorganic materials, which is beneficial for wearable or portable devices. Despite the benefits of organic TE materials, their low electrical conductivity reduces the TE performance and hinders commercialization. Chemical doping can be used to improve the electrical conductivity of CPs as it increases the charge carrier (polarons) concentration. However, the main limiting factor of electrical conductivity in organic semiconductors is their poor structural order and crystallinity. In addition, the strong coulombic attraction between the formed polarons (carriers) and the dopant counter ions hinders carrier delocalization, further limiting the TE performance. AnisoTEP will focus on developing highly conducting and crystalline polymer thin films to achieve high TE performance. We will use methods based on epitaxial orientation and mechanical rubbing to prepare oriented and crystalline P3HT thin films. Once oriented and crystallized, thin films will be doped by unique dopants based on dodecaborane (DDB) clusters, which stabilize their electron density in their core, and the negative charge of the DDB anions stays far away from the polarons, leading to a more delocalized polaron and high conductivity. Novel doping strategies based on ion exchange will be used to introduce counter ions of different ionic radii into P3HT to investigate the impact of counterion size on the polaron delocalization and TE performance. All the anisotropic TE parameters will be estimated, including the anisotropy in thermal conductivity and the final ZT anisotropy. This work would be the first attempt to experimentally determine the mobility anisotropy and charge transport mechanism in oriented polymers by AC Hall effect measurement.