Thermoelectric properties of crystalline and amorphous polypyrrole: A computational study

Organic thermoelectric (TE) materials are flexible, cost-effective, and eco-friendly. Their state-of-the-art ZT values are, however, far below inorganic thermoelectrics. In this work, we use first-principles calculations based on density-functional theory (DFT) and the Boltzmann transport equation to study the electronic transport properties of polypyrrole (PPy), which is one of the conducting polymers. We apply molecular dynamics simulations for its thermal transport properties. For hexafluorophosphate (PF6-) doped PPy (PPy-PF6), we find that the crystalline phase has exceptionally high electrical conductivity, while the amorphous phase possesses a high Seebeck coefficient and a low thermal conductivity. The ZT value along the chain direction of the crystalline phase is higher than that of the amorphous phase. The results may shed light on further improving ZT of PPy and conducting polymers in general for potentially energy-efficient thermoelectric applications. (C) 2016 Elsevier Ltd. All rights reserved.