Polymer-based thermoelectric fibers and composites: Individual and combined approaches towards enhanced efficiency

In the actual context of excessive pollution and the energy crisis, finding alternative and green energy sources has become a great challenge for today's scientific society and community. On this matter, the conversion of the temperature gradient directly into electricity, without moving parts or working fluids, is regarded as a highly appealing solution for these issues. Hence, in this review, we propose an overview of the thermoelectricity concept in polymeric materials, emphasizing the specific charge transport mechanism and effective strategies to improve their thermoelectric (TE) properties that mainly depend on charge carrier concentration and carrier mobility, even though it is a great challenge to achieve a high TE performance of these materials. Achievements in molecular doping and post-treatment strategies will be presented and analyzed, as they are widely used to modulate the concentration and mobility of carriers. Since transport properties and charge carriers' concentration are inversely correlated, the TE efficiency is limited. To this end, this review paper showcases state-of-theart approaches to developing new TE materials based on hybrid fibers, composite polymers, and nanomaterials. Special recognition will be given to nanotechnology, given that it is pushing further these frontiers, specifically through the energy filtering effect and quantum confinement.