Correlating the Seebeck coefficient of thermoelectric polymer thin films to their charge transport mechanism

Abstract

Room temperature flexible heat harvesters based on conducting polymers are ideally suited to cover the energy demands of the modern nomadic society. The optimization of their thermoelectric efficiency is usually sought by tuning the oxidation levels of the conducting polymers, even if such methodology is detrimental to the Seebeck coefficient (S) as both the Seebeck coefficient and the electrical conductivity (σ) are antagonistically related to the carrier concentration. Here we report a concurrent increase of S and σ and we experimentally derive the dependence of Seebeck coefficient on charge carrier mobility for the first time in organic electronics. Through specific control of the conducting polymer synthesis, we enabled the formation of a denser percolation network that facilitated the charge transport and the thermodiffusion of the charge carriers inside the conducting polymer layer, while the material shifted from a Fermi glass towards a semi-metal, as its crystallinity increased. This work sheds light upon the origin of the thermoelectric properties of conducting polymers, but also underlines the importance of enhanced charge carrier mobility for the design of efficient thermoelectric polymers.

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

“…Carriers in conductive polymers are mostly localized, and only a limited portion can be transported through inter‐ or intrahopping. Models designed for crystalline TE semiconductors, whose carriers are delocalized, fail to accurately predict the relationships between n and S 2 σ in conductive polymers . Theoretical studies utilizing the ab initio technique and molecular dynamics models hold the potential to predict electrical properties under different doping levels and guide experimental design …”

Flexible and Stretchable Self‐Powered Multi‐Sensors Based on the N‐Type Thermoelectric Response of Polyurethane/Nax(Ni‐ett)n Composites

“…The behavior of σ with the Na x (Niett) n amount is expected from percolation theory; [21] the conductivity increases due to a densifying conductive network until it reaches a plateau determined by the conductivity of Na x (Ni-ett) n . [23] The PF of the NL composite films reaches 0.9 × 10 −3 and 1.3 × 10 −3 µW m −1 K −2 for films with Na x (Ni-ett) n concentration of 50 and 70 wt%, respectively. [22] This phenomenon has been explained by enhancement of www.advelectronicmat.de carrier mobility as the percolated network becomes more robust upon densification.…”

Influence of residual sodium ions on the structure and properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

“…The electrical conductivity of PEDOT:PSS can be determined from the product of carrier concentration and carrier mobility. 36,37 It is widely demonstrated that the mechanism for the electrical properties enhancements of PEDOT:PSS is owing to the phase separation by decreasing the interaction between PEDOT and PSS chains. This is because that the phase separation causes partial reorientation of PEDOT chains and reduces the distance between PEDOT grains.…”