Violation of the Wiedemann-Franz law in Conducting Polymers

The free-electron gas model proposed by Drude and Sommerfeld has been enormously successful at describing the electronic and thermal properties of highly electrically conducting materials. A prediction of the free-electron gas model is that the ratio of the electronic component of the thermal conductivity to the electrical conductivity is proportional to a constant multiplied by the absolute temperature. This prediction is known as the Wiedemann-Franz law, and has been widely validated across various classes of materials. The validity of this law however has not been extensively studied in conducting polymer systems, primarily due to the challenges associated with fabricating highly electrical conductivity polymer devices for which both the electrical and thermal conductivity could be measured. Here, we investigate the relationship between thermal and electronic transport in conjugated polymers across a wide range conductivities, and find that the Wiedemann-Franz law is strongly violated. These results demonstrate that the link between charge transport and heat transport is fundamentally different in conjugated polymer systems than in the vast majority of high-conductivity materials.