Conjugated polymers, organic electronics, thermal conductivity

Conjugated polymers are the kingpin of thin film organic electronic devices: they are high-performing semiconductors offering solution-processability, semi-transparency, lightness and flexibility at low cost. This makes conjugated polymers ubiquitous in the upcoming generation of internet-of-things devices, in which portability, versatility and building-integration are a must. In such nascent field, the acknowledgement of the thermal conductivity is essential to allocate the corresponding thin film application. Tentatively, polymer-based thermoelectric generators require low thermal conductivity to maximize efficiency, whereas transistors and solar cells need proper heat dissipation to minimize degradation and extend device lifetime. In this talk, we overview the origin of thermal conductivity in conjugated polymers highlighting their inherent anisotropic character. Accordingly, we present electrical and optical characterization methods to assess both the in-plane and out-of-plane components of the thermal conductivity of conjugated polymer thin films. By exploiting such techniques on a broad selection of state-of-the-art conjugated materials, we show how chemical features of the polymer backbone affect thermal conductivity (and the extension of its anisotropy). X-ray diffraction experiments suggest that the observed trends are intimately related to the film microstructure, which serves us to identify at least two different conjugated polymer subfamilies based on such criteria: largely amorphous and semi-crystalline counterparts. In semi-crystalline polymers, the thermal conductivity increases steadily as the backbones become more ordered in solid-state, thus in agreement with classical kinetic theory. Conversely, the thermal conductivity in largely amorphous conjugated polymers is found to correlate negatively with the mass and size of the polymer’s repeating unit. In both scenarios, we show how film texturing could open up new routes for decoupling charge and thermal transport in conjugated polymers by exploiting the anisotropy of their intra- and intermolecular interactions in solid-state.