Linköping University, Sweden
Dr. Xabier Rodríguez-Martínez (XRM) completed his bachelor and master's degrees in Nanoscience and Nanotechnology at the Autonomous University of Barcelona in 2015. In early 2016, he enrolled as PhD candidate in the Nanostructured Materials for Optoelectronics and Energy Harvesting (NANOPTO) group at ICMAB-CSIC, supported by Dr Mariano Campoy-Quiles as research supervisor.
In October 2020, he obtained his PhD cum laude in materials science for the development of organic solar cells by high-throughput combinatorial methods. In parallel to his main PhD topic, Dr. XRM did an extensive thermal characterization of conjugated polymer films by AC methods such as the 3w approach; as well as by optical methods such as Raman thermometry. His main research interests focus on organic electronics for energy harvesting applications (photovoltaics and thermoelectricity), including thin film processing, spectroscopy, and applied machine-learning methods. Since January 2021, Dr. XRM works as principal research engineer in Prof. Olle Inganäs’s group in Linköping University, Sweden.
Conjugated polymers, organic electronics, thermal conductivity
Taking the temperature to conjugated polymers’ fever
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.