Plasmonic Nanospectroscopy for Thermal Analysis of Organic Semiconductor Thin Films

Journal article, 2017

Organic semiconductors are key materials for the next generation of thin film electronic devices like field-effect transistors, light-emitting diodes and solar cells. Accurate thermal analysis is essential for the fundamental understanding of these materials, for device design, stability studies and quality control because desired nanostructures are often far from thermodynamic equilibrium and therefore tend to evolve with time and temperature. However, classical experimental techniques are insufficient because the active layer of most organoelectronic device architectures is typically only on the order of hundred nanometers or less. Scrutinizing the thermal properties in this size range is, however, critical because strong deviations of the thermal properties from bulk values due to confinement effects, and due to pronounced influence of the substrate become significant. Here, we introduce plasmonic nanospectroscopy as an experimental approach to scrutinize the thickness dependence of the thermal stability of semi-crystalline, liquid-crystalline and glassy organic semiconductor thin films down to the sub-100 nm film thickness regime. As the main result we find a pronounced thickness dependence of the glass transition temperature of ternary polymer:fullerene blend thin films, and their constituents, which can be resolved with exceptional precision by the plasmonic nanospectroscopy method, that relies on remarkably simple instrumentation.