Displays based on organic semiconductors can nowadays be found in nearly every high-quality cell phone, but this materials class also holds high promise for a variety of other applications. These include solid-state lighting, solar cells and photodetectors, flexible electronics, and also thermoelectric devices. In all these devices, heat transport is of crucial relevance. This, on the one hand, applies to removing waste heat generated by irradiation with IR light, through non-radiative carrier recombination, and as Ohmic losses as a consequence of charge transport processes. On the other hand, for thermoelectric applications it is crucial to maintain a sufficiently large temperature gradient, which can be achieved by a minimized thermal conductivity. Nevertheless, very little is known about the thermal conductivity of organic semiconductors. This in particular applies to the relationship between the thermal transport coefficients and the structure of the material. In this context, structure has several meanings, namely the atomistic structure of the used molecules, their relative arrangement in a molecular crystal, and the types of interaction between individual molecules within the crystals. To close this knowledge gap, the current project aims at developing detailed structure-to-property relationships for thermal transport in (crystalline) organic semiconductors, addressing especially the aspects mentioned above. The primary strategy for achieving that will be computer simulations, due their inherent flexibility and efficiency. Additionally, it is planned to perform project-relevant experiments with collaboration partners in Austria (Materials Center Leoben), Italy (University of Bologna), Belgium (Free University of Bruxelles), and Japan (University of Nara). As far as the simulations are concerned, we will pursue a dual strategy, studying heat transport in real and in reciprocal space. This means that we will study the thermal conductivity spatially resolved at an atomistic level employing molecular dynamics approaches to identify, which parts of the molecular crystals act as heat-transport bottlenecks. Additionally, we will relate the thermal conductivity to the properties of the (quasi)particles that actually carry the energy – the so-called phonons. These phonons are intimately linked to the vibrational properties of the crystals and by changing the chemical structure of the molecules and their relative arrangement, it will be possible to modify these vibrational properties. This will result in modified energies, velocities and lifetimes of the phonons and, thus, in varying heat transport properties. As the key outcome of the present project, the developed structure-to-property relationships will allow a knowledge-based design of new materials with either maximized or minimized thermal conductivities, depending on the specific application the materials are meant for.
|Effective start/end date
|1/02/21 → 30/01/25
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