FWF-TIS - Tuning of the Interaction Strength at Inorganic/Organic Interfaces

Abstract Interfaces between inorganic materials and organic molecules are highly interesting the viewpoint of fundamental science, interesting since the flexibility of organic chemistry allows systematically tuning the strength of the interaction between the two components. At the same time, the properties of organic and inorganic materials often complement each other, which led to many practical applications, such as organic light-emitting or harvesting devices. For these applications and many other, emerging technologies to finally succeed, an in-depth atomistic insight into the quantum processes at the relevant interfaces is absolutely crucial. For instance, two different phenotypes of charge-transfer between inorganic and organic can be observed for physisorbed and weakly chemisorbed systems. While for unreactive, semiconducting substrates, the charge in the organic material is found to be strongly localized, for weakly reactive, metallic substrates, the charge is found to be completely delocalized. At present unclear, however, is how, e.g., degenerately doped semiconductors, which show quasi-metallic conductivity, fit into this classification. In this project, we will study by means of first principle calculations (density functional theory and beyond) (a) how the localization of charge is affected for a given interface as the nature and strength of the substrate/adsorbate interaction is gradually modified, and (b) how this affects observables at the interface. To this aim, we will investigate the adsorption of small, conjugated organic molecules on semiconductors with different doping concentrations and metals which reactivity will be modified through alloying. As a third approach, bulky spacer groups will be introduced into molecules, which mitigating the wave-function overlap and, thus, the interaction strength between inorganic substrate and organic adsorbate. Throughout the project, the choice of the density functional will be validated by many-body perturbation theory – thereby giving an impetus to method development. In addition to the added value for the fundamental understanding of surfaces and interfaces, the project will provide in-depth atomistic insight into the quantum processes at interfaces relevant for nascent technologies, such as organic thermoelectric materials or spintronic devices.