Hybrid Interfaces in Thermodynamic Equilibrium

The structure in which organic molecules assemble is crucial for their properties. This is exploited in many modern applications, especially in the context of organic electronics. One example for this is the performance of OLED displays (e.g., the screen of your mobile phone), where the polymorph in which the organic molecules crystallize critically determine the power consumption, i.e. how fast an active screen drains the battery. In principle, the structure of the organic material can be influenced by the growth conditions, e.g., by using a different temperature, pressure, solvent, or similar. Because trying out all these different conditions is tedious, ideally, the choice of the best would be guided be theoretical predictions. Although these predictions, driven by a combination of quantum-mechanical calculations and machine-learning algorithms, have made great progress in the past years, their accuracy has practically hit a dead-end. This is in part because the analysis of these data rely on several assumptions that have originally be made for relatively simple inorganic materials (such as silicon), but never be validated for more complex organic matter. The situation is further complicated by the fact that good experimental data that allow to validate these assumptions are scarce. The fundamental target of this project, therefore, is twofold. First, we will create an experimental benchmark dataset, where we collect the structure of various organic molecules, deposited at different organic materials, for different deposition conditions. Here, care must be taken that the material can find its correct structure. To achieve this, we will build a new, dedicated experimental chamber, that allows unprecedented control over the conditions while simultaneously measuring the structure. In parallel, we will assess all the different approximations made for inorganic materials and see to which point they are also appropriate for organic materials. This will provide us with new insight into the physics that govern the structure of organic polymorphs, and help us to design new, better materials for technological applications.