Modelling of materials for organic electronics: Nanoscale morphology, interfaces and charge transport properties

Abstract

Progress in the development of advanced and multi-functional materials for organic and hybrid electronic and optoelectronic devices is often hampered by the lack of a detailed understanding of structure/property relationships, and especially of the link between molecular structure, nanoscale aggregation and electronic properties. This issue affects particularly interfaces among molecular layers in thin-film materials for organic devices, where the chemico-physical complexity of the system leads to difficult interpretation of experimental results. The overall performance of the organic electronic and optoelectronic devices are related to the charge transport properties of the materials constituting the active layer, which, in turn, depend on the morphology at the interface between the layers. These properties are affected by several factors, such as the fabrication parameters, processing, and the interactions between the materials composing the layers. In this thesis, the development of computational tools able to model the nanoscale morphology and the electronic properties of materials, in realistic environments, targeting specific interfaces for organic electronics, is outlined. These tools make use of methods at different scales, based on molecular dynamics (MD), density functional theory (DFT) and coarse-grain (CG) simulations. In particular, MD simulations were performed for the modelling of materials used in organic electronic and optoelectronic devices, including organic semiconductors based on small molecules, polymer dielectrics, electrodes and 2D materials, investigating the growth and aggregation of organic materials and layered systems at the interfaces. These morphologies were then used to investigate electronic properties occurring between materials by performing DFT calculations. The CG method allows the extension of the length and time scales of the systems under investigation. The approach proposed in this thesis enables a better understanding on the aggregation of organic materials in complex environments and the related electronic processes, by mimicking realistic processing techniques, and finally correlating the results with experiments.