Multiscale modelling of structural and electronic properties of organic thin films

In this thesis, we develop aspects of a framework for the multi-scale modelling of charge transport in several organic semiconductors relevant for technological application. In the first chapter, we build a coarse-grained model for fullerene multi-adducts which clearly distinguishes between the influence of energetic and structural disorder. The model reveals that charge transport in fullerene multi-adducts is limited by energetic disorder due to different isomers. Solar cells containing single isomers of higher fullerene adducts are expected to achieve higher power conversion efficiencies. Secondly, we create a multi-scale model to investigate the effect of beta-phase conformers on hole transport in poly(9,9)dicotylfluorene. A combination of quantum-chemical calculations and charge transport simulation confirms that beta-phase conformers act as traps and, when torsional disorder of the polymer backbone is included, can explain the experimentally observed mobility reduction due to beta-phase. In the third project, grain boundaries in tri-isopropylsilylethynyl (TIPS) pentacene are characterised. On the basis of two-grain structures with varied mutual orientation generated with atomistic molecular dynamics, we compute energy landscapes and electronic coupling elements. We find that the effect of the grain boundary is relatively weak for long interfaces, but that small contact areas between grains may impede charge transport more strongly due to highly non-uniform energy barrier heights. The final chapter focuses on one-dimensional organic magnetoresistors with alternating acceptor, spacer and donor units. Combining quantum-chemical calculations and kinetic Monte-Carlo simulations allow us to define design rules for high magnetoresistance, among which minimising the offset between HOMO and LUMO energy levels is the most challenging one. Within the range of researched materials, polymers built from dicyanoqyinonediimine (DCNQI) acceptors, fluorene spacers and 3-ethylendioxythiophene (3-EDOT) donors are most promising for magentoresistance application.Open Acces