Organic photovoltaics (OPVs) offer a low-cost and environmentally friendly solution to the global energy transition given their scalable vacuum- or solution-based production processes and abundant inexpensive raw materials. Furthermore, their properties are highly tuneable due to wide range of possible organic molecules. Efficient OPVs consist of a photovoltaic active bulk hetero-junction (BHJ), i.e. a mix of donor molecules (D) and acceptor molecules (A). Their efficient operation relies on a particular microstructure in the BHJ, not too finely mixed, not to much phase separated, to reach high efficiencies. This microstructure depends on many factors, from molecular structure to processing. In this proposal, we plan to use the capabilities of ISIS to investigate how the microstructure forms and how we can influence it such that we can improve the efficiency of OPV further.