In situ X-ray tools for characterising vacuum thermally evaporated small molecules for use in organic photovoltaics*

Organic photovoltaics (OPV) provide an environmentally friendly solution to meet the ever-increasing global energy demand, therefore understanding how to maximize their efficiency is crucial. This work seeks to demonstrate a suite of in situ X-ray techniques for characterising the morphology of OPV made via vacuum thermal evaporation. The microstructure of OPV governs device performance and fabrication processes are a key element of tuning morphological properties. Strategies for tuning microstructure on this project include annealing processes and templating layers. To track how these processing conditions impact the morphology of the film growth, in situ grazing incidence wide angle X-ray scattering (GIWAXS) and resonant soft X-ray scattering (RSoXS) are employed on a set of high performing molecules used in OPV, including DCV5T and DTDCPB. In situ GIWAXS taken during film growth is used to show how the molecular orientation changes as a function of distance from a templating layer interface. In situ RSoXS will be taken with different annealing processes being performed, to show the evolution of mixing behaviour of two energetically offset molecular species when thermally or solvent vapour annealed. It has previously been shown that thermal annealing has a positive correlation with domain size in a bulk heterojunction mixture.