For the development of high-performance and efficient materials, the "Structural Research with XFELs and Synchrotron Radiation" working group from the Institute of Experimental Physics is creating essential prerequisites with its basic research.

To this end, the team, in cooperation with national and international research institutions, is using a new method to analyse the processes in a model system for organic solar cells in detail for the first time within femtoseconds, which are barely perceptible to humans. A femtosecond is one millionth of a billionth of a second. In their research, the Freiberg scientists are working closely with the European X-Ray Free-Electron Laser (EuXFEL), the free-electron laser FLASH, DESY in Hamburg, the Advanced Light Source in Berkeley (USA) and the synchrotron BESSY II at the Helmholtz Centre Berlin.

The key to real-time analyses and measurements of internal parameters are ultra-fast flashes of light at EuXFEL and FLASH in Hamburg. The latter is the world's first free-electron laser in the X-ray range. The team is utilising the unique properties of these X-ray sources to add time-resolved X-ray photoemission spectroscopy (TR-XPS). This method is based on the external photoelectric effect. Albert Einstein had already explained this and received the Nobel Prize in Physics for it in 1921.

This makes it possible to analyse charge separation and recombination processes as well as their dynamics when light hits a model system. Such a system can be an organic solar cell, i.e. a solar cell consisting of hydrocarbon compounds. This measurement method can be used to obtain information about charge transfer processes and thus improve the physical properties of components. Charge transfer processes play an important role in many current research topics related to sustainability and renewable energies. In recent years, for example, contributions have been published on understanding the processes following light excitation in model systems for organic solar cells.

These findings can be used to develop high-performance and more efficient solar cells and also offer opportunities for optimisation in the field of materials science. In future, this measurement methodology is to be extended to the investigation of charge transfer dynamics in photo-catalytic reactions, such as sustainable hydrogen production.