Processes in a model system for organic solar cells that were first analyzed in the femtosecond range – ScienceDaily


The key is the ultra-fast flashes of light that Dr. Friedrich Roth works at FLASH in Hamburg, the world’s first free-electron laser in the X-ray field. “We took advantage of the special properties of this X-ray source and extended it with time-resolved X-ray photoemission spectroscopy (TR-XPS). This method is based on the external photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize in Physics in 1921.

“For the first time, we were able to directly analyze the specific charge separation and subsequent processes when light hits a model system such as an organic solar cell. We were also able to determine the efficiency of the charge separation in real time.” explains Dr. Roth from the Institute for Experimental Physics at the TU Bergakademie Freiberg.

With photon science to better solar cells

In contrast to previous methods, the researchers were able to identify a previously unobserved channel for charge separation. “With our measuring method we can carry out a time-resolved, atom-specific analysis. This gives us a fingerprint that can be assigned to the associated molecule. We can see when the electrons excited by the optical laser reach the acceptor molecule, how long they stay and when or how they disappear again “, explains Prof. Serguei Molodtsov the measuring method. He heads the research group “Structural Research with X-ray Free Electron Lasers (XFELs) and Synchrotron Radiation” at the Freiberg Institute for Experimental Physics and is Scientific Director at the European X-ray Free Electron Laser (EuXFEL).

Analyze weak points and increase quantum efficiency

Real-time analyzes and the measurement of internal parameters are important aspects of basic research from which the solar industry in particular can benefit. “With our measurements, we draw important conclusions about the interfaces at which free charge carriers are formed or lost, and thus weaken the performance of solar cells,” adds Dr. Roth added. With the findings of the Freiberg researchers, for example, optimization possibilities at the molecular level or in the field of materials science can be derived and the quantum efficiency of newly emerging photovoltaic and photocatalytic systems can be optimized. The quantum efficiency describes the ratio of the incident light to the photon current (current that is generated). The team published the results in a recent journal, Nature Communications.

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