This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Physicists at the University of Graz (Austria), in collaboration with colleagues from Marburg University and Forschungszentrum Jülich (Germany), have achieved a scientific breakthrough. For the first time, the generation of electrical energy from light has been filmed and described theoretically.
This work is of far-reaching significance, not least for optimizing sustainable energy production from photovoltaics. It provides fundamental building blocks for understanding the physical processes that take place, for example, in organic solar cells. The paper is published in the journal Physical Review X.
Whether in solar cells or during photosynthesis, when light strikes a surface, its particles, photons, are absorbed by the material and thereby energize electrons. In the process, their spatial distribution—the wave function—changes, and a bond forms between an electron and the resulting electron hole. These "excited pairs" are known as excitons.
They play a key role in modern optoelectronic materials. However, although they have been known for decades, their internal quantum-mechanical structure has remained largely hidden until now. "We have now succeeded for the first time in experimentally reconstructing the spatial distribution and temporal evolution of an exciton's wave function in the very first moments of its existence," reports Peter Puschnig, professor of electronic structure of nanomaterials at the Department of Physics, University of Graz.
"The measurements show that, after its formation, the electron-hole pair extends across approximately three molecules and then shrinks by around 25% within the first 400 femtoseconds—each a quadrillionth of a second," explains the researcher. To film this process, the scientists first excited the exciton with an ultrashort light pulse and then ejected the electrons from the electron-hole pair bond using a second high-energy laser pulse. The latter process is known as photoemission.
"If we then measure the energy and direction of the electrons, theoretical models allow us to infer their quantum-mechanical state. By varying the time delay between the excitation and the subsequent laser pulse, one obtains different snapshots of the exciton, which can be pieced together to form a video of the quantum world," Puschnig explains. The work was carried out in close collaboration among three leading international research groups.
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