To unravel this mystery the researchers used time- and angle-resolved photoemission spectroscopy, a cutting-edge technique to observe the dynamics of electrons on the femtosecond time scale, which is a billionth of a millionth of a second. This ultrafast electron movie camera enabled them to capture images of the fleeting excited electrons for the first time.
"Seeing these electrons was crucial to decipher the process," says Alexander Neef, from the Fritz Haber Institute and the first author of the study. "An excited electron not only has a specific energy but also moves in distinct patterns, which are called orbitals. It is much easier to tell the electron apart if we can see their orbital shapes and how these change over time."
With the images from the ultrafast electron movie at hand, the researchers decomposed the dynamics of the excited electrons for the first time based on their orbital characteristics. "We can now say with certainty that only one electron is excited directly and identified the mechanism of the excitation-doubling process," adds Alexander Neef.
Knowing the mechanism of exciton fission is essential to using it for photovoltaic applications. A silicon solar cell enhanced with an excitation-doubling material could boost the solar-to-electricity efficiency by one-third. Such an advance could have enormous impacts since solar energy will be the dominant power source of the future. Already today large investments are flowing into the construction of these third-generation solar cells.
Research Report:Orbital-resolved observation of singlet fission
Related Links
Fritz Haber Institute of the Max Planck Society
Understanding Time and Space
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