image: Artistic representation of the hybrid exciton wavefunction, with the electron shown in red and the hole distribution shown as a blue cloud
Credit: Lukas Kroll
Faster, more efficient, and more versatile – these are the expectations for the technology that will produce our energy and handle information in the future. But how can these expectations be met? A major breakthrough in physics has now been made by an international team of researchers from the Universities of Göttingen, Marburg, the Berlin Humboldt in Germany, and Graz in Austria. The scientists combined two highly promising types of material – organic semiconductors and two-dimensional semiconductors – and studied their combined response to light using photoelectron spectroscopy and many-body perturbation theory. This enabled them to observe and describe fundamental microscopic processes, such as energy transfer, at the 2D-organic interface with ultrafast time resolution, meaning one quadrillionth of a second. The combination of these properties holds promise for developing new technology such as the next generation of solar cells. The results were published in Nature Physics.
In the experiment, the researchers used an advanced form of photoelectron spectroscopy called momentum microscopy to visualize the electronic structure as it is being manipulated by light. The resulting “movie” shows how excitons (quantum-mechanical particles consisting of an electron bound to an electron-hole) are first excited and then transformed into new exciton species. Based on the unique spectroscopic fingerprint of each exciton species and supported by theoretical calculations of the exciton landscape, the researchers were able to see exactly how energy is absorbed and distributed over the 2D-organic interface. Notably, they found that the absorption of a photon in the 2D material can lead to energy transfer into the organic layer within less than one ten-trillionth (10-13) of a second.
“The key to this ultrafast energy transfer is the formation of ‘hybrid excitons’, for which we have now found a tell-tale experimental signature,” explains Professor Stefan Mathias, University of Göttingen. But what exactly are “hybrid excitons”? Excitons are created by light absorption in semiconductors and thus play a central role in optoelectronic devices such as solar cells and light-emitting diodes. Depending on the material, excitons exhibit very different properties: in organic semiconductors, excitons are typically immobile – they are very much stuck in one place – whereas excitons in two-dimensional semiconductors are extremely mobile, freely floating all over the material. At the interface of an organic and a 2D semiconductor, however, both the material properties and those of excitons might hybridize, potentially leading to the formation of new, hybrid, excitons. This is exactly what the researchers observed at the interface of the 2D material WSe2 and the organic semiconductor PTCDA.
“Our results allow us to better understand and efficiently harness the fundamental processes behind energy and charge transfer in semiconductor nanostructures. This is a crucial step towards the development of efficient solar cells, ultrafast optoelectronic components, and novel applications in quantum technology,” explains Wiebke Bennecke, University of Göttingen and first author of the study, before adding, “As we mark the 100th Anniversary of the development of quantum mechanics, our findings powerfully illustrate its relevance today for the technology of the future.”
The research was supported by the German Research Foundation (DFG) Collaborative Research Centres (CRC) “Control of Energy Conversion on Atomic Scales”, “Mathematics of Experimentation”, “Pushing Electrons with Protons” in Göttingen, the DFG CRC “Hybrid Inorganic/Organic Systems for Opto-Electronics” in Berlin, the Austrian Science Fund and the European Research Council.
Original publication: Bennecke W et al: “Hybrid Frenkel–Wannier excitons facilitate ultrafast energy transfer at a 2D–organic interface” Nature Physics (2025). Doi: 10.1038/s41567-025-03075-5
Contact:
Dr Wiebke Bennecke
University of Göttingen
Faculty of Physics
Ultrafast Dynamics in Quantum Materials
Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
Email: wiebke.bennecke@uni-goettingen.de
Professor Stefan Mathias
University of Göttingen
Faculty of Physics
Ultrafast Dynamics in Quantum Materials
Friedrich Hund Platz 1, 37077 Göttingen, Germany
Tel: +49 (0)551 39-27601
Email: smathias@uni-goettingen.de
www.mathiaslab.uni-goettingen.de
Journal
Nature Physics
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Hybrid Frenkel–Wannier excitons facilitate ultrafast energy transfer at a 2D–organic interface
Article Publication Date
29-Oct-2025