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

A research team has discovered a unique quantum state at the interface between organic materials and two-dimensional semiconductors.

Faster, more efficient, and more adaptable technologies are widely seen as essential for the future of energy generation and information processing. Achieving those goals, however, requires new ways of understanding how materials behave at the smallest scales. An international research team from the Universities of Göttingen, Marburg, Humboldt University of Berlin in Germany, and the University of Graz in Austria has now reported a significant advance in this area.

The researchers brought together two classes of materials that have attracted intense interest in recent years: organic semiconductors and two-dimensional semiconductors. By examining how this combined system responds to light, using photoelectron spectroscopy together with many-body perturbation theory, they were able to probe ultrafast processes at the boundary between the two materials. These measurements capture events that unfold within one quadrillionth of a second, offering a direct view of microscopic energy transfer.

This unique blend of material properties could open the door to new technologies, including more efficient solar cells. The findings were published in Nature Physics.

Watching Excitons in Motion

To carry out the study, the team relied on a specialized technique known as momentum microscopy, an advanced form of photoelectron spectroscopy. This method allowed them to track changes in the electronic structure of the materials as light interacts with them in real time.

The data can be viewed as a “movie” that reveals how excitons (quantum-mechanical particles consisting of an electron bound to an electron-hole) are created by light and then evolve into different types of exciton states.

By identifying the distinct spectroscopic signatures associated with each exciton type and comparing them with detailed theoretical models of the exciton landscape, the researchers were able to follow how energy moves across the 2D-organic interface. One key result showed that when a photon is absorbed by the two-dimensional material, energy can be transferred to the organic layer in 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.

Hybrid Excitons

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.

Observing Hybrid Excitons Directly

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.”

Reference: “Hybrid Frenkel–Wannier excitons facilitate ultrafast energy transfer at a 2D–organic interface” by Wiebke Bennecke, Ignacio Gonzalez Oliva, Jan Philipp Bange, Paul Werner, David Schmitt, Marco Merboldt, Anna M. Seiler, Kenji Watanabe, Takashi Taniguchi, Daniel Steil, R. Thomas Weitz, Peter Puschnig, Claudia Draxl, G. S. Matthijs Jansen, Marcel Reutzel and Stefan Mathias, 29 October 2025, Nature Physics. DOI: 10.1038/s41567-025-03075-5

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.

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