Faster, more efficient, more versatile - these are the expectations for technologies that will generate energy and process information in the future. How can these expectations be met? A research team from the Universities of Goettingen and Marburg, Humboldt University of Berlin, and the University of Graz has now achieved a breakthrough: the researchers combined two types of materials - an organic and a two-dimensional semiconductor - and investigated their joint response to light. To this end, they employed photoelectron spectroscopy and many-body perturbation theory. This allowed them to observe and describe fundamental processes such as energy transfer at the interface between the materials within a fraction of a second. The combination of these different semiconductors with their respective properties is promising for the development of new technologies, such as modern tandem solar cells. The results were published in Nature Physics.

In the experiment, an advanced form of photoelectron spectroscopy was used: momentum microscopy. The researchers visualized the arrangement of electrons in the 2D semiconductor and in the organic semiconductor while this electronic structure was modified by light. This resulted in a "film" showing how excitons are first excited by energy and then transformed into new types of excitons. Excitons are quantum-mechanical particles. Excitons are quantum-mechanical quasiparticles formed when an excited electron remains bound to the positively charged vacancy it leaves behind, creating a correlated electron-hole pair held together by Coulomb attraction. They are generated in semiconductors by light absorption, that is, by the uptake of energy from light radiation. For this reason, they play a central role in optoelectronic devices such as solar cells and light-emitting diodes (LEDs). Depending on their properties, different types are distinguished.

The researchers were able to observe in detail how energy is absorbed and redistributed across the interface between the 2D semiconductor and the organic semiconductor. This was achieved using the unique spectroscopic fingerprint of each exciton type, which Ignacio Gonzalez Oliva and CSMB member Prof. Claudia Draxl determined by means of DFT, G0W0 and BSE calculations. In this way, they found that the absorption of a photon in the 2D layer can lead to energy transfer into the organic layer in less than 0.0000000000001 seconds - one ten-trillionth (10^-13) of a second.

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