Hybrid excitons speed ultrafast energy transfer at 2D organic interface

by Robert Schreiber
Berlin, Germany (SPX) Dec 19, 2025

Researchers from the Universities of Goettingen, Marburg, Humboldt University in Berlin, and Graz have identified a new quantum state at the interface between an organic semiconductor and a two dimensional semiconductor. They report that this state, a hybrid exciton, combines properties from both materials and enables energy transfer on femtosecond timescales, with potential applications in future solar cells and optoelectronic devices. The work appears in Nature Physics as part of efforts to better understand microscopic energy conversion at semiconductor interfaces.

The team stacked a monolayer of the two dimensional semiconductor tungsten diselenide (WSe2) with a layer of the organic semiconductor PTCDA and investigated how the combined system responds to light. Using an advanced form of photoelectron spectroscopy known as momentum microscopy, they tracked changes in the electronic structure of the heterostructure while it was driven by ultrashort laser pulses. This approach produced a time resolved map of how excitons, bound pairs of electrons and holes, form and evolve after photoexcitation.

From the spectroscopic fingerprints in these measurements, supported by many body perturbation theory calculations of the exciton landscape, the scientists reconstructed how energy flows across the 2D organic interface. They observed that when a photon is absorbed in the WSe2 layer, energy can transfer into the organic PTCDA layer in less than one ten trillionth of a second, around 10-13 seconds. This ultrafast transfer is attributed to the formation of hybrid excitons whose wavefunctions extend across both materials.

Professor Stefan Mathias from the University of Goettingen explained that the team identified a clear experimental signature for these hybrid excitons, which arise when excitations in the organic and 2D layers couple at the interface. In organic semiconductors, excitons usually remain localized, while in two dimensional semiconductors they can move freely over the material, so the hybrid state combines localized and mobile character. According to the researchers, this mixed behavior helps to connect light absorption and charge or energy transport in a single, interface confined quantum state.

Lead author Wiebke Bennecke from the University of Goettingen stated that understanding and controlling energy and charge transfer in such semiconductor nanostructures is essential for designing efficient solar cells and ultrafast optoelectronic components. The team also points to potential uses in quantum technologies, where coherent excitonic states at engineered interfaces could serve as functional elements. Bennecke noted that, as the 100th anniversary of quantum mechanics is marked, the results show how quantum concepts continue to shape technologies under development today.

The study involved collaboration between experimental and theoretical groups in Germany and Austria. Funding came from several Collaborative Research Centres of the German Research Foundation (DFG), including Control of Energy Conversion on Atomic Scales, Mathematics of Experimentation, Pushing Electrons with Protons in Goettingen, and Hybrid Inorganic Organic Systems for Opto Electronics in Berlin, as well as from the Austrian Science Fund and the European Research Council.

Research Report:Hybrid Frenkel-Wannier excitons facilitate ultrafast energy transfer at a 2D-organic interface