Sunday, September 06, 2026

Electrifying discoveries: Researchers film the first moments on the way from light to electricity

University of Graz

Physicists at the University of Graz (Austria), in collaboration with colleagues from Marburg University and Forschungszentrum Jülich (Germany), have achieved a scientific breakthrough. For the first time, the generation of electrical energy from light has been filmed and described theoretically. This work is of far-reaching significance, not least for optimising sustainable energy production from photovoltaics. This is because it provides fundamental building blocks for understanding the physical processes that take place, for example, in organic solar cells. The paper was published in the journal Physical Review X, one of the world’s most prestigious physics journals.

Whether in solar cells or during photosynthesis – when light strikes a surface, its particles, the photons, are absorbed by the material and thereby energise electrons. In the process, their spatial distribution – the so-called wave function – changes, and a bond is formed between an electron and the resulting electron hole. These ‘excited pairs’ are known as excitons. They play a key role in modern optoelectronic materials. However, although they have been known for decades, their internal quantum-mechanical structure has remained largely hidden until now. “We have now succeeded for the first time in experimentally reconstructing the spatial distribution and temporal evolution of an exciton’s wave function in the very first moments of its existence,” reports Peter Puschnig, Professor of Electronic Structure of Nanomaterials at the Department of Physics, University of Graz. “The measurements show that, after its formation, the electron-hole pair extends across approximately three molecules and then shrinks by around 25 per cent within the first 400 femtoseconds – a quadrillionth of a second,” explains the researcher.

To film this process, the scientists first excited the exciton with an ultrashort light pulse and then ejected the electrons from the pair bond using a second high-energy laser pulse. The latter process is as known photoemission. “If we then measure the energy and direction of the electrons, theoretical models allow us to infer their quantum-mechanical state. By varying the time delay between the excitation and the subsequent laser pulse, one obtains different snapshots of the exciton, which can be pieced together to form a video of the quantum world,” explains Puschnig.

Leading international research

The work was carried out in close collaboration between three leading international research groups. Stefan Tautz and his team at Forschungszentrum Jülich produced the organic semiconductor samples, characterised them and transported them to Marburg under ultra-high vacuum conditions, ensuring that their exceptional quality was maintained right up to the measurement. “The samples consist of wafer-thin, ordered films of the rod-shaped 6T molecule that have been deposited onto a specially prepared copper surface. The precise alignment of the molecules and their targeted decoupling from the substrate are important for maintaining the exciton long enough to make its formation visible,” explains Monja Stettner, who prepared the samples as part of her dissertation and assisted with the experiments in Marburg. The group led by Ulrich Höfer at Marburg University carried out the high-precision photoemission experiments and analysed the measurement data.

At the University of Graz, Peter Puschnig’s team developed the theoretical concepts for describing photoemission from excitons, carried out the quantum mechanical simulations and developed an analytical model that enabled the interpretation of the experimental data. “Using our model, it is possible to deduce the spatial shape and the internal quantum-mechanical phase of the exciton wave function directly from measured photoelectron images,” explains Siegfried Kaidisch, who made a key contribution to this work as part of his PhD thesis.

The experimental method underlying the research – Photoemission Orbital Tomography (POT) – was also developed in Peter Puschnig’s group and has, in recent years, been expanded in collaboration with Stefan Tautz’s team at Forschungszentrum Jülich into an internationally established tool for investigating electronic states in organic materials.

EU research project

The current publication marks one of the most significant milestones to date in the EU project ‘Orbital Cinema’. Funded by an ERC Synergy Grant, the research project aims to visualise the dynamics of electrons in materials with unprecedented spatial and temporal resolution. “In the next step, we want to observe the separation of electrons and holes in so-called donor-acceptor systems. This process determines how efficiently light can be converted into electrical current and is therefore central to future developments in organic photovoltaics,” says Puschnig.

https://orbital-cinema.eu/

Publication

Observing the spatial and temporal evolution of exciton wave functions in organic semiconductors

Marcel Theilen, Siegfried Kaidisch, Monja Stettner, Sarah Zajusch, Eric Fackelman, Alexa Adamkiewicz, Robert Wallauer, Andreas Windischbacher, Christian S. Kern, Michael G. Ramsey, François C. Bocquet, Serguei Soubatch, F. Stefan Tautz, Ulrich Höfer, and Peter Puschnig

Physical Review X, 28 August 2026

https://doi.org/10.1103/3zmg-276c

Images and video footage are available at https://bilderpool.uni-graz.at/s/wQKgiSxpqFxzqT2

Journal

Physical Review X

DOI

10.1103/3zmg-276c

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Observing the spatial and temporal evolution of exciton wave functions in organic semiconductors

Photoemission Orbital Tomography (IMAGE)

University of Graz

In time-resolved Photoemission Orbital Tomography, a pump laser pulse (blue) generates a bound electron-hole pair (exciton) in the organic semiconductor material alpha-sexithiophene. The subsequent high-energy UV laser pulse ejects an electron from the exciton, and the energy and direction of this electron are measured.

The measured energy and angular distributions of the emitted electrons allow the exciton wave functions to be reconstructed. It is observed that the size of the exciton shrinks by 25 per cent over the first 400 femtoseconds, from an initial value of approximately 1.5 nanometres.
Credit
Andreas Windischbacher, University of Graz

The evolution of an exciton [VIDEO]

The evolution of an exciton: The animation is based on data calculated using the model developed by Peter Puschnig’s research group at the University of Graz. It shows an amplified version of what was measured in the experiment, in order to make the processes more clearly visible. In principle, however, the wave function (right) can be inferred from experimental photoemission data (left).
Credit
Siegfried Kaidisch, University of Graz

Post-combustion reaction model for aluminum in thermobaric effects field

KeAi Communications Co., Ltd.

image:
(1) Through systematic experimentation and theoretical investigation, this work elucidates the underlying mechanism of the afterburning effect and proposes effective enhancement strategies.
(2) The dynamic evolution characteristics of the explosion fireball morphology as a function of time are revealed for TNT and thermobaric explosives.
(3) Integrating theoretical analysis, numerical modeling, and experimental results to elucidate the afterburning reaction mechanisms and quantify the combustion extent of aluminum powder under thermobaric conditions.
view more
Credit: Wen-xiang Bian, Hai-jun Zhao, Jian Li, Bo-liang Wang and Ya-ning Li

Introduction

Thermobaric explosives generate their characteristic effects through the coupling of detonation, metallic-fuel combustion and subsequent interactions with oxygen in the surrounding environment. Yet the role of aluminum post-combustion in sustaining the high-temperature blast field has remained difficult to quantify.

In a study published in Energetic Materials Frontiers, Wen-xiang Bian and co-workers compared two CL-20-based thermobaric formulations containing different potassium perchlorate contents with volume-equivalent TNT charges. Their experiments tracked fireball temperature, morphology and hotspot migration, while pressure sensors captured the corresponding blast-wave response. A theoretical model was established to connect fireball temperature and aluminum particle size with combustion completeness.

“Our analysis indicated that the thermobaric effect is not determined solely by the initial detonation,” shares Bian. “Instead, the subsequent combustion of aluminum provides an important source of energy that modifies both the thermal field and the development of the blast wave.”

The results suggested that controlling the balance between oxidizer-driven early combustion and later oxygen-assisted afterburning is central to understanding the performance of thermobaric formulations.

A concentrated fireball reveals the distinctive nature of thermobaric combustion

Infrared imaging shows that thermobaric explosives develop a concentrated and relatively localized hotspot, maintaining a volumetric explosion character throughout the evolving fireball. "This behavior contrasted with the more fragmented combustion observed for TNT,” says Bian. “The difference is also reflected in temperature evolution: immediately after detonation, thermobaric fireballs can exceed same-volume TNT fireballs by more than 1500 °C, while remaining hotter as the fireball expands.”

Oxidizer content determines the balance between early combustion and afterburning

The comparison between TBX30% and TBX5% revealed a clear temporal crossover. During the first 30 ms, the higher-oxidizer TBX30% maintained the higher fireball temperature because more oxidizing products promote rapid ooxygen-deficient combustion of aluminum. After approximately 30 ms, however, TBX5% became hotter as its larger amount of unreacted aluminum participated in secondary combustion with entrained ambient oxygen. After about 60 ms, the temperature histories of the two systems converged. TBX5% also showed more pronounced secondary afterburning and greater hotspot migration, highlighting the different roles of oxidizer-rich and oxidizer-lean formulations.

A temperature-based model identifies a route toward stronger thermobaric output

The team's theoretical analysis provided a quantitative link between fireball temperature and aluminum consumption. The Average Fireball Temperature model predicted mean temperatures of 2863 K for TBX5% and 3001 K for TBX30%, corresponding to aluminum burn-off times of 88 and 43 ms, respectively. “The model predicted that more than 95% of the aluminum can undergo complete combustion in both systems,” says Bian. “The hotter TBX30% fireball enabled a faster and more intense reaction, showing how increasing the early thermal environment can broaden the range of aluminum particles capable of reacting during secondary combustion.”

These findings provide a practical framework for understanding how post-combustion contributes to sustained blast-wave energy, particularly in the far field.

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Contact author details:

School of Chemistry and Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China. E-mail address: lyn_00446@163.com (Y.-n. Li)

The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).