How can advancements in technology, like solar cells, be enhanced? An international research team is seeking answers to such questions using a novel approach. For the first time, they can precisely track the creation of minuscule particles, known as dark excitons, in both time and space. These energy-carrying entities are critical for the next generation of solar cells, LEDs, and detectors.
How can advancements in technology, like solar cells, be enhanced? An international research team, spearheaded by the University of Göttingen, is working to address such inquiries through a new method. This breakthrough allows for the precise tracking of the formation of tiny particles called dark excitons, both temporally and spatially. These invisible energy carriers will be essential for future solar cells, LEDs, and detectors. The findings were published in Nature Photonics.
Dark excitons are minute pairs consisting of an electron and the vacancy (hole) it leaves behind upon excitation. They transport energy but do not emit light—hence the term “dark.” To visualize an exciton, you can picture a balloon (representing the electron) that floats away, leaving a void (the hole) still linked by a force referred to as Coulomb interaction. Researchers refer to these “particle states” as challenging to detect, yet critically important in ultra-thin, two-dimensional structures found in specialized semiconductor materials.
Previous research led by Professor Stefan Mathias from the Faculty of Physics at the University of Göttingen successfully demonstrated how dark excitons are generated in an incredibly brief period and characterized their dynamics through quantum mechanics. In their latest study, the team introduced an innovative method called “Ultrafast Dark-field Momentum Microscopy” for the first time. This allowed them to observe the formation of dark excitons in a unique composite material made of tungsten diselenide (WSe₂) and molybdenum disulphide (MoS₂) over an astonishingly swift duration of just 55 femtoseconds (0.000000000000055 seconds), with precision resolution of 480 nanometres (0.00000048 metres).
“This technique allowed us to accurately measure the dynamics of charge carriers,” states Dr. David Schmitt, the lead author from Göttingen University’s Faculty of Physics. “The findings give us essential insights into how the material’s characteristics affect charge carrier movement. Therefore, this technique could potentially be employed to specifically enhance the quality and efficiency of solar cells.” Dr. Marcel Reutzel, Junior Research Group Leader in Mathias’ team, notes, “This methodology is applicable not only to these specialized systems but also to the exploration of new materials.”
The research received support from the DFG-funded Collaborative Research Centres “Control of Energy Conversion on Atomic Scales” and “Mathematics of Experimentation” in Göttingen, as well as the Collaborative Research Centre “Structure and Dynamics of Inner Interfaces” in Marburg.
