In a new study published in Physical Review B, researchers led by professor Zeila Zanolli and PhD candidate Riccardo Reho from Utrecht University, explored the impact of stacking, twisting, and interlayer distance on the electronic and optical properties of structures made of specific two-dimensional quantum materials. The study revealed that these factors could significantly alter exciton energy levels by hundreds of milli-electronvolt. “The insights could pave the way for new technologies, including flexible electronic devices and high-performance solar cells.”
Two-dimensional materials, particularly Transition Metal Dichalcogenides, have garnered interest for their exceptional properties and potential applications in photodetectors, LEDs, and lasers. These ultra-thin materials, only a few atoms thick, exhibit exceptional interaction with light, leading to the formation of stable particles known as excitons. When reduced to a single layer, Transition Metal Dichalcogenides reveal direct band gaps in the near-infrared range, enhancing their photoluminescence and making them ideal for various light-based technologies.
Moreover, Transition Metal Dichalcogenides can be layered on different surfaces to create structures with a relatively weak bond between the layers. These structures are called van der Waals heterostructures, and their electronic and optical properties can be finely tuned. In these structures, excitons can either exist within the same layer (intralayer) or between different layers (interlayer), a feature that is particularly beneficial for the development of efficient thin-film solar cells.
Gaining control
However, achieving precise control over these materials remains a significant challenge. Factors such as encapsulation and the surrounding dielectric environment play a crucial role in their performance. To address these challenges, scientists rely on computational modelling to predict how these materials absorb and emit light.
The new study looked at how the way layers are stacked, twisted, and spaced affects the properties of the structures made of two different Transition Metal Dichalcogenides, molybdenum diselenide and tungsten diselenide. The researchers found that these factors can change exciton energy levels by hundreds of milli-electronvolt. The study also introduced “grey” excitons, which are weakly light-absorbing particles.
Paving the way
The researchers found that their theoretical predictions matched well with experiments and discussed the limitations of their methods. “We believe that our insights into the behaviour of Transition Metal Dichalcogenides and Van der Waals heterostructures facilitate the development of new technologies, including flexible electronic devices and high-performance solar cells”, Reho says. He is first author of the study. “This research highlights the immense potential of 2D quantum materials in advancing next-generation technology development.”
This research is part of QuMat-materials for the quantum age, which received an NWO Gravitation grant of 21.5 million euros in 2022, and Quondensate, which received an EIC Pathfinder grant of 3 million euros in 2023.
Text from UU press release: https://www.uu.nl/en/news/new-study-highlights-potential-of-2d-materials-in-advanced-light-based-technologies