Researchers at SUPERVenice have shown that stacking two ultrathin materials can make an atomically thin semiconductor emit six times more light at room temperature.
What happens when two crystals, each only a few atoms thick, are placed on top of one another? They do not simply retain their individual properties. Their electrons begin to interact across the interface, and the resulting structure can behave in ways that neither material would on its own.
Researchers of SUPERVenice at Ca’ Foscari University of Venice, have used this principle to substantially improve light emission from molybdenum diselenide (MoSe₂), one of the most widely studied two-dimensional semiconductors.
The team combined a single layer of MoSe₂ with a thin crystal of palladium diselenide, PdSe₂. When illuminated with green light, the resulting heterostructure emitted approximately six times more light than MoSe₂ alone.
The work has now been published in Nano Letters.
Helping excitons find the bright path
When a semiconductor absorbs light, it creates temporary electron–hole pairs known as excitons. These excitons can recombine and release their energy as light, but they can also lose it through other processes, producing heat instead of photons.
The challenge is therefore not only to create excitons, but also to guide them towards the pathways that produce light.
This is what the PdSe₂ layer appears to do. Although it is not itself a strong light emitter, its electronic interaction with MoSe₂ changes the way excitons relax inside the material. Energy that would otherwise be lost is redirected towards the bright excitonic state responsible for light emission.
The result is an estimated photoluminescence quantum yield of about 6%, compared with approximately 1% for an untreated MoSe₂ monolayer.
The effect works across a broad range of excitation wavelengths and does not require chemical treatments or significant mechanical strain. The properties of the MoSe₂ layer are improved simply through its interaction with the material placed beneath it.
More than brighter emission
Two-dimensional semiconductors are promising candidates for future LEDs, lasers, optical sensors and quantum technologies. Their extreme thinness makes them compact and highly responsive, but their light emission is often limited by processes that waste the absorbed energy.
The new results show that these losses can be controlled by carefully selecting which materials are stacked together. Not every combination works. When the researchers replaced MoSe₂ with the closely related semiconductor MoS₂, the same enhancement was not observed. The electronic structure and energy alignment of the two materials must therefore match in the right way.
This turns the experiment into something more useful than a single bright heterostructure: it provides a possible design principle for engineering other two-dimensional materials with improved light-emission properties.
A study led from Venice
The research was led by the LION team at Ca’ Foscari University of Venice. Petr Rozhin, first author of the study, is a postdoctoral researcher in the LION group.
The work brought together experimental and theoretical expertise from Ca’ Foscari University of Venice, Friedrich Schiller University Jena, the University of Crete and FORTH, Politecnico di Milano, the University of Chemistry and Technology Prague, and the National Institute for Materials Science in Japan.
The article, “Highly Efficient Exciton Modulation in MoSe₂/PdSe₂ Heterostructures,” is available open access in Nano Letters.