Researchers attempted to combine materials to create a new type of efficient photovoltaic (solar) cell. Instead, they created new material properties and a special particle that might be used to simulate quantum systems.
Sometimes, when a project is launched, not everything pans out as originally intended.
This happened to researchers from Aarhus University, who were trying to develop better photovoltaic cells but inadvertently discovered a new type of particle that could be useful in developing quantum computers.
According to a researcher behind the discovery, sometimes researchers should follow the gold nuggets inadvertently discovered by research.
“We work with some crazy materials which, if they behaved optimally, could lead to the development of better photovoltaic cells. However, when we put them together, we got something unexpected that might be used for something even crazier,” explains Søren Ulstrup, Associate Professor, Department of Physics and Astronomy, Aarhus University, Denmark.
The research has been published in Nature Communications.
Photovoltaic cells can be improved
Søren Ulstrup envisions being able to replace conventional semiconductors in photovoltaic cells and electronics with materials that can be much more than just semiconductors.
Semiconductors in electronics consist of silicon, which can switch the flow of electrons on and off, and this property makes silicon suitable in these areas.
Søren Ulstrup wants to develop materials that can do more than just switch the flow of electrons on and off. For example, he wants to develop a material for photovoltaic cells that is better than silicon at converting light into energy and better at transporting the electricity away from the photovoltaic cell and out into the system.
“This would make photovoltaic cell technology much more efficient, which is a major goal for the future,” he adds.
Bonding two ultrathin materials together
In the experiments that led up to the unusual discovery, Søren Ulstrup and colleagues investigated the possibility of combining two materials to obtain one material with improved conversion of sunlight into energy and better conductivity.
To achieve this, the researchers primarily examined tungsten disulfide, which is present in oil for bicycle chains, since it is also an excellent lubricant.
This material is also a good semiconductor that can very efficiently harvest energy from sunlight by exciting electrons to a higher energy level.
Finally, extremely thin layers of tungsten disulfide of just a few atoms can be made. In this very thin layer of atoms the interaction between light and electrons is very strong and efficient.
The second layer in the sandwich the researchers wanted to design is graphene, which is extremely efficient at conducting electricity and at a speed approaching the speed of light.
Graphene also consists exclusively of carbon with a thickness of a single layer of atoms.
“Graphene is known to be very good at conducting electrons. The idea of putting tungsten disulfide together with graphene in a sandwich was to create a material with the optimal properties from these materials, so that we could both harvest the energy in the sunlight very efficiently and transport this energy rapidly in the form of electricity,” says Søren Ulstrup.
New particle emerged
However, when the researchers bonded the two ultrathin layers, something unexpected occurred.
Instead of a good photovoltaic cell material, they got a different type of material with surprising properties.
Søren Ulstrup explains that when graphene and tungsten disulfide bond, the electrons start oscillating inside the graphene layer, and these oscillations interact with electrons that are excited to higher energy levels in tungsten disulfide, creating a new particle called a polaron.
A polaron is also called a quasiparticle within the physics of condensed matter, and this term covers quantum systems in which a single electron interacts with the oscillations of the surrounding electrons or atoms.
The formation of polarons means that the graphene–tungsten disulfide sandwich cannot be used as a material in efficient solar cells, but the discovery indicates that the quantum properties of the combined material can be controlled, which can be particularly useful when designing solid materials that can perform quantum simulations and thus be used as basic hardware in a quantum computer.
“All the electrical and optical properties of the material change when this polaron is created. This is the first time anyone has observed this kind of interaction between two atomically thin materials. This is why the study is groundbreaking. The fact that we cannot use the combination of graphene and tungsten disulfide as an efficient photovoltaic cell is a pity, but if the interactions across the materials can be controlled, this opens up interesting opportunities for designing new types of quantum systems,“ concludes Søren Ulstrup.
