What is it about?

Quantum mechanics affects particles that are smaller than atoms – and at the University of Gothenburg, researchers have used an electromagnetic field to combine light and matter into a hybrid state. Their manipulation should, among other things, be able to contribute to more easily produced and stable organic solar cells.

– We enclose electromagnetic fields in the system with the help of mirrors. If you put two mirrors very close to each other, a standing wave arises between them. You can liken it to a musical instrument – depending on how you tune your guitar, you get a standing wave that is the specific tone you hear. But we do it in the visible area, says Karl Börjesson who is a professor of physical chemistry at the University of Gothenburg.

He is the lead author of the study that has been published in Nature Communications.

Why did they do this?

Organic solar cells are made of light-absorbing polymeric materials and are also called plastic solar cells. They have the advantage that they can be made thin and bendable.

A Swedish company that works with developing organic solar cells is Epishine, which Ny Teknik has written about several times, for example here.

But organic solar cells are not yet as stable and efficient as silicon-based solar cells.

To get electricity out of the organic solar cell, a photon must move from the place where it is absorbed to a surface interface where the two different materials of the solar cell meet. The materials must be made thick enough to absorb the light, but the problem is that the energy travels very slowly in the materials, which means that it is lost as heat before it reaches the surface interface.

The previous solution

To solve the problem, you can do a so-called bulk heterojunction solar cell. Then the two materials are mixed first, followed by phase separation. Then very small channels are formed by the different materials, which means that the energy only needs to travel a very short way to reach the surface interface after the light has been absorbed.

However, you can get problems when using bulk heterojunction. Materials that look optimal do not necessarily work. The next problem may be that you get systems that are not stable over time. Especially when the cell heats up, molecules can start to migrate, which changes the size of the channels and thus how well the solar cell works.

This is how the new method works

With a bulk heterojunction you have to take into account how mixtures change over time, which is a much smaller problem if you use so-called flat systems where the layers are not mixed.

Researchers at the University of Gothenburg have used the electromagnetic wave to accelerate how fast energy can move. The scale should have the same frequency as the transition in the molecule.

– We connect the electromagnetic field and the material so strongly that you get new states that have new properties. The electronic states of the molecules are modified, says Karl Börjesson.

What significance can the research have?

According to Karl Börjesson, the most important step forward is to propose a new solution to the problem of how energy should reach the interface, and instead of using bulk heterojunction you can make flat systems. However, he believes that it is difficult to say what effect their work may have on organic solar cells.

– Then we have the perspective photodiodes, and there the potential is probably a little bigger. But perhaps the biggest is from the quantum mechanical perspective. We have not previously thought so much that these quantum mechanical conditions can do photochemistry, says Karl Börjesson.