“Chemistry can be used to find solutions to today's problems, such as the energy crisis.”

Chemistry often appears in the news with a negative aftertaste. mistake! It's much more than just PFAs, plastic pollution, or the nitrogen crisis. Tessel Bowens, 30, just spent 45 minutes talking about her research on molecular machines in solar cells, and she really needs to get this off her chest. “Chemistry has fundamentally improved life, it has greatly improved nutrition and materials. I believe chemistry will also be very important in finding solutions to the problems we currently face, such as the energy crisis.”

Bowens is certainly committed to that. She received her PhD from the University of Amsterdam in September 2021 on a molecular “shuttle bus” that ensures that electrons in an innovative type of solar cell reach their destination, making solar cells more efficient. She is now working on similar ideas as a postdoctoral researcher at the University of Cambridge, in the hope of sparking artificial photosynthesis.

Dye-sensitized solar cellsInnovative solar cells, as they are called, are made of different materials than the silicon cells used in standard solar panels. The top layer of the dye is the functional part. When sunlight hits the pigment, electrons flow and generate electricity. Solar cells can be manufactured in all kinds of colors – Bowens orange – making them suitable for integration into buildings. They can also be transparent, making windows a potential surface for energy generation. Also nice: it actually works in low light.

Electrons that are not moving properly

“Unfortunately, the efficiency of these solar cells is much lower than that of silicon solar cells,” says Boyens. “There are two types Dye-sensitized solar cells, one yields a return of about 15 percent and the other 2.5 percent. This is really exciting. So I focused on that genre.”

The problem with this solar cell is that the electrons are not moving in the right direction. Electrons have to get from A to B, but they often don't get to B. They turn around midway, go back to where they came from and don't produce any energy.

“Many people, including my professor at UCLA, have been trying to solve this problem for some time,” says Bowens. Meanwhile, during her master's degree course, she became interested in molecules that can move, called molecular machines. “That's how I found rotaxane, which is a molecular wire with a ring around it that can move along the wire. I thought we needed those solar cells, because we want to move those electrons from A to B. My teacher also thought it was a good idea. “I have applied for my own grant to conduct this research.”

Dissolved molecular rings

The solar cell designed by Bowens consists of a glass sheet with a semiconductor through which a layer of pigment molecules is attached to a molecular wire. Below this layer is a layer of liquid electrolyte where the molecular rings are dissolved. Below this is the electrode to which electrons are transferred from the pigment via the molecular machine.

“The chemical properties of the molecules ensure that the electron likes to sit on the ring,” Bowens explains. “And the ring wants to attach to the molecular thread attached to the dye. They then form a supramolecular bond. The molecules feel each other, but the bond is not strong and so it can come loose easily. That is also the intention. Once the ring is in place on the wire, the electron can then jump around.” “The connection is automatically broken, causing the ring to 'fire'. The electron then leaves place A. A new ring will be placed where the ring was. So there is no way back. The electron must go to point B.”

“It was an ambitious idea, and I had to know enough about solar cells and molecular machines. Sometimes it wasn't possible to make a solar cell, and other times it wasn't possible to get the right dye. It wasn't until the end of my PhD that “Everything came together. And then I still had to prove it worked. We couldn't measure this properly at the UvA. Fortunately, the University of Twente had new equipment that made this possible. Without their help I wouldn't have been able to provide the evidence.”

A new scholarship has been applied for

There's more in store. “I still have many ideas I want to implement. Ultimately, you can also use these solar cells in chemical synthesis, where a certain molecule is converted into another. Plants do something similar in photosynthesis; under the influence of light they convert simple molecules into Complex molecules. After I got my PhD, I applied for a new grant and now I'm in Cambridge for two years with a research group working on this.

“I really enjoy doing research. With chemistry you make something that no one has made before. But working in academia also involves difficult things, like temporary grants. My grant here expires in six months, and I am now in several places in Europe looking at how to continue.” “I don’t know yet where I will live next year.”

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