A sundial of a different kind

Powering smartwatches with solar energy: Researchers Tobias Henschel (left) and Bernd Stannowski have performed significant contributions at the HZB Competence Centre Photovoltaics Berlin (PVcomB).

Powering smartwatches with solar energy: Researchers Tobias Henschel (left) and Bernd Stannowski have performed significant contributions at the HZB Competence Centre Photovoltaics Berlin (PVcomB). © WISTA Management GmbH

© HZB

Extra power thanks to solar energy.

Extra power thanks to solar energy. © Garmin

Turning a scientific question into a product is the requirement that the winners of the HZB Technology Transfer Prize should fulfil. The team led by Tobias Henschel, Bernd Stannowski and Sebastian Neubert won more than just a prize.

Tobias, what exactly is your project about, for which you received the Technology Transfer Prize?

Tobias: We are working on transparent solar cells that can be seamlessly integrated into all the little electronic helpers we carry around with us every day. The display of a smartwatch, a smartphone, a navigation device or a tablet would thus not only be a display element, but also an energy supplier at the same time. This is currently working very well for smartwatches, which our industry partner Garmin has already successfully placed on the market.

So, you make solar cells invisible. That sounds somehow like science fiction.

Bernd: The topic is not really new. There are already technologies in which individual areas of the solar cell are lasered away to achieve transparency. Schott in Germany, for example, has already done something like that. It can be used quite well for buildings, but for our purposes it is a bit crude. That's why we went a different way.

And what does that look like? What is your secret?

Bernd: The project uses photolithography, which is also used to produce computer chips. This allows us to etch away extremely small areas in the solar cell. In principle, this then has many tiny holes, like a sieve. Depending on how big the structures are and how much we etch away, they are more or less transparent. So, we can adjust the transparency very flexibly. The secret is a clever contacting system developed by Garmin, which ensures that the energy can be tapped from the solar cell despite the many tiny holes.

Tobias: To give you a better idea: Currently, the width of the individual solar cell units is about 10 micrometers. That corresponds to about a fifth of the thickness of a human hair. And their power is in the milliwatt range. This is not yet enough for energy-hungry smartphones. But a 10 to 20 percent longer battery life or emergency power in places without energy supply are already possible.

How did you get involved in the project?

Bernd: We were approached by a French company - Sunpartner. That was in 2015, and we started by running a few tests and depositing various layers on glass. We didn't really know what the idea behind the project was. And then, month by month, it became a little more concrete. Since Sunpartner was obviously very satisfied with our work, new orders came in steadily over the first year. This finally developed into a permanent cooperation. And only then we fully realised the context in which the whole thing stood.

With your background, you were obviously the right person for the project.

Bernd: Well, yes. It's true that I come from the technology field of thin-film silicon. I did my doctorate on it in Utrecht in Holland at the end of 2002. And I also worked on this topic in industry for eight years. Thus, I think that it was my experience in this field that gave me the initial impulse. I was able to answer many of the questions because I had already been involved in this field before. So, we were able to find good solutions quite quickly. That helped the whole project a lot at the beginning. A little later, Sebastian Neubert joined us, whom I already knew from my time in industry and who contributed a lot to the further success of the project at HZB.

And you Tobias, how did you get involved in the project?

Tobias: I have been at HZB for a good eight years now. As a student, I had an internship here, which first led to my Bachelor's thesis and then to my Master's thesis. That's how long I've been working with Bernd, and I've been a process development engineer in his group for five years. I mainly supervise the systems for plasma-assisted vapour deposition. These are used to deposit thin silicon layers. After Bernd took over the project together with Sebastian Neubert, I did measurement work for him from time to time. And when Sebastian left the institute two and a half years ago and founded his own technology consulting company, I followed in his footsteps. Now I manage the project and Bernd supports me with his know-how.

The project has been running for six years now. What has it brought you so far?

Bernd: Definitely a very fruitful cooperation. Through research and development contracts, through the pilot production of the solar cells here at HZB and in France, and also through licensing agreements from the time with Sunpartner, we have steadily generated income. In total, Helmholtz-Zentrum Berlin has raised a little more than 1.3 million euros through this cooperation. And of course we should not forget the reputation. Because the project is a really good example of how a cooperation between research and industry converts an idea into a product that can be bought all over the world today.

Tobias: That's right. And beyond the success, the cooperation is also a very interesting experience. Especially the completely different approach to development work. For us researchers, it's mainly about understanding why things work or why they don't work through clever experiments. In industry, the approach is different. In the end, a product has to come out and the deadlines are much tougher. So, it's easy to say: this approach doesn't work, it will be discarded. Then we as researchers have to put the brakes on and say: Yes, this is not working right now. But the approach has much greater potential. We must continue to work in this direction. And making the other side understand that was a challenge that I really grew with.

Now you have also been to the Asian manufacturers who produce the solar cells. What impressed you most there?

Tobias: It was super exciting to see a huge factory hall that is a complete clean room. We know clean rooms from our institute, of course. We also work in them there. But these are completely different standards. Here, they are the size of a flat and the entire factory is a single clean room. I found it fascinating to see the same type of coating plant there as in our laboratory. But five times as big. The feeling is indescribable. In the factory in Asia, you can walk under the equipment, while we have to squeeze underneath it in the lab for repair work. It's just impressive.

And now you have also been awarded the HZB Technology Transfer Prize for your project. Was that actually foreseeable for you?

Tobias: Well, we have an interesting project in which the transfer from research to industry has already taken place. And there is already a product on the market of which 100 million units have already been sold. That's why we thought we had a chance of winning the prize. But of course the other participants also had incredibly interesting projects. That we won in the end is a really good feeling. It not only honors the commitment of the whole team, but also gives us more visibility for our other projects.

But surely this is not the end of this exciting story? What else can we look forward to in the future?

Tobias: In terms of research, we have now reached a stage where we can transfer this principle to larger areas. In the future, the technology should be applicable to every conceivable display. However, you have to look at what really makes sense. A smartphone that is almost always in your pocket is less likely to benefit from a transparent solar cell. But there are other devices and areas of application. However, we are not yet allowed to reveal what these are. So, you will have to remain a little in suspense.

Kai Dürfeld

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