in the workplace

“Flexible solar cells are the future”

19 January 2018 • 4 min reading time

Mirjam Theelen destroys solar cells. In recognition of this work, her colleagues voted her ‘Outstanding Researcher of 2017’. That needs an explanation.

After graduating in chemistry, Mirjam Theelen went on to do PhD research on solar cells. She has now been working at TNO for ten years. Her work here focuses on ultra-thin CIGS cells, which are named after the chemical elements of which they are composed: Copper, Indium, Gallium and Selenium. The great advantage of CIGS cells is that they are only a few thousandths of a millimetre thick, which means they are potentially flexible. Unlike the more familiar types of solar cell, you can bend these panels into any shape you require. That opens up a range of new applications. Part of Mirjam’s work involves destroying these solar cells.

You destroy beautiful solar panels. Why?

“Every solar cell manufacturer tests their products’ resistance to rain, hail and sunlight. They base their guarantees on these results. But what I really want to know is why – and under what conditions – solar cells break. After all, if you understand the causes, you can devise improvements that make the cells last longer. One question, for example, is what is the best way to protect thin CIGS cells from moisture. You can’t just encase them in a layer of glass, because then they wouldn’t be bendy any more. And that bendiness is exactly what we want.”

“I want to know why solar cells break, and under what conditions. After all, if you understand the causes, you can come up with improvements to make the cells last longer”

What has your research revealed?

“We now have a better idea of how to make this type of solar cell longer lasting and more stable. One way to do this is by tweaking the composition of the various elements. We also have a better understanding of how to improve cell quality, without pushing up the cost price.”

What is the greatest challenge you face?

“The main difficulty is to create testing equipment that faithfully simulates the effects of all kinds of weather within a short period of time. It’s fairly easy to simulate rain and heat in a climate chamber. However, these are not usually combined with other factors, such as sunlight, that also affect the product’s service life.”

“We now have a better understanding of how to improve the quality of these solar cells, without increasing the cost price”

TNO also leads the field in this testing equipment technology, doesn’t it?

“That’s right. Our climate chamber enables us to check the effects of humidity and temperature, while also exposing the test panels to sunlight. In addition, this testing equipment enables us to closely monitor the samples’ behaviour. That is quite exceptional. In fact, the small-scale innovative companies that supplied parts for the initial testing equipment are now manufacturing this technology for major solar panel manufacturers and test institutes. So they are now exporting our expertise through TNO’s Technologie zoekt Ondernemer (Technology seeks Entrepreneur) programme. Indeed, others can also make use of it. That is actually an enormous compliment for TNO. Together, we have created something that has international added value.”

How will your research benefit society?

“These flexible solar panels have a great future. For example, far fewer raw materials are needed to produce them. Moreover, the flexibility of these cells means they can be integrated into all kinds of materials and objects, such as backpacks. Or bicycles with integrated solar cells. Numerous novel applications are within reach. My research will help to boost quality without any additional production costs.”

“Flexible solar panels have a great future. For example, far fewer raw materials are needed to produce them”

What is the importance of this research for TNO?

“Many of TNO’s departments are working on solar energy. Our research will help them to conceive and develop new applications. The great thing about TNO is that we all share our expertise, thus making each other stronger. For instance, while the testing equipment was my idea, others played a huge part in its construction, especially my colleague Henk Steijvers.”

Were you surprised that your colleagues voted you the ‘Outstanding Researcher of 2017’?

“I’m very proud of the fact that my colleagues value my research. Not only that, I’m very proud of the work itself. I think it’s really cool to work on something with such enormous social relevance. That’s a great incentive.”

Are there any other goals you’d like to pursue?

“I want to apply for a European grant, to fund my research. That would allow us to broaden the scope of the research and to take on some PhD students and postdocs. Incidentally, I don’t want my future to be entirely restricted to scientific research. I get a real kick from widening my professional development portfolio. For example, I have held seats on the works council and on the board of the staff association. I also worked in a library for seven years, while studying at university. At heart I am a scientist, but I have always had a great fondness for books and history. Hence my broad range of interests.”