“I want to contribute to the energy revolution”

Klaus Jäger sits in his blue office chair at a desk with a monitor; behind him a shelf of books. “I don’t have a lab,” he says with an Austrian accent. The physicist works on optical simulations of solar cells at the Helmholtz-Zentrum Berlin für Materialien und Energie. Born in Tyrol, he has been working at the research center in Adlershof since 2015.

The scientist sees his work here as a kind of service. “I help my colleagues who are doing the experiments, to improve their solar cells,” he says. Jäger’s work revolves around the question of how to design a solar cell so that it absorbs light as effectively as possible. “Simulations are an important tool for understanding this,” says Jäger. Using a computer-designed model of the solar cell, he can predict the behavior of light, such as how much light is reflected orabsorbed, and where in particular this happens.

There are two tricks to making the most of the light. “One trick is to adjust the thickness of the layer,” Jäger explains. He takes a sheet of paper and a pen, draws two horizontal lines one above the other, and two wavy lines vertically on top of them, which meet at the bottom horizontal line. “Some of the light that falls on a solar cell passes through the thin film, and some is reflected.” The thickness of the material is critical. It can be used to adjust how much light is reflected and how much goes into the solar cell. “I simulate this and can then tell my colleagues exactly what thickness for the layer is optimal,” he explains.

Another trick is to add structures to the solar cell layers. “If you look at a standard solar cell under a microscope, you will see a pyramid structure. This allows the solar cell to absorb light more effectively,” says Jäger. He draws a zigzag line on the back of the sheet and several arrows pointing in different directions. “Light falls on a pyramid. Some of it goes in, some of it is reflected, but then it hits a second facet.” He points to a diagonal line. “This trick allows more light to enter the solar cell, no matter which direction the light comes from. Sunlight doesn’t always hit the solar cell at a right angle.”

Jäger’s eyes light up when he talks about his work: “I’m interested in how we can contribute to the big transformation processes in the energy sector.” At the age of 14 Jäger knew he wanted to be a physicist. “I was sure of it without knowing exactly what it meant,” he says. After graduating from high school, he began studying physics at the University of Innsbruck, but soon transferred to ETH Zurich.

During his time at ETH he experienced a pivotal moment that would have a strong influence on his professional development. “As part of the atomic and particle physics lectures, we visited a nuclear power plant,” says Jäger. “At the end of the tour, the employee who had showed us aroundsaid: ‘Humans are facing big problems in terms of energy supply. Society expects you physicists to help solve these problems.’ This phrase had such an impact on him that he began to focus more on energy in his studies.

In addition to research, sharing his knowledge with others is important to Jäger. He is often invited to give lectures. “I think it is very important to interact with non-scientists,” he says. “The world has become very complex, and if you don't have a basic scientific education, it’s very difficult to get a good overview of the situation. I believe that we as scientists can help to improve this. It makes sense to give talks in places outside larger towns and cities where people have less access to scientific events.”

Jäger’s engagement, however, goes far beyond this. In 2019, he and a friend and fellow scientist founded LGBTQ STEM Berlin. The idea was inspired by groups like “Unicorns in Tech,” which he got to know when he came to Berlin. Such groups are common in the English-speaking world. “I realized that the visibility of LGBTQ people in Germany is still a niche topic,” says Jäger. “That means that an LGBTQ identity is not necessarily seen as a problem, but that people don’t talk about it.”

Jäger is concerned that the issue of diversity is becoming increasingly politicized. “In some cases, a culture war is being staged in which we as LGBTQ+ people could come under pressure again if the situation gets worse,” says Klaus Jäger. That worries him.  

With all the issues that keep Jäger busy, he needs something to unwind from time to time. “During the pandemic, I realized that the best way for me to relax was to go for walks in nature,” he says. Back then, he worked a lot from his apartment in Steglitz. From there, it’s not far to the Grunewald forest, where he likes to go hiking. But even though he only needs his laptop to work, he is happy to be back in the office. Direct communication with his colleagues is very important to him.