ERC Advanced Grant for René Janssen and his research on more efficient solar cells

The grant of three million euros is awarded by the European Research Council (ERC), and it is intended for established scientists with groundbreaking, high-risk research proposals. The award is a personal grant, and the researcher can use the funding for his or her research over the next five years.

Perovskite efficiency

Janssen is receiving an ERC Advanced Grant for the second time. In 2013, he used the grant to investigate how to use organic semiconductors in solar cells. He then specifically looked into how the cells can most efficiently split water into hydrogen and oxygen, and how carbon dioxide can be reduced.

Now, Janssen is looking at perovskite, a promising material for solar panels. Current solar panels are typically made with silicon and have a maximum efficiency of about 27%. Perovskite should be able to match that efficiency value. Janssen’s goal is to develop solar cells that can produce twice as much energy in comparison to silicon solar panels.

And that’s important because we are still using solar panels and wind turbines to generate just two terawatts of the total 19 terawatts of power needed worldwide. If we aim to generate all of our energy in a green manner globally, we would need ten times more.

Splitting solar rays

To achieve this, a great deal of research is still needed. Janssen is specifically working on stacking several – three or as many as four – different perovskite solar cells that are designed to each convert one part of the total solar light spectrum very efficiently. Collectively, this leads to higher efficiency and better utilization of the available solar energy.

During his previous ERC research, he already worked on this stacking technique, back then though it was via solar cells containing organic semiconductors. Now, he wants to apply the technique learned in that research to the material perovskite. Janssen: “We split a solar ray into the different wavelengths that make it up. The upper cells where the solar ray first hits the panel absorb only the blue part of the spectrum while the cells at the bottom absorb infrared wavelengths. In this way, we use a large portion of the available photons and convert them all into energy as efficiently as possible.”

Extinguishing with buckets of water

“Materials that absorb the blue-green part of the spectrum, in particular, are currently the least stable; we will have to work on that for a few more years. For a stacked solar cell like this to work properly, all of the cells must also all be able to supply the same amount of current. Imagine putting out a fire with a chain of people with buckets. If one person cannot keep up the pace, all of the buckets will pile up there. So, small defects or instabilities have a huge effect.”

An additional difficulty is the fact that the solar spectrum changes over the course of the day. And on top of that, also the position and orientation relative to the sun matters. Just think of whether a roof with solar panels faces east or south. Janssen can imagine that a different type of solar cell will be optimal for an east-facing roof in comparison to a south-facing roof. In this way, you can achieve the highest efficiency everywhere.

First step

Next to the stacking challenges, there is also a major challenge in making the material stable. Perovskite has a soft structure with different phases it can go into, making the material unstable when trying to scale up. Janssen expects that it will take at least another 10 years before the technique can really be used. He therefore sees the ERC grant as a first step.

Research on perovskite in solar cells is a competitive field of research with about a thousand groups working on the subject worldwide. Janssen is working specifically on stacking three or four solar cells with just perovskite. Besides his research group, only a few other groups around the world are working on this challenge so far.

Making a contribution

Janssen hopes to be the first to achieve an energy efficiency of 35 to 40% with perovskite solar cells. “You always lose a record. I’d rather be the first than briefly the best.” Yet he also remains level-headed: “If we have solved this problem in 10 to 20 years, a new problem will have presented itself. An awful lot of serious problems have already been solved through science, like HIV, acid rain, the hole in the ozone layer, and the corona virus.”

“But the biggest problem is still ahead of us: our climate. That’s a scale bigger and more unmanageable than anything we’ve had so far. It’s up to science to take all of the steps possible to solve this problem, to make the small contribution at the origin of the solution. I am very happy to do my bit,” Janssen concludes.