[Image above] Researchers from the École Polytechnique Fédérale de Lausanne (EPFL) in Lausanne, Switzerland, say their new technique for creating perovskite crystals maximizes solar cell efficiency. Credit: EPFL; YouTube

The sun provides one of most powerful, readily available natural sources of energy. But that power is variable—when the sun sets each night, we lose that power if it’s not efficiently stored.

Enter: perovskite solar cells. They’ve been making news for their great potential for high efficiency and low cost. The challenge, however, lies in perovskites’ well-documented instability.

At ACerS Materials Challenges in Alternative and Renewable Energy (MCARE) conference in Clearwater, Fla., in April, Md. K. Nazeeruddin (École Polytechnique Fédérale de Lausanne, Switzerland) presented his research about perovskite solar cells and the challenges associated with developing them for efficient solar energy storage.

“Stability is the biggest problem with perovskites and we have to come up with solutions,” Nazeeruddin said.

Stateside, a team led by Brown University researchers was awarded $4 million last summer by the National Science Foundation to study the potential of perovskite solar cells.

“We want to understand better the basic science behind these solar cells, look for ways to develop new technologies based on that understanding, and investigate scalable production methods that could one day bring perovskite solar cells to market,” ACerS member Nitin Padture, professor in the School of Engineering and director of Brown’s Institute for Molecular and Nanoscale Innovation, said last year about the research.

And last month, Padture and his team—in collaboration with the National Renewable Energy Laboratory (NREL) and the Chinese Academy of Sciences’ Qingdao Institute of Bioenergy and Bioprocess Technology—revealed they’re getting closer to commercializing perovskite production.

Now, researchers from the École Polytechnique Fédérale de Lausanne (EPFL) in Lausanne, Switzerland, say they’re “pushing the limits of solar cell performance” and were able to achieve the “highest performance ever measured for larger-size perovskite solar cells, reaching over 20% efficiency, matching the performance of conventional thin-film solar cells of similar sizes,” according to an EPFL video released last week.

“We found a very simple method to make nice crystals out of perovskites and deposit them onto conductive glass to make into solar cells,” Michael Graetzel from EPFL’s Laboratory of Photonics and Interfaces explains in the video.

To do this, the scientists dissolve a selection of compounds in a liquid to make some “ink.” Then they place the ink on a special type of conductive glass and spin it while the ink is still wet to flatten the ink and wick away excess liquid.

When the ink is dried, it leaves behind a thin film that crystallizes on top of the glass that, when Graetzel and his team apply their new “vacuum flash technique,” creates seeds for crystal formation, leading to very regular, shiny, highly conductive perovskite crystals with increased photovoltaic yields.

The vacuum flash technique applies mild heat to the ink-coated glass and selectively removes the volatile components of the inky liquid to enable formation of smooth, large-grain perovskite crystals needed for more stable perovskite solar cells. 

Check out this video to see the process in action.

Credit: École Polytechnique Fédérale de Lausanne; YouTube


The research, published in Science, is “A vacuum flash–assisted solution process for high-efficiency large-area perovskite solar cells” (DOI: 10.1126/science.aaf8060).