Fixing Perovskite Film Cracks Made Easy

A new Brown University study found that cracks in brittle perovskite films can be easily healed with compression or mild heating. This is a good sign for the use of perovskites in next-generation solar cells.

The study, published in the journal Acta Materialia, found that though perovskite films tend to crack easily, those cracks are easily healed with some compression or a little bit of heat. That bodes well, the researchers say, for the use of inexpensive perovskites to replace or complement pricey silicon in solar cell technologies.

Nitin Padture, the Otis E. Randall Professor in Brown’s School of Engineering and director of Brown’s Institute for Molecular and Nanoscale Innovation said, “The efficiency of perovskite solar cells has grown very quickly and now rivals silicon in laboratory cells. Everybody’s chasing high efficiency, which is important, but we also need to be thinking about things like long-term durability and mechanical reliability if we’re going to bring this solar cell technology to the market. That’s what this research was about.”

Perovskites, a broad class of crystalline materials, were first incorporated into solar cells in 2009. Those first perovskite solar cells had a power conversion efficiency of around 4%, but now that exceeds 25% – essentially the same as traditional silicon. The advantage of perovskite solar cells is that they can be made for a fraction of the cost of silicon, potentially cutting the cost of solar power installations. Perovskites can also be made into thin films that are semi-transparent and flexible, potentially clearing the way for energy-generating windows or for lightweight, flexible solar cells in tents or backpacks.

But the low-cost and ease of making perovskite solar cells comes with a cost.

Padture, who led the study, said, “In material science, things that are easy to make also tend to be easy to break. That’s certainly true of perovskites, which are quite brittle. But here we show they’re also quite easy to fix – cracks in perovskite films can be healed by compressing them or with moderate heat.”

For the study, Srinivas Yadavalli, a doctoral student working in Padture’s laboratory and the first author of the paper, deposited perovskite films on plastic substrates. He then bent the substrate to put tensile (pulling apart) stress on the perovskite film while using a scanning electron microscope (SEM) to detect cracks. Once the film was cracked, the researchers then bent the substrate in the opposite direction to see if compressive stress might heal those cracks.

Sure enough, SEM imaging showed that the cracks had disappeared. To make sure the cracks were fully healed and not merely hidden, the researchers used a technique known as X-ray diffraction. By measuring the size of a material’s atomic lattice, the technique can reveal whether a formerly cracked area is now able to carry a mechanical load – a surefire sign that the crack is healed. Those tests also indicated fully healed cracks.

The researchers found that heat was just as effective in healing cracks. Temperatures around 100° Celsius – quite modest heating by material science standards – were enough to completely heal cracks in perovskite films.

Padture says that the research was aimed at better understanding the basic properties of perovskite materials, and more work needs be done to develop methods of applying this information in a commercial setting. But knowing that perovskite films are easily healed could be useful as these kinds of solar cells move toward commercialization.

“It’s good news,” Padture said. “It suggests that fairly simple healing methods may help maintain performance in these kinds of solar cells.”

Professor Padture is quite right, its excellent news that a procedure can be developed now to make repairs to an installation. And even more correct to continue the research so that repairs would be a very rare thing. Perovskite as a material has a huge potential, and research is getting it closer to being a quality consumer product.