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Solar panels are reaching their limit.  These crystals could change that.

When the Biden administration announced a $ 128 million initiative at the end of March to improve solar energy costs, a significant portion of the money was spent on finding materials named after an obscure geologist and 19th century Russian nobleman: Lev Perovski.

Among the projects listed: $ 40 million for research and development of so-called perovskite materials that scientists use to push the limits of the efficiency and adaptability of solar cells.

And while perovskites are nothing new – they were first found in the Ural Mountains of Russia in 1839, and they are relatively common – their more recent applications in solar power technology have raised hopes that humans will use them to better harness the thousands of megawatts of energy from the sun that falls to Earth every hour.

“Perovskites, I would say, are one of the most exciting opportunities for solar cells in the immediate future,” said David Mitzi, professor of mechanical engineering and materials science at Duke University, who has studied the materials since the 1990s.

Any new solar power technology had to compete with silicon solar cells, an ingrained technology that has been used for more than 50 years, Mitzi said. But perovskites had the potential to both improve the efficiency of silicon cells and possibly compete directly with them: “I think there are definitely opportunities.”

Efficiency is only one of the characteristics. Perovskite cells can be easily made into a variety of electricity-generating materials, and at much lower temperatures – and therefore potentially at lower costs – than silicon cells. But the stability and durability of perovskite cells will need to be addressed before they can fully replace silicon.

Scientists have now discovered a whole class of perovskite materials that share a specific structure, incorporating three different chemicals into a cubic crystal form. They recognized years ago that some perovskites were semiconductors, like silicon used in electronics. But it wasn’t until 2009 that researchers discovered that perovskites could also be used to build solar cells, which turn sunlight into usable electricity.

The first perovskite cells had very low yields, so most of the sunlight that fell on them was not used. But they quickly improved.

“The efficiency with which the solar cells that contain these perovskite materials convert sunlight into electrons has increased at a truly incredible rate, to the point that now the yields are close to that of silicon solar cells in the lab,” said Lynn Loo, professor. of Chemical Engineering at Princeton University and director of the Andlinger Center for Energy and the Environment. “This is why we are so excited about this class of materials.”

Perovskite solar cells can also be made relatively easily – unlike silicon cells, which have to be refined at very high temperatures and therefore require a lot of energy. Perovskites can be made as thin sheets at low temperature or as inks that can effectively be “printed” onto substrates of other materials, such as flexible rolls of plastic.

This could lead to their use on surfaces where silicon solar cells would not be practical, such as the exteriors of cars or trucks; or they can even be printed on fabric to power portable electronics. Another possibility is to apply thin layers of perovskites to window glass, where they would let most of the light through while using some of it to generate electricity.

But one of the most promising uses for perovskite cells is to combine them with silicon cells so that they use more solar power than silicon alone. The best silicon cells approach their theoretical maximum efficiency of around 29%. But perovskite cells can be tuned to generate electricity from wavelengths of light that silicon cells do not use – and thus cover silicon solar cells with semi-transparent films of the cells. perovskite could overcome this fundamental limitation.

Oxford University physicist Henry Snaith, a leading researcher in perovskite solar cells, sees it as a way to combine the industrial dominance of silicon with the technological advantages of perovskites. He believes that “tandem” silicon and perovskite cells with yields above 40% could be commercially widespread within 10 years, and that they may soon be followed by multi-layered cells with yields above 50%.

The potential of perovskite solar panels has also caught the government’s attention at home and abroad. In addition to creating new business opportunities for US companies, perovskites could become a relatively inexpensive way for solar power to challenge fossil fuels to generate electricity. “I think a lot of us are yearning for the technology to really start solving some of the climate change issues that need to be addressed by 2050,” said physicist Joe Berry, who leads research on solar perovskites. at the National Renewable Energy Laboratory in Golden, Colorado.

However, perovskite solar cells still face issues, and one of those issues is the issue of stability. Partly because they are easy to make, perovskite cells also degrade quickly due to moisture and heat. Some experimental perovskite cells have been stable for tens of thousands of hours, but they still have a long way to go to reach 25 or 30 years of silicon cell use, Snaith said.

Some of the most promising perovskite materials for solar power also contain lead, which can be released into the environment when perovskite cells break down. Researchers are studying alternatives to lead-based perovskites, such as tin-based perovskites, and similar crystal structures that incorporate other, safer substances.

“I think there are challenges to overcome,” Loo said. “Whether [perovskites] will play an important role depends on the ability to overcome these challenges. ”

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