When the Biden administration announced in late March a $128 million initiative to improve the costs of solar power, a significant chunk of the money went to research into materials named after an obscure 19th century Russian geologist and nobleman: Lev Perovski.
Among the projects listed: $40 million for research and development into so-called perovskite materials that scientists are using to push the limits of just how efficient and adaptable solar cells can be.
And while perovskites aren't anything new — they were first found in Russia’s Ural Mountains in 1839, and they are relatively common — their more recent applications in solar power technology has sparked hope that humans will use them to better harness the thousands of megawatts of energy from the sun that falls on Earth every hour.
“Perovskites, I would argue, are one of the most exciting opportunities for solar cells in the immediate future,” said David Mitzi, a 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 entrenched technology used for more than 50 years, Mitzi said. But perovskites had the potential to both enhance the efficiencies of silicon cells, and perhaps to compete with them directly: “I think there definitely are opportunities.”
Efficiency is just one of the features. Perovskite cells can be easily manufactured into a variety of electricity-generating materials, and at much lower temperatures — and therefore potentially lower costs — than silicon cells. But the stability and durability of perovskite cells will have to be addressed before they can entirely replace silicon.
Scientists have now discovered a whole class of perovskite materials that share a specific structure, incorporating three different chemicals within a cubic crystal shape. They recognized years ago that some perovskites were semiconductors, like the silicon used in electronics. But it was only in 2009 that researchers found perovskites could also be used to build solar cells, which turn sunlight into usable electricity.
The first perovskite cells had very low efficiencies, so most of the sunlight that fell on them wasn’t used. But they’ve rapidly improved.
“The efficiency with which solar cells that have these perovskite materials convert sunlight to electrons has increased at a really incredible rate, to the extent that now the efficiencies are close to those of silicon solar cells in the lab,” said Lynn Loo, a professor of chemical engineering at Princeton University and the director of the Andlinger Center for Energy and the Environment. “That's why we are so excited about this class of materials."
Perovskite solar cells can also be made relatively easily – unlike silicon cells, which need to be refined at very high temperatures and so need a lot of energy to make. Perovskites can be made as thin sheets at low temperatures, or as inks that can effectively be “printed” onto substrates of other materials, such as flexible rolls of plastic.
That could lead to their use on surfaces where silicon solar cells wouldn’t be practical, such as the exteriors of cars or trucks; or they might even be printed onto cloth to power wearable electronics. Another possibility is to apply thin films of perovskites to the glass of windows, where they’d let through most of the light while using a part of it to generate electricity.
But one of the most promising uses of perovskite cells is to combine them with silicon cells so that they use more of the sun’s energy than silicon alone. The best silicon cells are approaching their theoretical maximum efficiency of about 29 percent. But perovskite cells can be tuned to generate electricity from wavelengths of light that silicon cells don’t use – and so covering silicon solar cells with semi-transparent films of perovskite cells could overcome that fundamental limit.
Physicist Henry Snaith at the University of Oxford, a leading researcher in perovskite solar cells, sees this as a way to combine the industrial dominance of silicon with the technological advantages of perovskites. He thinks “tandem” silicon and perovskite cells with efficiencies above 40 percent efficiency could be commercially widespread within 10 years, and that they could soon be followed by multilayered cells with efficiencies of over 50 percent.
The potential of perovskite solar panels has also caught government attention, both here and overseas. As well as creating new commercial opportunities for U.S. companies, perovskites could become a relatively inexpensive way for solar power to challenge fossil fuels for generating electricity. “I think a lot of us have aspirations for the technology to really begin to address some of the climate change issues that need to be handled by 2050,” said physicist Joe Berry, who leads research into solar perovskites at the National Renewable Energy Laboratory in Golden, Colorado.
Perovskite solar cells still face problems, however, and key among these is the issue of stability. In part because they’re easy to make, perovskite cells also degrade quickly from humidity and heat. Some experimental perovskite cells have stayed stable for tens of thousands of hours, but they still have a long way to go to meet the 25 or 30 years of use of silicon cells, Snaith said.
Some of the most promising perovskite materials for solar power also incorporate lead, which can be released into the environment when the perovskite cells degrade. 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 some challenges ahead,” Loo said. “Whether [perovskites] are going to play a significant role depends on whether we can overcome these challenges."