In Swift Solar’s lab, more than a dozen pairs of elbow-length rubber gloves hover horizontally in midair, inflated like arms. The gloves are animated by gaseous nitrogen and jut out of waist-high, glass-walled enclosures, designed to keep the workspaces dry and airtight to protect the delicate solar materials inside.
In a corner, technician Roger Thompson slides his hands into a pair and begins slotting small glass slides into a metal plate. Soon, a conveyor belt will carry the plate behind a metal door, where “black box magic,” as Swift CEO Joel Jean calls it, will add a chemical coating designed to conduct electrical current.
Swift, which operates this facility in a quiet industrial neighborhood in Silicon Valley, is one of a growing group of companies experimenting with next-generation solar technology. The startup is racing to produce commercially viable solar cells that layer the traditional silicon with materials called perovskites.
Stacking these two materials, which absorb different wavelengths of sunlight, allows solar panels to reach higher efficiencies and produce more electricity per panel. That means perovskite tandem solar cells could reduce costs and boost the amount of renewable electricity on the grid.
The promise is significant. But companies and scientists have been tinkering with the technology for over a decade without any commercial deployment. As a solar material, perovskites are fickle—they’re sensitive to water, heat, and light. And some researchers warn time may be running out.
“I have a feeling that if in the next two to three years there’s no perovskite products, the market may decrease its confidence in this technology,” says Bin Chen, a research assistant professor who focuses on perovskite technology at Northwestern University.
Researchers and startups including Swift are working feverishly to develop those products, emboldened by recent progress on making perovskites more durable. In recent months, some of the world’s largest solar companies have also given the technology votes of confidence, by investing in pilot manufacturing lines or purchasing perovskite startups.
Now these companies must prove they can overcome the struggles that have bedeviled perovskites for years, while producing millions of panels that perform with record-breaking efficiency.
‘On the back’ of silicon
The key to success for perovskites, many of these companies believe, will be integrating them with proven solar technologies, which could lend perovskites some of their stability and their hard-earned market confidence.
“The main entry point for perovskites to the market is literally on the back of silicon,” says Barry Rand, a professor of electrical and computer engineering at Princeton University.
Today, more than 90% of solar panels sold worldwide are made from crystalline silicon. Decades of experience with that technology mean developers know how to plan projects around it, and financiers know how to price investments for projects that use it.
Layering perovskites onto these panels could give solar companies an edge in a highly competitive industry. “If you can crack it—make a better solar module—you will make money out of it,” says Jenny Chase, a solar analyst at the research service BloombergNEF. “The idea is to make something that’s cheaper to manufacture per watt, and then you can sell it at a premium because it will be quite high efficiency.”
That’s easier said than done. Perovskites, which are composed of metal halides and share a unique crystal structure, face two big challenges: increasing durability and scaling up production. Perovskites can react with oxygen in the air, or degrade when exposed to light—a pretty big problem for a solar product.
To make perovskite tandems with more stable structures, companies plan to layer perovskites on other solar cells, using evaporation, printing (like ink on a newspaper), and even “spin-coating,” a technique that looks like spin art from the ‘90s. Changing the composition of the perovskite layer could also help them last longer.
Chen and Rand are collaborators on two newly funded efforts, backed by millions of dollars from the US Department of Energy, to test perovskite-silicon configurations that could be more durable and quicker to commercialize. Other participants include universities, several perovskite startups (including Swift), and the US National Renewable Energy Laboratory.
Staying power
Rand, whose team at Princeton studies how to stop perovskites from degrading, says the field has come a long way in the last seven years. Today’s panels are better encapsulated to keep out water. Now he says it’s simply a game of elimination—determining which chemical components in a cell are most likely to react, and swapping them out. But he doesn’t think that further experimentation should hold back commercialization.
“The results are, I think, promising enough to make those investments,” he says. “But it shouldn’t be thought about as [a] ‘job done.’ There’s still many breakthroughs, mainly with respect to stability, to still emerge.”
Tomas Leijtens, a cofounder and the chief technology officer of Swift, says the company can now expose its cells to temperatures up to 70 °C while operating them in light without degradation. “That was something that was, I would say, unthinkable five years ago,” he says, seated at a table ornamented with a hot-pink perovskite model.
But the industry must ensure that every cell will be that durable; worldwide, companies manufacture hundreds of millions of solar panels every year, each containing dozens of cells. Before they’re used in projects, panels must pass rigorous industry tests, like enduring quick temperature changes, humidity, and hail. Swift, which was founded in 2017, hasn’t started independent tests yet; for now it’s subjecting its cells to some of those conditions in its own lab and has one panel wired up on its roof.
Startups like Swift and Oxford PV—a UK company spun out of a university research lab where some Swift founders once worked—are working alongside the industry’s largest companies to get tandems to market. Oxford PV says it will start shipping perovskite tandem panels to customers later this year. In May, Arizona-based First Solar, the largest solar manufacturer in the US, bought a European perovskite company called Evolar.
In a release on its Evolar acquisition, First Solar CEO Mark Widmar said the company believes “high-efficiency tandem PV modules will define the future.” Just a few days later, Korea-based Hanwha Q Cells, another top manufacturer, said it was investing $100 million to set up a perovskite tandem pilot line. In 2022, Q Cells helped start Pepperoni, a European collaboration to advance tandems.
Researchers working on perovskites say commercial tandem cells could be years, not decades, away. Jean says Swift hopes to have a product ready to commercialize within four years. Incentives in the Inflation Reduction Act, which included credits for US-made clean energy products, should help.
But perovskites have skeptics as well as supporters. Chase says today’s silicon panels are already good enough to help the world transition to clean energy and fight climate change. She has long questioned perovskites’ ability to upend the solar industry’s status quo.“You cannot make a semiconductor tech with momentum,” she says. “You need the tech to work.”
Given how much solar energy will be needed to decarbonize the grid, however, perovskite backers say every bit of added efficiency will be important.
“While it’s true that silicon is great, tandems are better,” says Leijtens. “In the fight to tackle climate change, we need to accelerate, not just say, ‘Oh, this is good enough—we’re done.’ Everything can continue to be improved.”