Nitin Padture sees huge promise in perovskites, crystal structures that could be used to replace conventional silicon in solar panels.
PROVIDENCE, R.I. — Nitin Padture is soft-spoken, so when he describes new solar power technology that he is researching his words are all the more striking because they’re delivered without bombast and with only a hint of excitement.
"This," he says in his office at Brown University, "is a game changer."
Padture, a professor of materials engineering, is talking about perovskites, crystal structures that could be used to replace conventional silicon in solar panels. Making them is cheap and, using a method Padture has patented, also relatively easy.
But the real promise lies in their versatility. Perovskites can be made in layers 1,000 times thinner than a human hair that can be applied to flexible films. They are semi-transparent and can be tinted yellow, red and other colors.
Instead of limiting the placement of photovoltaic panels to roofs or fields, imagine affixing them to walls as shingles or siding or even to windows as a special coating. The possibilities for generating electricity from sunlight could be significantly expanded.
“The vision is painting your house with solar cells,” says Padture.
Padture, who is director of Brown’s Institute for Molecular and Nanoscale Innovation, is leading a team of researchers that was recently awarded a $4 million grant from the National Science Foundation to investigate the potential of perovskite cells. He and other professors and students at Brown are working with the University of Nebraska-Lincoln and Rhode Island College on the four-year project.
Solar power has spread dramatically across the United States in recent years, but it still represents a small fraction of the nation’s energy mix at only 0.4 percent of total generation, according to the U.S. Energy Information Administration.
Despite the rise of leasing schemes offered by companies such as SolarCity and Sunrun, the main barrier for consumers is the high upfront cost of photovoltaic panels.
The cost has come down dramatically over the past four decades, from about $60 a watt in the 1970s to 60 cents a watt these days. But a homeowner could still pay thousands of dollars to buy and install a relatively small rooftop system.
Perovskite panels could be part of a remedy. With a price, according to Padture, of less than 10 cents a watt, they could make solar power affordable to many more people. And he’s not alone in believing that they’re a major breakthrough.
“Time will tell, but many of us believe this is the field’s biggest breakthrough since the original invention of the solar cell sixty years ago,” Varun Sivaram, a solar researcher and fellow at the Council on Foreign Relations, writes in a recent blog post.
Perovskite crystals were discovered in the 1830s in the Ural Mountains in Russia and named after a Russian mineralogist. Although there are many varieties of crystal structures in the world, very few have the right “band gap” that allows them to absorb sunlight while still being able to generate electricity. Padture calls it the “Goldilocks sweet spot.”
Perovskites hit that sweet spot. They were first used in solar cells in 2009 and were soon recognized as a possible replacement for silicon cells because of their ease of manufacture.
While silicon cells must be fabricated in a complicated process that requires high temperatures and vacuums, perovskites can be made with less fuss in a lab.
Brown PhD student Yuanyuan Zhou demonstrates this in the university’s Advanced Ceramics and Nanomaterials Lab. After mixing a couple compounds in a solution, in no time he is able to separate the perovskite crystals for use in the research project. A stack of solar cells that he has already made rests on a shelf inside a sealed box he is using.
“They look simple to make, but making good cells is not easy,” Padture says while looking on. “We’re trying to come up with altogether new methods. That’s what drives us.”
Padture grew interested in perovskites in 2011 after leaving Ohio State University to take up his current position at Brown. His research until then had focused mainly on composites and high-performance ceramics, such as coatings that could withstand the extremely high temperatures in jet engines.
He read about the first work on perovskites, which was done in South Korea, and thought he could bring his expertise in developing new materials to a field dominated by chemists and physicists.
By 2013, with help from Zhou, Padture developed an innovative way of making crystals using different chemical solutions at room temperature as an alternative to using heat, a more common technique but one that limits production.
Efficiency at issue
The biggest question facing perovskite cells is efficiency — how well they convert sunlight to electricity. Silicon cells have peaked at about 25 percent efficient. The first perovskite cells were less than 4 percent efficient. Advances in research have pushed that number to 20 percent and Padture has gotten it as high as 18 percent. But if the new cells are to compete with conventional ones, efficiency must go up even higher.
As part of the work being funded through the NSF, the research team will look at ways to enhance the efficiency of the cells. Members will also study ways to make them more durable and consider whether they can be made lead-free.
Padture says that solar power holds more promise than any other renewable source “because the available energy is everywhere.” Harnessing all that energy is the challenge. He believes that perovskites could be the key.
“We’ve tested small samples, but the potential is there,” Padture says. “This could be a transformative technology.”
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