As the world begins to pivot away from fossil fuels, solar energy offers a promising alternative that is both clean and renewable. However, a major barrier preventing widespread adoption of this renewable energy source is cost. Panels are typically made using silicon which entails a lengthy and expensive production process.
Meet perovskite, a silicon alternative that is simple to make and cheap to produce, requiring only a few laboratory salts and an inkjet printer. Perovskite commercialization is currently in the early stages and growing. However, deep within perovskite’s crystal core there are costly structural weaknesses that render it inefficient. The source of these weaknesses has long eluded scientists.
But a UNC Chapel Hill research team found that strengthening the composition of the perovskite crystal may lead to a more stable solar panel, in a study published in May in the journal Science.
If this technology is going to succeed, we need to make it reproducibly at large scales, efficiently, and it needs to operate for many years in real world operating conditions. And I think this work really is a good step in that direction.Laura Schelhas
“My initial thoughts are excitement,” said Laura Schelhas, a group leader at the National Renewable Energy Lab, who is not affiliated with the study. “If this technology is going to succeed, we need to make it reproducibly at large scales, efficiently, and it needs to operate for many years in real world operating conditions. And I think this work really is a good step in that direction.”
Strengthening Perovskite's Crystal
Solar panels are typically large refrigerator-sized plates that can fit on a roof. In this study, the solar panels were shrunk down into small modules– rectangular sheets around the size of a Pop-Tart. Perovskite solar modules are multilayered, like a sun-powered sandwich. Perovskite, the proverbial ‘meat’, powers the module and is sandwiched by transport layers that either let the sunlight come in or electric current flow out.
At the connection between the bottom transport layer and perovskite, there is a disturbance, says Jinsong Huang, a professor in the Department of Applied Physical Sciences at UNC Chapel Hill, who headed the research team.
The molecules of crystalline structures follow a distinct and predictable pattern which leads to a stable structure. But if one molecule breaks the pattern, bending ever so slightly, then the material has formed a weak spot. Perovskite’s uniform, strong crystalline structure has an Achilles heel right at the bottom layer, making the entire module unstable. Researchers call this disturbance an “amorphous phase”.
Full crystal structures are much more robust than ones that have amorphous phases, says Huang. “I think of it as if comparing mud and rocks. Rocks are crystals, mud is more amorphous.”
A solid rock solar panel would be more efficient, stable, and have a higher performance compared to a panel with oozy mud spots.
“Everything we are doing is so we reduce the percentage of amorphous materials inside perovskite,” Huang explains.
Huang and colleagues targeted perovskite’s amorphous phases to see if remedying these weak pockets would strengthen overall solar module performance. They applied lead chelation molecules that would mend the amorphous phase, similar to applying a patch to a ripped pair of jeans. These molecules ultimately stabilized perovskite’s structure.
“We found an interfacial modification that can reduce the amount of amorphous phase inside perovskite, so that we can make them much more durable,” says Huang. “And also, they become much more efficient to convert light into electricity.”
The perovskite solar modules used in the Huang lab were exclusively tested indoors, using solar simulator instruments to mimic rays from the sun. Testing solar modules outside adds a new, but necessary level of complexity to solar panel development.
“You’ll see in the paper that they tested indoors under very, like real life conditions, but not quite,” said Schelhas. “So those are still very controlled conditions and there’s a lot of additional aspects to operating these in the real world.”
Preliminary outdoor stability tests with the perovskite modules are currently underway in the Huang lab and “testing results are good so far,” writes Huang.
UNC Chapel Hill’s ongoing perovskite study joins a growing body of research that may shape how we approach, design, and apply solar panels in the future.
