For a greener alternative to silicon, researchers have focused on thin-film perovskites – low-cost, flexible solar cells that can be produced with minimal energy and virtually no CO2 emissions. While perovskite solar cells are promising, significant challenges need to be addressed before they can become commonplace, not least of which is their inherent instability, which makes manufacturing them at scale difficult.
“Perovskite solar technology is at a crossroads between commercialization and flimflammery,” said Stanford University postdoctoral scholar Nick Rolston. That’s why a new perovskite manufacturing process developed at Stanford is so exciting, Rolston said.
In a new study, published in the Nov. 25 issue of the journal Joule, he and his colleagues demonstrate an ultrafast way to produce stable perovskite cells and assemble them into solar modules that could power devices, buildings and even the electricity grid.
Perovskite solar cells are thin films of synthetic crystalline made from cheap, abundant chemicals like iodine, carbon and lead. Thin-film cells are lightweight, bendable and can be grown in open-air laboratories at temperatures near the boiling point of water, a far cry from the 3,000-degree Fahrenheit furnaces needed to refine industrial silicon.
Scientists have developed perovskite cells that convert 25 percent of sunlight to electricity, a conversion efficiency comparable to silicon.
“Most work done on perovskites involves really tiny areas of active, usable solar cell. They’re typically a fraction of the size of your pinky fingernail,” said Rolston, who co-lead the study with William Scheideler, a former Stanford postdoctoral scholar now at Dartmouth College. Unlike rigid silicon cells, which last 20 to 30 years, thin-film perovskite eventually degrades when exposed to heat and moisture.
“Conventional processing requires you to bake the perovskite solution for about half an hour,” Rolston said.
“Our innovation is to use a plasma high-energy source to rapidly convert liquid perovskite into a thin-film solar cell in a single step.”
Using rapid-spray processing, the Stanford team was able to produce 40 feet of perovskite film per minute – about four times faster than it takes to manufacture a silicon cell. In addition to a record production rate, the newly minted perovskite cells achieved a power conversion efficiency of 18 percent.
The Stanford team estimated that their perovskite modules can be manufactured for about 25 cents per square foot – far less than the $2.50 or so per square foot needed to produce a typical silicon module.
Perovskite manufacturers will eventually have to build stable, efficient modules to be commercially viable. Toward this end, the Stanford team successfully created perovskite modules that continued to operate at 15.5 percent efficiency even after being left on the shelf for five months.
To compete with silicon, perovskite modules would have to be encapsulated in a weatherproof layer that keeps out moisture for at least a decade.
“If we can build a perovskite module that lasts 30 years, we could bring down the cost of electricity below 2 cents per kilowatt-hour,” Rolston said.