Stanford scientists invent ultrafast way to make perovskite solar cells

30 Nov 2020

Rapid manufacturing boosts potential of this greener alternative to conventional silicon solar panels.

Seeking a greener alternative to silicon solar cells, in recent years researchers have focused on thin-film perovskites, which enable low-cost, flexible solar cells that can be produced with minimal energy and virtually no CO₂ emissions.

But while perovskite solar cells are promising, significant challenges need to be resolved 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,” commented Stanford University postdoctoral scholar Nick Rolston. “Millions of dollars are being poured into startups. But I strongly believe that in the next three years, if there isn’t a breakthrough that extends cell lifetimes, that money will start to dry up.”

Rolston says he is excited about a new perovskite manufacturing process developed at Stanford. In a new study, published in Joule, he and his colleagues present an ultrafast way to produce stable perovskite cells, which could be assembled into solar modules.

“This work provides a new milestone for perovskite manufacturing,” said study senior author Reinhold Dauskardt, the Ruth G. and William K. Bowes Professor in the Stanford School of Engineering. “It resolves some of the most formidable barriers to module-scale manufacturing that the community has been dealing with for years.”

“Most work done on perovskites involves really tiny areas of active, usable solar cell. They’re typically a fraction of the size of your little fingernail,” said Rolston, who co-lead the study with William Scheideler, a former Stanford postdoctoral scholar now at Dartmouth College.

Attempts to make bigger cells have produced defects and pinholes that significantly decrease cell efficiency. And unlike rigid silicon cells, which last 20 to 30 years, thin-film perovskite eventually degrades when exposed to heat and moisture. “You can make a small demonstration device in the lab,” Dauskardt said. “But conventional perovskite processing isn’t scalable for fast, efficient manufacturing.”

Volume production

The Stanford scientists have developed a robotic device that manufactures perovskite solar cells at a rate of 40 feet (12 meters) per minute. The record-fast processor uses two nozzles to make thin films of photovoltaic perovskite. One nozzle spray-coats a chemical solution onto a pane of glass, while the other releases a burst of highly reactive ionized gas or plasma. The patented device was invented by Prof. Reinhold Dauskardt and his Stanford Engineering colleagues.

The technology uses a robotic device with two nozzles to quickly produce thin films of perovskite (see video, below). One nozzle spray-coats a liquid solution of perovskite chemical precursors onto a pane of glass, while the other releases a burst of highly reactive ionized gas known as plasma.

“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 (12 meters) of perovskite film per minute – about four times faster than it takes to manufacture a silicon cell.

“We have achieved the highest throughput of any solar technology,” said Rolston. “You can imagine large panels of glass placed on rollers and continuously producing layers of perovskite at speeds never accomplished before.”

In addition to a record production rate, the newly minted perovskite cells have achieved a power conversion efficiency of 18 percent. “We want to make this process as applicable and broadly useful as possible,” Rolston said. “A plasma treatment system might sound fancy, but it’s something you can buy commercially for a very reasonable cost.”

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.

Silicon solar cells are typically connected together in encapsulated modules to boost their power output and withstand harsh weather conditions. 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.

Video explainer

Professor Reinhold Dauskardt’s lab has shown that perovskite modules can be produced cheaper and four times faster than conventional silicon panels, as the following video shows: