New perovskite solar cell design could outperform existing commercial technologies

New perovskite solar cell design could outperform existing commercial technologies
A tandem perovskite solar cell boosts efficiency by absorbing high- and low-energy photons from the sun. Credit: Rongrong Cheacharoen/Stanford University

A new design for solar cells that uses inexpensive, commonly available materials could rival and even outperform conventional cells made of silicon.

Writing in the Oct. 21 edition of Science, researchers from Stanford and Oxford describe using tin and other abundant elements to create novel forms of perovskite - a photovoltaic crystalline material that's thinner, more flexible and easier to manufacture than silicon crystals.

"Perovskite semiconductors have shown great promise for making high-efficiency at low cost," said study co-author Michael McGehee, a professor of materials science and engineering at Stanford. "We have designed a robust, all-perovskite device that converts sunlight into electricity with an efficiency of 20.3 percent, a rate comparable to silicon solar cells on the market today."

The new device consists of two stacked in tandem. Each cell is printed on glass, but the same technology could be used to print the cells on plastic, McGehee added.

"The all-perovskite tandem cells we have demonstrated clearly outline a roadmap for thin-film solar cells to deliver over 30 percent efficiency," said co-author Henry Snaith, a professor of physics at Oxford. "This is just the beginning."

Tandem technology

Previous studies showed that adding a layer of perovskite can improve the efficiency of . But a tandem device consisting of two all-perovskite cells would be cheaper and less energy-intensive to build, the authors said.

New perovskite solar cell design could outperform existing commercial technologies
Cross-section of a new perovskite tandem solar cell created by Stanford and Oxford scientists. The front perovskite cell (red) absorbs high-energy light waves, and the rear cell (brown) absorbs lower-energy light. Together, the cells can achieve a 20.3 percent power conversion efficiency. Credit: Giles Eperon
"A silicon solar panel begins by converting silica rock into silicon crystals through a process that involves temperatures above 3,000 degrees Fahrenheit (1,600 degrees Celsius)," said co-lead author Tomas Leijtens, a postdoctoral scholar at Stanford. "Perovskite cells can be processed in a laboratory from common materials like lead, tin and bromine, then printed on glass at room temperature."

But building an all-perovskite tandem device has been a difficult challenge. The main problem is creating stable perovskite materials capable of capturing enough energy from the sun to produce a decent voltage.

A typical perovskite cell harvests photons from the visible part of the solar spectrum. Higher-energy photons can cause electrons in the perovskite crystal to jump across an "" and create an electric current.

A solar cell with a small energy gap can absorb most photons but produces a very low voltage. A cell with a larger energy gap generates a higher voltage, but lower-energy photons pass right through it.

An efficient tandem device would consist of two ideally matched cells, said co-lead author Giles Eperon, an Oxford postdoctoral scholar currently at the University of Washington.

"The cell with the larger energy gap would absorb higher-energy photons and generate an additional voltage," Eperon said. "The cell with the smaller energy gap can harvest photons that aren't collected by the first cell and still produce a voltage."

The smaller gap has proven to be the bigger challenge for scientists. Working together, Eperon and Leijtens used a unique combination of tin, lead, cesium, iodine and organic materials to create an efficient cell with a small energy gap.

"We developed a novel perovskite that absorbs lower-energy infrared light and delivers a 14.8 percent conversion efficiency," Eperon said. "We then combined it with a perovskite cell composed of similar materials but with a larger energy gap."

The result: A tandem device consisting of two perovskite cells with a combined efficiency of 20.3 percent.

"There are thousands of possible compounds for perovskites," Leijtens added, "but this one works very well, quite a bit better than anything before it."

Seeking stability

One concern with perovskites is stability. Rooftop solar panels made of silicon typically last 25 years or more. But some perovskites degrade quickly when exposed to moisture or light. In previous experiments, perovskites made with tin were found to be particularly unstable.

To assess stability, the research team subjected both experimental cells to temperatures of 212 degrees Fahrenheit (100 degrees Celsius) for four days.

"Crucially, we found that our cells exhibit excellent thermal and atmospheric stability, unprecedented for tin-based perovskites," the authors wrote.

"The efficiency of our tandem device is already far in excess of the best made with other low-cost semiconductors, such as organic small molecules and microcrystalline silicon," McGehee said. "Those who see the potential realize that these results are amazing."

The next step is to optimize the composition of the materials to absorb more light and generate an even higher current, Snaith said.

"The versatility of perovskites, the low cost of materials and manufacturing, now coupled with the potential to achieve very high efficiencies, will be transformative to the photovoltaic industry once manufacturability and acceptable stability are also proven," he said.


Explore further

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More information: "Perovskite-perovskite tandem photovoltaics with optimized bandgaps" Science, science.sciencemag.org/lookup/ … 1126/science.aaf9717
Journal information: Science

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Oct 20, 2016
And 10 years from now they will still be doing research on it while the rest of the world is still using silicon panels because you can actually buy those....

Oct 20, 2016
The progress will come mainly from the new ways in which the solar cells can be used, eg https://www.youtu..._qG21R08

Oct 20, 2016
Yep 24volts - let's not do any research - let's just keep using what we already have. Who needs progress any way....


That's not what I said is it? I said they will still be doing research... We have been seeing articles like this for 10 years at least and you still can't buy the panels anywhere that I've found so far. That's the point I was making and not what you tried to be insulting about and your going back on my ignore list where I had you at because all you do is insult people and rarely add anything worthwhile to a conversation..

Oct 21, 2016
"We have been seeing articles like this for 10 years at least and you still can't buy the panels"

You are aware that the first patent on useful (6% efficient)silicon cells was from the 1950's? And that it took nearly another 4 decades before you could buy them in the store for larger scale energy generation (apart from solar powered watches and calculators which were available earlier)?
https://en.wikipe...ar_cells
Perovskite research is barely a decade old and going at an incredible rate. If it takes another 10 years to get to market that will still be amazingly fast by comparison.

Oct 21, 2016
AP, You could buy silicon solar panels in the early 70's. They were not as good as the ones today's are but they WERE available. If scientists had of had the same attitude toward those as they do these we would STILL be waiting to see them hit the market. Same things goes with fuel cells and batteries. We've seen many, many advances on fuel cells and batteries in the last 10 years just on this site but I haven't been able to find a single damn new type battery for sale with all the new stuff. A lot of companies supposedly make them but try finding dealers for those companies.... You might as well look for the holy grail! The same types of lithium batteries on the market now have been on the market now for the last decade or more. Some of the companies need to tell their research scientists to either come up with something sellable or find another job so they can waste some other company's money for multiple years without coming up with a usable sellable product.


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