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ScienceFebruary 10, 2017

Soaking up the sun: how a miracle mineral may hold the key to a solar energy revolution


The unique properties of Perovskite provide hope for a wholly sustainable future, ‘propelling the next stage of human advancement’, says Henry Snaith, a guest at next week’s AMN8 conference in Queenstown.

Professor Henry Snaith has a vision of the future. Ever growing cities are powered cleanly and efficiently. Third world countries have easy access to electricity. There are no coal power plants. No nuclear. No gas.

In the Oxford University physicist’s vision you don’t need any of them. All you need is the sun.

Power, says Snaith, is at the root of how humans go about their lives. So what if you could increase production and efficiency of it while bringing down the cost? Well, then you might very well change the world.

“It’s about propelling the next stage of human advancement,” says Snaith who is in New Zealand as part of the MacDiarmid Institute’s ANM8 conference in Queenstown.

Seventy years ago when the world’s first practical solar cells were created for the commercial market they were only 2% efficient and cost US$1,785 per watt produced. This was the beginning of the story of consumer photovoltaics (PV), as the field is known. It was also the beginning of the silicon revolution – a compound which had been found to be able to convert light into energy.

It is an industry that is growing at between 40% and 70% a year. Over the decades the production ramped up and the costs came down. However, global energy production from solar power still amounts to less than .1% of total energy used. And, in 2017, the best silicon is only 22% efficient.

So what is needed to keep propelling human advancement, says Snaith, is something that is better than silicon but easy to manufacture and relatively inexpensive. Then, perhaps, the means of producing the other 99.9% of energy might become obsolete.

Henry Snaith is speaking at a public event in Wanaka on February 13. Details here.

Since he was a child, Snaith had concerns about pollution and environmental degradation. As his interest in science grew into an undergraduate degree in physics, he knew that his knowledge and efforts were best directed into finding better ways of creating energy.

Before he studied his PhD he had worked with a material known as “organic-inorganic perovskite”–  named after a mineral that was discovered in the Ural Mountains of Russia in 1839.

Henry Snaith. Photo: Oxford PV

There had been some studies done to understand how it worked. A Japanese scientist had looked at it as a material for absorbing sunlight. But for solar power to operate there needs to be three elements – light absorption, electrical charge generation and charge transport. Usually light absorber materials are not very good at the other two functions.

But when Snaith tested them he found something curious. Perovskite seemed to fly in the face of many of the things scientists understood these sorts of materials. Usually, semiconductors need to be incredibly pure and thus usually very expensive to work effectively. But Perovskite didn’t. Furthermore, not only did it seem to work as a very good absorber, it could also generate charge and transport it.

“We discovered this material works all on its own,” Snaith says. “It came out of nowhere and has forced people to reconsider their understanding of semiconductors.”

One of the material’s unique properties is that scientists can tune the way in which it absorbs light. Unlike silicon, which can only absorb certain wavelengths of light, perovskite can absorb much more. This makes it potentially much more efficient.

One of the strongest potentials is combining perovskite with silicon, Snaith says. By putting perovskite on top of a traditional silicon wafer you can increase its efficiency by 4%. It might not sound like a lot but in a commercial market where the slightest competitive edge can mean huge returns, 4% is a big deal.

By using this method Snaith says a revolution in the solar power industry might not be so disruptive. It would simply mean retrofitting factories to be able to handle perovskite along with silicon.

Snaith says if you consider how far silicon has come in its efficiency – 2% in 1955 to 22% in 2017 – there is no reason to believe that perovskite solar cell efficiency could not get up to 40%.

“I am obviously entirely biased but there is no reason, that if it increases in terms of dollar per watt value by a factor of 10, that it should stop there.”

Which is where we come to his vision. If such a forecast does come true then it could make all other means of energy production uneconomical.

“I see no reason why it couldn’t be the primary means of energy production,” Snaith says.

So instead of power plants you would have large storage facilities to hold all the excess power being creating by perovskite-based solar cells. He says if storage becomes a bigger industry the cost of expensive lithium storage batteries would come down. You could have emergency generators in case of catastrophic weather. And for countries which are not known for their sunny disposition, all that is needed is a good means of transporting energy across regions.

“I truly believe we could make the world completely sustainable – no fumes, no pollution, all electric vehicles.”

Snaith says places in remote India which do not have any power would not need to build a large power grid or 2 gigawatt plant to produce electricity. Instead there could be 100 megawatt solar farm that could produce power and store it efficiently.

The way Snaith speaks, it is unsurprising that he has used his discovery to spin out a company that is dedicated to developing his vision.

Oxford PV has been working for the last four years at proving the stability of perovskite. Snaith needs to know that a solar cell using the material is going to last at least 30 years, which is similar to the life span of a silicon-based cell.

But he has interest. The company has funders which have allowed it to buy a factory in Germany to test perovskite’s potential. Oxford PV has also partnered with an existing silicon company that is is working alongside to produce a final product.

“In principle over the next 24 months it is likely it will be ready for mass production,” Snaith says.

The discovering of perovskite’s potential has not gone unnoticed. It is becoming a large field of research in its own right. There are an increasing number of startups looking to do exactly what Snaith is proposing.

“But somehow I don’t feel stressed about it,” he says. “I’m more stressed about making sure we deliver.”

This is part of a series of articles for the Spinoff about and from AMN8, The Eighth International Conference on Advanced Materials and Nanotechnology, in Queenstown from February 12-16 2017. For details on public events in Christchurch, Wanaka, Queenstown and Nelson, click here. This content series is sponsored by the conference’s hosts, The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.

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