New Tin Perovskites could be the Holy Grail of Solar Panel Materials

Why is the engineering world getting so excited about perovskites? Despite sounding like an Eastern European bird of prey (the name actually stems from Russian mineralogist, L.A. Perovski, and refers to compounds with the same crystal structure as calcium titanium oxide or CaTiO3), these versatile minerals are in fact the holy grail of solar panel materials.

What are perovskites exactly?

Science reports that, “Perovskites are a broad class of crystalline minerals that have been known for well over a century. But their ability to convert solar energy to electricity came to light only in 2009.

“Since then, the efficiency of perovskite solar cells has climbed from 3.8% to 19.3%, a pace of improvement unmatched by any other solar technology. By comparison, crystalline silicon solar cells, the leading commercial technology, convert about 25% of solar energy to electricity.”

And yet, given all their promise of solar conversion efficiencies, their lead-based make up entails dubious environmental credentials. Lead toxicity and green energy solutions don't exactly mix. As a sustainable source of renewable energy perovskites have posed somewhat of a moral dilemma.

Until now that is, with new breakthroughs using...tin.

The pros and cons of tin-based perovskites

University researchers at Oxford and Northwestern have reported separate successes in developing tin-based perovskite solar cells. The plusses are that as a fellow group 14 element, tin bears enough similarities with its toxic relative to make it not only a safer alternative but also a cheaper one at that.

Sounds like a win win situation doesn't it? Yes and no. There is much instability in the force – well the tin-based perovskites actually. They can only be processed in an inert environment and their long term efficacy is also unknown. “The technology exists to manufacture these materials and once hermetically sealed for final use, the cells should be stable,” report Engineering.com.

“How they will perform over the span of decades is less certain. Longevity, not just efficiency, is expected to be a key area of research as well,” they add.

So they're fiddly to produce and raise questions of long term reliability. Surely they must pack a whole lot of solar-conversion-punch to get excited about?! Erm, no actually. Not yet. Currently tin-based perovskites are managing to squeeze out a modest 6% worth of energy conversion from sunlight.

What does the future hold for these new perovskites then?

As with the renewables market as a whole, this is a slow-burn process – a view to the future if you will – that bears significant potential. “Tin perovskites might offer an insurance policy if lead perovskites do turn out to be an environmental problem,” IEEE Spectrum suggests.

“But looking for alternative metals is also smart science, because they might actually improve the cells’ performance. The tin-based cells, for example, actually produce a higher voltage than the original lead perovskite cells.”
Couple that with the fact that these 'eureka' discoveries have occurred at a much faster rate than with the pre-cursor lead technology and that 6% efficiency could very well shoot upwards at a rate of knots.

Science continues, “[...] that’s about how efficient leaded devices were only 3 years ago. So if the lead-free versions improve as quickly as their leaded cousins did, it could help propel perovskites into the marketplace.”

It's an intriguing prospect for sure. And one that Mercouri G. Kanatzidis, leader of the Northwestern research team, sees grounds for positivity looking ahead.

”Other scientists will see what we have done and improve on our methods,” Kanatzidis admits in Salon's recent account. “There is no reason this new material can’t reach an efficiency better than 15 percent, which is what the lead perovskite solar cell offers,” he said. Fingers crossed.

Watch this video on Perovskites - The emergence of cheaper, high efficiency solar cells: