Spray-on ultrathin solar panel perovskite

18 November 2019

Interview with 

Sascha Feldmann, University of Cambridge

PHOTOVOLTAIC

Photovoltaic Cell

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Solar power makes an important contribution to renewable energy production. But the present generation of PV - or photovoltaic - panels are based on extremely heavy chunks of silicon. These are the black slabs that you see on the roofs of houses. And not only do they cost a lot in energy terms to make and install, they’ll be a hefty recycling cost to pay in a few years time when they need replacing. Which means that the discovery by Cambridge University scientists of a new panel material, known as a perovskite, that works as well as silicon but is so thin you can spray it onto a surface, is welcome news. Speaking with Chris Smith, Sascha Feldmann...

Sascha - We discovered a new material that could actually revolutionize solar panels on your rooftop. It's a so-called perovskite, and a perovskite is a class of crystal structure that is based on a mixture of organic and inorganic building blocks.

Chris - In terms of its ability to generate electricity, will the basic principale be the same?

Sascha - It will to some extent. We will still absorb sunlight, and the energy that light carries will then generate current that we can use to store electrical energy. But the way this one works is slightly different, in that usually you would expect for something like silicon, very precisely engines atomic crystal structure, where every atom sits exactly where it's supposed to be. That matters because if you absorb light and generate charges you also want to extract those charges and get them out of this material, so you don't want them to be stuck at disordered sites. But here we now have actual disorder that we wanted to be there because it's helps to localise these charges.

Chris - What's the material, the perovskite you've invented made from?

Sascha - So there's quite the mixture of different ions in there but most pronounced are lead and iodide and then also some bromide. They self assemble into a very disordered energy landscape. You can think of a mountain and valley kind of structure and this material and the charges will just roll down to the minimum which is the valley and then they will just accumulate and we get more and more of them and then we extract them very easily.

Chris - So when you say, you you get a landscape you get peaks like the mountains and then valleys it dips between them so it's self assembles into that sort of architecture, in energy terms and when the sunlight hits it the charges will roll down like rainwater going into the valley and you get a puddle there. Rather like we would tap off a river, you can tap off the flow of charges that have collected there?

Sascha - Exactly. That's exactly right. And the funny thing is we did not anticipate that this would happen. We actually wanted to make a very flat landscape and just found this to assemble in this way. But then we found out that as you say it's actually easier to extract from these fields charge bottles.

Chris - How do you get a pipe into the puddle then, to draw off the charge - if it's so disorganised? How do you know where those puddles are going to be and therefore how do you get at the charge.

Sascha - We actually don't. So far we just randomly Petter and substrates and then hope that some of these puddles actually lines with our electrodes at the bottom, but due to the fact that these are so incredibly thin, which is just through 100 nanometres or so or thousandth of the diameter of a human hair. It's quite easy to just somewhere have an electrodes sitting because these pilots are still quite small.

Chris - I suppose a massive advantage is given it's so thin, compared with a massive slab of silicon we currently put on the roof where you've got arrays of solar panels weighing a ton or so to to generate a modest amount of electricity. This is gonna be extremely light. So there must be enormous numbers of benefits of not having to transport heavy materials, not having to recycle enormously heavy metals etc. that come from this.

Sascha - Yes. So you can envision actually something like flexible electronics from this because we work on such thin films, we can just print them like an inkjet printer on top of plastic substrates so to say. You could even integrate them into something like a jacket for example and then your jacket that you wear, actually powers your phone and the answer that would be the dream.

Chris - To become a human solar panel?

Sascha - Yes basically. And also it can be used as a display in the same way that we absorb light energy to get electrical energy out. We can now think of putting electrical energy and get light out.So this seems to work. as well.

Chris - In terms of its performance though because that's the key thing isn't it, is how good is it and can it give silicon the traditional technology a run for its money. Is it any good?

Sascha - So actually it's performing astonishingly well, around 25 percent efficiency and you have around the same number of for silicon. So it's it's reaching that level of efficiency which is really stunning given how easy and cheap this will be to produce.

Chris - And in terms of its environmental footprint your materials got lead in it. That's not very nice. Is it? We're trying to reduce our lead usage if we can, because it has toxic and has other effects. What's the environmental footprint of this?

Sascha - So that is correct there is lead in this composition and we need it as of now. But if you have a bit of a comparisons to  the dimensions of lead we need here, you need to envision just coating a whole football fields full of our solar material because it's so thin - just a hundred nanometres or so. The amount of lead you will need to do this job is still less than what's on the top of your nail off your thumb for example. So compared to something like a lead sulphide based battery that every one of us has in their cars right now that's really very, very, small amount of that.

Chris - and it won't fall apart in five minutes?

Sascha - So they do fall apart in a much shorter time than silicon does right now. But given that we only have been working on this for the last eight years or so, the increasements we got into lifetimes are astonishingly high!

Phil - Gosh that's so cool. I can't get over it spray on solar panels. That's Cambridge University Sasha Feldman. That work appeared this week in the journal Nature Photonics.

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