The effort to green our energy sources rests heavily upon the ability to manufacture cheap, easily made, transported and installed, and efficient photovoltaic (PV)solar panels. A breakthrough may have come from CSIRO in Australia, which has found a way to print lightweight flexible solar panels cheaply. This could open PV panels to a wider range of applications, previously impractical due to cost or physical restrictions. Read more

Printing flexible solar panels

Desley Blanch on Radio Australia (30 May 2013):

A whole new world opens up as a way is found to print lightweight solar panels using existing printing technologies

Audio: A way to print lightweight flexible solar panels cheaply

DESLEY BLANCH :  Solar panels coated onto buildings to provide power is the future now that Australian scientists have figured a method to print large but extremely lightweight solar panels onto flexible plastic.

The paper-thin and flexible solar cells which will produce 10 to 50 watts of power per square metre are now being produced in sizes equivalent to an A3 piece of paper – 10 times the size of what was previously possible thanks to a new solar cell printer that is now installed at CSIRO, Australia’s national scientific research agency.

CSIRO Materials scientist Dr Scott Watkins believes printing cells on such a large scale opens up a huge range of possibilities that include off-grid power, low-cost solar lighting and water purification in developing countries.

DR SCOTT WATKINS : What we’re developing are some organic semiconductors so these are polymers and perhaps the example that people will be most familiar with is something like polystyrene or something and the chemicals that we’re using are very similar to those in their nature but they do conduct small amounts of electricity.

And so these polymers are coated onto a surface and then are sandwiched between two electrodes and when the light hits those polymers they absorb the light and then generate the charges and that creates a voltage and that’s how the solar cell works.

DESLEY BLANCH : Having the ability to print cells on such a large scale and such a size will open up a huge range of potential applications. So what do you believe will now be possible as you talk of laminating these panels to windows of skyscrapers?

DR SCOTT WATKINS : That’s a key example in the medium term of being able to use solar panels or install them into places that we don’t currently consider. So all of the residential panels that you’ll see around the world are always angled and facing north when we’re in the southern hemisphere to capture as much sun as possible; but if solar could be cheap and easily applied to a range of surfaces, then those considerations don’t necessarily have to be primary in deciding where to put them.

So putting them onto the sides of buildings is a prime example. And I always use the example–we use curtains to keep the sun out of our houses. Why don’t we make them out of flexible solar panels and be producing some power all the time.

DESLEY BLANCH : Now in countries where villages have thatched roofs that can’t support heavier solar panels like we have in more Western countries these ultra-low cost solar cells based on plastics, well, they’re opening up another world, so in what ways do you see this happening?

DR SCOTT WATKINS : Well, in many places around the world where grid connected power is not present, things such as kerosene lamps are used to provide lighting inside the houses at night and that requires transport of the liquid fuels and then has the associated risks of fire and health problems with burning that fuel.

Providing lighting that’s powered by solar opens up the opportunity for them to do away with the kerosene lamps and as you say, they’re more compatible with structures that perhaps don’t have a rigid roof, so having these lightweight panels that you can potentially put on less rigid roofs or just leave lying around in the sun and move around more easily than you can traditional silicon panels is a real opportunity for these sort of places around the world.

DESLEY BLANCH : You see an immediate future in supplementing battery power. In what ways do you see this?

DR SCOTT WATKINS : There’s also examples in other places where you might want to use it for purifying water for example and so you could use it to charge up a battery that does power a pump, for example, to purify the water, those sort of things, integrating into a lighting battery power system and then more generally in things like cases to power electronics, and so that could be laptops or tablets or phones whereby an extra hour of battery life could be achieved just by leaving your case out in the sun, so if the solar cell is integrated into the case it’s providing supplementary charging for the device that extends the life of your portable device.

DESLEY BLANCH : I can see this on my mobile phone, on the back of it, somehow. Is that what you’ve got in mind?

DR SCOTT WATKINS : That’s an example. You just have to leave it out facing up to the sun and not in your pocket, but definitely bags and things like that we see as a real short term possibility. And increasingly we’ve got a lot of mobile devices and a need to have them connected at all different times and battery life is a key limitation for mobile devices. So any little extra power that we can get is a benefit.

DESLEY BLANCH :  Now this research is being carried out by the Victorian Organic Solar Cell Consortium and your partners in this are the University of Melbourne and Monash University here in Melbourne. And the reason you can now print these flexible solar panels is you’ve acquired a printer and you’ve got it located at CSIRO. Now the beauty of this machine is it’s based more along the lines of a traditional printer, which gives just about anyone, I guess, access to your technology. So tell us how you see this future when we can do our printing of our own solar cells or whatever.

DR SCOTT WATKINS : Yeah. A large part of what we’re doing and the collaboration that you mentioned is really, really important with the university partners that we’ve got there. But it’s about trying to lower the barrier to entry to manufacturing. So at the moment to produce silicone solar panels you have to spend up to a billion dollars to set up a plant but by using traditional established printing technologies and printers that are industry standard in many ways, it lowers the cost to entry or it even opens up the opportunity for existing manufacturers to expand their product line and produce printed electronic devices.

So what we and collaborators we have at the University of Melbourne and Monash University have been doing is trying to develop the process as far down the track towards commercialisation as we can so that we can demonstrate the process on equipment that companies and people are familiar with; they see them, they recognise them. So things like screen printing that you’d make T-shirts from, we’re actually using screen printing to put down the top electrodes on these devices. So it’s using these established printing techniques to lower the barrier to entry to manufacturing to make it as accessible as possible.

DESLEY BLANCH : So how did you rework standard printers so it might print a solar cell?

DR SCOTT WATKINS : Well, there’s a huge range of little tweaks and modifications that we’ve had to do. We have to control how well the ink goes down. The inks that we have are different from what might be used for T-shirts or for paper, for example so we’ve had to tune their properties, change how we heat them, how we dry them, how they get rolled back up, how we pattern the things down onto the electrodes. So there’ve been many, many things.

And my colleagues through the Victorian Organic Solar Cell Consortium have done a huge amount of work in developing all these little tweaks to be able to translate what we initially do on solar cells about the size of a fingernail. So up until two years ago, that was as big as we were making and now to translate that process up to A3 size has been a huge effort from a lot of people and it’s been a very exciting process to go through but the knowhow that we’ve developed is really valuable and we are now really looking to translate that to someone who can turn these into products.

DESLEY BLANCH : Commercialise time!

DR SCOTT WATKINS : Yeah.

DESLEY BLANCH : Now, do you actually print onto plastics or are you sticking them onto plastics?

DR SCOTT WATKINS : No, we just start with plastics, so we buy in a plastic that’s made from PET, so the same as what’s in soft drink bottles and it’s by the roll and it has an electrode, a transparent electrode coated onto it and then we coat down three or four layers of materials on the top of that by a couple of different printing techniques, so really starting from plastic and building the device up from there.

DESLEY BLANCH : Will it be possible to print straight onto some kinds of building material, say roofing?

DR SCOTT WATKINS : Yeah, well, in our consortium Blue Scope Steel is a very big partner in our consortium and they have obviously a dominant position in the roofing market in Australia. They have been helping us to develop the techniques to be able to apply them directly to steel and that remains a key goal. Glass as well is obviously a very good sub-strate for doing these sorts of things and coating directly onto the building materials presents an opportunity to integrate the solar cell directly into the building, rather than sticking them on the roof or attaching them or mounting them onto the roof.

DESLEY BLANCH : So how do you get the power from the solar cell to the device that needs that power? How does that work, do you need wires for that?

DR SCOTT WATKINS : Yeah, but we can print the wires.

DESLEY BLANCH : Of course.

DR SCOTT WATKINS : (laughs) That’s actually probably the easiest part of the whole process. We have the cells and they end up with two electrodes and when you connect them up you get DC power out of that. And as with traditional solar cells, if you want AC power you pass them through an inverter to create that AC power.

But you can also tune the voltage and current that you get out of these solar cells by varying the pattern of the electrode that we print on top. So if there is a specific application that needs a higher voltage or a higher current, for example, we can tune the properties of the solar cells just by printing it in a slightly different way to match the output of the solar cell to the application.

DESLEY BLANCH : You mention PET  but how available is the plastic that you’re using to construct these solar cells? Is it readily available to you?

DR SCOTT WATKINS : Well at the moment the sources of that PET are the same as what goes into drink bottles and essentially, the amount of material we’re putting onto the top of it is of the order of the label that goes onto soft drink bottles, for example, so we’re not introducing much in the way of contamination.

So in the same way that drink bottles can be recycled our solar cells could be recycled in that same way too. None of the materials we’re using are toxic or dangerous or need to be handled in any special way.

DESLEY BLANCH : And how much power output will this technology produce?

DR SCOTT WATKINS : In the lab right now, on our very small scale devices, so back on the finger nail size, we’re getting closer to more like 80 watts per square metre. So what the project really now is moving about is translating that sort of efficiency across to the larger area. And in the short term to medium term the numbers that we’ve been saying in that sort of 10 to 50 watt range we think we can consistently do that. But in the longer term, higher values are possible.

But it’s really about this is an opportunity for solar to be used in different ways and it’s about matching the power output that we can do to the particular application.

DESLEY BLANCH : I’m thinking about the life span of these systems where you’ve got  these materials, they’re embedded with solar cells and they’re exposed to the weather.

DR SCOTT WATKINS : Yeah, it is an issue and we won’t ever challenge silicon for absolute lifetime, a silicon panel that you’ll buy for on your roof will last you for 25 years and that will be a challenge for an organic device. But we are using very low cost materials, it’s very small amounts so the waste that you generate is low and you can recycle them as I said. And so the initial opportunities are really in those short term applications and the more we develop the technology the longer the lifetime will be. But there will still be a need to replace them or replenish them.

One example, you could just sort of imagine leaving the basic structure, the wires and the connectors there on your roof and just replacing it periodically with a new sheet in much the same way that, say, people replace the thatching in those sort of roofs. You could refresh your solar panel.

DESLEY BLANCH : So where does your organic photovoltaics  solar cells fit with these now familiar silicon crystal solar cells?

DR SCOTT WATKINS : Well, it’s complementary. It’s a big market–energy for the world and no one technology is going to dominate and no one solar technology is going to dominate.

There are opportunities for actually putting organic solar cells on top of silicon solar cells to use them in a tandem device and so that’s where the organic solar cells can do better at capturing some of the light that the silicon cell doesn’t absorb and so you can use them to increase the efficiency of the silicon cell.

But there are other advantages of the organic solar cells, for example, they do perform better under low light conditions, so early in the morning or late at night or in cloudy areas or under trees and things like that. They still will put out a fairly stable voltage whereas a crystalline silicon cell will drop off in voltage there. So it’s again about matching the solar cell, whether it’s the voltage that it delivers or the absolute power it gives to the application and complementing what’s out there with large scale silicon. It means that we’re opening up the possibility of using more solar power to do more things.

DESLEY BLANCH : Why do you call it organic?

DR SCOTT WATKINS : Well, the polymers that we’re using are mainly carbon-based, and so in the traditional sense, that, chemistry based around carbon materials is called organic chemistry, they’ve been coined organic solar cells. So yeah there aren’t too many elements in there, a little bit of sulphur and a little bit of silver on top, but it’s mainly carbon.

DESLEY BLANCH :  So what is next for the project, where to from here?

DR SCOTT WATKINS : So we’re working with a couple of partners at the moment about integrating directly into their materials and expanding the technology.

But even in the last week, the number of contacts we’ve had from new partners and new people interested in this has been very positive. And we’re really looking at some very short term applications now. We’re in deep discussions with them about just proving the technology on a manufacturing scale. So we’ve up to now, been doing things in the lab and really one or two off type things, but moving them into a scale where we can show repeat manufacture of something and look at manufacturing yields and things like that will give confidence the investors, whether they be private or government as we’ve had a lot of support from our state and federal governments so far, give them confidence that we are continuing to go down the track of producing a real product.

And this is one of the things that differentiates us from other energy technologies in that if you build a geothermal plant or something you’re only going to provide power to the grid, it’s a long term plan. But this sort of flexible solar has the potential to deliver short term benefits, short term applications on the way to those long term applications where we’re powering large areas.

DESLEY BLANCH : Dr Scott Watkins leads the Organic Photovoltaics Group at  CSIRO Future Manufacturing Flagship which is part of the Victorian Organic Solar Cell Consortium with research partners in the University of Melbourne and Monash University.

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