Now, in the last session, we finished up with the freeOPV, which represents

a completely scaled organic solar cell, manufactured by full processing.

So it has discretely processed steps,

some of them inline processed steps, all the way through the process.

To testing, to packaging, to final,

should we say, processing into a product.

So, the product being the small module you receive, with a small context on it, so

you can do measurements.

There's a 2D bar code on the back of it.

And this 2D bar code is actually a registration code that enables us to go

all the way back through the process to the very foil that we purchased

somewhere and put into the machine with our solar cell art originally.

Now this freeOPV then is a test example of OPV scaling,

OPV manufacture, OPV should we say shipping

to a customer which is you, for you to test.

So it's a big experiment where we pretend that we make a real product and

we can follow it all along the production process.

We can follow, get input from the end user, and

put it all the back into the process.

It could be for instance that you observe the particular property with one of

the solar cells that were received and

we would be able to link this back into the process.

If indeed the reason for whatever observation you made were rooted in

a process error or in a particular aspect of the process.

The reason we've set it up like this is that of course we need to be able to do

fault analysis, to do recursive process learning, so that we can back and improve.

That's how processing works.

You never develop a product that is finished from the beginning you always go

to the end and then you find out that there are some deficiencies and

you go back again.

So the freeOPV is all this.

It is a vehicle for us to develop and

it's a meaningful purpose to take those solar cells, the ones that work at least,

and send them out to people that can learn something from it.

And in addition, we also learn something from it, and we, in the end,

hopefully become highly professional at making organic solar cells.

Now the freeOPV, of course, as great as it may be,

it's of relatively little use to society, but it's a great teaching tool, and

it's a great development tool, and it's a great learning tool for both us and you.

Big question is, can we based on all what you've learned in all the previous weeks,

take this OPV technology, with the present performance,

with the present processing methods, and turn it into something that can

actually address the big question we set out with in the beginning.

Namely, the challenge of supplying humankind with energy.

Now, the OPV as you've seen it has a relatively limited efficiency.

And at least the freeOPV you received maybe has an efficiency of around

somewhere between 1 and 2% after a while or when you receive it.

The question is can you do something with a low efficiency like that?

The quick answer, if you have little area available, is of course no.

But if you have plenty of land mass, as it's called, then perhaps, I mean,

any power received or converted is enough.

We've seen the surface of the Earth receives

much more energy than we will ever need.

So even an energy housing technology that is not very good at it, if it's a percent

or 2%, it is largely sufficient in supplying man with all the energy we need.

And certainly, we also have the land mass.

The question is then, in terms of energy, is it worth it?

Now, you saw in the lifestyle analysis modules that OPV itself actually

embodies very little energy, both in the materials,

that it's constituted by, but also in the process.

So in principle,

it should be possible with even a low power conversion efficiency to quickly pay

back the energy you invested in the solar cell in the process and in the materials.

We set out to prove this point, and

we thought that during the course we assumed that the landmass is available.

We then wanted to take full advantage of the fact that the solar cell has to be

viewed not as a discreet panel or module but has to be a role.

We have to be able to make use of the fact that in principle it could be

an endless solar cell.

Where we only need it to make contact at the opposite ends of the foil.

So we have one end that is the perhaps that's perhaps the plus and

the other end that is the minus.

The big question is it possible to do this?

The second question is if we can do it,

how would we then realize that I have this device based on the solar cell roll.

A light harvesting device is if we start out there it's a pretty simple one.

We need a large area so we make us all a park with some platforms, and

on those we just simply roll out a solar cell from the roll.

Perhaps it's more simple to say then to do it, but

we actually realized this platform in a small prototype of 1,000 square meters.

And the idea is that we have a trolley or wagon that can be moved

over the platforms and in the process of moving it we can apply solar cells.

We can also re-extract solar cell that may have finished its service life.

We saw it in one of the earlier modules that stability of solar cells

is perhaps not as good as the inorganic ones.

So also this concept would have to encompass the possibility of

replacing solar cells that maybe don't perform so well anymore.

And in the analysis, we also have to include the impact of this.

So how often do we have to replace it?

What is the energy investment we make when we do the exchange?

Now the advantage here is that we getting stalled,

while we remove the old one we are basically saving a.

In principle, the replacement of the solar cell comes at little extra cost and

it also enables us to efficiently re-extract the resources that are found

in the solar cells.

For instance if you want to re-extract or

recycle silver material that was contained within the particular solar cell.

We also developed this solar park so

that we could actually have many of those lanes and it serves this wagon or trolley,

serves a small train that both applies and re-extracts the finished solar cell.

Now big question is, of course, when you serially connect all those solar cells.

The advantage of making serial connection is that we don't require thick conductors.

If we wanted to connect them in parallel, and we imagine that we have a length of

solar cell foil that is 100 meters or even a kilometer long.

Currents that were to be carried by the conductors would be huge.

This would require us to have thick conductors, and

this would impact our life cycle analysis.

So we really want to step up our voltage.

You all know that high voltage is one of the best ways to

transport energy at very little loss,

when you are thinking of transporting electrical energy in a conductor.

10% ohm loss.

So the big question is, from the printing point of view,

can we print all those cells so they are all in a series?

And this answer is yes,

we can do everything with printing as you've seen so far in this course.

Now what happens if you serially connect many solar cells?

Well, from the silicon solar cells that are very perfect aisles,

we've learned that even a small shadow of one of the cells

totally affects the performance of the entire array.

So we've made a small model here, where we've taken 80 silicone solar cells, and

put them in series and we shadow just one of them.

When we shadow just one of those solar cells, we lose 90% of the performance.

Now, this of course, if we imagine we have a printed solar cell where maybe we have

thousands and thousands of solar cells in series,

this is likely to be a complete show stopper for your organic solar cell.

Now all those tests, if the organic solar cell, which we know is a different diode

to a traditional semiconductor diode, like silicon solar cell is.

We want to make a small experiment.

So we also took 80 cells and put those in series, 80 organic solar cells.

And much to our surprise, we actually did not see any

big effect of shadowing on one cell, we only lost a little.

And in fact we had to shadow completely more than 20% of the organic

solar cells in order to lose 90% of the performance.

Which was the case for the silicon solar cell with just one shadowed cell.

With partial shading or partial shadow of the solar cell,

you can hardly see anything for the organic cell.

And this was a great discovery, because it meant that it would be possible to realize

this dream of a solar park where [COUGH] energy was harvested through infinite or

near-infinite serial connection of small solar cells.

Where all the power could be extracted over large distances with no real ohm loss

due to transmission.

Going Large Scale

Organic Solar Cells - Theory and Practice

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