So, having established that we in principle connect many, many cells and series, and that such an array of maybe 10 or 20 or 40 thousands serially connected organic solar cell junctions is inherently robust towards shading or pass shading or one or more of the junctions. The equations can then realize that we're printing. Now, you've seen in the previous weeks, that we can both make inks, we can print, we can upscale, scale to roll to roll processing using the right combination of printing coat and techniques. Using the right combination of inks. Perhaps inks develop for the purpose perhaps materials specifically for this purpose. So, we set out to make this infinity type solar cell. Where in principle, when we start printing the roll, and the machine is running, it is connecting every single printed cell in series, and it only stops when we stop. So, which means that, in principle we can just make an infinite array of serial connected cell to cell junctions. Now to do it? We of course have to develop a full printing technique. True to the art in this course, where we don't use vacuum, we don't use scarce, it has to be. Scalable and using only printing methods, low temperatures, liquid processing. It has to be true to the life cycle analysis because what we also wanted to show, once we realize this, was of course that we could meaningfully extract the energy, and that the energy payback time, would indeed be as short as we wanted. So to underline, would justify the case for the organic solar cell. Now, we set out developing this printing process using what is known as the IOne process, which is a process where we first print a silver grid, then we print a PEDOT layer as the semi transparent conductor. Then we print the hole blocking zinc oxide layer. Then the active layer, which could be anything, but this particular case where we needed large amounts, we used P3HT PCBM. We then print another PEDOT layer. A final silver grid and then, we would package using UV lamination with a back barrier. And also printed the solar cell directly on the barrier. Now printing on thin foils like barriers when you print over hundreds of meters. Suddenly foil shrinks, foidlstretches, foil expands, and it does so differently over a length of 100 meters or even over a kilometer. And this makes a registration challenge that we discussed in previous session, quite challenging. So that means, while you print, if the foil, during the process, is suddenly shrunk. The motif that you are now printing doesn't fit anymore. If it's stretched, it also doesn't fit. If it's stretched in a direction, perpendicular to the web direction or stretched in this direction, also again side registration perhaps the motif will not fit at all. And this particular case where we have many, many cells in series it would imply that some of the devices would get shorted or simply wouldn't work. So, what we also need to make this a success, is we need a very, very high technical yield. Now to give you an example, the first process we developed, we use a grid type front electrode. So a flexographic silver printed with hexagons. So, a hexagonal pattern that comprised the front electrode. Is was not possible for us to get the high technical yield required to make a hundred meters without a rope, we could only make 80 meters. So, if you think you think about sounds like 80 meters. Well that's, that's really not a lot but its actually 16,000 solar cells in series, and all of those 16,000 solar cells they all have to work. There must not be an open circuit cause then the whole chain is lost. If there is a short it could lead to burn so we need an exceptionally high technique to. achive this. And of course this high technical yield of course has to be in every single printing step. So it has top be extremely robust. It took a long while, to develop this and redevelop it. In the end we abandoned the hexagonal front grid we had many, many different attempts so we did the slanted grid. The slanted grid has the advantage of we have a front and back grid electrode. That are slanted in opposite directions only slightly, by about five degrees plus or minus. That means that they only cross each other once or maximally twice along the way and we can thus handle stretching and shrinking a lot without getting accidental, overlap of the grid electrodes that would increase the chance for instance of a short. And this was the final process that we then developed. And this worked extremely well, in fact, it was so good now that we could print 700 meters of foil without an error. That's more than 140,000 solar cells. All in series and they all work. So, put in a number, the technical yield we have is 99.9993. So, it's a crazy high technical yield, which proves, and underlines the case for the organic solar, as a robust technology that can be printed in exceptionally high with very little loss. Exactly what we wanted from the life side analysis. And what was assumed in order to make the energy budget fit. Now, having done it all we needed to do was to install it. So, basically this went much more easy than we thought, we just roll out the solar cells, and it was very fast. You can see in the movie here we can install a hundred meters of solar cell, in significantly less than a minute. So that is actually a very, very fast installation speed. And even with a relatively poor performance of in this case the active material P3HT PCBM, a hundred meter stress like that gives 260 watts of electrical power. The output voltage is more than 10 kilovolts so of course it's only for professionals. And you have to take real care when you work with this. You canan generate huge sparks and in fact a solar cell array like that can sustain a continuous spark of several centimeters once its full. So the arc is just standing there when the sun shines. Even though it's dangerous, it was quite gratifying the first time to see that you can make printed plastic produced such high energy, such high voltages, that it could sustain a continuous electrical spark. So the solar cells in operation, they actually proved exactly as we expect, very robust with partial shading, they perform very well with thousands of hours. And since we've done the process at quite a large scale, we can do detailed life cycle assessments. And we were actually able to make complete life cycle analysis of the entire system, so that is the solar cell, the scaffold on which we mounted, the wagon, the holding stage. We actually demonstrated that the energy payback time for this system, as installed on a real scale is 180 days or about half a year. And the solar cells, they have been demonstrated already to last much longer when mounted outside, so that means we already have in a laboratory setting, generated or created an energy producing technology. That has shorter energy payback time than many many other energy technologies. With a potential to go much much further. Go as low as just a few days in energy payback time. It can be installed at exceptionally high speed. It can be de-installed at high speed. We can remove it again. At even higher speed than we installed it. So, that means we have this technology now, that already competes with existing technologies, and it's been developed at a reasonably little research intensity, and a low development investment. So, the case for organic solar cells, is very convincing, and it shows that it's actually possible. To generate this technology that is energy producing, with low embodied energy, doesn't require a lot of materials, and then it even installs much faster. It's easy to produce, the investment you need in the equipment to manufacture is very low compared to all other energy technologies. So, the future of the organic photovoltaics is very bright. And you have to remember that this was achieved, with a very low performance of only about 2%. So, with this course, you've actually seen how it's possible to create an entirely new energy producing technology, that. From the outside, looked as it was low performing, it's only 2%, so much lower performance than all other PV technologies. But by having the right philosophy of mind, by developing the surrounding structure, and the methodologies for it, and the way to think about it. In the correct manner it is possible to take such a technology and lift it to a level in performance that actually exceeds, already existing and established technologies and already and competes with existing technologies, like wind and other technologies in terms energy payback time, in terms of embodied energy, in terms of installation speed so. It's speed at which you can manufacture and install a given energy producing unit is already very fast. It is inherently easy to recover and recycle. It has, because the philosophy of mind is correct, it is lifted to this level. Not because of the performance which much be viewed as mediocre. But this underlies the fact that, with a small development intensity, for instance, increasing the lifetime, all in improving the performance of the materials. You could take this technology, to totally outperform any known energy technology. And finally and most importantly, it is in a scaled version. So, I will not come afterwards and say to you, yes it's good, it could solve the answers. But you can't make it fast enough, or we can't make an upgrade. Because, the OPV can be made on exactly the scale we need.
