In this module we'll talk about polymer solar cells. When you think back to the other kinds of solar cells we' ve talked about already. So we have silicon solar cells made on rigid wafers and in result the light can be quite brittle. The other type of solar cell we talked about is thin-film solar cells. The example I have here is an amorphous silicon solar cell, and as you can see it's put on a glass substrate so now it's rigid, but in theory we can have flexible versions of thin-film solar cells. Polymer solar cells come in a form factor where they're typically completely flexible, and this is because they are printed on P-T substrates, so plastic substrates. The main advantages of these types of solar cells lies in their fabrication. But we'll talk more about this throughout the module. First, let me introduce you to Professor Frederik Krebs, who is an expert on polymer solar cells, and he'll introduce the topic. The access material, so the material that actually does the conversion, it absorbs the sunlight or the light, and converts it into an electrical current that is a polymer or organic molecule. A consequence of having organic actually that can be manufactured, disposed as a solar cell in a particular way also takes with it a lot of other things that are impossible for some technologies, things such as very low embodied energy, very fast manufacture, very thin outline, very high absorption cross section is possible. The very principle benign in environmental impact both in making, in the use phase, and also in the disposal phase. So as you can see, there are many advantages to polymer solar cells. I have another example here. So you really can see how they're flexible, and this is how they come out of the printer. So another thing you can actually, another big advantage of polymer solar cells is that we can manufacture them in really large lengths, and within these length all of the solar cells can be connected. So in this case, they are all connected in a series, and then they're connected over here. So that means we can cut any link off this roll, and we can just hook a wire up, and we don't need to assemble modules like we did with silicon solar cells. With all of this being said, they are of course also some disadvantages to polymer solar cells. So let's hear Frederik talk a little bit about this. It has been very difficult to increase the power conversion efficiency. So basically, the efficiency with which they can convert sunlight into useful electric energy. They started around 1990 with presenting meaningful efficiencies of the order of a percent. Today, at least record efficiencies are up to 12 for the organic technologies that's being demonstrated. You take a panel of silicon solar cells, and you take a panel of polymer solar cells, and then the area corresponed as if power effect of three to four. So you need a four times larger panel of polymer solar cells to produce say 100 watts of power, compared to a silicon solar cell panel. Another disadvantage is the stability in terms of, when you shine light of organic molecules they tend to react with oxygen and water, and therefore they break down. That is another example of a disadvantage that can in part be overcome by packaging, and also design of the materials. Outdoor stabilities, at least on the northern latitudes have been demonstrated for many many years, for four to five years already, and while it is unlikely maybe that with today's technology that 25 years is commonly reached with silicon, the organic source cells certainly has the potential to easily reach the ten years by today's standards. As you can see, there are plenty of disadvantages with polymer solar cells. That being said, they do have some major advantages that no other technology really has, and that is mostly that they can be fabricated so easily, because all the layers can be made from solution. They potentially contain no scarse elements, no toxic elements. We will come back to all of this later in the module to see how the fabrication steps work, how the solar cells work in general, and what types of materials are used.
