During the last three modules, we talked about silicon solar cells, thin film solar cells, and polymer solar cells. When you read about solar cell technologies, you often see them covered as three generations of solar cells. So silicon solar cells represent the first generation. Thin film represents the second generation. And, for example, polymer solar cells can represent the third generation. The third generation can typically include all sorts of different kinds of novel solar cell technologies. So in this generation we see, for example, the polymer solar cells. We see the really, really highly efficient multi-junction solar cells. And we see other upcoming solar cell technologies like perovskite solar cells or quantum dot solar cells. If we take a look at this graph from NREL that plots all the best research, efficiencies that they've obtained over the years, we can see that all of the generations of solar cells we have are represented here. The crystalline silicone solar cells are represented in blue, so it's basically this area here. They range in efficiencies from the low 20s to 26 plus percent, depending on whether or not we use concentrated or non-concentrated light. The silicon solar cells of course represent the first generation. The second generation of solar cells is right here in green, and we can see that it includes six solar cells, cadmium telluride and amorphous silicon, and we can see that the efficiencies are in this area here. So, at the bottom, we have the amorphous silicon. That was one of the problems, if you remember, back with amorphous silicon, is that they are lacking in efficiency. We have the cadmium telluride and six solar cells with quite reasonable efficiencies that are actually quite near to what we see for silicon solar cells. Moving beyond the thin film and crystal silicon solar cells, we go into the third generation of solar cells and these basically includes the remaining areas of this graph. So we see the multijunction solar cells with extremely high efficiencies, up to 46%. And this is under concentrated light. So this means we'd not see this even if we bought a solar cell and mounted it. It needs to be at hundreds of suns of intensity. At the same time this types of solar cells are extremely expensive and complicated to produce. So you only see them in space applications. If we were to see them or when we are to see them in terrestrial applications, it'll be in the form of concentrate assistance where we can use a really small module with a light concentrating system, and to have a more reasonable price point. There is also on this graph emerging PV, so we see here Dye-sensitized solar cells, perovskite solar cells, organic solar cells, quantum dot solar cells, and so on. All of these technologies are in the lower part of this graph. The only real exception is perovskite solar cells with 22.1%, perovskite solar cells is a relatively new solar cell technology that really become a hot topic in research. We've seen an impressively fast growth in the efficiency of perovskite solar cells over a really short period, as you can see here. So perovskite solar cells is a really interesting area of emerging PV. Of course we also see the polymer solar cells so here basically we see dye-synthisized and so on. So this is basically an overview of all the different solar cell technologies. If we look at it from a really general perspective, the main advantages of silicon solar cells is that there's abundant materials. They give good efficiencies and they last a long time. They have really long life times. The main drawback here is the energy payback time. The energy payback time for these kinds of solar cells are quite high. Going to thin film, we see some of these problems solved. We see that the energy payback times are lower because the fabrication doesn't require the same amount of energy. We don't need to start out from wafers. However especially for six and cadmium telluride, we see that we use gas materials and we can even have toxicity problems. Moving then to the emerging PV field. We're looking into systems where we truly solve all of these scarcity problems. And where we can have a much better energy payback times. especially if we look at polymer solar cells who have really low energy payback times. So that's an overview of the three generations of solar cells, going from silicon, to thin film, and to polymer solar cells.
