Welcome to this tutorial on terms and abbreviations associated with OPV. In this video I'll try to give you an overview of the terms and abbreviations that you normally encounter. So let's get started. There are a lot of terms and abbreviations, of course, associated with OPV. And we use all of these during this lecture. So I encourage you to go to plasticphotovoltaics.org. We put up this list of terms and abbreviations in our learning center. There's of course also a link to this in your syllabus. Let's move on. In this video, I'll go through some of the layers of the solar cell. Explain you what the different layers are called. What their function is. You of course learn a lot more about this in the coming weeks. I'll talk about solar cell geometries. I'll talk about some special solar cells, some tandem cells, triple junction cells just to tell you what they are. I'll go through some solar cell parameters and definitions of those. Okay, so let's get started. So, here we see the solar cell layer stack. So, what the layer stack is, it's basically all the different layers that's comprising the solar cell. So let's go through these layers one at a time. So, first we have the electrodes. So this is where we extract the current from the cell. This is why we can connect it to an external circuit. Secondly, we have the electron transport layer, or ELT. Then, then you have the hole transport layer, the HTL and lastly you have the active layer. And the active layer is in many ways the most important layer. It's the layer that absorbs the photons. So let's dive into the active layer and see what, what it comprises of. So the active layer is typically a heterojunction layer, that means it's a mixture of two different materials. One, the donor material and two, the acceptor material. So, in this case I just put in some examples. So, a very common example of the donor material would be P3HT. A very common, acceptor material is PCBM, as we see here. And these names P3HT and PCBM, you'll see a lot in course later on, because these are materials that we use in, in many of our solar cells that we make here. Okay, so here we see again the, the solar cell stack. We see the electrodes. We see the active layer. And we see the, the charge transport layers, the hole transport layer and the electron transport layer. Of course this is just one way to arrange the cell, and this we call the normal geometry in this configuration here. And other very obvious way is to switch the hole transport layer and the electron transport layer, use some other electrodes and we can make what we call an inverted geometry cell. The inverted geometry cell as you can see has switched positions for hole transport and electron transport layer. This is a geometry we use a lot. This inverted geometry. It has some benefits, since for example, in the normal geometry we can see we use an aluminum electrode, where in the inverted geometry in this case for example, you use a simple electrode. The aluminum electrode has some disadvantages when it comes to degradation, so the stability's not as good. So in that way, we can for example, make it a more stable solar cell. This however, not the main reason we use inverted geometry cells. The main reason we do it is typically that it's easier to roll to roll coat. And for that reason we use the inverted geometry. So let's move on. So another important aspect that I want to, to introduce you to is tandem solar cells. Because of course, the active layer can only absorb so much light. It has a specific bandgap. And with that bandgap it is only possible to extract a certain portion of the visible light spectrum. So of course we can do, we can make a solar cell where we basically stack two solar cells on top of each other. In this way, we can have one active layer like before that absorbs one color, and on top of that we can have another active layer that absorbs another color. In that way we can, we can extract a lot more of the photons from the light and we get more energy out of it. So this is in theory a more efficient system. It has a higher theoretical efficiency. The other thing we can of course do is we can, we can increase this even further. So we can make what we could call a triple junction solar cell. So while we basically have that tandem solar cell, well we put even another solar cell on top. The tandem solar cells are quite common now these days at least. There are a lot of examples of them for OPVs. But, triple junction solar cells are not that common within OPVs. They are however, common when you look at these efficiency tables, where you see the most efficient solar cells in the world. And typically the most efficient solar cells will be triple junction solar cells. They will not be organic solar cells but they will be triple junction solar cells. Moving on now, we have solar cell parameters and definitions. So when you measure a solar cell there are a few values that you'd like to extract. And let's just go through the most important ones, one at a time, just briefly. So, of course, we have the voltage that the solar cell is producing. And let me just show you here. We have a a solar cell. This is our solar cell. A freeOPV solar cell. And we hooked it up to voltmeter. In this case, it's set to measure voltage. As you can see now, the voltage not very high, but of course, we just need to turn on the light and it'll start producing, so let's do that. So now we can see the solar cell in this case, is producing four volts. And, then what we then can do of course is, we can look at what is happening this situation. What has happening is we connected a voltmeter. And a voltmeter has an almost infinitely high resistance. So that means no current is running through the, the voltmeter. At least in an ideal case. And that means that voltage we are measuring right now, is the maximum voltage that the solar cell can produce. We can also look at the current we can measure in this way. It's called the Isc, so that stands for short circuit current. And what happens there is we would turn the knob on the multimeter so it goes into the current range instead. In that case, we would have a, almost all of the current that the solar cell could be producing. Or, in an ideal case, all of the current that the solar cell is producing will run through the multimeter and when that happens, you get the maximum current that the solar cell can produce and that's called Isc or short circuit current. The Voc is called Voc because it's open circuit. That means there's no current running through it. So another important parameter we need to look at is then the P-max. There will be a maximum effect that the solar cell can produce. A maximum number of watts. This maximum number of watts is not equal to Voc times Isc. And there's a reason for this, because as we just discussed, for Voc we measure that when there's no current running through the multimeter. So in the case where we have Voc, current would be zero. So in the case where we have VOC, I would be zero. And in that case we would have P equals 0. As we remember P is equal to I times V. And in a similar fashion we can look at the ISC. When we measure ISC, the V will be zero. There has been no voltage. And then again that means we have P equals zero. So, that's why Pmax is not equal to VOC times ISC. Instead, Pmax would be the product where we have the highest combination of V and I. And how we measure that exactly we'll come back to next week. So the next parameter we look at is the fill factor. So the Fill Factor is basically defined as: So the fill factor is defined as P-max over Voc times Isc. It's a quality factor that'll tell us about how much of the, effect, we are actually extracting from the solar cell. So a high fill factor would a be a good solar cell, a low fill factor would be a bad solar cell. The last parameter we will want to look at is the PCE, so the power conversion efficiency. So of course, the power conversion efficiency, we need to calculate, so it will be based on some of the values we have. The PCE is defined as the power output over the power input. Of course the power output, we know that already, because that's P-max. The power input, we need to know and the way we often can calculate this, is we will know the amount of light coming in. If we're outside that would typically be around 1,000 watts per square meter. Under normal circumstances. When we have this number all we need to know is the area of the solar cell and then we can calculate the PCE. So let me just draw that up as an example. We can assume for example, that we have an area of 0.5 square meters. Okay, so that would be the formula to calculate PCE. And, with that, I'll conclude this tutorial. Thank you for following it, and see you next week.