0:05

Welcome to this tutorial on terms and abbreviations associated with OPV.

Â In this video I'll try to give you an

Â overview of the terms and abbreviations that you normally encounter.

Â So let's get started.

Â There are a lot of terms

Â and abbreviations, of course, associated with OPV.

Â 0:22

And we use all of these during this lecture.

Â So I encourage you to go to plasticphotovoltaics.org.

Â We put up this list of terms and abbreviations in our learning center.

Â There's of course also a link to this in your syllabus.

Â Let's move on.

Â In this video, I'll go through some of the layers of the solar cell.

Â Explain you what the different layers are called.

Â What their function is.

Â You of course learn a lot more about this in the coming

Â 1:06

So, here we see the solar cell layer stack.

Â So, what the layer stack is, it's basically

Â all the different layers that's comprising the solar cell.

Â So let's go through these layers one at a time.

Â So, first we have the electrodes.

Â So this is where we extract the current from the cell.

Â This is why we can connect it to an external circuit.

Â 1:34

Then, then you have the hole transport layer, the

Â HTL and lastly you have the active layer.

Â And the active layer is in many ways the most important layer.

Â It's the layer that absorbs the photons.

Â 1:47

So let's dive into the active layer and see what, what it comprises of.

Â So the active layer is typically a heterojunction layer,

Â that means it's a mixture of two different materials.

Â One, the donor material and two, the acceptor material.

Â So, in this case I just put in some examples.

Â So, a very common example of the donor material would be P3HT.

Â A very common, acceptor material is PCBM, as we see here.

Â 2:24

Okay, so here we see again the, the solar cell stack.

Â We see the electrodes.

Â We see the active layer.

Â And we see the, the charge transport layers,

Â the hole transport layer and the electron transport layer.

Â 2:53

And other very obvious way is to switch

Â the hole transport layer and the electron transport

Â layer, use some other electrodes and we can

Â make what we call an inverted geometry cell.

Â The inverted geometry cell as you can see has

Â switched positions for hole transport and electron transport layer.

Â 3:11

This is a geometry we use a lot.

Â This inverted geometry.

Â It has some benefits, since for example, in

Â the normal geometry we can see we use an

Â aluminum electrode, where in the inverted geometry in

Â this case for example, you use a simple electrode.

Â The aluminum electrode has some disadvantages when it

Â comes to degradation, so the stability's not as good.

Â So in that way, we can for example, make it a more stable solar cell.

Â This however, not the main reason we use inverted geometry cells.

Â The main reason we do it is typically that it's easier to roll to roll coat.

Â And for that reason we use the inverted geometry.

Â So let's move on.

Â So another important aspect that I want to,

Â to introduce you to is tandem solar cells.

Â Because of course, the active layer can only absorb so much light.

Â It has a specific bandgap.

Â And with that bandgap it is only possible to

Â extract a certain portion of the visible light spectrum.

Â 4:10

So of course we can do, we can make a solar cell

Â where we basically stack two solar cells on top of each other.

Â In this way, we can have one active layer like before that absorbs one color,

Â and on top of that we can have another active layer that absorbs another color.

Â In that way we can, we can extract a lot more of

Â the photons from the light and we get more energy out of it.

Â So this is in theory a more efficient system.

Â It has a higher theoretical efficiency.

Â 4:40

The other thing we can of course do is we can, we can increase this even further.

Â So we can make what we could call a triple junction solar cell.

Â So while we basically have that tandem solar cell,

Â well we put even another solar cell on top.

Â The tandem solar cells are quite common now these days at least.

Â 5:04

They are however, common when you look at these efficiency tables,

Â where you see the most efficient solar cells in the world.

Â And typically the most efficient solar cells will be triple junction solar cells.

Â They will not be organic solar cells but they will be triple junction solar cells.

Â 5:22

Moving on now, we have solar cell parameters and definitions.

Â So when you measure a solar cell there are a few values that you'd like to extract.

Â And let's just go through the most

Â important ones, one at a time, just briefly.

Â 5:37

So, of course, we have the voltage that the solar cell is producing.

Â And let me just show you here.

Â We have a a solar cell.

Â This is our solar cell.

Â A freeOPV solar cell.

Â And we hooked it up to voltmeter.

Â In this case, it's set to measure voltage.

Â 5:54

As you can see now, the voltage not very high, but of course, we

Â just need to turn on the light and it'll start producing, so let's do that.

Â So now we can see the solar cell in this case, is producing four volts.

Â And, then what we then can do of course

Â is, we can look at what is happening this situation.

Â What has happening is we connected a voltmeter.

Â And a voltmeter has an almost infinitely high resistance.

Â So that means no current is running through the, the voltmeter.

Â At least in an ideal case.

Â And that means that voltage we are measuring right now,

Â is the maximum voltage that the solar cell can produce.

Â We can also look at the current we can measure in this way.

Â It's called the Isc, so that stands for short circuit current.

Â And what happens there is we would turn the knob

Â on the multimeter so it goes into the current range instead.

Â In that case, we would have a, almost all

Â of the current that the solar cell could be producing.

Â Or, in an ideal case, all of the current that the

Â solar cell is producing will run through the multimeter and

Â when that happens, you get the maximum current that the solar

Â cell can produce and that's called Isc or short circuit current.

Â The Voc is called Voc because it's open circuit.

Â 7:27

This maximum number of watts is not equal to Voc times Isc.

Â And there's a reason for this, because as we just discussed, for

Â Voc we measure that when there's no current running through the multimeter.

Â So in the case where we have Voc, current would be zero.

Â 7:47

So in the case where we have VOC, I would be zero.

Â And in that case we would have P equals 0.

Â As we remember P is equal to I times V.

Â And in a similar fashion we can look at the ISC.

Â When we measure ISC, the V will be zero.

Â There has been no voltage.

Â 8:08

And then again that means we have P equals zero.

Â So, that's why Pmax is not equal to VOC times ISC.

Â Instead, Pmax would be the product where we

Â have the highest combination of V and I.

Â And how we measure that exactly we'll come back to next week.

Â So the next parameter we look at is the fill factor.

Â So the Fill Factor is basically defined as:

Â So the fill factor is defined as P-max over Voc times Isc.

Â It's a quality factor that'll tell us about how much

Â of the, effect, we are actually extracting from the solar cell.

Â So a high fill factor would a be a good solar

Â cell, a low fill factor would be a bad solar cell.

Â The last parameter we will want to look

Â at is the PCE, so the power conversion efficiency.

Â So of course, the power conversion efficiency, we need to calculate,

Â so it will be based on some of the values we have.

Â The PCE is defined as the power output over the power input. Of course

Â the power output, we know that already, because that's P-max.

Â The power input, we need to know and the way we often

Â can calculate this, is we will know the amount of light coming in.

Â If we're outside that would typically be around 1,000 watts per square meter.

Â 9:43

We can assume for example, that we

Â have an area of 0.5 square meters.

Â Okay, so that would be the formula to calculate PCE.

Â And, with that, I'll conclude this tutorial.

Â Thank you for following it, and see you next week.

Â