Welcome to this video tutorial. We are to talk about IV curves. It'll talk about how we can measure IV curve. I'll talk about how we can extract parameters from an IV curve. So, first of all, we have a set up or a picture of a setup that can measure the IV curve. Basically, this is a really simple set up. We have our solar cell, then we have two multimeters. These two, and then we have our resistor. Here, what we do is we have a load we can vary. When we vary the load, the current readout and the voltage readout will change. In this way, we can get the load characteristics or the IV curve of the solar cell. Of course, we can change the systems with these knobs, but this one, we can change the resistance from the low. Here, we have 10 times the changes. In this way, it's really easy to get the load characteristics of the IV curve of the solar cell. The circuit, of course, looks like this. What we have is, we have our solar cell just like before. We have a voltmeter, an ampmeter so we can measure both voltage and current, and lastly, we have our variable resistor. Our current will look like this before we start populating it. What we do is we start out with a resistor value then we readout the voltage and the current from the ampmeter and the voltmeter. So we get readings like this and then we chance the resistor, get another reading, read again, and we just keep repeating until we fill out. That's overload characteristics of the IV curve. Of course, you only populate one-quarter of the part here. We'll get back to why an IV curve can look a little bit different later on, but for now, let's just look at the IV curve as is and try to extract some parameters. First of all, let's see what is the maximum voltage we can read out. That we call the Voc, open circuit voltage. That's when there's no load and we just have to read out the voltage, and this, of course, we can measure right here, so this is Voc. Then, of course, we have the maximum current. That's called Isc, short circuit. That's when we just connect the wires together and measure the current voltage in a short circuit. The definition of course is when we have zero voltage along this line, we can find the maximum current. In some case, they won't be reading here, we have to extrapolate or interpolate the data depending on the information, and the same can be said for Voc. The next important parameter that we need to extract is the Pmax. The Pmax, the P will always be a product of V and I, voltage and current. Let's try and draw this out. This current that I've drawn here is the product of V and I. Here, you would have Pmax. Associated with the Pmax, that of course, a VPmax and IPmax. We can try and draw this area, but I just mark with VPmax and IPmax and get this area. Another area we can draw is, of course, the area that's defined by Voc and Isc. We could take the ratio between these two areas within the fill factor. The fill factor, FF, we already know it, is the IPmax so, FF= VPmax.IPmax/Voc.Isc. We also write this as, Pmax/Voc.Isc, and this is how we calculate the fill factor. Moving on. As I said, there's another way to measure an IV curve and often when you see an IV curve, it's drawn like this. What happened is we didn't measure it using that set of drawn here. That other set up, we didn't have the voltmeter, we don't have the variable resistor. We still have the ampmeter, but what we have is we have a voltage source here. We can basically drive the solar cell both in forward and in reverse bias so we can get the quadrants outside of the area here. When we look at calculating the variables, it's exactly the same as before. We still have Voc here, we still have Isc down here. We have some additional information, but for now, this is just exactly the same. As I'll ask here, I'd like to show you how to calculate PCE. The PCE is Power Conversion Efficiency. Of course, the definition of efficiency is, of course, we have Pout/Pin. The output power, of course, we know already, that is Pmax. We have from the curve before. Pin, we typically have to calculate based on the area of the cell. Often, we know the power density so typically, we know that, the sun is giving out 1,000 W/m2 and we typically know the area of our cell. Let's say the area of our cell was 0.5 m2. What we then have to calculate the PCE, what we need to do is take Pmax because our power output, we take that, divided by 1,000 divided by our area, which is 0.5. If we look at units here, you can see that square meters, canceled each out. Pmax is course in watts so this ratio becomes unitless. Okay, this is all for my short tutorial about IV curves.
