In this video we'll talk about the IV curve. The IV curve is essentially what you measured in the last assignment and we can see an example of an IV curve here. So the important points along the IV curve are the ones we got introduced to in the last video, namely the VLC and the ILC. Now we will talk more about all the specifics of the IV curve. And to introduce the topic more in details, I'll refer to Nicholas from DTU Fotonik. >> When we look at the power out from a TV module, we look at what's called the IV curve, so the current voltage curve. The IV curve simply represents all of the possible operating points that a PV device could be at for a given set of test conditions, so for a given irradiance, temperature and spectrum. So, the IV curve represents a familiar diode curve. The key difference between the IV curve of a solar cell and a typical diode curve is that on the IV curve of a solar cell, the Y axis is superpositioned in the first quadrant based on how much light intensity reaches the cell. So there's a few parameters of interest on this IV curve, namely, they are the short circuit current, or ISC, the open circuit voltage, or VOC, and the max power point, or PMP. >> So just to iterate, we had the short circuit current, the VOC or open circuit voltage, and somewhere along here we'll find the maximum power point. So let's go more into details with each of them. >> If we start with the ISC, the ISC is the point on the IV curve that the PV device would operate at if a zero resistance load or near zero resistance load was affixed to the PV device. So it's the highest current with zero voltage. The ISC varies linearly with light intensity. So every change in light intensity is observed directly in the ISC parameter. VOC, if we look at VOC, that's the point on the curve where the PV device would operate if you attached a load with very high or near infinite resistance. So it's the point with the highest voltage at zero current. The VOC is sensitive to a irradiance but not so much as say ISC. VOC varies logarithmically with light intensity. >> As we saw earlier from the IV curve, we can calculate the maximum power output and find the maximum power point. >> If you look at the two axes of the IV curve, you have current and voltage. So the product of those two is power, electrical power. So if we look at the IV curve, the point in the IV curve where the product of those two is at its maximum, is called the maximum power point and it's typically found on the knee of the curve. So the PMP, the max power point is of utmost interest to us because it ultimately is the numerator in our efficiency equation, and it's also of high interest to end users of PV. So the people who design PV systems really look at the maximum power point of all points on the IV curve because it represents what's the real power that we can actually extract from the PV device under a given set of conditions? >> So just to reiterate, we find the maximum power point by multiplying together the voltage and the current, and then drawing out the power curve. At some point, we'll find a maximum and this is our maximum power point. And the next thing we can look at is a quality parameter we call the fill factor. >> The fill factor is essentially an indication of how nice of a square does the IV curve make. And the classic example is, how well does a little square fit inside a big square? So, the little square being PMP and the bigger square being ISC times VOC. The theoretical maximum for the fill factor is around 0.85 and the theoretical minimum is 0.25, 0.25 would be a peer resistive load. >> So we find the fill factor as the ratio between the two squares we can draw. So if we have the maximum power point here, we cab draw one square inside and another square which is a defined by the VOC and the ISC, and the ratio between the two areas of these two squares is the fill factor. The fill factor is a really good parameter to compare different solar cells together. If we have a low fill factor, we typically have a lower quality device.