So again, just so we're familiar, this is our base. This is a very good solar cell, so the diffusion length is really long, and all these carriers that are just generated there will be able to make our junction. If they can only explore a very short area, they're not going to make it. How far or how much volume can it explore? And that volume it can explore is described by some characteristic radius, and that radius is known as the diffusion length.Īnd it's really important to solar cells, because when you think about these carriers that you're generating. If you generate- let's say, a photon comes in and hits a silicon atom and generates an electron pair over here. So without further ado, here are minority curve, diffusion length. And then also talk about the last material parameter, which is mobility, which discusses of how well these excited charges can move around in your material. Also look at how your excess carrier concentration changes as a function of lifetime and generationally. We're also going to look at some of the things that limit lifetime, some of the basic recombination mechanisms. And possibly some of you, when you're making cells, will be able to do that measurement. We're going to describe how it's actually measured in a solar cell, which is actually a really cool measurement, and we actually have the capabilities in our lab.
What are the parameters of determinants? So mainly diffusivity and lifetime. Hopefully you guys have some idea coming to lecture, but today we're going to talk about it a little more in depth, and why it's important, and how it's affected. So what we're going to learn today is what is minority carrier diffusion length. And to a certain extent, we'll talk about open circuit voltage, because your GSC really has a large effect on your open circuit voltage. And the diffusion length is often limited by certain defects in our materials, and we're going to get into why that is. Today we're going to mainly be focused on short circuit current and things like internal quantum efficiency, which are highly affected by our diffusion length. We talked a little bit last lecture about fill factor and how that's influenced by different resistive losses in our solar cell. Now we can split up that again into open circuit voltage, short circuit current, and fill factor. And that gives our output energy, or output power, and we divide that by the input power, which is the solar insulation. Again, we talked about our GSC, our short circuit current, our open circuit voltage, and our fill factor. And our efficiency, there's several parameters that go into it. What this is saying what's the thing we care about most in our solar cells? Well, as scientists, other than dollars per watt, we want to maximize our efficiency for a certain price. So the weakest aspect of your solar cell is really what's going to limit your device performance, and especially if any of you here are trying to make devices, it's really important to think about all of these things when building it. And it's always important to remember that your device is like a leaky bucket, and you're limited by the largest hole in that bucket. And again, this is kind the progress we've made, so we're almost all the way through explaining basic device physics and basic semiconductor physics so you can understand simple devices. And so that is coming in the future, but we're still doing fundamentals today.Īnd so I know you're probably all aware of this equation. So we're going to complete this in probably the next three lectures and then move on to a lot of the kind of cross cutting themes in PV- some advanced concepts, different device architectures, and that kind of thing. I'm sure you guys are loving this right now. So we've been talking a lot about the fundamentals. Today we're going to talk a lot about different material properties and how they affect certain device characteristics, and mainly just affect our output efficiency.
#Pc1d tutorial paper series#
So today- our last lecture we talked about different device parameters, mainly our series resistance and shunt resistance, and how that affects our efficiencies. PROFESSOR: All right, so let's get started. To make a donation or view additional materials from hundreds of MIT courses, visit MIT OpenCourseWare at. Your support will help MIT OpenCourseWare continue to offer high quality educational resources for free. The following content is provided under a Creative Commons license.
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