EPISODE 107: PEROVSKITE SOLAR CELLS

Transcript

Lyndsey McMillon-Brown: My favorite thing about solar cells is they help NASA to explore the new frontier, the next frontier. So, I really love this ability to help us to explore the Moon and to explore Mars and to learn more about our universe.

I think it’s going to transform the way we think about space power because before this, we were thinking we’re going to have to take everything with us. So, the ability to manufacture where we are gives us this ability to scale up that we have not previously had access to.

Deana Nunley (Host): Welcome to Small Steps, Giant Leaps, a NASA APPEL Knowledge Services podcast where we tap into project experiences to share best practices, lessons learned and novel ideas.

I’m Deana Nunley.

Perovskites are a new type of solar cells that offer many advantages over the current state of the art, including flexibility, lower costs, and the ability to manufacture large solar arrays in space.

Research Electrical Engineer Lyndsey McMillon-Brown and her team at NASA’s Glenn Research Center are working on advanced solar cells that could aid in safe, sustainable exploration of the Moon and Mars.

Lyndsey, welcome to the podcast. Thank you for joining us.

McMillon-Brown: Thank you. I’m so happy to be here. Thank you for having me.

Host: Sure. What are some of the innovative materials you and your team are experimenting with to adapt this solar cell technology for space?

McMillon-Brown: That’s a great question. So, we’re looking at a lot of different materials to help ready these perovskites. I like to think of solar cells kind of like sandwiches in that they have a lot of different layers that help kind of give you this ideal final product. So, the perovskite itself is the active layer. That’s where all the action happens. If you had a sandwich, that’s your meat. So, it does the work of absorbing the light and converting it to electricity. But we need the lettuce, the tomatoes, the cheese to help make everything run more smoothly and to run better. So, we’re tuning those materials and we’re working with metal oxides like copper oxide or zinc oxide, and we’re working with protective layers. And our protective barrier layers would be like your bread. It’s the outermost layer that helps keep everything in and helps protect the meat in the sandwich. And for that, we’re looking at silicon, silicon-based materials, and glass actually. For us, it’s SiO2, which is silica, and we evaporate it and it makes a wonderful encapsulant. So right now that’s our favorite bread.

Host: What are the advantages over traditional solar cells?

McMillon-Brown: Yeah, so the biggest advantage is these materials are really thin and really flexible. So, we really like that because that allows them to be lightweight. So, it would be really nice for us to deploy them in lots of different applications and it makes it easier for us to deliver them to where we need the power. So those are some of our favorite characteristics.

Host: Could you explain how you test the technology for space application?

McMillon-Brown: Yeah, so we have lots of different tests, and this is some of my favorite things to do because we’re trying to test them for their electrical performance. We’re really interested in how efficiently do we convert the sunlight to electrical energy. And that’s done by using a solar simulator. So, we have this light that’s been really specially designed to match the Sun spectrum as closely as possible. So, we shine this light onto our cells and we have electrical leads coming off of our devices, and we measure how much voltage and current our device generates when it’s illuminated under the Sun. And that’s one of the biggest tests that we conduct on our solar cells now.

Some other testing that we do is environmental testing. And that’s because in space we have a lot of unique environments, like we have very high temperatures and low temperatures. There’s vacuum, there’s ultraviolet light, there’s atomic oxygen, there’s electrons zipping around. So, we recreate these devices individually on the ground to test how durable is our material against these. And that involves a lot of different chambers, and inside those chambers we’ll recreate those space environments and then we’ll pull the device out afterwards and go shine light on it and see how it behaves.

Host: Do you also do some testing on the International Space Station?

McMillon-Brown: We do. We use the Materials International Space Station Experiment platform, which we call MISSE. And MISSE is a great opportunity for us to see how all those space environments interact at once. So I like to think of MISSE like a suitcase, and you put your samples into these different slots, and the suitcase gets shipped, if you will, launched up to the space station, where the astronauts do a spacewalk and install it on the outside of the International Space Station. And then they open the suitcase and our devices get a chance to ride on the outside of the space station for six months, sometimes a year. As they orbit the Earth, they’re exposed to all the different environments. Then they’re returned to us. And that’s really special because rarely can you send something to space and get it back. And then we can investigate it closely in the lab.

Host: And you learn a lot as you investigate it in the lab.

McMillon-Brown: We learn so much and it’s amazing because we don’t always know what to expect. So, we’re just trying to be very curious and measure as much as we can and say, ‘You know, what if we did this, what about this? How might it react if we shine light on it? What if we make it warm and shine light on it?’ Just getting clever to learn as much as you can. You’re a bit of a detective at that point.

Host: How do you envision the manufacturing process working in space, namely on the Moon and Mars?

McMillon-Brown: Yeah, we have a couple ideas of how that might work. And we’re really excited that you could send up your constituent materials either in a powder form or in the form of an ink, and then when you get there, you would print it out just kind of how we print newspapers here on Earth. So you would have your rolled up spool of your substrate, which is how for your newspaper, that’s your newsprint, your paper. And we would unroll that and print on it like ink how we print at home, and that would allow us to develop these really large, long arrays, as many as you need. You’ll just have to click print and wait patiently.

Host: Wow. And in that environment, say the Moon or Mars, what size are we talking about?

McMillon-Brown: Yeah, so they’ll have to be quite large. We’re thinking we’ll need at least a couple of football fields of size of arrays to deliver the amount of power that Artemis will need. So it will be quite a large scale. If you think of some of the solar array installations you see here on Earth, they will be quite large. But we’re really excited that we have the ability to manufacture this on the Moon instead of having to ship that up individually in a lot of different launches.

Host: What are some of the other future applications that you see for this technology?

McMillon-Brown: So, we think that this perovskite solar technology is going to enable a few things that we currently can’t do, or at least make things more accessible. So, one great application we’ve been talking about is this really large arrays on the surface of the Moon and then later on Mars. But also perovskite devices are lightweight and a lot more affordable than the current state of the art. So, let’s say if you’re at a university or a school and you’d like to launch a small satellite to do an experiment of your own, this should lower the barrier to entry for people who don’t have really large budgets, because instead of spending 10 or $20,000 on your solar array, it’ll maybe just be a few hundred or a couple thousand dollars. So, we’re thinking this will allow a lot more people access to smaller experiments in space with a cheaper power source.

Host: Would you say then that this is a potentially transformative technology?

McMillon-Brown: Absolutely. I think it’s going to transform the way we think about space power because before this, we were thinking we’re going to have to take everything with us. So, the ability to manufacture where we are gives us this ability to scale up that we have not previously had access to. And that means we’ll be able to explore a lot more on the Moon and Mars and power a lot more scientific equipment, power larger habitats than we’ve been able to before. So, I think our astronauts might find themselves living a bit more luxurious than they initially thought.

Host: What are some of the challenges or obstacles you face with this research?

McMillon-Brown: So, the challenges are research doesn’t always go to plan. And the most important thing to remember with that is it is research, and we’re doing it because we don’t know the answers. So, we have to be patient with ourselves. We have to be clever and creative, and we have to remain curious because we’re designing something that does not currently exist. So that means sometimes you’re going to make a material and you think it’s going to do well and it is not going to necessarily do well. But we try to learn from everything that we do and see everything as a learning experience. And even those failures, you have to go through them to get to the success on the other side.

Host: How do you solve problems?

McMillon-Brown: I think I solve problems in a kind of holistic manner. So, I think of a problem almost like a sphere or a marble, and I try to look at all different sides of it and then get really close to it and get really far from it. So, what that means is first I’m thinking of what is the problem and what are some potential solutions, what might be some unintended side effects of the solutions that I’m thinking of? Because I also want to be good for the environment, I want to be good for humanity, so I want my solution to do as little or do no harm whenever possible.

So, I zoom in and zoom out. I always think about nature. How does nature solve this problem? Because nature is fascinating with the amount of engineering and design, so to speak. So, a lot of times when I’m really stumped, I’ll go for a walk, or look through a National Geographic or something like that and see how is this motion done in nature? How does nature absorb light? What are the trees doing? And how might I learn from this great system that we already live within?

Host: Could you give us a real-life example of how you’ve applied these kinds of approaches to your problem solving in the lab?

McMillon-Brown: So, when we’re thinking about solar cells, they are kind of the nearest neighbors to trees. Because our trees, the leaves do photosynthesis, they absorb the light, and then generate energy for the plant. So, when we’re designing solar cells, I often think about how does the leaf do its work? So, we have taken a look at nature’s way of scattering light and tried to apply that to the solar cells. So, a lot of times we will achieve this by using nanoparticles, which help to scatter the light within the solar cell and extend the lifetime of the light, giving our cell more opportunities to absorb it and generate more power for us.

Host: That’s really a great example. Thank you for sharing that with us. Lyndsey, have you experienced what you would consider a breakthrough during your research?

McMillon-Brown: We certainly have, and the most exciting breakthrough we’ve accomplished was after our MISSE spaceflight. So, we flew a sample on the International Space Station for 10 months, and this is the first time anyone had done a long duration space flight of this material. So, we didn’t know what to expect, and we were thrilled that it returned to us and was still in good condition and survived. So that was already a huge breakthrough for the community for us to prove that, hey, this material can stand up to space and it can survive. And from exploring and kind of investigating this material upon its return, we were able to learn a lot about the benefits, actually, shockingly, that this material experienced from being in the space environment.

So, for example, we realized that being in space imparted some strain on the film, and that was caused by the thermal cycling, because every time the International Space Station orbits, it goes to high temperatures when it’s in the sunlight to cold temperatures when it’s shadowed by the Earth. And the thermal stress put a strain on the film. But we learned that when we shine light on the film when it was back in our lab, just standard light for 15 hours, we were able to relax that strain in the film and reclaim all of the electrical properties that the film had before. So, this identification of the ability to heal this material through light soaking was a huge breakthrough that we are very excited about.

Host: What got you interested in researching this?

McMillon-Brown: So, I became interested in perovskites because they were really popular amongst people conducting research for terrestrial solar cells. So, I was already conducting research about solar cells for space, which is a different technology that we call III-V because they’re based on elements in groups 3 and 5 on the periodic table. But when I saw perovskites having a lot of success with researchers looking at how they might apply them to the Earth, I started to wonder what utility these might have in space. Because I mentioned they are really thin and flexible. They’re lightweight. They’re really affordable. And there was a lot of doubt on whether or not these materials could be made strong enough to endure the harsh environments of space, because they’re not a perfect material. They’re sensitive to moisture and oxygen. But when you think about it, neither of those are present in space. So I saw a lot of potential in this material. And I always love an underdog. So I said, ‘Let me see what I might be able to do to help prove to people, including myself, that this technology might be suitable for applications in space.’

Host: What do you love about your work?

McMillon-Brown: So, I’m really passionate about our environment. And my favorite thing about solar cells is they help NASA to explore the new frontier, the next frontier. So, I really love this ability to help us to explore the Moon and to explore Mars and to learn more about our universe and our background, and I’m really passionate about that, but I love the application that my work also has here on Earth. So I feel really good that I’m helping us explore space, but also helping humanity to generate green energy technologies and to help us be more sustainable in our future.

But something else that I really love about my work is how much it can excite the next generation of scientists and explorers. So, I love talking to young folks, to the up and coming leaders of our future, and to let them know that they can do work like this and that they can harvest their love for art and nature and their curiosity all in one career as a researcher. So that’s also one of my favorite things.

Host: Lyndsey, this has been so interesting and a lot of fun. Thank you so much for taking time to talk with us today.

McMillon-Brown: Thank you for having me. It’s been a great time.

Host: Lyndsey’s bio, a show transcript, and links to topics discussed during our conversation are available at APPEL.NASA.gov/podcast.

If there’s a topic you’d like for us to feature in a future episode, please let us know on Twitter at NASA APPEL – that’s APP-el – and use the hashtag Small Steps, Giant Leaps.

As always, thanks for listening.