Pushing solar technology beyond Earth: an interview with Lee Seung-min

Solar power has become the foundation of the global clean energy transition, but some of its most promising innovations are being developed far beyond Earth. At the Korea Advanced Institute of Science and Technology (KAIST), there is ongoing research to design perovskite solar cells to withstand the extreme temperature fluctuations of space, where durability is as critical as efficiency. In this interview, Lee Seung-min, a solar cells researcher at the KAIST Department of Materials Science & Engineering, discussed the scientific challenges of building solar cells for space, the potential of perovskite technology, and how breakthroughs for space applications could ultimately strengthen renewable energy systems on Earth.

First, could you tell us about the research you’re currently working on?

I’m currently conducting research on a material called perovskite at KAIST. “Perovskite” is not a term that specifically refers to a particular element, such as silicon or other substances, but rather a name that describes a specific crystal structure. It has been discovered that when materials with this crystal structure are combined in a specific way, they exhibit excellent light-absorbing properties for use in solar cells. 

And it has been proven that their performance can reach levels comparable to that of silicon semiconductors—which we’ve been using for the past 10 years and are commonly found in everyday devices like computers. I’m conducting solar cell research using perovskite, and more specifically, my goal is to develop solar cells for use in space.

Solar cells used in space sound like a very novel topic just from the name—what do you think distinguishes space solar cells from ordinary solar cells?

Since there’s no air in space, there’s no way to dissipate heat once it’s absorbed. So, in space—if we take Earth as a reference point and imagine the planets orbiting like this—the Sun is way out there. Light from the Sun reaches us, and when the solar cell is facing the Sun, the temperature rises to over 150 degrees. So, when it’s facing the Sun, the temperature goes up to 150 degrees, and when it’s not facing the Sun, it drops to minus 100 degrees. Generally speaking, when it’s not receiving light, the temperature is very low, just as we’d imagine, but when it receives sunlight, the temperature rises sharply. 

Furthermore, our goal is to eventually attach these solar cells to satellites. Satellites orbiting Earth typically complete between 10 and 16 orbits per day, at the very least. To put it another way, it’s as if we had to alternate between a hot bath and an ice bath 15 times a day. Therefore, the ability to cope with these rapid temperature fluctuations is widely recognized—not just in our view, but in general—as the most critical factor reducing efficiency in the space environment. We are currently conducting research on how to address these challenges. Therefore, the most difficult technical challenge at present is how to maintain efficiency when temperatures fluctuate rapidly.

Even if you haven’t found a complete solution yet, do you think there’s a technology among those we already have that can best handle such temperature fluctuations?

So far, when we talk about space-grade solar cells—or, more specifically, when we launch a satellite into space—it ultimately has to last for several years to several decades once it’s launched, right? Right? In fact, for all semiconductors and other equipment used in space, stability is absolutely the top priority. That’s because we can’t simply retrieve the satellite, replace the parts, and send it back up again. That’s why, even now, the solar cells attached to satellites in space are made from the most expensive and most stable materials available.

Think about train tracks—there are rails underneath, right? Since there’s thermal expansion and contraction, we build in a certain amount of clearance to accommodate it. Similarly, as I mentioned earlier, solar cells will expand and contract as temperatures rise and fall. If two different materials are bonded together—one contracting significantly while the other contracts only slightly—the two will naturally separate. So, in my view, the most practical solution is to manufacture solar cells using materials that are identical or similar—materials that expand and contract similarly in response to heat.

It's kind of fascinating to hear that what I knew about trains is actually being applied to these space-based solar cells. Aside from that, as technology continues to advance through research, do you think it could also be applied to terrestrial solar power generation or carbon-neutral technologies?

Well, I definitely think they’ll be utilized. First of all, as I mentioned earlier, space is an even more extreme environment than Earth, so the technology needs to be durable enough to withstand those conditions. In fact, if it can be used in space, that means it can generate power on Earth for an even longer period of time. That’s why I believe that as space-grade solar cells advance, they’ll naturally be applicable to power generation on Earth as well, and in the long run, I think this could contribute to goals like carbon neutrality.

As you mentioned, beyond the space industry itself, if space-grade solar cells continue to advance, do you think they could make a significant contribution to the future energy industry—especially given that energy security is becoming increasingly important these days?

Yes, to answer your question directly, I absolutely believe so. First, as we all know, satellites and space stations ultimately require electricity, and in an environment where electricity is not readily available, I believe the only way to generate it is through solar power. Second, we can’t just focus on perovskites alone. Ultimately, when it comes to space-based solar cells, the lighter they are, the easier it is to launch them into space. Therefore, how to manufacture these lightweight solar cells is a critical issue, and I believe the solar cells we’re developing have an advantage in that regard.

Furthermore, if we think about it, in the past, when we talked about the space industry, launching spacecraft into space was something only national governments—such as South Korea, China, the Soviet Union, the United States—but now that technology has expanded to private companies like SpaceX. This means the scope of the space industry is broadening to include contributions from private investors and companies, so I believe this integrated industry will become a crucial issue in the future energy sector as well.

I believe that solar power generation is currently expanding rapidly on the ground in many countries. Aside from space-based solar panels, what do you think is the most pressing issue that needs to be resolved regarding the technology currently used on Earth?

In solar power, I actually think—and I believe everyone would agree—that the most important factors are ultimately how well efficiency is maintained and, in other words, from a consumer’s perspective, when we purchase solar energy or solar panels, how much longer and at what cost we can produce that energy. I believe these two factors are the most critical. Therefore, from the perspective of solar panels, the most important issue is how long we can guarantee efficiency and lifespan—that is, how long we can guarantee over the long term—will be the most critical issues. Second, from the solar power industry’s perspective, how we respond to climate change and the extent to which we can contribute to addressing it will ultimately be important, though I don’t think we can evaluate that quantitatively at this point. For now, I believe these issues need to be resolved in the solar cell and solar power sectors.

On the other hand, as someone conducting research on a very large scale, such as space solar cells, what do you consider to be the moment when you felt the most fulfilled, or what achievement do you think will be the most memorable in the future?

In my opinion, when it comes to research on solar cells for space applications, it’s actually very difficult to replicate the conditions they’ll face in space. While the negative 150 degrees we’re considering is a temperature that can be achieved even on a gas stove, reaching extreme temperatures ranging from minus 100 to 150 degrees is a very challenging problem. We’re conducting research on this, but creating that environment is currently very difficult.

So, by placing solar cells in that environment and observing how they change—if we build up our understanding step by step from the basics—I believe we’ll make even greater discoveries in the future. For now, I find it very rewarding to actually implement this environmental simulation. Furthermore, when we predict how the solar cells will behave under that simulation and then see whether the results deviate from our expectations or match them exactly—it’s these two types of research that make me feel —and seeing those ideas materialize exactly as we envisioned is what gives us the greatest sense of fulfillment.

Yes, that makes sense. As you mentioned earlier, simulating the extreme temperature fluctuations found in space must be incredibly difficult. As you continue to take on these challenges, what would you say is your ultimate research goal?

If I had to name an ultimate research goal, it would actually be to have my research published in textbooks. Of course, the research I’ve done is ultimately based on my own ideas, and while people may recognize those implementations and we may share information with one another, I believe that, in the end, it will serve as the foundation for something greater. So, my goal for my research is to leave a mark—even if it’s just a small one—where my work is recognized by everyone, published in textbooks, and people can see that this kind of research has been done.