Solar panels: commonly seen as cumbersome, unappealing, and expensive. Stevens Assistant Professor Stephanie Lee’s solar panels: thin, flexible, unassuming, and cheap to manufacture.
Growing up in Randolph, New Jersey, Lee majored in Chemical Engineering for her undergraduate degree at MIT, followed by Princeton for her Ph.D., and NYU for her postdoc. During her time at MIT, one of her professors, Dr. Jefferson Tester, now a professor of sustainable energy systems at Cornell, inspired her to pursue sustainable energy. “He lives what he researches. He drove one of the first hybrid cars, and his home was heated and cooled by geothermal energy. That was really inspiring to me. With the climate change crisis and the issue of peak oil, society as a whole needs to be looking at other energy sources. So that is what motivated me to pursue solar energy in my research,” Lee said.
During her time at Princeton, Lee began her research in sustainable energy with a focus on emerging photovoltaics (devices that generate electricity directly from sunlight) and continued her research at Stevens as a professor. Today’s traditional photovoltaics, or solar panels, are made out of silicon, with around a 15% efficiency rate (15% of the sunlight can be converted into electricity). These stable systems, commonly seen on rooftops and in solar panel fields, can last for 15 years or longer. However, traditional solar panels are extremely heavy, brittle, and expensive, preventing their widespread adoption — in 2018, less than 2% of the total energy produced in the U.S. was generated from solar panels.
Lee wants to develop photovoltaic systems that are the opposite: light, flexible, and reasonably priced. To do so, her team is replacing inorganic silicon with organic materials: carbon-based polymers and molecules that can dissolve into a solution to make a photoactive ink. “You can take these inks and load them into an inkjet printer, for example. You can print out your solar panels instead of having to process materials at extremely high temperatures in sterile environments that are required for producing traditional panels,” Lee explained. “If we move to these organic-based systems, we can make our solar panels flexible. We can also produce them over large areas at high throughputs, which will increase our production capacity of solar panels and drive down the manufacturing costs.”
One of the most promising materials for these emerging solar panels is metal halide perovskites. These materials can be dissolved into organic solvents, absorb wavelengths across a broad range of the solar spectrum, and can conduct electrons efficiently. Lee noted that the “perovskite solar cells have gotten to over 23% efficient, which is very high for these types of materials.”
A main issue with perovskites is that they can only be tested in nitrogen environments. When exposed to oxygen and moisture, they can break down within hours or days. “This is just one of several challenges facing their commercialization,” Lee noted.
When explaining the process of dissolving the molecules into a solution to make photoactive inks, Lee notes the difficulty of “drying time.” “When you write with a pen, the ink dries within seconds — during the time that the ink is drying is the amount of time that we have to control molecular assembly,” Lee said. While these thin-film solar cells are flexible and more lightweight, the ways in which the molecules are assembled in the films is extremely important. The molecules in the films typically crystallize, or solidify, into ordered structures. Because the size and orientation of crystals are critical to efficiently converting photons into electrons, the details of the crystallization process largely determine the overall efficiency of the solar cells. Lee’s team is trying to engineer strategies to control crystallization as the ink dries.
“My group is examining how to improve the processing of emerging solar panels. In the few seconds that we have to assemble the molecules, what strategies can we use to get them to crystallize the way that we want in the direction that we want and the size that we want?” Lee said.
When asked about her team’s goals, Lee replied that their target is always moving since they can always do better. “I think that’s the fascinating thing about being in academia. Projects morph and change and your interests change, and there are so many unanswered questions in the world. I never see projects as having a finite goal that needs to be completed. I’m always thinking about the next interesting questions that our current research raises and where these paths are going to lead us,” Lee said. “I really love the freedom academia provides to explore uncharted territories and pursue our scientific passions.”
Lee began as an assistant professor at Stevens in 2014, teaching undergraduate chemical engineering thermodynamics and graduate soft matter physics. “When I was looking for faculty positions, I was drawn to Stevens because I went to a tech institute for undergrad and I just loved the environment. In high school, I was part of a small group of students interested in math and science and technology. And I was pretty much the only girl who was interested in any of these areas. At MIT, I was surrounded by students who are just as geeky and nerdy as me, and I loved it,” Lee said. “I was really attracted to Stevens because of its mission as a technology-centric university and the types of students it attracts.”
Lee’s journey to becoming a professor in academia was not a direct path. “Coming to the point where I thought I could be a professor was actually a very long route. I went to grad school because I didn’t want to go to industry, and then I went to my postdoc because I still wasn’t ready to go to industry. But during that entire time I never seriously considered becoming a professor. I didn’t have a lot of examples of women professors. Most of my professors were men, older, and extremely smart. So it took me a while to get there,” Lee said.
She thanked her postdoc advisor at NYU, Michael Ward, for encouraging her and giving her the space to explore academia. “I taught my first course at NYU: thermodynamics. I hated thermodynamics as a student. I was terrified of teaching the course. But when I sat down to teach it, I fell in love with it. It was a defining moment in my life where I realized that I love teaching. I love interacting with students and helping them to understand difficult concepts,” Lee said.
Lee also thanked her supportive family. “My parents never put limits on me because of my gender. I was interested in science from an early age, and they always nurtured that interest. My dad’s an engineer, so I was inspired to go into engineering because of him,” Lee said.
Lee noted that for her, “having a supportive spouse is also really critical to success. My husband has always been my biggest cheerleader and is always encouraging me to take opportunities.” When talking about her two young children, Lee noted how supportive Stevens has been in terms of her being a working parent. “I always knew I wanted to have a family, and I think that desire was one of the things holding me back from becoming a professor at first because the two didn’t look compatible to me. But Stevens has been really amazing. I have a crib in my office. When they were infants, I would take them to my office all the time. It was really special to have that time with them, and I could come back to work much earlier after giving birth than I would have if I took a traditional maternity leave.”
“In terms of family, I think a lot of people would have told me not to have kids as an assistant professor. But everyone has their own vision of how they want to be as a parent and in their career. So I think it’s just figuring out what that balance is for you. It’s not the same for everyone. I would say that being a professor has given me flexibility that has been fantastic,” said Lee.
When offering advice to others unsure of their career paths, Lee provided reassurance in first pursuing smaller objectives. “I think it took me a long time to figure out my path and what I ultimately ended up doing. But I think during that time, I was always working towards some other goal. I think it’s really important to keep up the momentum, even if you’re not exactly sure of the path that you’re going on. Always be working towards some goal and working hard, getting tangible results. Pursue success at each step of the way as you’re finding your calling.”
“For women engineers, I would say to be very cognizant of biases that you may be placing on yourself. I think I saw myself in a certain way because I’m a woman in a field with not many women professors or professionals; I was subconsciously placing limits on what my career could and could not be. This internal bias almost prevented me from pursuing a career in academia. I wish I had opened up the possibility to myself earlier on that I could be doing this. Exploring possibilities and being open to challenging yourself is really important,” Lee said.
Awarded with both the 2019 Stevens Early Career Award for Research Excellence and the 2019 National Science Foundation Career Award, Lee will continue to break barriers in the scientific world and beyond.
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