A New Way of Looking at Solar Energy

You may find Dr. Jeffrey Christians in his office in VanderWerf Hall, or else in his Schaap Science Center lab, or perhaps at a renewable energy conference across the country; he’s a scientist, engineer and solar energy researcher, linking fields — and the students studying them — in his quest for sustainable energy at a sustainable cost.

“I think access to clean and inexpensive energy has as much effect as anything on issues like poverty and public health, as well as climate change,” Christians says. “In a lot of ways, that’s one of the most important, most pressing challenges facing scientists and engineers.” To facilitate this energy access, Christians is working to develop a solar-energy-capturing material that can be applied to existing windows — eliminating two major costs currently associated with implementing solar energy: glass and installation.

The task is challenging, but finding student researchers — future chemical, electrical and mechanical engineers, chemists and physicists — who share his passion for the research and its potential is not.

“The real-world applications of this project make this research really interesting, especially with the ongoing climate change crisis,” says junior Cedric Porter of Holland, Michigan, an electrical engineering major working in Christians’ lab. “Solar cells could have a huge impact on the world stage. Working in that domain is a lot of fun.”

The science comprising that domain, at least in the Christians lab, focuses on the materials (specifically, a synthetic substance known as halide perovskites) to create better solar cells and the means of making that material even better. One way the lab achieves the latter is by studying the surface features of miniscule perovskite crystal specks known as “quantum dots.”

“In a crystal, whether it’s table salt or a halide perovskite, you have this periodic pattern of repeating atoms. At the surface, that pattern just stops,” Christians says. “So how you end the pattern becomes really important for what the properties are like.” By crunching the crystal into ever-smaller bits, Christians and his students can study those properties and the surfaces of these little crystals, which are only about 100 atoms across. The goal is to find the surface structure that has the fewest defects, or trouble points, to give better solar energy harvesting.

With the right solar-capturing properties, the researchers could apply a thin coat of quantum dots — about 200 times thinner than a conventional solar panel — to glass windows, transforming them into viable solar cells.

“I think access to clean and inexpensive energy has as much effect as anything on issues like poverty and public health, as well as climate change… In a lot of ways, that’s one of the most important, most pressing challenges facing scientists and engineers.”

Dr. Jeffrey Christians, assistant professor of engineering

“It’s a potentially easy area that you could piggy-back solar energy off of those costs that are already there,” Christians says. Given that the glass production and installation costs have already been taken care of in existing windows, “you could get a window that’s also a solar cell for little added cost. But the challenge of that is: If you want to make a solar cell it has to absorb light. If you want to make a window, it has to transmit light,” Christians says. Simply coating the windows with solar-capturing material — however thin that material might be — defeats their initial purpose as windows.

“Solar cells are black and windows are clear, so how do you marry these two things?” Christians says. “What if, instead of having this compromise, we could make something that’s dynamic?”

The lab has found a way to do just this, though they’re still working out the details. Apply a particular gas molecule (methylamine) to the dark, perovskite-coated glass, and it turns instantly clear. Pumping a small amount of this gas into the space between two windowpanes could effectively allow the solar cell to swap between dark solar panel and clear window just by changing temperature, but there’s a catch. Just as a battery can only be discharged and recharged so many times before it can no longer hold any charge, the perovskite crystals clump together, reducing the solar panel performance after repeated switching between dark and clear.

“How do we design a battery that instead of charging and discharging one time or 10 times — how do we make it do that 100 times?” Christians says. That’s the next step in their research. “We’re working on how to improve the cycle-ability of this color change,” he says. They’re also exploring alternative (and potentially more convenient) ways of prompting the perovskite to change color. Transitions eyeglass lenses, for example, change color when exposed to light. Other materials change color in response to a temperature change or an infusion of electricity. The last is especially appealing to Christians’ group. If they can devise a way to swap between window and solar panel with the flip of a switch or the press of a button, it would introduce unprecedented convenience to the end product.

There’s an excitement that accompanies an unsolved challenge — one that Christians’ students share.

“The real-world applications of this project make this research really interesting, especially with the ongoing climate change crisis… Solar cells could have a huge impact on the world stage. Working in that domain is a lot of fun.”

Junior Cedric Porter

“A good amount of what is going on in this research, we haven’t been prepared for,” says senior chemical engineering major Claire Hallock of Lakeland, Florida. “Some of this involved inorganic chemistry stuff, and none of us have taken that specific class. So part of our research and part of the time that Dr. Christians has allotted for us is to take time to learn some of those fundamental concepts, and that’s been really helpful. Reading about some of those things that we haven’t had in classes yet, and showing up and figuring out how to find that information is a little bit of the research game.” It is also a good bit of the science experience — exposure that is one of the demonstrated benefits of Hope’s nationally acclaimed emphasis on teaching through collaborative faculty-student research.

Dr. Jeff Christians Lab

“In science, you have questions, and you have to try to find answers, and you go where the answers are,” Christians says. “So you end up, sometimes, in areas that you have very little expertise in, and you have to try to figure out what you’re doing in that area. That’s part of the challenge that I enjoy.” Science, and engineering in particular, is a dynamic, interdisciplinary field. Christians’ lab embraces the inherent difficulty of combining fields in search of new answers.

“This summer we have two chemical engineers, an electrical engineer and a mechanical engineer, and we’re doing a lot of chemistry,” Christians says. “It’s an interesting mix of physics and chemistry and engineering all mixed together. That’s been one of the things that I’ve definitely noticed, working in this area: You have to be interdisciplinary to be able to look at these problems and understand what’s happening.”

Increasingly, you also have to be collaborative.

“Something that I’ve noticed from my little time of doing research is that we are working together with people all across the country,” says sophomore mechanical engineering major Liz Cutlip of Middleville, Michigan. “Everybody wants to have this new thing that can potentially be super good for our environment. So it’s very different from industry, where ideas and processes are kept secret because they don’t want someone else to figure out the idea.” Collaboration opens up community for young and seasoned researchers alike.

“It’s been fun to be a part of the community to see some of the different ideas that people have,” Christians says, “and how this can be integrated into our everyday lives in the future — and be something different than just a rectangular panel sitting on your roof.” Something different — and something more.

“I see energy as one of the very important issues of justice,” Christians says. “The tie between access to clean and cost-effective energy and things like public health and economic independence is a very close tie. I think it’s a way that I, as an engineer, can contribute to some of these big, global challenges.”