MHC professor makes super-efficient solar cells.

Husna Anwar ’15 works with Professor Alexi Arango in his solar-cell lab at Mount Holyoke College. Photo by Jerrey Roberts

Mount Holyoke College physics professor Alexi Arango seeks new ways to produce solar cells

By Fran Ryan, Gazette contributing writer

Reproduced with permission from February 11, 2015, Daily Hampshire Gazette.

In the custom-designed, state-of-the-art solar cell fabrication laboratory at Mount Holyoke College, Alexi Arango and his students are performing cutting-edge research on new semiconducting materials.

Arango, 39, an assistant professor of physics, is exploring ways to advance renewable energy through the use of semiconductors in the production of solar cells.

Arango studies “quantum dots”— tiny particles of a semiconducting material, molecular dyes, metal oxides, and other novel semiconductors—and the ways in which they can be incorporated into third-generation solar cells.

Simply put, solar cells are divided into three main categories called “generations.”

First-generation solar cells use silicon semiconductors and have an efficiency level of about 15 percent to 20 percent. They are also expensive to produce. These types of solar cells dominate the market and are mainly those seen on rooftops.

Second-generation solar cells use compound semiconductor material composed of copper, indium, gallium, and selenium. These have a low efficiency, but are much cheaper to produce, which means the cost-per-watt is lower than the first-generation cells.

Third-generation solar cells are being made from a variety of new materials and they are very efficient.

“There is a vast array of materials that are not what you would normally think of as semiconductors, like paint on a wall, dyes in clothing, and there is a type of plastic that is a semiconductor as well,” Arango said. “Here we work with little tiny chunks of semiconductors small enough that we can make inks out of them so they can be printed.”

The goal is to make third-generation solar cells cheaper to produce, easier to use, and accessible in a variety of applications.

“Imagine if you could create a large roll in a factory, and you could lay that on your roof in about 10 minutes,” he said.

Groundbreaking work

“The work he is doing is groundbreaking in terms of energy for the future,” Mount Holyoke College President Lynn Pasquerella said.

While there are many innovative ideas regarding solar energy, research on solar technology has been slow, Arango said, adding that it is not a lack of creativity which has hindered progress, but rather too little funding and research.

“All of the scientific questions have not been asked, much less answered,” he said. “In terms of research and development we are just at the tip of the iceberg.”

Arango said that while government funding for research in nuclear power, fossil fuels, and even coal has been consistently made available, “Solar has been just limping along.”

“There aren’t a lot of people looking at the problem,” Arango explained. “But what that means is that there is a lot to be done, and a lot of progress to be made, which makes it a very exciting field.”

Still, there are some new and improved applications of solar power that have arrived, or are expected to arrive on the market very soon. These are some of the innovations that Arango teaches to students in his renewable energy course.

“On the consumer side, we are gradually seeing more efficient solar panels and more options in terms of how they look, whether they are hidden or integrated into the roof,” he said. “The major new technology coming down the line is going to be the ability to store electricity on site at your home.”

Arango said that battery technology is moving at an extremely rapid and unprecedented speed.

“There are benefits to having a grid that is able to shuttle energy from place to place,” he added. “But, what’s appealing about batteries is that you get to completely take responsibility for your own energy generation and usage.”

Arango has done just that.

Living the lessons

Working with GO Logic LLC, an architecture and construction company based in Belfast, Maine, Arango has built an off-the-grid passive house of his own in Amherst. The 1,000-square-foot home is completely powered by solar energy.

GO Logic is the 12th building company in the United States to be certified by the Passive House Institute U.S., to design and build “passive homes” that meet the highest international standards for energy efficiency. These houses typically use less than 10 percent of the energy required to heat standard-built homes.

Arango’s home is super-insulated and tightly sealed. The windows are triple-paned for extra insulation. The first floor is concrete, which absorbs heat during the day and releases it at night.

For both heating and cooling his home, Arango has an energy-efficient “mini-split” heat pump that he says is four times more efficient then a standard unit.

“When I turn on every light in my house, it uses about 300 watts of electricity,” he added. “That equals what three or four incandescent light bulbs use, and I have about 25 or 30 bulbs in my house.”

Arango, who is engaged to a woman attending law school in New York City, lives alone in the house. He said that one of the most illuminating aspects of his home is having a monitor that shows him exactly how much energy each electrical appliance is using.

“I designed the house with energy monitoring in mind. Every appliance in the house has a sensor that tells me the amount of energy used and at what time,” he said.

To demonstrate this while sitting in his campus office, Arango opened a tablet and pulled up a program that allows him to see the peaks and lows on a graph of the energy used by all his appliances.

“It is lots of fun experimenting to see things like the difference between putting dishes in the dishwasher or washing them by hand,” Arango said. “I can also see how much energy is used by leaving lights on or the TV, or how much energy it took to make my oatmeal on the stove this morning.”

Arango frequently takes students to his home to show them the practical applications of energy-efficient construction.

Among Arango’s students is Mount Holyoke senior Husna Anwar, a physics major from Pakistan, who said she has firsthand experience with the impact that energy shortages have on communities.

“I am driven to find alternative energy solutions,” she said.

Under Arango’s guidance, Anwar works on finding ways to improve the overall efficiency of solar cells by trying to increase their voltage output. She said she combines her love of oil painting with her desire to create improved solar technology.

“For me, the process of creating and designing solar cells out of colorful dyes and materials is just like any of my paintings or art projects, except I get to use my mind to think about the physics behind what happens when those colors mix,” Anwar said. “It is the perfect balance between using your hands, creativity, imagination and scientific knowledge to produce something that could potentially make a difference.”

She added, “I eventually want to be a professor just so I can keep doing research while teaching and inspiring new scientists—particularly women—to do it too, just as my adviser has done for me.”

Originally from San Francisco, Arango has taught classes in renewable energy, electromagnetism, and mathematical methods for scientists at Mount Holyoke for five years. He has a doctorate in electrical engineering from the Massachusetts Institute of Technology.

Through his research, Arango hopes to help in producing technology for real-world applications that will make a difference.

“If you look at trends, it could take decades to significantly replace fossil fuels, but we have this ticking clock called climate change to deal with,” he said. “The fundamental physics and economics will push renewable energy ahead of fossil fuel slowly but surely.

Arango added, “We are living in a revolutionary time in renewable energy. We are looking at wind, new drilling techniques are opening up for geothermal, we are just starting to explore wave energy.

“It is an amazingly hopeful and transformative time.”