A Mount Holyoke College professor and his students are exploring new, potentially revolutionary solar cell technologies in a custom-built lab at the College.
Alexi Arango, assistant professor of physics, set his students a tough task this summer. They were asked to fabricate and test the first solar cells ever made at the College, using equipment they helped build and techniques they learned in his lab.
They’ve succeeded. The first solar cells—layers of incredibly thin semi-conducting material and electrodes sitting on a half-inch-square sliver of glass, or substrate—were made on July 2.
Adding to the team’s celebrations, the National Science Foundation has awarded Arango a $300,000 grant that will enable the team to install some crucial pieces of lab equipment that will be used to make even better-performing solar cells.
“The progress we’ve made this summer is impressive,” said Arango, reflecting on the team’s success. “Making a solar cell at an undergraduate college is a big deal.”
Not only is it unusual for a solar research team to almost exclusively comprise undergraduates, but the research itself is focused on making breakthroughs in manufacturing new generations of solar cells.
To that end Arango’s lab doesn’t work with silicon, the expensive material used in the solar industry to manufacture solar cells.
Instead, Arango and his students are investigating how plentiful, relatively inexpensive semiconductors such as polymers, quantum dots, molecular dyes, and metal oxides can be used to make solar cells that are both highly efficient and less expensive to manufacture and install than silicon-based solar cells. Through the photovoltaic process, solar cells made of these semi-conductors are able to separate charges to produce a current directly from the sun's energy.
By combining solar cell technology advances with increases in manufacturing scale and sophistication, Arango imagines a future where, for example, solar cells made from layers of semi-conducting dyes could be printed into huge rolls of paper-thin film and applied to almost any surface.
“Since 2004, the solar industry has grown at 40 percent each year in the United States,” he says.
“We will soon get to the point where it will become difficult to make all the solar panels we need using existing technologies and materials. There’s room in the market for new ways to manufacture solar panels.”
Shehzeen Samarah Hussain ‘14 has worked in Arango’s lab for a year. Making the first solar cell is just the beginning, she says. Her next project is to measure the cell’s efficiency - the amount of light that that the cell converts into usable electricity. That efficiency, expected to be about 4 percent, will serve as a benchmark against which future cells will be tested. She first has to assemble and install a solar simulator, a lamp that casts light in the same manner as the sun.
Hussain, who plans on pursuing graduate studies in electrical engineering, appreciates the hands-on experience provided by her research.
“I’ve done everything from repairing equipment to actually making a solar cell. Soon I get to experiment with how we make the cells with different chemistry and materials and processes.”
The lab, which opened two years ago, is a one-of-a-kind, Arango says. Unlike in a research university, where equipment would be housed in several buildings, Arango’s lab has all the tools and instruments needed to build solar cells from scratch.
The lab has a chemical hood, where liquid versions of the semi-conductors are made; a wet deposition glove box, where the liquid films are turned into solid layers a few nanometers thick; a thermal evaporator, where the films are applied on glass substrates to become solar cells; and a characterization box, where the efficiency of the cells is tested.
In an unusual move for a research lab, the equipment design and layout has been set up to be as user-friendly as possible, so the students can focus their creativity on the process of scientific discovery and innovation, Arango says.
“I wanted it to be a space where students can work on every stage of building solar and testing solar cells, and where they could move their projects along quickly,” he says.
“Every student starts out by getting the engineering basics through working hands-on with the lab equipment. When they complete their advanced classes in physics and chemistry, they’re ready to do the real science in the lab.”
Arango believes the experience will set the students up for careers as solar entrepreneurs or scientists, roles that he says are essential to advancing the solar industry.
“I’d like to see them go off to start solar companies and develop products or go to grad school and push the frontiers of solar cell science,” he says.
“They’re amazingly capable of taking ideas and turning them into reality.”