DOE Pulse
  • Number 352  |
  • December 12, 2011

NREL solar scientist has come a long way from the swimming pool

NREL's Kirstin Alberi

NREL's Kirstin Alberi.

Kirstin Alberi just wanted to have fun.

It’s taken her a long way, from coastal Maine, to MIT and Cal-Berkeley, and ultimately to DOE’s National Renewable Energy Laboratory, where her ability to see connections between disparate data was critical to the success of a game-changing new silicon ink.

Alberi, 30, grew up in Cape Elizabeth, Maine, on the chilly North Atlantic, where she swam for the high school team and immersed herself in math and science classes.

“I had some great teachers in high school,” Alberi, a senior scientist at NREL, recalled. “My parents were both engineers so that kind of put me on a path toward engineering and science.”

In fact, both parents and her only brother are mechanical engineers. “That’s all I was exposed to my whole life, engineering,” she said.

“It’s nice to be able to think about how to build something,” she said, before adding, “Although I guess in my family I never really had a choice.” She did manage to break out of the family business enough to gravitate toward science rather than engineering.

That was at the Massachusetts Institute of Technology, where she earned a bachelor’s degree in materials science and engineering while swimming competitively all four years – she swam the 100-yard backstroke in less than a minute.

Summers, she worked in internships at National Semiconductor in South Portland, Maine, where she jumped into the study of electronic materials.

“I enjoyed it, and decided I wanted to go to graduate school and learn more,” Alberi said.

Why graduate school?

“It was pretty simple, really,” she said. “I looked around and saw that the fun jobs were ones where people have PhDs. I wanted to have fun.”

So she was off to the University of California at Berkeley.

Finding the unexpected benefits of odd alloys

There, she joined the lab of Professor Oscar Dubon where she studied materials science and engineering, especially as they apply to the research and development of semiconductor alloys.

“I looked at unique semiconductor alloys, learning how to pattern and fabricate them into something useful,” Alberi said. “I learned how to grow and characterize semiconductor materials.

“Most of my Ph.D. work focused on developing a fundamental framework from which to understand the properties of unconventional compound semiconductor alloys,” Alberi said. “Basic research is always a predecessor to application and innovation.”

Building devices at NREL

With her newly minted doctorate in materials science, she landed a job at NREL where senior scientist David Young was in need of a post-doc in silicon.

“I kind of wanted a change, to learn more about devices,” Alberi said. “At Berkeley we always motivated each other by saying our research may someday prove useful for solar cells or other devices.

“But I had never made a full device. NREL was a good opportunity for me to explore that.”

Her first two years at NREL, she worked on a Cooperative Research and Development Agreement with Innovalight, a small start-up from Sunnyvale, Calif., as well as helping develop thin crystalline silicon solar cells that are grown on inexpensive substrates.

On the latter project, she learned how to melt elements together, to pull a seed out of that melt to grow silicon in bulk. She learned how to grow thin films via physical deposition and molecular-beam epitaxy, and she learned evaporation and sputtering techniques.

“It was an invaluable experience for me because it connected the applied side of research to the basic research experience I had in grad school,” Alberi said. “It’s important to understand both basic research and the applied side in order to effectively make an impact. David Young gave me that chance.”

Designing experiments to prove the value of liquid silicon

Innovalight had come up with an ingenious way to suspend silicon in a solution without the tiny particles glomming onto one another or sinking to the bottom of the container.

But could that Silicon Ink prove useful for solar cells?

Dopants or impurities are used to change the conductivity of silicon and to create the internal electric fields needed to turn photons into electrons and thus into electricity. One of the great challenges is to distribute the exact concentrations of dopants in precisely the correct locations throughout the device.

What Innovalight’s potential customers and investors wanted to know was whether the ink can deliver high concentrations of dopants to extremely localized regions of the emitter, which is necessary to increase a solar cell’s efficiency. And to do it without having the ink spread all over the place.

Alberi and Young listened to what Innovalight wanted to prove and then suggested some experiments.

“They didn’t know how to go about proving this, and that’s where we were able to help,” Alberi said. “If you have a broad knowledge of semiconductor characterization and a good knowledge of your repertoire of techniques, it becomes easier. We have experts in every one of these techniques.”

There wasn’t a “Eureka” moment, but the dawning realization that the Silicon Ink was performing exactly as well as Innovalight had hoped was extremely gratifying, Alberi said.

“It was nice seeing that the results were exactly what they hoped they would be,” Alberi said.

The scorecard: Silicon Ink, used in a low-cost screen-printing process, delivered a 7 percent increase in power output for a typical 15%-efficient cell – at a cost that is so low that it basically goes unnoticed at large solar-cell manufacturing plants.

NREL and Innovalight shared a coveted R&D 100 award for 2011 for the Silicon Ink technology.

Alberi is well-organized, well-read, works well with everybody and always is willing to try something new, her mentor, David Young, said.

“She is a creative experimenter and easily sees connections between data,” Young added. “With Innovalight, she designed experiments to prove the doping profile of their inks.” One of those experiments placed microscopic markers on the samples using a focused ion beam to correlate two essential measurements.

“Those measurements ultimately proved Innovalight’s process,” Young said. “And that’s what gave them the confidence to move forward.”  Innovalight, recently purchased by DuPont, now has contracts with five of the biggest solar-cell manufacturers in the world.

Using aluminum to make a brilliant green light

In 2010, Alberi switched to the solid state spectroscopy group at NREL for a new challenge: finding a better way to produce a green light-emitting diode – the most difficult color in producing the inexpensive, long-lasting, energy-stingy white light that can revolutionize indoor lighting.

At that time, Angelo Mascarenhas and his team had just startled the LED world by producing a brilliant green LED made of gallium indium phosphide.

“I learned a lot about device requirements for LEDs and how to engineer materials for them,” Alberi said. “We’ve actually switched materials. We think aluminum indium phosphide can work better, although it’s been traditionally difficult to grow and fabricate.

“The big challenge is to learn how to make it and study its fundamental properties,” Alberi said. “That’s where my experiences came full circle, combining applied and basic sciences into use-inspired basic research. My past experiences have shaped my outlook on science. And Angelo has been a great mentor in that regard.”

Using a luminescence mapping technique she examines areas on samples the width of a human hair for defects in real time. Defects interfere with electronic carriers’ ability to recombine to emit light.

Recently, while aligning the laser that excites the carriers that create photons, Alberi joked, “These glasses make me look like Elton John,” pointing to the thick-rimmed safety glasses that offer more function than form.

It takes a grand vision – and slavish attention to details

Alberi says her scientific style strikes a balance between a focus on details to answer important questions and keeping in touch with the grand vision and needs of the scientific community.

Outside of work, she and her husband Jeff hike, run, bicycle, and get up to the Colorado mountains.

“I mostly like just being outdoors and hanging around with friends,” she said, vowing that she’ll also soon get back in the pool.

Meanwhile, she hopes her stays in Colorado and at NREL are permanent ones.

“The people at NREL are fantastic,” she said. “This is probably the nicest place I’ve ever worked. We have totally friendly people, and everyone here is so knowledgeable about solar materials. It’s nice to be around those kinds of people.”– by Bill Scanlon

Submitted by DOE's National Renewable Energy Laboratory