Lottery winners don’t get to keep all their money — they have to pay a sizable federal tax. Similarly, solar energy involves a tax, albeit a very different kind. The light that becomes heat in solar cells doesn’t make its way into homes or stores.
Employing a new polymer, however, scientists at Brookhaven National Laboratory and Columbia University have started a process that may enable them to keep more energy from sunlight.
Using something called “singlet fission,” they figured out a way to cut down on solar energy lost as heat.
Through a multiplication process, one absorbed unit of light creates two electrical charge carriers.
Other researchers had produced materials that benefited from singlet fission. They hadn’t, however, created a substance that works while dissolved in liquids, which creates the potential for industrial-scale manufacturing.
“Not many materials do singlet fission,” said Matthew Sfeir, a scientist at BNL and one of the leaders on the project. The material Sfeir and co-investigator Luis Campos of Columbia University used can be made through solution processing, which includes material such as ink.
Sfeir explained that the discovery of this polymer was something of a fortunate accident. Campos, whom he describes as a “great organic chemist,” was attempting to create a molecule for an application that did not work. “It failed spectacularly,” Sfeir recalled.
Campos and Sfeir took a closer look at what was happening. As it turns out, by examining the materials with a strobe laser at the Center for Functional Nanomaterials at BNL, Sfeir and Campos recognized that this polymer was “behaving like nothing else with this class of organics.” They were, indeed, creating singlet fission.
Campos and Sfeir tested how well their sensitizer might work to tap into the heat energy. “A failure in one context [was turned into] a spectacular success in another,” Sfeir said.
Sfeir and Campos, along with John Miller at the Laser-Electron Accelerator Facility and postdoctoral student Erik Busby in Sfeir’s lab and postdoctoral student Jianlong Xia in Campos’s lab, started these experiments in September, 2013. They recently published their results online in the journal Nature Materials.
Sfeir explained that the technology at BNL enables scientists to test materials and ideas. “My research lab uses ultrafast lasers to evaluate how well materials might perform in actual devices, without building actual devices,” Sfeir explained.
Using lasers, he puts light energy into a system and then tries to measure where the energy goes and how fast it gets there.
Sfeir and Campos are looking at a material that works even better than the one for which they published their recent results. The original polymer included a small amount of a minority project that they are trying to minimize.
A resident of Bethpage, Sfeir lives with his wife Margot, their 6-year-old daughter Katy and their son Jonah, who will be 2 in a few months.
Sfeir was born in Buffalo while his wife was born in Minnesota. When they first met in Chicago, he said Margot would only use a scarf and mittens instead of a winter coat, even in cold weather. Living in the New York City area since 2000 has reduced their resistance to frigid temperatures.
When he was younger, Sfeir learned some lessons in a seemingly unrelated field when he worked at Hector’s Hardware, a small chain owned by his father Ken’s extended family. While he did other jobs like unloading concrete bags, mixing paint and cutting and threading pipe, Sfeir developed an expertise in window and screen repair.
In college, Sfeir discovered a passion for quantum mechanics and was fascinated by light and the way it interacts with matter.
In Sfeir’s first job at a research lab, one of his first responsibilities was fixing the water cooling lines on a laser. “I called my dad right away to thank him for the lessons about compression fittings,” Sfeir said.
As for his work, he said he thoroughly enjoys the opportunities. “I love working at BNL because its mission resonates strongly with me,” he said. “Sometimes, this research evolves into readily identifiable technological applications and sometimes it evolves our understanding of some of the most basic questions about our world. Both are very important to me.”