Quantum dots' efficiency multiplies with ARL, SUNY collaboration

When Kimberly Sablon was hired at the Army Research Laboratory in 2009 she recognized potential in quantum dots that would ultimately further energy possibilities.

Sablon, a research scientist with the Energy Conversion Team, Electro-optic/Infrared Materials and Devices Branch of the Sensors, Electrons & Devices Directorate, suggested a way of minimizing quantum dot recombination losses that raises solar cell efficiency.

Quantum dots are portions of matter, or semiconductors, discovered in the '80s with characteristics similar to the size and shape of the individual crystal.

The team experimented with selectively doping the inter-dot space of quantum dots to create potential barriers around the dot, while little did they know researchers at the State University of New York at Buffalo funded by the Air Force Research Laboratory were on the same track from a theoretical perspective.

When Sablon presented her experimental research at an international conference in Greece in 2010, she met Dr. Vladimir Mitin, a distinguished professor at SUNY who approached her about his findings.

ARL had experimental quantum dot devices with specific structures and the team at SUNY had a theoretical understanding of the physics involved in the process of the harvesting, Mitin said.

That single chance meeting led to a co-authored paper, Effective harvesting, detection, and conversion of IR radiation due to quantum dots with built-in charge that was published in Nanoscale Research Letters in November 2011.

Together ARL and SUNY have shown the potential to boost the efficiency of quantum dot solar cells by as much as a factor of two from what the current values are.

They have taken steps toward solving the challenge of recombination losses and subsequent degradation of the device performance associated with introducing dot states into the gap of solar cell structures, Sablon said.

"The fundamental application of our research is to reduce the weight carried by Soldiers in the field, which increases Soldiers' endurance," said Parvez Uppal, EO/IR Materials and Devices Branch Chief, in the Electro-Optics & Photonics Division of SEDD.

Any time there is the potential to decrease the size of a solar battery charger or replace a heavier energy source for a lighter one, there are significant implications for the Soldier, Department of Defense and the commercial market, Uppal said. "This is a perfect example of how partnership with academia and industry in basic research could take a concept to the next level for the good of the Soldier."

Sablon, who took the lead on the research, made the right connections for collaboration. She is dedicated to her work, said her team chief, Senior Research Scientist John Little. ARL knew the potential of quantum dots. But what Sablon did was propose a modification to the structure that started the branch in a different direction.

"She took the ball and ran with it," he said. "Different backgrounds and views help solve problems. In this case what the combined group of researchers accomplished was more than either team would have on their own."

Research is often a collection of projects in which one project stems from another project. Sometimes a project works and other times it doesn't, but when it does, it's nice, Sablon said.

"I've always wanted to utilize quantum dots for solar cells," Sablon said. In past research she learned to control the quantum dots, but said "so what if you can't make something useful. Bringing the technology to the functioning device stage is what the team at ARL has done."

After what she calls a "small success," Sablon is already concerned with the next level of inquiry concerning quantum dots.

"The quantum dot research findings give people hope about the direction," she said. "There is so much more opportunity to make the transition toward solar use."

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Quantum dots' efficiency multiplies with ARL, SUNY collaboration