Researchers have studied a new phenomenon that uses ultrathin cells to harness hot electrons and increase solar power efficiency.

The research builds on a study by Krzysztof Kempa, professor of physics, and Michael J. Naughton, the Evelyn J. and Robert A. Ferris professor of physics, at Boston College.

Researchers have long theorized about the benefits of harnessing hot electrons for solar power through so-called third generation devices.

When light is captured in solar cells, it generates free electrons in a range of energy states. The electrons must reach the bottom of the conduction band to share these charges. However, these highly energized “hot” electrons lose energy to heat along the way.

The research team used ultrathin solar cells around 30 nanometers thick to develop a mechanism that would extract hot electrons, creating an “escape hatch” through which they typically do not travel.

"We have shrunk the size of the solar cell by making it thin," Mr. Kempa explained. "In doing so, we are bringing these hot electrons closer to the surface, so they can be collected more readily. These electrons have to be captured in less than a picosecond, which is less than one trillionth of a second."

The light cells were able to increase solar power efficiency by approximately 3 percent. While the researchers acknowledged that the cells’ efficiency is limited by the negligible light collection of ultrathin junctions, combining the film with better light-trapping technology – such as nanowire structures – could significantly increase efficiency in an ultrathin hot electron solar cell technology.

Hot electrons have also been observed in other devices, such as semiconductors. But their high kinetic energy can cause these electrons to degrade a device.

In addition to Mr. Naughton and Mr. Kempa, the research team included Zhifeng Ren, professor of physics; Andrzej A. Herczynski, research associate professor and laboratory director; Yantao Gao, research scientist; Timothy Kirkpatrick, a doctoral student; and Jakub Rybczynski of Massachusetts-based Solasta Corporation.