University of California Davis and U.C. Santa Cruz researchers were recently awarded three-year, $1.5 million National Science Foundation grant to research a method of producing multiple electrons from one photon. The research could yield much more efficient photovoltaics in the future.

The research builds on the discovery of multiple-exciton generation (MEG) in nanoparticles by the Klimov group at the Los Alamos National Laboratory, explained Gergely Zimanyi, U.C. Davis professor of physics and principal investigator of the NSF grant.

This discovery verified the earlier theoretical proposition of Arthur Nozik (National Renewable Energy Laboratory).

“We plan to contribute by developing a synergistic group effort,” Klimov said, “where the theoretical analysis of the process is closely integrated with the synthesis and characterization of the nanoparticles, eventually embedding them into a functioning solar cell.”

Normally the production of electrons via photovoltaics is on a direct relationship: one photon produces one electron. But the research being conducted by the universities could produce up to seven electrons from one high-energy photon, according to Zimanyi’s home page at U.C. Davis.

The research uses nanoparticles of germanium, silicon and other materials to produce photovoltaics with a potentially much higher efficiency rating than currently available photovoltaics.

"In conventional solar cells, one incident photon induces one electron. But the MEG process may produce several electrons for the incoming photons,” he said. “The basic mechanism of this process is probably that a high energy solar photon induces a high energy electron, which then excites other electrons through a strong interaction.

“In today's solar cells, the high-energy electrons simply heat up the cell, wasting their excess energy. We plan to understand this process in detail, and will try to optimize the energy conversion efficiency of solar cells assembled from nanoparticles," he said.

At this point the research is preliminary, but the group developed a prototype cell prior to winning the grant. The prototype cell only exhibited about 8 percent efficiency, but limited resources went into the device’s construction, according to a U.C. Davis press release.

Ultimately, the research could produce a photovoltaic cell that is between 42 percent and 65 percent efficient at converting sunlight into electricity. Much higher than the theoretical maximum of 31 percent for conventional photovoltaics, the release stated.

Pictured: An electron micrograph of nanoparticles in an experimental solar cell. Image courtesy of UC Davis.