electrons are held as somewhat of a “Holy Grail” in the solar
cell research community and reportedly will form the basis of
so-called "Third Generation" cells. When light
strikes a solar cell, it produces electrons in a variety of energy
states. Energy from mid-range electrons is commonly harvested,
but the high-energy hot electrons typically lose most of their high
kinetic energy to heat before they reach the conduction band.
new ultra-thin film -- less than 30 nm thick -- allows hot electrons
to instead use an "escape hatch" and avoid losing their
energy. The team, led by Michael J. Naughton, the Evelyn J. and
Robert A. Ferris Professor of Physics at Boston College, focused on
minimizing the routes in the environment that electrons can escape
While the quantum physics behind this endeavor is complex,
the paper's lead author Professor of Physics Krzysztof Kemp says that
what they were doing was basically going from trying to heat a pool
with a pot of boiling water, to a more reasonable task of trying to
heat a sink with boiling water. He elaborates, "We have
shrunk the size of the solar cell by making it thin. 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
Typical cells commercial photovoltaics offer
efficiencies of somewhere between 10 to 20 percent, but are expensive
to produce. The new cells used a mere fiftieth of the thickness
and still retained 3 percent efficiency, thanks mainly to harvesting
the hot electrons. Capturing the hot electrons had the extra
benefit of reducing waste heat, which saps voltage.
combining the technology with nanostructures, such
as nanowires, the researchers predict that much higher
efficiencies can be achieved. The end will result will likely
be much cheaper cells with efficiencies similar to today's,
ultimately lowering costs.
Other members of the research team
included Professor of Physics Zhifeng Ren, Research Associate Professor and
Laboratory Director Andrzej A. Herczynski, Research Scientist Yantao
Gao, doctoral student Timothy Kirkpatrick, and Jakub Rybczynski of
Solasta Corp., of Newton MA, which supported the research.
The research is published in the journal Applied Physics
Letters. The abstract can be viewed
quote: Typical cells commercial photovoltaics offer efficiencies...