University physicists have found
new properties within a material that could lead to the
production of less expensive and more efficient plastic solar cells.
Podzorov, co-author of the study and assistant professor of physics
at Rutgers University, along with his research team have discovered
that organic semiconductors allow energy-carrying particles -- which
are created by "packets" of light -- to journey a thousand
times farther than researchers previously thought.
semiconductors are promising for solar
cells and other uses, such as video displays, because they can be
fabricated in large plastic sheets," said Podzorov. "But
their limited photovoltaic conversion efficiency has held them back.
We expect our discovery to stimulate further development and
and his team came to these conclusions by observing excitons, which
are particles that consist of an electron and an electron hole where
a positive charge is attributed to the absence of an electron.
Excitons form when semiconducting materials absorb photons, which are
problem with organic semiconductors up until this point was that they
were observed to travel less than 20 nanometers. This is an issue
because electrons and the holes move to the two opposite sides
when they "hit" a semiconductor junction or boundary.
If these excitons only diffuse "tens of nanometers," the
only ones that generate photo-voltage are those closest to the
boundaries or junctions.
we lose 99 percent of sunlight," said Podzorov.
now, Podzorov and his team have observed that excitons can journey a
thousand times farther than previously thought in rubrene, which is
an extremely pure crystal organic
is the first time we observed excitons migrating a few microns,"
said Podzorov. "Once the exciton diffusion distance becomes
comparable to the light absorption length, you can collect most of
the sunlight for energy conversion."
within the rubrene crystal acted like excitons in inorganic crystals,
which means better opto-electronic properties, increased efficiency
and lower costs. Podzorov and his team hope, with further
development, that solar cells based on this technology can replace
silicon solar cells.
the midst of this research Podzorov also discovered a new way of
measuring excitons based on optical
spectroscopy. Excitons are hard to measure because they are not
charged, so the Rutgers University research team created a new method
called polarization resolved photocurrent spectroscopy, which
"dissociates" excitons at the surface of the crystal and
exposes large photocurrent.
study will be in an upcoming issue of Nature
where Podzorov has submitted other
relevant and recent
research on organic semiconductors.