UCLA researchers create polymer solar
cells with higher efficiency levels
UCLA solar polymer films and the corresponding
device characteristics made from these films.
The films are actually semitransparent.
Currently, solar cells are difficult
to handle, expensive to purchase and complicated to install.
The hope is that consumers will one day be able to buy solar
cells from their local hardware store and simply hang them like
posters on a wall.
A new study by researchers at the
UCLA Henry Samueli School of Engineering and Applied Science
has shown that the dream is one step closer to reality. Reporting
in the Nov. 26 edition of the Journal of the American Chemical
Society, Yang Yang, a professor of materials science and engineering,
and colleagues describe the design and synthesis of a new polymer,
or plastic, for use in solar cells that has significantly greater
sunlight absorption and conversion capabilities than previous
polymers.
The research team found that substituting
a silicon atom for carbon atom in the backbone of the polymer
markedly improved the material's photovoltaic properties. This
silole-containing polymer can also be crystalline, giving it
great potential as an ingredient for high-efficiency solar cells.
"With the reality of today's
energy crisis, a new-game changing technology is required to
make solar cells more popular," Yang said. "We hope
that our newly synthesized polymer can eventually be used on
solar cells far beyond their current rooftop applications. Imagine
a house or car covered and powered by flexible solar films.
Our dream is to see solar cells used everywhere."
Polymers are lightweight, low-cost
plastics used in packaging materials and inexpensive products
like insulators, pipes, household products and toys. Polymer
solar cells utilize organic compounds to produce electricity
from sunlight. They are much cheaper to produce than traditional
silicon-based solar cells and are also environmentally friendly.
But while polymer solar cells have
been around for several years, their efficiency has, until recently,
been low. The new polymer created by Yang's team reached 5.1
percent efficiency in the published study but has in a few months
improved to 5.6 percent in the lab. Yang and his team have proven
that the photovoltaic material they use on their solar cells
is one of the most efficient based on a single-layer, low-band-gap
polymer.
At a lower band gap, the polymer
solar cell can better utilize the solar spectrum, thereby absorbing
more sunlight. At a higher band gap, light is not easily absorbed
and can be wasted.
"Previously, the synthesizing
process for the polymer was very complicated. We've been able
to simplify the process and make it much easier to mass produce,"
said Jianhui Hou, UCLA postdoctoral researcher and co-author
of the study. "Though this is a milestone achievement,
we will continue to work on improving the materials. Ideally
we'd like to push the performance of the solar cell to higher
than 10 percent efficiency. We know the potential is there."
"We hope that solar cells
will one day be as thin as paper and can be attached to the
surface of your choice," added co-author Hsiang-Yu Chen,
a UCLA graduate student in engineering. "We'll also be
able to create different colors to match different applications."
The study was funded by Solarmer
Energy Inc. and a UC Discovery Grant. Solarmer Energy Inc. has
recently licensed the technology from UCLA for commercialization.
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Wileen Wong Kromhout
11/26/2008
