See-Through Solar Film:

See-Through Solar Film:
Researchers Double Efficiency of
Novel Solar Cell
July 29, 2013 — Nearly doubling the
efficiency of a breakthrough
photovoltaic cell they created last
year, UCLA researchers have
developed a two-layer, see-through
solar film that could be placed on
windows, sunroofs, smartphone
displays and other surfaces to harvest
energy from the sun.
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The new device is composed of two
thin polymer solar cells that collect
sunlight and convert it to power. It's
more efficient than previous devices,
the researchers say, because its two
cells absorb more light than single-
layer solar devices, because it uses
light from a wider portion of the
solar spectrum, and because it
incorporates a layer of novel
materials between the two cells to
reduce energy loss.
While a tandem-structure transparent
organic photovoltaic (TOPV) device
developed at UCLA in 2012 converts
about 4 percent of the energy it
receives from the sun into electric
power (its "conversion rate"), the
new tandem device -- which uses a
combination of transparent and semi-
transparent cells -- achieves a
conversion rate of 7.3 percent.
Researchers led by Yang Yang, the
Carol and Lawrence E. Tannas, Jr.,
Professor of Engineering at the UCLA
Henry Samueli School of Engineering
and Applied Science, said the new
cells could serve as a power-
generating layer on windows and
smartphone displays without
compromising users' ability to see
through the surface. The cells can be
produced so that they appear light
gray, green or brown, and so can
blend with the color and design
features of buildings and surfaces.
The research was published online
July 26 by Energy & Environmental
Science , a Royal Society of Chemistry
journal, and it will appear later in a
published edition of the journal.
"Using two solar cells with the new
interfacial materials in between
produces close to two times the
energy we originally observed," said
Yang, who is also director of the
Nano Renewable Energy Center at the
California NanoSystems Institute at
UCLA. "We anticipate this device will
offer new directions for solar cells,
including the creation of solar
windows on homes and office
buildings."
The tandem polymer solar cells are
made of a photoactive plastic. A
single-cell device absorbs only about
40 percent of the infrared light that
passes through. The tandem device --
which includes a cell composed of a
new infrared-sensitive polymer
developed by UCLA researchers --
absorbs up to 80 percent of infrared
light plus a small amount of visible
light.
Chun-Chao Chen, a graduate student
in the UCLA materials science and
engineering department who is the
paper's primary author, said using
transparent and semi-transparent
cells together increases the device's
efficiency, and that the materials
were processed at low temperatures,
making them relatively easy to
manufacture.
Other authors of the study were
Gang Li, a staff researcher in the
materials science and engineering
department at UCLA; Jing Gao, a
materials science and engineering
graduate student; and Letian Dou and
Wei-Hsuan Chang, graduate students
in the UCLA materials science and
engineering department and the
California NanoSystems Institute.
The research was funded by the Air
Force Office of Scientific Research,
the Office of Naval Research and EFL
Tech.