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New Low-cost Solution Processing Method Developed For CIGS-based Solar Cells

July 7, 2009

Though the solar industry today predominately produces solar panels
made from crystalline silicon, they remain relatively expensive to
make. New players in the solar industry have instead been looking at
panels that can harvest energy with CIGS
(copper-indium-gallium-selenide) or CIGS-related materials. CIGS panels
have a high efficiency potential, may be cheaper to produce and would
use less raw materials than silicon solar panels. But unfortunately,
manufacturing of CIGS panels on a commercial scale has thus far proven
to be difficult.

Recently researchers at the UCLA Henry
Samueli School of Engineering and Applied Science have developed a
low-cost solution processing method for CIGS-based solar cells that
could provide an answer to the manufacturing issue. In a new study to
be published in the journal Thin Solid Films on July 7, Yang
Yang, a professor in the school’s Department of Materials Science and
Engineering, and his research team show how they have developed a
low-cost solution processing method for their copper-indium-diselenide
solar cells which have the potential to be produced on a large scale.

“This
CIGS-based material can demonstrate very high efficiency,” said William
Hou, a graduate student on Yang’s team and first author of the study.
“People have already demonstrated efficiency levels of up to 20
percent, but the current processing method is costly. Ultimately the
cost of fabricating the product makes it difficult to be competitive
with current grid prices. However, with the solution process that we
recently developed, we can inherently reach the same efficiency levels
and bring the cost of manufacturing down quite significantly.”

The
copper-indium-diselenide thin-film solar cell developed by Yang’s team
achieved 7.5 percent efficiency in the published study but has in a
short amount of time already improved to 9.13 percent in the lab.

“We
started this process 16 months ago from ground zero. We spent three to
four months getting the material to reach 1 percent and today it’s
around 9 percent. That is about an average increase of 1 percent every
two months,” said Yang, also a member of the California NanoSystems
Institute, where some of the work is being done.

Currently,
most CIGS solar cells are produced using vacuum evaporation techniques
called co-evaporation, which can be costly and time-consuming. The
active elements “” copper, indium, gallium and selenide “” are heated and
deposited onto a surface in a vacuum. Using vacuum processing to create
CIGS films with uniform composition on a large scale has also been
challenging.

The copper-indium-diselenide material created by
Yang’s team does not need to go through the vacuum evaporation process.
Their material is simply dissolved into a liquid, applied and baked. To
prepare the solution, Yang’s team used hydrazine as the solvent to
dissolve copper sulfide and indium selenide in order to form the
constituents for the copper-indium-diselenide material. In solar cells,
the “absorber layer” (either copper-indium-diselenide or CIGS) itself
is the most critical to performance and the most difficult to control.
Their copper-indium-diselenide layer, which is in solution form, can be
easily painted or coated evenly onto a surface and baked.

“In
our method, material utilization is one advantage. Another advantage is
our solution technology has the potential to be fabricated in a
continuous roll-to-roll process. Both are important breakthroughs in
terms of cost,” said Hou.

The team’s goal is to reach an
efficiency level of 15 to 20 percent. Yang predicts three to four years
before commercialization.

“As we continue to work on
enhancing the performance and efficiency of the solar cells, we also
look forward to opportunities to collaborate with industry in order to
develop this technology further. We hope this technology will lead to a
new green energy company in the U.S., especially here in California so
that it may also bring job opportunities to many who need it,” said
Yang.

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University of California – Los Angeles

 




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