From: University of California - Berkeley
Published February 19, 2009 09:26 AM
Cheaper Materials Could Be Key To Low-cost Solar Cells
Unconventional solar cell materials that are as abundant but much less
costly than silicon and other semiconductors in use today could
substantially reduce the cost of solar photovoltaics, according to a new
study from the Energy and Resources Group and the Department of Chemistry at
the University of California, Berkeley, and the Lawrence Berkeley National
Laboratory (LBNL).
These materials, some of which are highly abundant, could expand the
potential for solar cells to become a globally significant source of
low-carbon energy, the study authors said.
The analysis, which appeared online Feb. 13 in Environmental Science &
Technology, examines the two most pressing challenges to large-scale
deployment of solar photovoltaics as the world moves toward a carbon neutral
future: cost per kilowatt hour and total resource abundance. The UC Berkeley
study evaluated 23 promising semiconducting materials and discovered that 12
are abundant enough to meet or exceed annual worldwide energy demand. Of
those 12, nine have a significant raw material cost reduction over
traditional crystalline silicon, the most widely used photovoltaic material
in mass production today.
The work provides a roadmap for research into novel solar cell types
precisely when the U. S. Department of Energy and other funders plan to
expand their efforts to link new basic research to deployment efforts as
part of a national effort to greatly expand the use of clean energy,
according to Daniel Kammen, UC Berkeley professor of energy and resources
and director of the Renewable and Appropriate Energy Laboratory.
Kammen and colleagues Cyrus Wadia of LBNL and A. Paul Alivisatos of UC
Berkeley's Department of Chemistry embarked on an intensive research project
to explore the question of whether high-impact materials have been
overlooked or underdeveloped during the last several decades of solar cell
research.
"The reason we started looking at new materials is because people often
assume solar will be the dominant energy source of the future," said Wadia,
a post-doctoral researcher who spearheaded the research. "Because the sun is
the Earth's most reliable and plentiful resource, solar definitely has that
potential, but current solar technology may not get us there in a timeframe
that is meaningful, if at all. It's important to be optimistic, but when
considering the practicalities of a solar-dominated energy system, we must
turn our attention back to basic science research if we are to solve the
problem."
The most popular solar materials in use today are silicon and thin films
made of CdTe (cadmium telluride) and CIGS (copper indium gallium selenide).
While these materials have helped elevate solar to a major player in
renewable energy markets, they are still limited by manufacturing
challenges. Silicon is expensive to process and mass produce. Furthermore,
it has become increasingly difficult to mine enough silicon to meet
ever-growing consumer demand.
Thin films, while significantly less costly than silicon and easier to mass
produce, would rapidly deplete our natural resources if these technologies
were to scale to terawatt hours of annual manufacturing production. A
terawatt hour is a billion kilowatt hours.
"We believe in a portfolio of technologies and therefore continue to support
the commercial development of all photovoltaic technologies," Kammen said.
"Yet, what we've found is that some leading thin films may be difficult to
scale as high as global electricity consumption."
"It's not to say that these materials won't play a significant role," Wadia
added, "but rather, if our objective is to supply the majority of
electricity in this way, we must quickly consider alternative materials that
are Earth-abundant, non-toxic and cheap. These are the materials that can
get us to our goals more rapidly."
The team identified a large material extraction cost (cents/watt) gap
between leading thin film materials and a number of unconventional solar
cell candidates, including iron pyrite, copper sulfide and copper oxide.
They showed that iron pyrite is several orders of magnitude better than any
alternative on important metrics of both cost and abundance. In the report,
the team referenced some recent advances in nanoscale science to argue that
the modest efficiency losses of unconventional solar cell materials would be
offset by the potential for scaling up while saving significantly on
materials costs.
Finding an affordable electricity supply is essential for meeting basic
human needs, Kammen said, yet 30 percent of the world's population remains
without reliable or sufficient electrical energy. Scientific forecasts
predict that to meet the world's energy demands by 2050, global carbon
emissions would have to grow to levels of irreversible consequences.
"As the U.S. envisions a clean energy future consistent with the vision
outlined by President Obama, it is exciting that the range of promising
solar cell materials is expanding, ideally just as a national renewable
energy strategy takes shape," said Kammen, who is co-director of the
Berkeley Institute of the Environment and UC Berkeley's Class of 1935
Distinguished Chair of Energy.
The study by is by Wadia, Kammen and Alivisatos and will appear in the March
print issue of Environmental Science & Technology.
The work was supported by the U.S. Environmental Protection Agency, the
Energy Foundation, the Karsten Family Foundation Endowment of the Renewable
and Appropriate Energy Laboratory and the Class of 1935. |