Purdue researcher Rakesh Agrawal is leading work to develop solar cells that might be manufactured using special ink printed onto sheets of a supporting material. The approach could lead to new low-cost solar cells economically competitive with other energy technologies. Photo: Purdue University/Mark Simons |
Researchers are developing solar cells that might be
manufactured using special ink printed onto sheets of a supporting material, an approach that could lead
to new low-cost solar cells economically competitive with other energy
technologies.
The project, funded by the United States Department of
Energy, strives to achieve critical requirements not met by other solar
technologies: It should be able to be mass-produced at low cost and not limited
by the availability of materials.
“To date, none of the photovoltaic technologies
simultaneously meets all these constraints,” said Rakesh Agrawal, Purdue University’s Winthrop E. Stone
Distinguished Professor in the School
of Chemical Engineering.
The new solar cells hinge on developing an ink using tiny
“nanocrystals” made of a material called copper zinc tin sulfide, or
CZTS. Because the materials are abundantly available, the CZTS technology poses
no resource hurdles, he said.
Agrawal’s
laboratory was the first to make CZTS nanocrystals, which enabled creation of a
light-absorbing ink.
“The concept is that, once you have an ink you can
print photovoltaic cells very fast, so they become very inexpensive to
manufacture,” Agrawal said.
The project is led by Agrawal; Mark Lundstrom, Purdue’s Don and Carol Scifres Distinguished Professor of Electrical and Computer Engineering;
Ashraf Alam, a Purdue professor of electrical and computer engineering; and
Eric Stach, a researcher at Brookhaven National Laboratory.
To be competitive with other energy technologies, solar
cells must be capable of generating terawatts, or trillions of watts, at a cost
of 50 cents per peak watt of electricity.
“These goals can only be met with a truly
transformational technology,” Agrawal said.
The cells might be produced in a process that includes
creating the nanocrystals, formulating the ink and printing it on a flexible
supporting material. After the ink is applied, the cells are heated to about
500 C, a procedure called “sintering,” to fuse the nanoparticles
together.
The research involves advanced modeling, nanoelectronics
and materials science. The researchers will create models showing how to
precisely heat nanoparticles so that they are properly sintered, leading to
optical and electrical properties.
“Manufacturing requires expertise in chemical
engineering, but optimizing solar cell efficiency also requires electrical
engineering expertise,” Lundstrom said. “Putting these two viewpoints
together is what makes this project so interesting.”
The work is funded with a $750,000 grant as part of DOE’s SunShot Initiative, which
includes work to improve solar technologies.
Agrawal’s
laboratory has produced the second-highest efficiency CZTS-based solar cells,
at 8.4% efficiency, and the goal of the research is to reach 15% efficiency or
higher, he said.
Unlike some materials used for solar cells, the inks do
not break down quickly in sunlight, offering promise as a long-lasting,
economical photovoltaic technology.
CZTS solar cells were invented in the 1990s but have
required the use of a procedure called chemical vapor deposition. That process,
performed inside a chamber, is expensive and impractical for mass production.
Using inks would make it possible to deposit the material at a lower cost. One
challenge will be to produce CZTS nanocrystals that are free of impurities.
Another aim is to increase efficiency by controlling its sintering and
optoelectronic properties.
