Inorganic surface ligands enable facile electron transport between quantum dots and opened novel opportunities for using nanostructures in solar cells. |
A team of researchers from the University of Chicago and the U.S.
Department of Energy’s (DOE) Argonne National Laboratory has
demonstrated a method that could produce cheaper semiconductor layers
for solar cells.
The
inorganic nanocrystal arrays, created by spraying a new type of
colloidal “ink”, have excellent electron mobility and could be a step
towards addressing fundamental problems with current solar technology.
“With
today’s solar technology, if you want to get significant amounts of
electricity, you’d have to build huge installations over many square
miles,” said team leader Dmitri Talapin, who holds a joint appointment
with Argonne and the university. But because current solar cells are
based on silicon, which is costly and environmentally unfriendly to
manufacture, they aren’t cost-effective over large areas. The challenge
for scientists is to find a way to manufacture large numbers of solar
cells that are both efficient and cheap.
One
possibility to make solar cells more economically would be to “print”
them, similar to how newspapers are printed. “You’d use a kind of ‘ink,’
stamped on using a roll technology with a flexible substrate,” Talapin
said.
Solar
cells have several layers of different materials stacked on top of each
other. The team focused on the most important layer, which captures
sunlight and converts it into electricity. This layer, made of a
semiconducting material, must be able to transform light into negative
and positive electrical charges but also easily release them to move
further along the material to generate electrical current.
Many
methods to grow the semiconductors need high temperatures, but a
cheaper approach would be to make them in solution. This, however,
requires a precursor that is soluble.
Arrays of quantum dots allow fabrication of solar cells by printing and other inexpensive techniques. |
The
team developed that precursor using quantum dots. Small grains of
semiconductors, suspended in a liquid, are “glued” together with new
molecules called “molecular metal chalcogenide complexes.” The process
heats the material to about 200 degrees Celsius, much lower than the
temperatures required for manufacturing silicon solar cells. The result
is a layer of material with good semiconducting properties.
“The
electron mobility for this material is an order of magnitude higher
than previously reported for any solution-based method,” Talapin said.
The
team used intense X-rays from the DOE Office of Science’s Advanced
Photon Source at Argonne to watch as the semiconductor film was created.
“We believe that we could make very competitive solar cells with these nanoparticles,” Talapin said.
Talapin
said the success played on the complementary partnership between the
University of Chicago and Argonne’s Center for Nanoscale Materials.
“At
the university we have great students and postdocs who can do a lot of
the theoretical chemistry, which requires a lot of manpower,” Talapin
said, “but Argonne is a fantastic place to do research that requires
sophisticated instrumentation and infrastructure.”
The
research was supported by the Office of Naval Research and a National
Science Foundation CAREER award. Work at the Center for Nanoscale
Materials and the Advanced Photon Source was supported by the DOE’s
Office of Science.
Study abstract: “Band-like transport, high electron mobility and high photoconductivity in all-inorganic nanocrystal arrays”
