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Using a specially constructed thin-film deposition and
scanning tunneling microscope system, researchers at JILA have
imaged nanometer-sized particulates that may be reducing the
efficiency of certain photovoltaic films.
Under a contract with the Department of Energy's National
Renewable Energy Laboratory, the researchers are studying the
growth of hydrogenated silicon films. These are light-sensitive
films that can be grown over large surfaces. They are used in
making solar energy panels and large flat-panel displays. The
efficiency of the film in converting light into electrical
current is best with homogenous, very thin films about 500 nm
thick.
STM images (above) were made by the JILA researchers after
an amorphous, hydrogenated silicon film was grown using a
technique called chemical vapor deposition. These images show
that 3-5 nm size particles form in the vapor and bond to the film
surface. As a new layer of hydrogen and silicon atoms deposits on
the surface, these clumps cause voids within the film in the same
way that a ball under an otherwise smooth blanket creates air
pockets.
Solar panel manufacturers also working on the NREL project
will use the JILA results to try to improve their processing
methods. JILA is jointly operated by NIST and the University of
Colorado.
Contact: Alan Gallagher, (303) 492-3936.
