This image, taken with a scanning electron microscope, shows a microchannel that was created using an ultrafast-pulsing laser. Credit: Purdue Univ. School of Mechanical Engineering image/Yung Shin
Researchers are developing a technology that aims to help
make solar cells more affordable and efficient by using a new manufacturing
method that employs an ultrafast pulsing laser.
The innovation may help to overcome two major obstacles
that hinder widespread adoption of solar cells: the need to reduce
manufacturing costs and increase the efficiency of converting sunlight into an
electric current, said Yung Shin, a professor of mechanical engineering and
director of Purdue Univ.’s Center for Laser-Based Manufacturing.
Critical to both are tiny microchannels needed to
interconnect a series of solar panels into an array capable of generating
useable amounts of power, he said. Conventional scribing methods, which create
the channels mechanically with a stylus, are slow, expensive, and produce
imperfect channels—impeding solar cells’ performance.
“Production costs of solar cells have been greatly
reduced by making them out of thin films instead of wafers, but it is difficult
to create high-quality microchannels in these thin films,” Shin said.
“The mechanical scribing methods in commercial use do not create
high-quality, well-defined channels. Although laser scribing has been studied
extensively, until now we haven’t been able to precisely control lasers to
accurately create the microchannels to the exacting specifications
The researchers hope to increase efficiency while cutting
cost using an ultrashort pulse laser to create the microchannels in thin-film
solar cells, he said.
The work, funded with a three-year, $425,000 grant from
the National Science Foundation, is led by Shin and Gary Cheng, an associate
professor of industrial engineering.
“The efficiency of solar cells depends largely on how
accurate your scribing of microchannels is,” Shin said. “If they are
made as accurately as possibly, efficiency goes up.”
Research results have shown that the fast-pulsing laser
accurately formed microchannels with precise depths and sharp boundaries. The
laser pulses last picoseconds. Because the pulses are so fleeting, the laser
does not cause heat damage to the thin film, removing material in precise
patterns in a process called cold ablation.
“It creates very clean microchannels on the surface
of each layer,” Shin said. “You can do this at very high speed,
meters per second, which is not possible with a mechanical scribe. This is very
tricky because the laser must be precisely controlled so that it penetrates
only one layer of the thin film at a time, and the layers are extremely thin.
You can do that with this kind of laser because you have a very precise control
of the depth, to about 10 to 20 nm.”
Traditional solar cells are flat and rigid, but emerging
thin-film solar cells are flexible, allowing them to be used as rooftop
shingles and tiles, building facades, or the glazing for skylights. Thin-film
solar cells account for about 20% of the photovoltaic market globally in terms
of watts generated. They are expected to account for 31% by 2013.
The researchers plan to establish the scientific basis for
the laser-ablation technique by the end of the three-year period.