Lasers, for more efficient solar cells
Lasers, for more efficient solar cells
“Sometime in the coming years,
renewable energy sources, such as
solar energy, will be competitive,
even without subsidization,”
predicts Dr. Arnold Gillner,
head of the microtechnology
department at the Fraunhofer
Institute for Laser Technology
(ILT) in Aachen, Germany.
Together with his team at
Fraunhofer, Gillner is developing
laser technologies now that will
allow faster, better, and cheaper
production of solar cells in the
future.
“Lasers work quickly, precisely, and
The tiny holes in the wafer—their the back, there is no shading caused by
without contact. In other words, they are
diameter only 50 micrometers—open up the electrodes, and the degree of efficiency
an ideal tool for manufacturing fragile
undreamt-of possibilities for solar cell increases. With this technique, it may one
solar cells,” said Gillner. “In fact, lasers are
developers. “Previously, the electrical day be possible to use unpurified “dirty”
already being used in production today, but
contacts were arranged on the top of the silicon to manufacture solar cells that have
there is still considerable room for process
cells,” said Gillner. “The holes make it poorer electrical properties, but that are
optimization.”
possible to move the contacts to the back, cheaper.
The ILT laser system drills more than
with the advantage that the electrodes, Drilling holes into silicon cells is only
3,000 holes within one second. Because
which currently act as a dark grid to absorb one of many laser applications in solar cell
it is not possible to move the laser source
light, disappear. And so the energy yield manufacturing. In the EU project Solasys—
at this speed, the experts have developed
increases. Next Generation Solar Cell and Module
optimized manufacturing systems which
“The goal is a degree of efficiency of Laser Processing Systems—an international
guide and focus the light beam at the
20 percent in industrially-produced emitter research team is currently developing new
required points.
wrap-through (EWT) cells, with a yield of technologies that will allow production to
“We are currently experimenting with
one-third more than classic silicon cells.” be optimized in the future. ILT in Aachen
various laser sources and optical systems,”
The design principle itself remains is coordinating the six million euro project.
Gillner explained. “Our goal is to increase
unchanged: In the semi-conductor layer, “We are working on new methods
the performance to 10,000 holes a second.
light particles, or photons, produce that make the doping of semiconductors,
This is the speed that must be reached
negative electrons and positive holes, each the drilling and the surface structuring
in order to drill 10,000 to 20,000 holes
of which then wanders to the oppositely of silicon, the edge isolation of the cells,
into a wafer within the cycle time of the
poled electrodes. The contacts for anodes and the soldering of the modules more
production machines.”
and cathodes in the EWT cells are all on economical,” Gillner explained. For
example, “selective laser
soldering” makes it
possible to improve
the rejection rates
and quality of the
contacting, and so
reduce manufacturing
costs. Until now,
the electrodes were
mechanically pressed
onto the cells, and
then heated in an
oven.
“But silicon cells
often break during
this process,” Gillner
16 – Global Solar Technology – July/August 2009
www.globalsolartechnology.com
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