Scientists at Purdue University [press
release] have completed another significant work aimed at improving the
efficiency of solar panels. Researchers used lasers to scribe
microchannels improving the efficiency of inter-cell power transfer, and the
overall efficiency of a mounted multi-cell thin-film solar cell mat.
I. Why Solar?
The Sun is one of the Earth's two great potential
energy sources (nuclear power being the other). While it may be
convenient to store solar energy in a portable form via technologies like algae
biofuel, ultimately nuclear and solar
will be the primary drivers of a Space Age high-tech nation.
Thirty years ago solar power existed, but it was
virtually useless for any practical purpose due to sky-high costs. Today
it's still a bit too expensive to serve as a comfortable replacement for coal,
but costs have plunged to the level where it can be contemplated as a
contributor to overall national power generation. Within twenty or thirty years
we may arrive at a point where solar is among the most cost-effective power
But to get there the slow and arduous pace of
iterative improvements must be maintained.
II. What's in a Connector?
Much work has gone into improving
the base efficiency of solar cells and find optimal materials for the cells. Purdue University's Center for Laser-Based
Manufacturing instead looked at another source of efficiency and power
loss -- cell interconnects.
Typically solar cells are manufactured similar to
microprocessors, using vapor deposition techniques on a semiconductor
substrate. Metal interconnects were used to link cells.
But more recently thin film solar cells have been
taking off. Thin films can be made to be flexible
and transparent. And they use less material, making them potentially
cheaper. However, they require new processes to create. Instead of
bulky metal interconnects, they use tiny interconnects called
"microchannels" to electrically connect individual cells allowing
thin film cell arrays to be created.
Traditionally these interconnects were produced by
a mechanical stylus. The result frequently featured efficiency dropping
imperfections and took a great deal of time, raising production costs.
Past studies had suggested using lasers as a
replacement. The Purdue team reports being the first to successfully
execute this approach, using an ultra-precise "ultrashort pulse
Yung Shin [profile], a
Purdue professor of mechanical engineering who led the study remarks, "The
efficiency of solar cells depends largely on how accurate your scribing of
microchannels is. If they are made as accurately as possibly, efficiency goes
Using the cutting edge laser, the team cut away
chunks of material using a process called "cold ablation".
Where similar efforts had failed in the past was that the cutting process
was too slow and heated the material, creating defects and damage.
The ultra-fast laser, though, creates pulses
lasting only picoseconds. It chips along creating a damage-free
ultra-smooth, sharply defined microchannel.
Describes Professor Shin, "It creates very
clean microchannels on the surface of each layer. 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 nanometers."
III. What's Next for Pulse-Laser
Currently thin film cells account for 20 percent
of the global market in terms of watts generated. In two years -- by 2013
-- that total is expected to rise to 31 percent.
Thus you can expect to see this microchanneling
technique to be incorporated into production designs sooner rather than later.
The researchers have already completed the most
important phase of their project, funded by a $425,000 USD National Science
Foundation (NSF) grant -- getting the basic process working.
Now they're continuing research to try to better
understand how the fast pulse method works on a microscopic level. That
could yield clues as to how to refine the technique even further. It
would also likely allow the team to patent their technique, removing the final
roadblock to commercialization.
The team has published [abstract]
a paper on their work in the Proceedings of the 2011 NSF Engineering
Research and Innovation Conference in January.
The paper's authors include Professor Shin; Gary
Cheng [profile], an industrial
engineering professor; and graduate students Wenqian Hu, Martin Yi Zhang
and Seunghyun Lee.
The total project is expected to last three years
and will hopefully continue to offer rewarding breakthroughs in terms of
improved efficiency and reduced production costs.
DailyTech is in the process of contacting the
authors of this work about further details about potential commercialization.