From time to time, the
good folks at Circuits Assembly magazine ask me to write a column for them
highlighting my thoughts on current industry issues. And because each of these
tends to focus on something I’m passionate about, I’ll always try to convert
these articles into blogs to keep you posted on what I’m thinking about when it
comes to our industry. Assuming you’re interested that is! Well, here goes; the
first in this series is on the subject of accuracy – something I know which is
close to all of our hearts.
One of the main issues
facing the solar industry is cell efficiency. I’d confidently go so far as to
say it’s key to solar’s medium and long-term success since it directly impacts
on cost per watt. Now, here comes the science: over 90% of PV cells are based on
silicon wafers, onto which light harvesting capacity is built using diffusion
techniques. On top of this, a grid of silver energy-collecting “fingers” and
bus bars is printed to route energy off the cell.
That’s
where our first challenge comes into play. Given that current industry practice
is to print all of these features on the light-gathering side, they effectively
shadow the underlying silicon substrate, rendering that real estate incapable
of doing what it was designed for.
One
obvious route to increased cell efficiencies is to give finer lines more
height, but the physical properties of printing screens, and the release
properties of standard silver screen printing pastes, effectively put a maximum
height on 50-60µm lines of about 15µm. “Not good enough!” I hear you say.
Agreed. So, one of the ways around this is to print the lines twice over, in a
Print-On-Print process that effectively doubles grid height, and therefore its
current-carrying capacity. Everyone’s a winner.
Providing
they do it right, of course. As we know from our experience with this procedure
for the semiconductor and biomedical sectors, repeatable accuracy is the key
here. Mainly because without it, this fine line work would simply be
impossible. Consider too that a high definition screen print relies on an
effective gasket between the substrate and the underside of the print screen,
so alignment must be perfect.
Wherever
you look in the solar cell and module assembly industry, repeatable print
alignment accuracy is at the heart of efficiency. If solar energy is to become
a widely available, cost-effective alternative energy source that excels on its
own merits, efficiency must increase while material costs and the cost-per-watt
needs to be driven down. Which is why efficiency is at the heart of our PV3000
metallization platform! It’s also why we’re edging closer to grid parity every
single day. See you there!
-
Darren Brown, Alternative Energy Business Manager.
Comments