I
recently posted a version of my Circuits Assembly column that outlined the
importance of repeatable accuracy to cell efficiency. If you read it, you’ll
know I feel strongly about this issue! Hope I didn’t scare you... Well, I’ve
since written an update to this in the magazine so thought I’d bring you, our
faithful blog readers, the next chapter of this particular story...
In
my previous post I mentioned that the PV industry is investing heavily in
reducing the width of the silver conductor grid that is screen printed onto the
front side of the cell and that effectively shadows the precious
light-capturing real estate below. With current feature widths at 100-120µm,
this shadow effect has been reduced as much as it can be using existing PV
processes. So, where next?
Finer line work, although it may not sound overly
complicated to anyone active in electronics production, requires a step change
in technique and approach. One solution is to print the conductors twice over,
effectively doubling their height. This is achieved using Print-on-Print (PoP)
technology, and enables us to print features down to 50-60µm wide without
compromising their precious conductive capacity.
PoP
capability also comes into its own in the Selective Etching cell structuring
technique. If you’re unsure what this is, it’s where an etchant is
screenprinted onto the cell's surface in a grid pattern identical to that of
the conductor grid. When it heats up, the etchant removes the cell's
non-reflective top layer and exposes the silicon underneath, so that in the
subsequent print pass, the silver grid comes into direct contact with the
cell's active energy-transforming layer.
In
similar vein, the Selective Emitter process aims to boost efficiencies by
printing extra n-type dopant in a pattern mirroring that of the collection
grid. With more and more attention being paid to these new PoP processes it’s
clear that, if not already, repeatable accuracy is soon to become the name of
the game for manufacturers of solar cells and modules.
This
will put even more pressure on us to ensure that our processes are accurate,
and repeatably, reliably so. Sophisticated, powerful metrics such as the
Process Capability Index (Cpk), long used by the semiconductor and circuit
board assembly sectors, will soon become critical for the PV industry too, as
manufacturers strive to maximise end of line yields, reliability, and bottom
line performance in an increasingly demanding marketplace. Here at DEK, we say
bring it on! We’re ready and waiting to help our customers realise new levels
of efficiency – for even higher returns.
Stay tuned folks; I’ll update you on our progress over
the coming months.
-
Darren Brown, Alternative Energy Business Manager.
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