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Mallinckrodt Baker FinalDR 18/12/09 09:29 Page 15
Scanning electron
microscope images
of a PSG on a textured
multicrystalline wafer;
PSG is visible as
crystalline material.
(Shown at different
magnifications –
indicated on each
current standard processes use a hydrofluoric acid opportunities to improve cell efficiencies is wafer
(HF) wet bath to remove phosphosilicate glass surface texturing. Currently, there are two wet
(PSG or phosglass) from the wafers, after which chemistry processes for multicrystalline wafer
the passivation layer – typically silicon nitride – is surface texturing used to reduce reflectivity, thus
applied. While this process does work for post- enhancing current output. One process involves a
emitter treatment, it does not yield the highest mixture of hydrofluoric acid and nitric acid – two
efficiency cell. toxic and hazardous chemicals that are not only
difficult to use, but may create safety concerns for
Mallinckrodt Baker, working with a leading solar plant personnel and require extensive (thus
research centre in Europe, developed a process to expensive) environmental and waste disposal
selectively etch excess phosphorous from emitters requirements when used in large quantities.
Issue VI 2009
prior to passivation. This revolutionary process
uses Mallinckrodt Baker’s award-winning PV-160 In addition, as wafers get thinner, the reaction is
solar cell surface modifier, an engineered wet too aggressive, leading to defect etching which
chemical solution that has been demonstrated to can impact yield. Current trends toward thinner
increase cell efficiency by 0.3 % absolute – a wafers suggest that this process using common
significant return on performance for a relatively bulk chemicals will be ineffective in the near term.
low-cost process enhancement. A modification to the process adds a surfactant to
the HF/HNO
bath. However, this process
The PV-160 solar cell surface modifier does more generates excess foam during the reaction,
than provide an optimized phosphorus removal necessitating frequent cleaning of the entire bath,
step; it fine-tunes the surface properties of the thus creating an environmental concern and
solar cell to contribute to cell efficiency. This is a forcing a costly line shutdown.
more advanced approach to post-emitter clean,
compared to using bulk HF dips. Another area Mallinckrodt Baker is currently developing
where engineered chemistries can offer engineered chemical additives which can improve
Mallinckrodt Baker is currently developing engineered
chemical additives which can improve the multicrystalline
texturing etch process
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