ElectroSperse™ S-Series Solar Inks
ElectroSperse™ S-series solar inks are designed for use as front side contacts and back surface field (BSF)
in the manufacture of silicon solar cells. S-series inks, made using Five Star's patented cavitation process,
represent a significant advancement in solar inks for silicon cells. ElectroSperse S-500 silver-based conductive
inks will allow solar cell makers to lay out front side grid lines as narrow as 80-100 microns – much thinner
than the 120-175-micron width of conventional contacts. The S-500 inks are also far superior to conventional
inks in dispersion uniformity, thus creating more consistent contact to emitter layers. The Company’s S-600
products – low-bow, lead-free, aluminum-based pastes, intended for back surface field layers – have been designed
to co-fire at temperatures compatible with the S-500 silver inks and thus simplify the latter’s adoption.
S-500 Front Side Contact Inks
- Fine line printing for higher efficiency designs
- Greater uniformity for consistent emitter contact
- Dense, highly conductive lines
- Demonstrated improvements in fill factor and efficiency
S-600 Back Surface Field (BSF) Aluminum Inks
- Excellent back surface field and Voc
- Low bow for use with thin wafers
- Pb and Cd-free
- Co-fireable with all S-500 products
The table above illustrates representative data prepared at Georgia Institute of Technology for monocrystalline silicon
cells using ElectroSperse S-540 silver paste and S-680 aluminum BSF paste. The results demonstrate the exceptional cell
efficiency and high fill factors that can be achieved with S-series inks. The consistency of performance is further shown
by the stable lot-to-lot results.
Uniform Dispersion Delivers More Consistent Performance
The ElectroSperse S-series represents a significant advancement in solar inks for silicon cells. Solar inks are sophisticated
blends of metal and electronic glass particles dispersed in an organic medium suitable for screen printing. After deposition,
they are processed at high temperature for only a matter of seconds. Because the high temperature firing is completed in just
a few seconds, the particle sizes of the powders and the quality of the dispersion are critical for the process to work. The
figure below depicts the basic construction and dimensions of a crystalline Si solar cell. The front side contacts are screen
printed directly on top of the ARC layer. Due to the very thin nature of the ARC and emitter layer regions, the kinetics of
the contact firing and the uniformity of the Ag paste formulation at the ARC interface are absolutely critical to the cell
performance.
Si Solar Cell Cross Section
As shown in the figure, with conventional inks, the complex penetration of glass through the AR coating and subsequent
interaction with the silicon emitter is simply not uniform enough to make consistent contact with the emitters. The advanced
process technology employed by Five Star produces inks that are far superior in dispersion uniformity, thus creating more
consistent contact to the emitter layer. The result is the dependable cell-to-cell performance of ElectroSperse S-series pastes.
Fine Line Printing Enables Advanced Designs
The ElectroSperse S-series is enabling a key advance in solar cells design – front side contact grids with much finer line
dimensions. The fine conductor lines which are screen printed onto the front side of the solar cell are typically 120-175
microns wide due to the limitations of the inks and the screen printing technology used in mass production. Solar cell
efficiency models and laboratory data agree that cell efficiency could be enhanced 5-9% if a somewhat higher number of lines
with reduced width were used.
Unfortunately, these advanced designs have been blocked by the limitations of current generation solar inks and screen
printer techniques. Current ink technology cannot produce the dispersion quality and particle size control required for
next-generation solar cell technology. Five Star’s unique cavitation technology overcomes these barriers by creating inks
capable of superior line definition.
ElectroSperse S-540 Product Information Sheet
ElectroSperse S-680 Product Information Sheet
Technical Bulletin-ElectroSperse S-540 and S-680 Processing Guidelines
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