Sep 26 2008
Five Star Technologies, the leader in fine particle dispersions for functional inks, announced the availability of ElectroSperse(TM) S-series solar inks for use in crystalline silicon photovoltaic cells. Five Star's S-500 series, 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 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.
To be introduced at Solar Power International 2008 in San Diego on October 13-16, the inks are aimed at solving one of the most challenging issues facing solar cell performance: maintaining consistent electrical contact with emitter layers.
"Our customers are telling us that assurance of consistent contact could improve manufacturing yields significantly and boost overall cell efficiency by as much as one full percentage point," says Tim Fahey, Vice President, Business Development, of Five Star Technologies. "Our patented hydrodynamic cavitation process enables us to produce inks and pastes with unmatched silver and glass particle uniformity and particle sizes in the low to sub-micron range. That, in turn, gives users the ability to screen print much finer lines and to achieve more consistent emitter contact."
According to recent tests conducted by the Georgia Institute of Technology, monocrystalline cells produced with S-540 demonstrated:
- Cell efficiencies of 17.4%.
- Fill factors approaching 78%.
- Virtually no variation in performance at firing profiles differing by as much as 20 degrees C.
- Almost ideal n-factor values, implying extremely low leakage current.
The broader range of firing profiles, says Fahey, should help solve a common solar cell manufacturing problem. "Current commercial pastes have a narrow process window, and cell manufacturers quite often have to modify the firing profile for different lots of material due to inconsistent dispersion in traditional pastes," he says. "ElectroSperse inks and pastes are easily adaptable to individual user processing conditions."
Initial grades of the inks are intended for screen printing applications, but Five Star says it can control rheology to match a variety of printing processes, including non-contact dispensing approaches. For all processes, the ability to print finer dimensions should give cell designers greater flexibility in adding more efficient collection configurations.