Product Briefing Outline: Five Star Technologies has introduced the ‘ElectroSperse’ 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.
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. The need for consistent contact could improve manufacturing yields significantly and boost overall cell efficiency by as much as one full percentage point, according to Five Star.
Solution: Patented hydrodynamic cavitation process enables Five Star to produce inks and pastes with 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% and fill factors approaching 78%. The company claims that there was virtually no variation in performance at firing profiles differing by as much as 20° C.
Applications: 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.
Platform: Five Star produces the ElectroSperse series of inks and pastes as well as a wide range of precision dispersions. ElectroSperse thick film conductor pastes are rheologically stable, easy-to-process materials, ideally suited for direct printing of fine features. Screen printable grades can be printed to features as small as 50 µm. Grades designed for extrusion and digital print processes are achieving even smaller print features, enabling replacement of thin film processing.
Availability: October 2008 onwards.