Photovoltaics

Metal Fingers on Grain Boundaries in Multicrystalline Silicon Solar Cells

Rita Ebner¹, Michael Radike¹, Viktor Schlosser², Johann Summhammer¹

¹Atominstitut of the Austrian Universities, Stadionallee 2, A-1020 Wien, Austria
²Institute of Material Physics, University of Vienna, A-1090 Wien, Austria.

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ABSTRACT

We have developed a method of applying a net-like finger grid to the front of multicrystalline (mc) silicon solar cells, which lies mainly on the grain boundaries (grain- boundary-oriented-finger GBOF grid). This net has no busbars. It is drawn by a plotter, using screen printing paste dispensed through a fine tube. The power output of cells contacted in this manner has been tested in a statistical study of pairs and triplets of cells of size 100 x 100mm² (Bayer) and l03 x 103mm² (Eurosolare). In the pairs study, pairs of neighbouring wafers of the original ingot were processed into solar cells. One wafer received a GBOF grid, the other got the same grid rotated by 90°, and so had little coverage of grain boundaries. In the study of triplets the third wafer of each triplet was equipped with a standard H-pattern of the same shading as the GBOF grid. In the pairs study, we find that under approximately standard conditions there is an 89% chance that the GBOF grid increases power output over cells with an identical, but 90° rotated, grid, the most probable increase being 2.6%. The triplets study shows that there is an 87% chance that the GBOF grid increases power output over cells with the standard H-pattern, the most probable increase being 2.5%.

KEY WORDS:

multicrystalline silicon; grain boundary; ohmic loss; recombination; contact resistance; solar cell metallization; finger grid; screen painting

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