Metal fingers on grain boundaries in multicrystalline silicon solar cells

We have developed a method of applying a net-like finger grid to the front of multi-crystalline (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 100 mm(2) (Bayer) and 103 x 103 mm(2) (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 90degrees, 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 90degrees 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%. Copyright (C) 2002 John Wiley Sons, Ltd.