A new circular contact grid pattern, designed for solar cells in a mechanical stack

Applying a genuine circular contact grid pattern to the constituent solar cells in a mechanical stack, makes the lower cell(s) relatively insensitive to any rotational misalignment with respect to the higher cell(s), because this generates relatively small secondary shadowing losses. Such a grid differs from the regular (radial) grid often applied to round solar cells, in that it has a lot less radial lines and many more concentric rings, to the effect that the rings now take on the role of fingers, while the lines serve as busbars. For a 16 mm² n-on-p GaAs cell and irradiances ranging from 1 to 1000 suns, optimised grids of this new circular design were compared to equivalent radial, square and inverted square grids. The circular grid was found to suffer less power loss than a comparable radial grid at low concentration ratios. At high concentration ratios, cells with a radial grid performed better, while comparable square and inverted square grids perform better over the entire range of concentration ratios. The effects of secondary shadowing were calculated for a range of translational misalignments, as well as rotational misalignment angles Δθ, for the four patterns optimised for an irradiance of 500 suns. The former only showed relatively small differences between the grids, but the latter confirmed the strength of the circular grid, since its shadowing loss hardly increases with increasing Δθ, while that of the other three patterns quickly approaches a doubling. When these secondary shadowing effects are taken into account, it is demonstrated that the application of a circular grid is a viable approach to minimise the losses associated with the rotational misalignment of mechanically stacked solar cells.