Development of Mechanically Stacked Multi-Junction Solar Cells Applying Thin, One-side Contacted III-V Cells

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 mm 2 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 ∆θ, 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 ∆θ, 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.

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Mechanically stacked solar cells for concentrator photovoltaics

Mathews

O’Mahony²,

Yu³

et al. 2011

REPQJ

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Access to the full text of the published version may require a subscription. Item AbstractThe power output of dual-junction mechanically stacked solar cells comprising different sub-cell materials in a terrestrial concentrating photovoltaic module has been evaluated. The ideal bandgap combination of both cells in a stack was found using EtaOpt. A combination of 1.4 eV and 0.7 eV has been found to produce the highest photovoltaic conversion efficiency under the AM1.5 Direct Solar Spectrum with x500 concentration. As EtaOpt does not consider the absorption profile of solar cell materials; the practical power output per unit area of a dual junction mechanically stacked solar cell has been modelled considering the optical absorption co-efficients and thicknesses of the individual solar cells. The model considered a GaAs top cell and a Ge, GaSb, Ga 0.47 In 0.53 As or Si bottom cell. It was found that GaSb gives the highest power contribution as a bottom cell in a dual junction configuration followed by Ge and GaInAs. While the additional power provided by a Si bottom cell is less than these it remains a suitable candidate for a bottom cell owing to its lower cost.

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Development of Mechanically Stacked Multi-Junction Solar Cells Applying Thin, One-side Contacted III-V Cells

Cited by 3 publications

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Optimization of multi-junction solar cell performance at infrared light by application of thin film Si:Ge solar cell

Optimization of multi-junction solar cell performance at infrared light by application of thin film Si:Ge solar cell

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

Mechanically stacked solar cells for concentrator photovoltaics

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