3 years ago

Multijunction solar cell design revisited: disruption of current matching by atmospheric absorption bands

Multijunction solar cell design revisited: disruption of current matching by atmospheric absorption bands
Daniel J. Friedman, John F. Geisz, William E. McMahon
This paper re-examines the impact of atmospheric absorption bands on series-connected multijunction cell design, motivated by the numerous local efficiency maxima that appear as the number of junctions is increased. Some of the local maxima are related to the bottom subcell bandgap and are already well understood: As the bottom subcell bandgap is varied, a local efficiency maximum is produced wherever the bottom cell bandgap crosses an atmospheric absorption band. The optimal cell designs at these local maxima are generally current matched, such that all subcells have nearly the same short-circuit current. Here, we systematically describe additional local maxima that occur wherever an upper subcell bandgap encounters an atmospheric absorption band. These local maxima are not current matched and become more prevalent as the number of junctions increases, complicating the solution space for five-junction and six-junction designs. A systematic framework for describing this complexity is developed, and implications for numerical convergence are discussed. Copyright © 2017 John Wiley & Sons, Ltd. This paper re-examines the impact of atmospheric absorption bands on series-connected multijunction (MJ) cell design, motivated by the complexity of solution space confronted as the number of subcells increases. All of this complexity can be characterised and understood using a taxonomy of ‘MJ types’ based upon the position of subcell bandgaps with respect to the ‘transmission bands’ between absorption bands in terrestrial spectra. Once this is performed, the full set of local efficiency optima can be quickly identified and described for arbitrarily large numbers of junctions, and deviations from the ‘current matching’ rule can be more easily characterised and understood.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/pip.2899

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