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Published November 1, 2014 | Published
Journal Article Open

Multijunction solar cell efficiencies: effect of spectral window, optical environment and radiative coupling


Solar cell efficiency is maximized through multijunction architectures that minimize carrier thermalization and increase absorption. Previous proposals suggest that the maximum efficiency for a finite number of subcells is achieved for designs that optimize for light trapping over radiative coupling. We instead show that structures with radiative coupling and back reflectors for light trapping, e.g. spectrum-splitting cells, can achieve higher conversion efficiencies. We model a compatible geometry, the polyhedral specular reflector. We analyze and experimentally verify the effects of spectral window and radiative coupling on voltage and power. Our results indicate that radiative coupling with back reflectors leads to higher efficiencies than previously studied architectures for practical multijunction architectures (i.e., ≤20 subcells).

Additional Information

© 2014 The Royal Society of Chemistry. Received 3rd April 2014; Accepted 15th July 2014; First published online 04 Sep 2014. This work is part of the 'Light–Material Interactions in Energy Conversion' Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001293. C. N. Eisler was supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. The authors wish to thank E. Kosten and E. Warmann for invaluable discussion as well as B. Kayes and Alta Devices for providing the GaAs cells used in this study.

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