Optically Enhanced Photon Recycling in Mechanically Stacked Multijunction Solar Cells

Myles A. Steiner, John F. Geisz, J. Scott Ward, Ivan Garcia, Daniel J. Friedman, Richard R. King, Philip T. Chiu, Ryan M. France, Anna Duda, Waldo J. Olavarria, Michelle Young, Sarah R. Kurtz

Research output: Contribution to journalArticlepeer-review

35 Scopus Citations


Multijunction solar cells can be fabricated by mechanically bonding together component cells that are grown separately. Here, we present four-junction four-terminal mechanical stacks composed of GaInP/GaAs tandems grown on GaAs substrates and GaInAsP/GaInAs tandems grown on InP substrates. The component cells were bonded together with a low-index transparent epoxy that acts as an angularly selective reflector to the GaAs bandedge luminescence, while simultaneously transmitting nearly all of the subbandgap light. As determined by electroluminescence measurements and optical modeling, the GaAs subcell demonstrates a higher internal radiative limit and, thus, higher subcell voltage, compared with GaAs subcells without the epoxy reflector. The best cells demonstrate 38.8 ± 1.0% efficiency under the global spectrum at 1000W/m2 and ∼42% under the direct spectrum at ∼100 suns. Eliminating the series resistance is the key challenge for further improving the concentrator cells.

Original languageAmerican English
Article number7322173
Pages (from-to)358-365
Number of pages8
JournalIEEE Journal of Photovoltaics
Issue number1
StatePublished - Jan 2016

Bibliographical note

Publisher Copyright:
© 2011-2012 IEEE.

NREL Publication Number

  • NREL/JA-5J00-64445


  • efficiency
  • four-junction
  • GaInAsP
  • gallium arsenide (GaAs)
  • gallium indium arsenide (GaInAs)
  • gallium indium phosphide (GaInP)
  • InP
  • series resistance
  • subcell voltage


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