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Title: Optically enhanced photon recycling in mechanically stacked multijunction solar cells

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 1000 W/m2 and ~ 42% under the direct spectrum at ~100 suns. As a result, eliminating the series resistance is the key challenge for further improving the concentrator cells.
 [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. Politecnica de Madrid (Spain)
  3. Arizona State Univ., Tempe, AZ (United States)
  4. Boeing-Spectrolab, Sylmar, CA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 2156-3381
Grant/Contract Number:
Accepted Manuscript
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 6; Journal Issue: 1; Related Information: IEEE Journal of Photovoltaics; Journal ID: ISSN 2156-3381
Research Org:
NREL (National Renewable Energy Laboratory (NREL), Golden, CO (United States))
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE four-junction; GaInP; GaAs; GaInAsP; GaInAs; InP; subcell voltage; efficiency; series resistance; multijunction solar cell; mechanical stack; photon recycling; luminescent coupling; III-V solar cell