Bandgap Engineering in High-Efficiency Multijunction Concentrator Cells

Research output: Contribution to conferencePaper


This paper discusses semiconductor device research paths under investigation with the aim of reaching the milestone efficiency of 40%. A cost analysis shows that achieving very high cell efficiencies is crucial for the realization of cost-effective photovoltaics, because of the strongly leveraging effect of efficiency on module packaging and balance-of systems costs. Lattice-matched (LM) GaInP/GaInAs/ Ge 3-junction cells have achieved the highest independently confirmed efficiency at 175 suns, 25 deg C, of 37.3% under the standard AM1.5D, low-AOD terrestrial spectrum. Lattice-mismatched, or metamorphic (MM), materials offer still higher potential efficiencies, if the crystal quality can be maintained. Theoretical efficiencies well over 50% are possible for a MM GaInP/ 1.17-eV GaInAs/ Ge3-junction cell limited by radiative recombination at 500 suns. The bandgap - open circuit voltage offset, (Eg/q) - Voc, is used as a valuable theoretical and experimental tool to characterize multijunction cells with subcell bandgaps ranging from 0.7 to 2.1 eV. Experimental results are presented for prototype 6-junction cells employing an active~1.1-eV dilute nitride GaInNAs subcell, withactive-area efficiency greater than 23% and over 5.3 V open-circuit voltage under the 1-sun AM0 space spectrum. Such cell designs have theoretical efficiencies under the terrestrial spectrum at 500 suns concentration exceeding 55% efficiency, even for lattice-matched designs.
Original languageAmerican English
Number of pages6
StatePublished - 2005
EventInternational Conference on Solar Concentrators for the Generation of Electricity or Hydrogen - Scottsdale, Arizona
Duration: 1 May 20055 May 2005


ConferenceInternational Conference on Solar Concentrators for the Generation of Electricity or Hydrogen
CityScottsdale, Arizona

NREL Publication Number

  • NREL/CP-520-38689


  • multijunction concentrator solar cells
  • photovoltaics (PV)
  • PV
  • semiconductors


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