Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs

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The development of compositionally graded buffer layers (CGBs) with enhanced transparency would enable novel five and six junction solar cells, with efficiencies approaching 50% under high concentration. We demonstrate highly transparent grades between the GaAs and InP lattice constants on both A- and B-miscut GaAs substrates, employing Al xGayIn1-x- yAs and highly Se-doped Burstein-Moss (BM) shifted GaxIn 1-xP. Transparency to >810 and >890 nm wavelengths is demonstrated with BM-shifted GaxIn1-xP on B-miscut substrates and Al xGayIn1-x- yAs/GaxIn1-xP(Se) combined grades on A-miscut substrates, respectively. 0.74 eV GaInAs solar cells grown on these transparent CGBs exhibit WOC= 0.41, V15mA/cm2, performance comparable with the state-of-the-art GaxIn1- xP grade employed in the four-junction-inverted metamorphic multijunction (IMM) cell. A GaAs/0.74 eV GaInAs tandem cell was grown with a transparent BM-shifted GaxIn1-xP CGB to verify the CGB performance in a multijunction device structure. Quantum efficiency measurements indicate that the CGB is completely transparent to photons below the GaAs bandedge, validating its use in 4-6 junction IMM devices with a single-graded buffer. This tandem represents a highly efficient two-junction band gap combination, achieving 29.6% ± 1.2% efficiency under the AM1.5 global spectrum, demonstrating how the additional transparency enables new device structures.

Original languageAmerican English
Article number7742321
Pages (from-to)347-353
Number of pages7
JournalIEEE Journal of Photovoltaics
Issue number1
StatePublished - Jan 2017

Bibliographical note

Publisher Copyright:
© 2011-2012 IEEE.

NREL Publication Number

  • NREL/JA-5J00-66503


  • III-V semiconductor materials
  • Photovoltaic cells
  • semiconductor device doping
  • semiconductor epitaxial layers


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