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

Abstract

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. Here, we demonstrate highly transparent grades between the GaAs and InP lattice constants on both A- and B-miscut GaAs substrates, employing Al xGayIn 1-x-yAs and highly Se-doped Burstein-Moss (BM) shifted Ga xIn 1-xP. Transparency to >810 and >890 nm wavelengths is demonstrated with BM-shifted Ga xIn 1-xP on B-miscut substrates and Al xGayIn 1-x-yAs/Ga xIn 1-xP(Se) combined grades on A-miscut substrates, respectively. 0.74 eV GaInAs solar cells grown on these transparent CGBs exhibit Woc = 0.41 V at mA/ cm 2, performance comparable with the state-of-the-art Ga xIn 1-xP grade employed in the four-junction-inverted metamorphic multijunction (IMM) cell. A GaAs/0.74cV GaInAs tandem cell was grown with a transparent BM-shifted Ga xIn 1-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. Furthermore, this tandem represents a highly efficient two-junction band gap combination, achieving 29.6% ± 1.2% efficiency under the AM1.5 global spectrum, demonstratingmore » how the additional transparency enables new device structures.« less

Authors:
 [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1342505
Report Number(s):
NREL/JA-5J00-66503
Journal ID: ISSN 2156-3381
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2156-3381
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; photovoltaic cells; III-V semiconductor materials; semiconductor epitaxial layers; semiconductor device doping

Citation Formats

Schulte, Kevin L., France, Ryan M., and Geisz, John F. Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs. United States: N. p., 2016. Web. doi:10.1109/JPHOTOV.2016.2619183.
Schulte, Kevin L., France, Ryan M., & Geisz, John F. Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs. United States. doi:10.1109/JPHOTOV.2016.2619183.
Schulte, Kevin L., France, Ryan M., and Geisz, John F. 2016. "Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs". United States. doi:10.1109/JPHOTOV.2016.2619183. https://www.osti.gov/servlets/purl/1342505.
@article{osti_1342505,
title = {Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs},
author = {Schulte, Kevin L. and France, Ryan M. and Geisz, John F.},
abstractNote = {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. Here, we demonstrate highly transparent grades between the GaAs and InP lattice constants on both A- and B-miscut GaAs substrates, employing AlxGayIn1-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 AlxGayIn1-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 V at mA/ cm2, performance comparable with the state-of-the-art GaxIn1-xP grade employed in the four-junction-inverted metamorphic multijunction (IMM) cell. A GaAs/0.74cV 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. Furthermore, 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.},
doi = {10.1109/JPHOTOV.2016.2619183},
journal = {IEEE Journal of Photovoltaics},
number = 1,
volume = 7,
place = {United States},
year = 2016,
month =
}

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  • Unrelaxed InAs{sub 1-x}Sb{sub x} layers with lattice constants up to 2.1% larger than that of GaSb substrates were grown by molecular beam epitaxy on GaInSb and AlGaInSb compositionally graded buffer layers. The topmost section of the buffers was unrelaxed but strained. The in-plane lattice constant of the top buffer layer was grown to be equal to the lattice constant of unrelaxed and unstrained InAs{sub 1-x}Sb{sub x} with given X. The InAs{sub 0.56}Sb{sub 0.44} layers demonstrate photoluminescence peak at 9.4 {mu}m at 150 K. The minority carrier lifetime measured at 77 K for InAs{sub 0.8}Sb{sub 0.2} was {tau} = 250 ns.
  • In this Letter, we report on the growth and properties of relaxed, compositionally graded Al{sub x}Ga{sub 1-x}N buffer layers on freestanding semipolar (2021) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 10{sup 6}/cm{sup 2} as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.
  • The properties of InAs{sub x}P{sub 1−x} compositionally graded buffers grown by metal organic chemical vapor deposition are investigated. We report the effects of strain gradient (ε/thickness), growth temperature, and strain initiation sequence (gradual or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes increased dislocation densities (>10{sup 6}/cm{sup 2}) and tilt of the epi-layer (>0.1°). A method of abrupt strain initiation is proposed which can result in dislocation densities as low as 1.01 × 10{sup 5} cm{sup −2} for films graded from the InP lattice constant to InAs{sub 0.15}P{sub 0.85}.more » A model for a two-energy level dislocation nucleation system is proposed based on our results.« less