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Concentrator and Space Applications of High-Efficiency Solar Cells-Recent Developments

Description: GaInP/GaAs cells invented and developed at NREL have achieved world-record efficiencies. We estimate that their production for space applications has grown to > $100 million/yr. Approximately 300 MW/yr of 1000X terrestrial concentrator cells could be fabricated with the existing manufacturing capacity at a cost of about 21{cents}/Wp. A resurgence of interest in terrestrial PV concentrators, together with the strength of the III-V space-solar-cell industry, indicate that III-V cells are also attractive for terrestrial applications.
Date: October 26, 1998
Creator: Kurtz, S. R. & Friedman, D. J.
Partner: UNT Libraries Government Documents Department

Enhanced-Depletion-Width GaInNAs Solar Cells Grown by Molecular-Beam Epitaxy

Description: The 3-junction, GaInP2/GaAs/Ge solar cell is a non-optimized structure due to excess light falling on the Ge junction. Because of this, a fourth junction inserted between the GaAs and Ge subcells could use the excess light and provide an increase in device efficiency. Unfortunately, the leading candidate material, GaInNAs, suffers from very low minority-carrier diffusion lengths compared to its parent compound, GaAs. These low diffusion lengths do not allow for the collection of adequate current to keep the overall 4-junction structure current matched. If the currents generated from the GaInNAs subcell are increased, the possibility exists for practical efficiencies of greater than 40% from this structure.
Date: January 1, 2005
Creator: Ptak, A. J. & Friedman, D. J.
Partner: UNT Libraries Government Documents Department

Exploration of GaInT1P and Related T1-Containing III-V Alloys for Photovoltaics

Description: This paper discusses the results of an attempt to grow GaInTlP for application as a 1-eV material for the third junction of a GaInP/GaAs/3rd-junction high-efficiency solar cell. Although early indications from the literature were promising, we are unable to produce crystalline homogeneous material, and so we conclude that this material is not a promising candidate for such applications as photovoltaics.
Date: November 2, 1998
Creator: Friedman, D.J.; Kibbler, A.E. & Kurtz, S.R.
Partner: UNT Libraries Government Documents Department

Photoconductive properties of GaAs{sub 1{minus}x}N{sub x} double heterostructures as a function of excitation wavelength

Description: The ternary semiconductor GaAs{sub 1{minus}x}N{sub x} with 0 < x < 0.3 can be grown epitaxially on GaAs and has a very large bowing coefficient. The alloy bandgap can be reduced to about 1.0 eV with about a 3% nitrogen addition. In this work, the authors measured the internal spectral response and recombination lifetime of a number of alloys using the ultra-high frequency photoconductive decay (UHFPCD) method. The data shows that the photoconductive excitation spectra of the GaAs{sub 0.97}N{sub 0.03} alloy shows a gradual increase in response through the absorption edge near E{sub g}. This contrasts with most direct bandgap semiconductors that show a steep onset of photoresponse at E{sub g}. The recombination lifetimes frequently are much longer than expected from radiative recombination and often exceeded 1.0{mu}s. The data were analyzed in terms of a band model that includes large potential fluctuations in the conduction band due to the random distribution of nitrogen atoms in the alloy.
Date: May 22, 2000
Creator: Ahrenkiel, R. K.; Mascarenhas, A.; Johnston, S. W.; Zhang, Y.; Friedman, D. J. & Vernon, S. M.
Partner: UNT Libraries Government Documents Department

New Materials for Future Generations of III-V Solar Cells

Description: Three- and four-junction III-V devices are proposed for ultrahigh-efficiency solar cells using a new 1-eV material lattice-matched to GaAs, namely, GaInNAs. We demonstrate working prototypes of a GaInNAs-based solar cell lattice-matched to GaAs with photoresponse down to 1 eV. Under the AM1.5 direct spectrum with all the light higher in energy than the GaAs band gap filtered out, the prototypes grown with base doping of about 10{sup 17} cm-3 have open-circuit voltages ranging from 0.35 to 0.44 V, short-circuit current densities of 1.8 mA/cm2, and fill factors from 61% to 66%. To improve on the current record-efficiency tandem GaInP/GaAs solar cell by adding a GaInNAs junction, the short-circuit current density of this 1-eV cell must be significantly increased. Because these low short-circuit current densities are due to short diffusion lengths, we have demonstrated a depletion-width-enhanced variation of one of the prototype devices that trades off decreased voltage for increased photocurrent, with a short-circuit current density of 7.4 mA/cm2 and an open-circuit voltage of 0.28 V.
Date: October 6, 1998
Creator: Geisz, J. F.; Friedman, D. J.; Olson, J. M.; Kramer, C.; Kibbler, A. & Kurtz, S. R.
Partner: UNT Libraries Government Documents Department

Profiling the Built-In Electrical Potential in III-V Multijunction Solar Cells (Poster)

Description: We have observed three electrical potentials at the top, tunneling, and bottom junctions of GnInP{sub 2}/GaAs tandem-junction solar cells, by performing the UHV-SKPM measurement. The effect of laser illumination was avoided by using GaAs laser with photon energy of 1.4 eV for the AFM operation. We also observed higher potentials at the atomic steps than on the terraces for both p-type GaInP{sub 2} epitaxial layer and p-type GaAs substrate, and found that the potential at steps of GaAs substrate depends on the step directions.
Date: May 1, 2006
Creator: Jiang, C.-S.; Friedman, D. J.; Moutinho, H. R. & Al-Jassim, M. M.
Partner: UNT Libraries Government Documents Department

Profiling the Built-in Electrical Potential in III-V Multijunction Solar Cells: Preprint

Description: We report on a direct measurement of the electrical potential on cross-sections of GaInP2/GaAs multiple-junction solar cells by using an ultrahigh-vacuum scanning Kelvin probe microscope (UHV-SKPM). The UHV-SKPM allows us to measure the potential without air molecules being adsorbed on the cross-sectional surface. Moreover, it uses a GaAs laser with photon energy of 1.4 eV for the atomic force microscope (AFM) operation. This eliminated the light-absorption-induced bottom-junction flattening and top-junction enhancement, which happened in our previous potential measurement using a 1.85-eV laser for the AFM operation. Three potentials were measured at the top, tunneling, and bottom junctions. Values of the potentials are smaller than the potentials in the bulk. This indicates that the Fermi level on the UHV-cleaved (110) surface was pinned, presumably due to defects upon cleaving. We also observed higher potentials at atomic steps than on the terraces for both GaInP2 epitaxial layer and GaAs substrate. Combining scanning tunneling microscopy (STM) and SKPM measurements, we found that the potential height at steps of the GaAs substrate depends on the step direction, which is probably a direct result of unbalanced cations and anions at the steps.
Date: May 1, 2006
Creator: Jiang, C.-S.; Friedman, D. J.; Moutinho, H. R. & Al-Jassim, M. M.
Partner: UNT Libraries Government Documents Department

0.7-eV GaInAs Junction for a GaInP/GaAs/GaInAs(1-eV)/GaInAs(0.7-eV) Four-Junction Solar Cell: Preprint

Description: We discuss recent developments in III-V multijunction solar cells, focusing on adding a fourth junction to the Ga0.5In0.5P/GaAs/Ga0.75In0.25As inverted three-junction cell. This cell, grown inverted on GaAs so that the lattice-mismatched Ga0.75In0.25As third junction is the last one grown, has demonstrated 38% efficiency, and 40% is likely in the near future. To achieve still further gains, a lower-bandgap GaxIn1-xAs fourth junction could be added to the three-junction structure for a four-junction cell whose efficiency could exceed 45% under concentration. Here, we present the initial development of the GaxIn1-xAs fourth junction. Junctions of various bandgaps ranging from 0.88 to 0.73 eV were grown, in order to study the effect of the different amounts of lattice mismatch. At a bandgap of 0.88 eV, junctions were obtained with very encouraging {approx}80% quantum efficiency, 57% fill factor, and 0.36 eV open-circuit voltage. The device performance degrades with decreasing bandgap (i.e., increasing lattice mismatch). We model the four-junction device efficiency vs. fourth junction bandgap to show that an 0.7-eV fourth-junction bandgap, while optimal if it could be achieved in practice, is not necessary; an 0.9-eV bandgap would still permit significant gains in multijunction cell efficiency while being easier to achieve than the lower-bandgap junction.
Date: May 1, 2006
Creator: Friedman, D. J.; Geisz, J. F.; Norman, A. G.; Wanlass, M. W. & Kurtz, S. R.
Partner: UNT Libraries Government Documents Department

Examination of 1D Solar Cell Model Limitations Using 3D SPICE Modeling: Preprint

Description: To examine the limitations of one-dimensional (1D) solar cell modeling, 3D SPICE-based modeling is used to examine in detail the validity of the 1D assumptions as a function of sheet resistance for a model cell. The internal voltages and current densities produced by this modeling give additional insight into the differences between the 1D and 3D models.
Date: June 1, 2012
Creator: McMahon, W. E.; Olson, J. M.; Geisz, J. F. & Friedman, D. J.
Partner: UNT Libraries Government Documents Department

PV Manufacturing R&D Project Status and Accomplishments under 'In-Line Diagnostics and Intelligent Processing' and 'Yield, Durability and Reliability': Preprint

Description: The PV Manufacturing R&D (PVMR&D) Project conducts cost-shared research and development programs with U.S. PV industry partners. There are currently two active industry partnership activities. ''In-line Diagnostics and Intelligent Processing'', launched in 2002, supports development of new in-line diagnostics and monitoring with real-time feedback for optimal process control and increased yield in the fabrication of PV modules, systems, and other system components. ''Yield, Durability and Reliability'', launched in late 2004, supports enhancement of PV module, system component, and complete system reliability in high-volume manufacturing. A second key undertaking of the PVMR&D Project is the collection and analysis of module production cost-capacity metrics for the U.S. PV industry. In the period from 1992 through 2005, the average module manufacturing cost in 2005 dollars fell 54% (5.7% annualized) to $2.74/Wp, and the capacity increased 18.6-fold (25% annualized) to 253 MW/yr. An experience curve analysis gives progress ratios of 87% and 81%, respectively, for U.S. silicon and thin-film module production.
Date: May 1, 2006
Creator: Friedman, D. J.; Mitchell, R. L.; Keyes, B. M.; Bower, W. I.; King, R. & Mazer, J.
Partner: UNT Libraries Government Documents Department

Optical Investigation of GaNAs

Description: A systematic study of the energy and time-resolved photoluminescence of GaInP/GaNxAs1-x double heterostructures has been performed for 0=x=1.3%. A large temperature-dependent optical-bowing coefficient (about 20-25 eV) is observed and the bandgap variation with temperature is found to depend on the nitrogen content. Finally, the minority-carrier lifetime is not simply related to the nitrogen content. Instead, the recombination rate is proportional to the majority-carrier concentration for x=0.3% and the carbon concentration for x=0.3%.
Date: September 28, 1998
Creator: Keyes, B. M.; Geisz, J. F.; Dippo, P. C.; Reedy, R.; Kramer, C.; Friedman, D. J. et al.
Partner: UNT Libraries Government Documents Department

Hydrazine N Source for Growth of GaInNAs for Solar Cells

Description: We evaluate hydrazine (Hy) as a nitrogen precursor source for the growth of GaNAs and GaInNAs for application in 1-eV solar cells lattice-matched to GaAs, and compare it to the more commonly used dimethylhydrazine (DMHy). The incorporation efficiency of N into the GaNAs alloy is found to be one to two orders of magnitude higher with Hy than with DMHy. This high N incorporation makes convenient the growth of GaNAs at higher growth temperatures, Tg=650 C, and arsine flows, AsH3/III=44, than are generally possible with the use of DMHy. GaInNAs and GaNAs solar cells are grown under these growth conditions and compared to a GaAs cell grown under the same conditions to determine the extent to which the poor minority-carrier properties routinely observed for the N-containing material can be attributed to the growth conditions. Finally, the background carrier concentrations for Hy- and DMHy-grown material are compared, and little difference is found between the two sources..
Date: May 25, 1999
Creator: Friedman, D. J.; Geisz, G. F.; Kurtz, S. R.; Norman, A. G. (National Renewable Energy Laboratory) & Yeh, Y. C. M. (TECSTAR, Inc.)
Partner: UNT Libraries Government Documents Department

On-Sun Comparison of GaInP2/GaAs Tandem Cells with Top-Cell Thickness Varied

Description: This study compares the on-sun performance of a set of GaInP2/GaAs tandem cells with different GaInP2 top-cell thicknesses. Because high-efficiency III-V cells are best suited to concentrating photovoltaic (CPV) applications, the cells were mounted on a two-axis tracker with the incident sunlight collimated to exclude all except the direct beam. Current-voltage (I-V) curves were taken throughout the course of several days, along with the direct solar spectrum. Our two major conclusions are: (1) GaInP2/GaAs tandem cells designed for an ''air mass 1.5 global'' (AM 1.5G) or a ''low aerosol optical depth'' (Low AOD) spectrum perform the best, and (2) a simple device model using the measured direct spectra as an input gives the same result. These results are equally valid for GaInP2/GaAs/Ge triple-junction cells.
Date: January 1, 2005
Creator: McMahon, W. E.; Emery, K. A.; Friedman, D. J.; Ottoson, L.; Young, M. S.; Ward, J. S. et al.
Partner: UNT Libraries Government Documents Department

Passivation of Interfaces in High-Efficiency Photovoltaic Devices

Description: Solar cells made from III-V materials have achieved efficiencies greater than 30%. Effectively ideal passivation plays an important role in achieving these high efficiencies. Standard modeling techniques are applied to Ga0.5In0.5P solar cells to show the effects of passivation. Accurate knowledge of the absorption coefficient is essential (see appendix). Although ultralow (<2 cm/s) interface recombination velocities have been reported, in practice, it is difficult to achieve such low recombination velocities in solar cells because the doping levels are high and because of accidental incorporation of impurities and dopant diffusion. Examples are given of how dopant diffusion can both help and hinder interface passivation, and of how incorporation of oxygen or hydrogen can cause problems.
Date: May 13, 1999
Creator: Kurtz, S. R.; Olson, J. M.; Friedman, D. J.; Geisz, J. F.; Kibbler, A. E. (National Renewable Energy Laboratory) & Bertness, K. A. (NIST, Boulder, Colorado)
Partner: UNT Libraries Government Documents Department

CuPt-B ordered microstructures in GaInP and GaInAs films

Description: The authors examine CuPt-B atomic sublattice ordering in Ga{sub 0.51}In{sub 0.49}P (GaInP) and Ga{sub 0.47}In{sub 0.53}As (GaInAs) III-V alloy films grown by atmospheric- and low-pressure metalorganic chemical vapor deposition on singular and vicinal (001) substrates. The influences of growth conditions and substrate miscut on double- and single-variant ordered microstructures are investigated using transmission electron microscopy (TEM). Relatively thick (>1-2 {micro}m) double-variant ordered GaInP and GaInAs films show complementary superdomain formation. Single-variant ordered films on <111>B-miscut substrates contain single-phase domains, separated by antiphase boundaries (APBs). The appearance of APBs in TEM dark-field images is anticipated from electron diffraction theory.
Date: March 1, 2000
Creator: Ahrenkiel, S. P.; Jones, K. M.; Matson, R. J.; Al-Jassim, M. M.; Zhang, Y.; Mascarenhas, A. et al.
Partner: UNT Libraries Government Documents Department

Nitrogen-Induced Modification of the Electronic Structure of Group III-N-V Alloys: Preprint

Description: Incorporation of nitrogen in conventional III-V compound semiconductors to form III-N-V alloys leads to a splitting of the conduction band into two nonparabolic sub-bands. The splitting can be described in terms of an anticrossing interaction between a narrow band of localized nitrogen states and the extended conduction-band states of the semiconductor matrix. The downward shift of the lower sub-band edge is responsible for the N-induced reduction of the fundamental band-gap energy. The modification of the conduction-band structure profoundly affects the optical and electrical properties of the III-N-V alloys.
Date: April 1, 1999
Creator: Walukiewicz, W.; Shan, W.; Ager III, J. W.; Chamberlin, D. R.; Haller, E. E. (Lawrence Berkeley National Laboratory); Geisz, J. F. et al.
Partner: UNT Libraries Government Documents Department

Next Generation Thin Films for Photovoltaics: InGaAsN; Preprint

Description: A new semiconductor alloy system, InGaAsN, has been identified as a candidate material for multi-junction solar cells having efficiencies greater than 40%. The introduction of small amounts of nitrogen ({approx}2%) into the InGaAs alloy system greatly reduces the band gap energy, with reductions approaching 0.4 eV for 2% nitrogen content! With the appropriate ratio of indium to nitrogen concentrations, InGaAsN can be lattice matched to GaAs.
Date: April 1, 1999
Creator: Jones, E. D.; Allerman, A. A.; Klem, J. F.; Kurtz, S.R.; Modine, N. R. (Sandia National Laboratories); Friedman, D. J. et al.
Partner: UNT Libraries Government Documents Department

Inverted GaInP/(In)GaAs/InGaAs Triple-Junction Solar Cells with Low-Stress Metamorphic Bottom Junctions: Preprint

Description: We demonstrate high efficiency performance in two ultra-thin, Ge-free III-V semiconductor triple-junction solar cell device designs grown in an inverted configuration. Low-stress metamorphic junctions were engineered to achieve excellent photovoltaic performance with less than 3 x 106 cm-2 threading dislocations. The first design with band gaps of 1.83/1.40/1.00 eV, containing a single metamorphic junction, achieved 33.8% and 39.2% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 131 suns, respectively. The second design with band gaps of 1.83/1.34/0.89 eV, containing two metamorphic junctions achieved 33.2% and 40.1% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 143 suns, respectively.
Date: May 1, 2008
Creator: Geisz, J. F.; Kurtz, S. R.; Wanlass, M. W.; Ward, J. S.; Duda, A.; Friedman, D. J. et al.
Partner: UNT Libraries Government Documents Department