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ABSTRACT: We have fabricated an In0.52Al0.48As solar cell lattice-matched to InP with efficiency higher than 14% and maximum external quantum efficiency equal to 81%. High quality, dislocation-free InxAl1−xAs alloyed layers were used to fabricate the single junction solar cell. Photoluminescence of InxAl1−xAs showed good material quality and lifetime of over 200 ps. A high band gap In0.35Al0.65As window was used to increase light absorption within the p-n absorber layer and improve cell efficiency, despite strain. The InAlAs top cell reported here is a key building block for an InP-based three junction high efficiency solar cell consisting of InAlAs/InGaAsP/InGaAs lattice-matched to the substrate.
Applied Physics Letters 02/2011; 98(9):093502-093502-3. · 3.84 Impact Factor
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ABSTRACT: The high efficiency of multijunction concentrator cells has the potential to revolutionize the cost structure of photovoltaic electricity generation. Advances in the design of metamorphic subcells to reduce carrier recombination and increase voltage, wide-band-gap tunnel junctions capable of operating at high concentration, metamorphic buffers to transition from the substrate lattice constant to that of the epitaxial subcells, concentrator cell AR coating and grid design, and integration into 3-junction cells with current-matched subcells under the terrestrial spectrum have resulted in new heights in solar cell performance. A metamorphic Ga0.44In0.56P/Ga0.92In0.08As/ Ge 3-junction solar cell from this research has reached a record 40.7% efficiency at 240 suns, under the standard reporting spectrum for terrestrial concentrator cells (AM1.5 direct, low-AOD, 24.0 W/cm2, 25∘C), and experimental lattice-matched 3-junction cells have now also achieved over 40% efficiency, with 40.1% measured at 135 suns. This metamorphic 3-junction device is the first solar cell to reach over 40% in efficiency, and has the highest solar conversion efficiency for any type of photovoltaic cell developed to date. Solar cells with more junctions offer the potential for still higher efficiencies to be reached. Four-junction cells limited by radiative recombination can reach over 58% in principle, and practical 4-junction cell efficiencies over 46% are possible with the right combination of band gaps, taking into account series resistance and gridline shadowing. Many of the optimum band gaps for maximum energy conversion can be accessed with metamorphic semiconductor materials. The lower current in cells with 4 or more junctions, resulting in lower I2R resistive power loss, is a particularly significant advantage in concentrator PV systems. Prototype 4-junction terrestrial concentrator cells have been grown by metal-organic vapor-phase epitaxy, with preliminary measured efficiency of 35.7% under the AM1.5 direct terrestrial solar spectrum at 256 suns.
Advances in OptoElectronics. 01/2007;
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ABSTRACT: It is well known that the Ge subcell in multijunction GaInP/GaAs/Ge based solar cells produces a significantly higher photogenerated current (nearly 2x) than the other two subcells connected in series. The excess current is converted into heat, and as a result, increases the cell operating temperature. Because the solar cell efficiency decreases with higher temperatures, it is desirable to maintain a lower cell operating temperature. This can be achieved by rejecting a part of the incident sunlight that would otherwise be absorbed and converted into heat by the Ge subcell. For many space applications, coverglass incorporated with infrared reflecting (IRR) coatings can be applied to these solar cells for the purpose of lowering the cell operating temperature and/or improving the power output from the solar arrays. Achieving higher power output requires an appropriate IRR coating design that carefully balances the reduction in the cell absorptance against the Ge subcell current output. In this paper, this key issue is discussed. Also, preliminary IRR coating designs have been evaluated by applying them on high efficiency 3-junction solar cells, and the performance data are used to help predict optimal designs
Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on; 06/2006
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ABSTRACT: Large-area (26.6 cm<sup>2</sup>), thin GaInP/GaInAs/Ge triple-junction (TJ) solar cells with thickness as low as 50 mum were demonstrated. The average conversion efficiency of fifty thin TJ cells is 28 %, 1-sun AMO. The thin TJ cells showed nominal performance after welding of interconnects and flexibility test (50 mm curvature radius). Prototype coupons made with these thin TJ cells met flexible solar module bending requirement of 100 mm radius. The thin-cell coupons showed a specific power of 500 W/kg and a power density of 325 W/m<sup>2 </sup>. Ultra-thin (<10 mum thick) GaInP/Ga(In)As dual-junction (DJ) cells with size ranges from 0.5 to 26.6 cm<sup>2</sup> were fabricated using 4" Ge or GaAs wafers. Preliminary test data of the ultra-thin DJ cells showed a specific power of 2067 W/kg and a power density of 283 W/m<sup>2</sup>. The ultra-thin solar cells continued to demonstrate nominal performance after handling and flexing to a radius of 12 mm. Our results suggested that both the thin cell and the ultra-thin cell technologies can be incorporated with current and future solar cell designs
Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on; 06/2006
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ABSTRACT: Large area, crack-free GaInP/GaAs double junction solar cells were grown by metal organic chemical vapor deposition on Ge/Si templates fabricated using wafer bonding and ion implantation induced layer transfer. Photovoltaic performance of these devices was comparable to those grown on bulk epi-ready Ge, demonstrating the feasibility of alternative substrates fabricated via wafer bonding and layer transfer for growth of active devices on lattice mismatched substrates.
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Daniel C. Law,
R.R. King,
H. Yoon,
M.J. Archer,
A. Boca,
C.M. Fetzer,
S. Mesropian,
T. Isshiki,
M. Haddad,
K.M. Edmondson,
D. Bhusari,
J. Yen,
R.A. Sherif,
H.A. Atwater,
N.H. Karam
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ABSTRACT: Future terrestrial concentrator cells will likely feature four or more junctions. The better division of the solar spectrum and the lower current densities in these new multijunction cells reduce the resistive power loss (I2R) and provide a significant advantage in achieving higher efficiencies of 45–50%. The component subcells of these concentrator cells will likely utilize new technology pathways such as highly metamorphic materials, inverted crystal growth, direct-wafer bonding, and their combinations to achieve the desired bandgaps while maintaining excellent device material quality for optimal solar energy conversion. Here, we report preliminary results of two technical approaches: (1) metamorphic ∼1 eV GaInAs subcells in conjunction with an inverted growth approach and (2) multijunction cells on wafer-bonded, layer-transferred epitaxial templates.
Solar Energy Materials and Solar Cells.
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ABSTRACT: In this study, we report synthesis of large area (>2cm^2), crack-free GaAs and GaInP double heterostructures grown in a multi-junction solar cell-like structure by MOCVD. Initial solar cell data are also reported for GaInP top cells. These samples were grown on Ge/Si templates fabricated using wafer bonding and ion implantation induced layer transfer techniques. The double heterostructures exhibit radiative emission with uniform intensity and wavelength in regions not containing interfacial bubble defects. The minority carrier lifetime of ~1ns was estimated from photoluminescence decay measurements in both double heterostructures. We also report on the structural characteristics of heterostructures, determined via atomic force microscopy and transmission electron microscopy, and correlate these characteristics to the spatial variation of the minority carrier lifetime.
