Multijunction III-V concentrator cells of several different types have demonstrated solar conversion efficiency over 40% since 2006, and represent the only third-generation photovoltaic technology to enter commercial power generation markets so far. The next stage of solar cell efficiency improvement, from 40% to 50%-efficient production cells, is perhaps the most important yet, since it is in this range that concentrator photovoltaic (CPV) systems can become the lowest cost option for solar electricity, competing with conventional power generation without government subsidies. The impact of 40% and 50% cell efficiency on cost-effective geographic regions for CPV systems is calculated in the continental US, Europe, and North Africa. We take a systematic look at a progression of multijunction cell architectures that will take us up to 50% efficiency, using modeling grounded in well-characterized solar cell materials systems of today's 40% cells, discussing the theoretical, materials science, and manufacturing considerations for the most promising approaches. The effects of varying solar spectrum and current balance on energy production in 4-junction, 5-junction, and 6-junction terrestrial concentrator cells are shown to be noticeable, but are far outweighed by the increased efficiency of these advanced cell designs. Production efficiency distributions of the last five generations of terrestrial concentrator solar cells are discussed. Experimental results are shown for a highly manufacturable, upright metamorphic 3-junction GaInP/GaInAs/Ge solar cell with 41.6% efficiency independently confirmed at 484 suns (48.4 W/cm 2 ) (AM1.5D, ASTM G173-03, 25 C), the highest demonstrated for a cell of this type requiring a single metalorganic vapor-phase epitaxy growth run.
The strain relaxation behavior of Si 0.82 Ge 0.18 films on silicon-on-insulator ͑SOI͒ substrates was investigated for films grown beyond the critical thickness and strain-relaxed during growth and metastable films, grown beyond the critical thickness, which relaxed during subsequent thermal annealing. The thickness of the top silicon layer of the SOI substrate was varied over a range from 40 nm to 10 m. In all cases, the SiGe film relaxation occurred via the nucleation and propagation of dislocations with the same onset of film relaxation and same relaxation rate for both SOI and bulk Si substrates. The SOI substrate does not serve as a compliant substrate but does alter the dislocation structure and motion. The buried amorphous oxide layer in the SOI substrate leads to the relaxation of the dislocation strain field through the removal of the dislocation line tension. This removal of the dislocation line tension drives dislocation motion and leads to the development of strain in the thin Si layer of the SOI substrate. Models of this dislocation behavior for SiGe growth on the SOI substrate are presented and calculation of the equilibrium strain of the thin Si substrate layer closely fits the measured strain of several SOI substrates. The article addresses the implications of the modified dislocation structure and kinetics for film relaxation on SOI substrates.
The surface morphology and structure of AlN deposited by metal organic vapor phase epitaxy (MOVPE) on Si (111) at growth temperatures ranging from 825 to 1175°C was investigated. Transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) techniques were used to study the resulting film structure. Growth at high temperatures but less than ~1100°C, resulted in a wire texture with some degree of in-plane alignment with ( ) / /( ) 0001 111
High efficiency Inverted Metamorphic (IMM) multi-junction solar cells have been under development at Spectrolab for use in space and near space applications This paper reviews the present state-of-the-art of this technology at Spectrolab with an emphasis on performance characterization data at in-flight operating conditions. Large area IMM3J and IMM4J solar cells with 1X AM0 efficiency greater than 32% at 28 °C have been fabricated and characterized. Degradation factors after exposure to 1 MeV electron irradiation for both IMM3J and IMM4J technologies is presented. A coupon utilizing large area, IMM solar cells has been assembled and subjected to thermal cycling. Pre-and post thermal cycling data have been collected. Preliminary temperature cycling data indicate that a small coupon populated with strings of these cells suffered no degradation.
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