AZUR's latest lattice-matched triple junction space solar cell product has been designed for a high EOL efficiency by focusing the development on radiation hardness right from the beginning. These solar cells named as 3G30-Advanced show an efficiency of 29.5% at BOL and of 28.1% for EOL at 5E14 (1MeV) e-/cm2 (AM0, 1367 W/m2, 28°C). Meanwhile more than 125,000 cells of this cell type have been delivered to customers worldwide. Cell thicknesses of 150 μm, 80μm or even as thin as 20μm are available. Besides the standard size of 8×4 cm2 (with cropped corners) larger sizes such as 8×8cm2 and 12×6 cm2 are also available and provide equal performance. AZUR's next generation product will comprise a metamorphic 4-junction device targeting at 30% efficiency at EOL to be qualified in 2015/16. Furthermore, for arriving at more than 30% EOL efficiency with 4 - 6 junction solar cells in a subsequent step, appropriate lattice-matched 1eV dilute nitride materials, inversely grown solar cells and semiconductor bonded cells are studied in cooperation with external partners.

AZUR SPACE's current CPV product 3C40C is an advanced lattice-matched In0.50Ga0.50P/In0.01Ga0.99As/Ge triple junction (3J) solar cell. Recently, efficiencies up to 41.2% (450-600 x AM1.5d) have been confirmed for this 40%-class product. This kind of solar cell structure has now reached its practical efficiency limit and went into production in 2010. AZUR offers customized cell structures, regarding size and grid design, as well as anti-reflection coatings adapted to the individual CPV system. Integration grades from diced wafers up to assemblies, such as dense arrays, are available. Special features and production results for the 3C40C structure are presented in this work. In order to further push efficiencies beyond 42% AZUR has successfully transferred the upright metamorphic cell from Fraunhofer ISE and advances this concept now for production. First results on metamorphic 3J solar cells at AZUR SPACE and the actual potential of this concept will be discussed. A target efficiency of 42% seems to be realistic.

Present developments of the lattice-matched In0.50Ga0.50P/In0.01Ga0.99As/Ge triple-junction solar cell incorporating a high bandgap top cell achieve average efficiencies of up to 40%. Metamorphic cell structures will further raise efficiencies above 40%. Both developments reduce the cost for CPV by increasing the performance of today's CPV systems. In order to directly decrease cell costs a lean production process with optimized MOVPE cycle time is under investigation. Due to the high amount of cells per wafer, precise cell testing with high throughput is an important issue. For highest performance on the module level, the cell design needs to be adapted to the customers' needs according to the concentrating ratio, optics used and installation site. This work summarizes recent achievements in CPV development, cost analysis and customizing.

The epitaxial lift‐off (ELO) technique can be used to separate a III–V solar cell structure from its underlying GaAs or Ge substrate. ELO from 4‐inch Ge wafers is shown and 2‐inch GaAs wafer reuse after lift‐off is demonstrated without degradation in performance of the subsequent thin‐film GaAs solar cells that were retrieved from it. Since a basic wet chemical smoothing etch procedure appeared insufficient to remove all the surface contamination, wafer re‐preparation is done by a chemo‐mechanical polishing procedure. Copyright © 2010 John Wiley & Sons, Ltd.

In the early 1950s, Bell Laboratories in the USA investigated possible applications of silicon semiconductors in electronics. While improving transistors, Bell scientists Gerald Pearson and Calvin Fuller invented the first silicon solar cell. That first effort was further improved for applications in remote humid locations by Darryl Chapin [1]. The first experiment with silicon yielded an efficiency of 2.3%. Improvements with regard to the dopants, the metallic contacts to the p- and n-side and the application of an antireflection coating led to efficiencies of 4%. In 1954, cells with 6% efficiency could be reliably manufactured.

This paper gives a review of the research efforts at Fraunhofer ISE and the industrialization status at AZUR SPACE Solar Power in respect to III-V-based triple-junction solar cells. These cells are used in space environment and in terrestrial concentrator systems. AZUR space cells based on the lattice-matched concept have reached efficiencies of up to 30.6 %. Furthermore, they exhibit exceptional radiation hardness. EOL efficiencies of up to 25.8 % after irradiation with 1 x 10 15 1 MeV electrons/cm² have been reached. In regard to terrestrial application in concentrator systems Fraunhofer ISE has developed metamorphic triple-junction solar cells reaching an efficiency of 41.1 % at 454 suns. The development of a suitable buffer and tunnel diode structure for the metamorphic growth approach is discussed in this paper.

GaInP/GaAs/Ge triple-junction cells became commercially available in the 90ies by US manufacturers. Today these triple cells are the most common power generator in space due to their high efficiency and radiation hardness. In Europe, AZUR SPACE and the Fraunhofer ISE have teamed up in the development and industrialisation of III-V multi-junction solar cells. The 2 generation of a European III-V multi-junction cell, the AZUR 3G-ID2* 28% class, has been qualified and is now in production. It shows a state-of-the-art BOL efficiency of 28% (AM0, 1367 W/m, T=28°C) and has a very radiation hard design with a remaining factor of 88% (10 1MeV electrons/cm) resulting in an excellent EOL efficiency of 24.6%. The next generation 30%-class cell will also be based on the lattice-matched GaInP/GaInAs/Ge triple cell concept. For future generations of space cells various concepts are under investigation, such as 4J, 5J and 6J cells as well as cell concepts based on metamorphic growth. Additionally a terrestrial market for III-V multi-junction concentrator cells is emerging. AZUR SPACE is presently offering a 35% efficient lattice-matched triple-junction concentrator cell (3C-35%). This rising interest in concentrators promises exciting times for III-V and a renewed synergy between space and terrestrial.

This paper gives a review of the work performed in the framework of the EC-funded project FULLSPECTRUM aiming for higher photovoltaic (PV) conversion efficiencies by investigating GaInP∕GaInAs∕Ge triple-junction concentrator solar cells. Lattice mismatched structures reached efficiencies beyond 35% at 600 sun concentration level. These cells are now ready to enter the terrestrial PV market. The perspectives and challenges associated with the market introduction of these cells are addressed. Specifically issues of reliability and on-wafer characterization are discussed. A new characterization tool MAPCON was developed and is presented.

The use of fully European triple junction (TJ) GaAs solar cell is an added value for the power generation system. Further more high efficiency TJ solar cells represent the best solution in terms of "delivered power/ mass ratio". The qualification campaigns, performed by RWE at solar cell level and by Galileo Avionica at assembly and sub-assembly level, show that all the components, material and processes used on the PVA are reliable for the ADM Aeolus mission. In the whole solar generator system design has demonstrated, during the analyses and tests phases, the ability to meet (and, in some cases, to exceed) the stringent mission requirements as long duration lifetime (high temperature long duration test on integral diode) and power demand

Besides the efficiency, the radiation hardness of a solar cell is one of the key parameters for space applications. Today's GaInP/GaInAs/Ge triple-junction solar cells achieve remaining factors for pmpp of 88 % after 1 MeV electron irradiation at a fluence of 1015 cm-2. The degradation is dominated by the GaInAs middle cell. New solar cell structures with 5 pn-junctions have been developed to further improve the radiation resistance and excellent remaining factors of 95 % for Voc and 93 % for pmpp are reported in this paper. The structure consists of AlGaInP, GaInP, AlGaInAs, GaInAs and Ge active pn-junctions. A 1.1 mum thin Ga0.99In0.01As 4th subcell with a radiation hard layer structure was developed. This subcell has now a remaining factor for Jsc of 95 %. This proves the high radiation hardness of the 5-junction space solar cell concept

The first generation of fully European triple junction solar cells is of 27% class (RWE3G-27%class) with an area of 8cmx4cm minus two cropped corners and an ID2 integral by-pass diode concept in which the adjacent cell is protected. An additional by-pass diode concept for extreme temperature applications is available by using a new structure of external Si diode. It is planned to use this triple junction GaAs cell (RWE3G27%class) for several European satellite projects such as Aeolus, Pleiades, Herschel (one section) and Proba 2. The paper reports the production experience and the output with this 27% class triple cell in the framework of these projects. The second generation is of 28% class (RWE3G28%class), with the same configuration and area. This cell has an improved EOL performance of R(Pmax) (1E15-1MeV electrons/cm 2 ) ≥0.85. Details on qualification testing and first production experience for this cell type will be presented. Finally the current development results for the third generation 29% to 30% class cell with further improved EOL performance of R(Pmax) = 0.88 and monolithic by-pass diode will be reported together with a road map of further potential development using cell structures made from III-V material system.

The Fraunhofer ISE has developed a characterization tool called spectrometric characterization. In this paper we discuss that this tool is extremely powerful to characterize triple-junction (3J) EOL cells. The current-mismatch of the subcells can be determined and the performance for current-matched subcells can be predicted. Additionally, lattice-matched AlGaInP/GaInP/AlGaInAs/GaInAs/Ge quintuple-junction (5J) cells are being developed at Fraunhofer ISE as a possible next-generation of space solar cells. This material combination aims at the same BOL efficiency as state-of-the-art 3J cells but higher EOL efficiency. Based on spectral response measurements it will be demonstrated that the 5J cells do in fact show a higher radiation hardness compared to the 3J cell.

Multi-junction solar cells made from III-V compound semiconductors are the highest efficient photovoltaic devices today. Different solar cell structures have been developed for space as well as terrestrial concentrator applications in a close collaboration between the Fraunhofer ISE and RWE-SSP in Germany. Efficiencies up to 29.1% (AM0) have been recently achieved for a 30.2 cm/sup 2/ GaInP/GaInAs/Ge device at RWE-SSP. Triple-junction solar cells with remaining factors up to 88 % after irradiation with 1 MeV electrons at a fluence of 10/sup 15/ cm/sup -2/ have been demonstrated at Fraunhofer ISE. Multi-junction solar cells with 5 and even 6 junctions for even higher radiation hardness are under development. On the other hand lattice mismatched triple-junction solar cells are an excellent solution for terrestrial concentrator applications. Efficiencies up to 35.2 % at a concentration ratio of 443-637 (AM1.5d, low AOD) have been obtained.

Fraunhofer ISE and RWE SSP have developed a lattice-matched GaInP/GaInAs/Ge triple-junction space solar cell with a begin-of-life efficiency of 28.0 % (AM0, 1367 W/m, T=28°C) and excellent remaining factors of 90.5% after 5x10 and 86.6% after 1x10 1 MeV electron irradiation per cm. This was accomplished by systematic optimisation of the middle cell design for maximum end-of-life performance. This new triple cell, the RWE3G-28%, constitutes the second generation of fully European triple-junction space solar cells which is now going into qualification. Future concepts such as light weight solar cells, five and six-junction cells and the use of metamorphic materials are under investigation.