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Research Papers

# Triple-Junction III–V Based Concentrator Solar Cells: Perspectives and Challenges

[+] Author and Article Information
C. Baur1

Fraunhofer Institut für Solare Energiesysteme, 79110 Freiburg, Germanycarsten.baur@esa.int

A. W. Bett, F. Dimroth, G. Siefer

Fraunhofer Institut für Solare Energiesysteme, 79110 Freiburg, Germany

M. Meusel

Fraunhofer Institut für Solare Energiesysteme, 79110 Freiburg, Germany, AZUR SPACE Solar Power GmbH, 74072 Heilbronn, Germany

W. Bensch, W. Köstler, G. Strobl

AZUR SPACE Solar Power GmbH, 74072 Heilbronn, Germany

1

Current address: European Space Agency, Keplerlaan 1, 2200AG Noordwijk, The Netherlands.

J. Sol. Energy Eng 129(3), 258-265 (Apr 20, 2006) (8 pages) doi:10.1115/1.2735346 History: Received November 08, 2005; Revised April 20, 2006

## Abstract

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.

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## Figures

Figure 1

Structure of a GaInP∕GaInAs∕Ge triple-junction solar cell. Different parts of the sun spectrum are absorbed in the different layers, i.e., the different subcells of the whole device. This results in a much more efficient use of the solar energy.

Figure 2

(Left) The “map” for the III–V semiconductor materials. Shown are bandgaps versus lattice constants for different material combinations. The broken vertical lines indicate the two approaches which are investigated in this paper: the “lattice matched” and the “lattice mismatched” or metamorphic approach. (Right) Limiting efficiencies of monolithic triple-junction cells depending on the band gaps of the top and the middle cell. The band gap of the bottom cell was set to 0.66eV—the band gap of germanium.

Figure 3

Comparison of EQE measurements for the lattice mismatched and the lattice matched GaInP∕GaInAs∕Ge triple-junction cell

Figure 4

Efficiency and fill factor of the European record concentrator cell. These high efficiencies were achieved by following the lattice mismatched approach which promises a higher efficiency potential than the lattice matched approach. The maximum efficiency of 35.2% was obtained at a concentration ratio of 600 suns.

Figure 5

I–V characteristic of the metamorphic structure at a concentration ratio of 850 suns. The dip in the I–V curve indicates that the current of the cell exceeds the peak tunneling current of one of the tunnel diodes.

Figure 6

Efficiency and fill factor of the best lattice matched concentrator cell. The maximum efficiency of 33.5% was obtained at a concentration ratio of over 1000 suns.

Figure 7

Evolution of the relative I–V parameters under one sun illumination of two (triangles and squares) dual-junction solar cells aged by application of a high (0.6A) forward-bias current

Figure 8

A wafer with two 8×4cm2 cells with cropped corners used for space applications and 184 concentrator cells (2mm in diameter). There is a 2mm exclusion zone around the perimeter of the wafer, where the epitaxial structure is not homogeneous and no cells can be placed.

Figure 9

Performance of a concentrator edge cell manufactured at RWE SSP. In the graph the FF (round symbols) and the efficiency (square symbols) versus concentration is given. A maximum efficiency of 32% under 620 suns is reached.

Figure 10

(Left) IV-MAPCON setup: automatic measurement tool for on-wafer characterization of multijunction concentrator solar cells. (Right) Up to eight cells can be contacted and measured at the same time.

Figure 11

Histogram of the VOC and the maximum power point PMPP. The results are taken from MAPCON measurements on four wafers with over 3700 concentrator cells altogether. The figures show a reasonable distribution. Please note that the x axis does not start from 0.

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