Single-junction GaAs Solar Cells Research Articles

Characterization of Ge-on-Si virtual substrates and single junction GaAs solar cells

A virtual substrate consisting of a Ge layer grown directly on Si without an intervening SiGe graded layer is characterized. The nominally 100% Ge overlayer is fully relaxed and contains a small amount (3%) of unintentional Si. A dislocation density of 108 cm−2 is estimated for the virtual substrate prior to GaAs epitaxial growth, which is reduced by a factor of 100 after the growth of GaAs. On this novel virtual substrate 1 cm2 single-junction GaAs photovoltaic cells were realized with an efficiency of 11.7% under AM0 compared with 20.2% for cells grown on a crystalline Ge substrate. Due to the high dislocation density a 50-fold higher dark current is measured in the virtual substrate cells compared to the crystalline Ge cells, leading to a lower short circuit current and open-circuit voltage of the cells fabricated on the virtual substrates. The post-GaAs growth dislocation density is estimated as 1 × 107 cm−2 in the base region and 4 × 105 cm−2 in the emitter region based on modelling and measurements.

Simulating single-junction GaAs solar cells including photon recycling

To improve and accelerate further developments of III-V solar cells an accurate and reliable modelling is necessary. In this work we present a comprehensive two- dimensional numerical model of single-junction GaAs solar cells. Using this numerical model we achieved good correlation between measurements and simulations of single-junction GaAs solar cells with different internal structures. We introduced the concept of optical coupling matrix in the numerical model to account for photon recycling effects. In addition, it is shown that thermionic currents have to be considered at the III-V hetero-interfaces. With this numerical model a powerful and flexible tool for solar cell simulation of III-V compound semiconductor materials is now available. Copyright © 2006 John Wiley & Sons, Ltd.

A high‐efficiency LPE GaAs solar cell at concentrations ranging from 2000 to 4000 suns

AbstractIII–V solar cells for terrestrial concentration applications are currently becoming of greater and greater interest. From our experience, concentrations higher than 1000 suns are required with these cells to reduce PV electricity cost to such an extent that this alternative could become cost competitive.In this paper, a single‐junction p/n GaAs solar cell, with efficiencies of 23ċ8 and 22ċ5% at concentration ratios of 2700 and 3600 suns respectively, is presented. This GaAs solar cell is well suited for use with non‐imaging optical concentrators, which possess a large aperture angle. Low‐temperature liquid phase epitaxy (LTLPE) has been the growing technique for the semiconductor structure as an attempt to use a simplified, cheap and clean technique, within a renewable energy perspective.The GaAs solar cell presented is compared with the highest efficiency tandem solar cells at concentration levels exceeding 1000 suns. The GaAs solar cell performance maintains high efficiencies up to 4000 suns, while tandem cells seem to drop very quickly after reaching their maximum. Therefore, single‐junction GaAs solar cells are a good candidate for operating at very high concentrations, and LPE is able to supply these high‐quality solar cells to work within terrestrial concentration systems, the main objective of which is the reduction of PV electricity costs. Copyright © 2003 John Wiley & Sons, Ltd.

Comparison of MOVPE grown GaAs solar cells using different substrates and group-V precursors

We have investigated the influence of substrate type (GaAs vs. germanium) and of group-V precursor (AsH 3 vs. TBAs) on the epitaxial quality of (In)(Al)GaAs layers. We evaluated these layers in terms of morphology, background contamination and doping characteristics. For final benchmarking of the individually optimised processes, we produced p-on-n single junction GaAs solar cells and compared their relative performance. This type of device is an excellent performance monitor for epitaxial layers as the fundamental operating mechanism is drift of minority carriers. The solar cell grown with TBAs on a germanium-substrate has a conversion efficiency under the AM1.5 solar spectrum, which compares favourably with the highest reported value for a p-on-n GaAs solar cell on Ge (Prog. Photovolt. Res. Appl. 8 (2000) 377).

More efficient solar cell developed

single-junction gallium arsenide (GaAs) solar cell that converts sunlight to electricity with 28.1% efficiency has been developed by Varian Associates in Palo Alto, Calif. The conversion efficiency is the highest yet achieved by a GaAs solar cell. In 1986, Varian had produced a single-junction GaAs solar cell with 26.3% conversion efficiency. The GaAs cell, which measures 5 mm X 5 mm, has applications in both terrestrial power systems and orbiting satellites, the company says. Small increases in efficiency can dramatically reduce operating costs in both applications, according to Alan J. Bennett, Varian's vice president of research. A one percentage point efficiency gain can significantly increase the number of communication channels on a satellite, while reducing construction expenses by millions [of dollars], Bennett says. He points out that silicon cells now in use on satellites have conversion efficiencies of about 14%. Additionally, the GaAs cells are more resistant than traditional silicon cells...