B.B. Van Aken

Influence of magnetic on ferroelectric ordering in LuMnO3

We have studied the influence of antiferromagnetic ordering on the local dielectric moments of the MnO5 and LuO7 polyhedra by measuring neutron powder-diffraction patterns of LuMnO3 at temperatures near T-N. We show that the coupling is weak, because the magnetic exchange coupling is predominantly in the ab plane of the MnO5 trigonal bipyramids, and the electric dipole moments, originating in the LuO7 polyhedra, are oriented along the hexagonal c axis. Anomalies in the dielectric properties near T-N are thus caused by the geometric constraints between the MnO5 and the LuO7 polyhedra.

Growth and multiferroic properties of hexagonal HoMnO3 films

Hexagonal, twin-free HoMnO3 (0001) films of 25–240nm thickness were grown epitaxially on Y2O3:ZrO2(111) substrates using pulsed laser deposition. Ferroelectric polar order and Mn3+ antiferromagnetism were observed by optical second harmonic generation. Magnetization data reveal Ho3+ ordering which is, with subtle deviations, similar to that of bulk crystals. However, three phase transitions below 6K and thermal hysteresis of magnetization at T<42K were detected.

Roll to roll fabrication process of thin film silicon solar cells on steel foil

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process chain are: 1) application of an insulating barrier layer which enables texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of the layers (reducing the total number of process steps). The barrier layer is primarily an enabler for monolithic series interconnection of cells, but we show that we can also fabricate any arbitrary sub-micron structure in this layer by hot embossing to achieve optimum light trapping in the solar cells. For deposition of doped and intrinsic silicon layers we use novel remote and linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. First pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil plus textured barrier layer yielded efficiencies of about 3.7%.

20.3% MWT Silicon Heterojunction Solar Cell—A Novel Heterojunction Integrated Concept Embedding Low Ag Consumption and High Module Efficiency

In this paper, we present the successful integration of a silicon heterojunction (HJ) solar cell with metal wrap through (MWT) architecture. This MWT-HJ cell and module technology combines all the advantages of the individual concepts. With this contribution, we demonstrate a record device efficiency of 20.3% achieved using commercial n-type Cz 6-in wafers. To our knowledge, this is the first time cell results for MWT-HJ architecture have been reported. We put this result in perspective, providing a solution for the reduced conductivity of low-temperature silver pastes used for HJ cell fabrication. We propose a method to further increase the solar cell performance up to 4%rel, together with a 50% cost of ownership reduction of the front contact silver, including via and conductive adhesive at the rear. This is possible solely by the optimization of the front metal grid in this MWT structure predicting efficiencies above 21%. MWT-HJ is a fully low-temperature integrated cell and module concept and is also compatible with next-generation thinner wafers.

High Efficiency n-Type Metal-Wrap-Through Cells and Modules Using Industrial Processes

We report on our high efficiency n-type metal-wrap-through (MWT) cell and module technology. In this work, bifacial n-type MWT cells are produced by industrial processes in industrial full-scale and pilot-scale process equipment. N-type cells benefit from high recombination lifetime in the wafer and bifaciality. Also low-cost screen printed cells can yield over 20% efficiency. When combined with MWT technology, high-power back-contact modules result, which can employ very thin cells. We report a cell conversion efficiency of 20.5% (in-house measurement, certification pending), a significant gain compared to our earlier work. We will discuss performance of thin cells relative to thicker cells, comparing experimental results to modeling. Recently, two aspects of (mainly p-type) MWT technology have received increased attention: paste consumption and performance under reverse bias. We will discuss MWT paste consumption, showing how MWT technology, like multi-busbar technology, can support very low paste consumption. We also report on behavior of cells and modules under reverse bias. We also discuss the robustness of MWT technology to dissipation in hot spots under reverse bias. Finally, full-size modules have been made and cell-to-module ratios of the different I-V parameters were analysed. Modules from cells with average efficiency over 20% are pending. This work shows that low-cost n-type bifacial cells are suitable for industrial high efficiency back-contact technology.

Electron energy-loss spectroscopy of boron-doped layers in amorphous thin film silicon solar cells

Electron energy-loss spectroscopy (EELS) is used to study p-doped layers in n-i-p amorphous thin film Si solar cells grown on steel foil substrates. For a solar cell in which an intrinsic amorphous hydrogenated Si (a-Si-H) layer is sandwiched between 10-nm-thick n-doped and p-doped a-Si:H layers, we assess whether core-loss EELS can be used to quantify the B concentration. We compare the shape of the measured B K edge with real space ab initio multiple scattering calculations and show that it is possible to separate the weak B K edge peak from the much stronger Si L edge fine structure by using log-normal fitting functions. The measured B concentration is compared with values obtained from secondary ion mass spectrometry, as well as with EELS results obtained from test samples that contain ∼200-nm-thick a-Si:H layers co-doped with B and C. We also assess whether changes in volume plasmon energy can be related to the B concentration and/or to the density of the material and whether variations of the volume...

Metal Wrap through Silicon Heterojunction Solar Cells and First Made Minimodules

In this paper we present the successful integration of a silicon heterojunction (HJ) solar cell with metal wrap through architecture (MWT) and foil basedback contact module technology. With this contribution we show a record cell efficiency of 20.3% achieved using commercial n-type Cz 6 inch wafers and demonstrate an encapsulated cell efficiency of 19.6% achieved on a 2×2 mini-module. To our knowledge this is the first time that module results of MWT-HJ architecture have been reported. In this studies , we propose a method to increase the solar cell performance up to 21% together with a 50% cost of ownership reduction of the front silver metal including via and conductive adhesive. This is possible solely by the optimization of the front metal grid. MWT-HJ is a fully low-temperature integrated cell and module concept compatible also with thinner wafers.

23% Efficiency metal wrap through silicon heterojunction solar cells

MWT-SHJ cells and modules combine the positive benefits of both underlying technologies: namely high Voc, higher Jsc and higher FF. Especially the FF is maintained before and after encapsulation thanks to the rear interconnection which strongly reduces cell to module FF losses. We obtained two record efficiencies for these devices with two different front metallizations: 22.6% using low temperature Ag paste and 23.1% using copper plating. Voc values above 730 mV have been achieved also in the new 6×6 vias metallization, demonstrating that the architecture maintains the exceptional passivation typical of heterojunction devices. The MWT cell and module structure offers even greater advantages on heterojunction solar cells: i) front side Ag consumption reduction up to a factor two; ii) concurrent low temperature cell interconnection and encapsulation. Our record MWT-SHJ solar cells and modules are manufactured using industrially proven tools and 6 inch commercial n-type Cz Si wafers. The metallization choice gives ample room to manufacturers for optimization based on internal cost structure, material costs and business strategy. MWT-SHJ behavior at reverse bias voltage and low illumination intensity is comparable to conventional HJ devices.

6.20 – Transgenic Plants and Associated Bacteria for Phytoremediation of Organic Pollutants

Transgenic plants and associated bacteria constitute a new generation of genetically modified organisms for the treatment of polluted soil and water. This article focuses on the latest progresses in the development of transgenic organisms, including plants and associated bacteria, for the phytoremediation of major classes of organic environmental pollutants, such as chlorinated compounds, explosives, and pesticides. Phytoremediation is defined as the use of higher plants for the cost-effective, environmentally friendly rehabilitation of soil and groundwater contaminated by toxic metals and organic compounds. Phytoremediation involves a range of mechanisms, including uptake of pollutants from soil (phytoextraction), enzymatic transformation inside plant tissues (phytotransformation), volatilization into the atmosphere (phytovolatilization), and microbial degradation in the root zone (rhizoremediation). However, many persistent organic pollutants (POPs), such as explosives and polychlorinated biphenyls, are only slowly taken up and degraded by plants, resulting in accumulation and potential release of toxic metabolites into the environment. Similarly, bacteria naturally living in symbiosis with plants often do not possess the enzymatic machinery necessary for the efficient biodegradation of POPs. These limitations have led to the idea of genetic modification of plants and their associated bacteria by the introduction of key bacterial or mammalian genes known to be involved in the metabolism of xenobiotic pollutants, following a strategy similar to that used for the development of transgenic crops.

Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates.

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: 1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sou rees, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil with textured barrier layer yielded efficiencies of about 3.7%.