199 research outputs found
Progress in the development of CuInS2 based mini modules
A sequential process is used to synthesise CuInS2 absorber layers for photovoltaic application. In this process CuIn precursor layers sputtered on molybdenum coated float glass are converted to CuInS2 via sulphurisation in an elemental sulphur vapour ambient. A re evaluation of process parameters has been performed including fine tuning of numerous minor aspects. Using optimised process conditions has lead to improved device performance, especially a narrowed distribution at higher module efficiencies is achieved. At the same time the process yield is improved resulting in fewer devices with poor electrical qualit
Electronic effects of Cd on the formation of the CdS CuInS2 heterojunction
The possibility of doping and Fermi level pinning of CuInS2 thin layer solar cell absorbers caused by the diffusion of Cd into the absorber during junction formation via chemical bath deposition was investigated. The analysis of thin CdS layers deposited on CuInS2 showed the amount of deposition induced band bending on the CuInS2 surface position of the Fermi level in the respective bandgaps was not experimentally reproducible. However, the value of the valence band offset between the two materials was reproducible between different depositions within the error of the measurement. Thus, the deposition of the CdS does not lead to a consistent pinning position of the Fermi level in the CuInS2 CdS heterojunction. The removal of the CdS layers with HCl left a thin Cd containing layer on the CuInS2 surface and it was shown that this surface was not doped by the remaining Cd. Furthermore, the influence of the HCl of the CuInS2 was explored and found to form a reproducible surface richer in Cu than CuInS2 etched in potassium cyanide solution
Stability of plasmonic metal nanoparticles integrated in the back contact of ultra-thin Cu(In,Ga)S2 solar cells
Ultra-thin solar cells on transparent back contacts constitute the basis for
highly efficient tandem solar devices which can surpass the single cell
efficiency limit. The material reduction related to ultra-thin high efficiency
devices additionally lowers the price. Despite the fact that they are ultra-
thin the absorbers still have to remain optically thick and therefore require
adequate light management. A promising approach for enhanced absorption is
plasmonic scattering from metal nanoparticles. In this paper we discuss the
experimental incorporation of Ag nanoparticles in ultra-thin wide-gap
chalcopyrite solar cells on transparent back contacts. A 6.9% efficient 500 nm
Cu(In,Ga)S2 solar cell on In2O3:Mo (at this point without nanoparticles) is
the starting point. For the predicted optimum design of including particles at
the rear side the stability of the nanostructures integrated in the back
contact is investigated in detail. As a first step towards proof-of-concept,
absorption enhancement from the nanoparticles included in the complete solar
cell is experimentally shown in optical properties
New iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
The present work reports on the new soft ferromagnetic Heusler phases
Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been
predicted to exist in a tetragonal regular Heusler structure. Together with the
known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and
characterized by powder XRD, 57 Fe M\"ossbauer spectroscopy, SQUID and EDX
measurements. In particular M\"ossbauer spectroscopy was used to monitor the
degree of local atomic order/disorder and to estimate magnetic moments at the
Fe sites from the hyperfine fields. It is shown that in contrast to the
previous predictions all the materials except Fe2NiGa basically adopt the
inverse cubic Heusler (X-) structure with differing degrees of disorder. The
disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse
Heusler phase. The experimental data are compared with results from ab-inito
electronic structure calculations on LDA level incorporating the effects of
atomic disorder by using the coherent potential approximation (CPA). A good
agreement between calculated and experimental magnetic moments is found for the
cubic inverse Heusler phases. Model calculations on various atomic
configurations demonstrate that antisite disorder tends to enhance the
stability of the X-structure. Given the fundamental scientific and
technological importance of tetragonal Heusler phases the present results call
for further investigations to unravel the factors stabilizing tetragonal
Heusler materials
Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn
In this work the theoretical and experimental investigations of Co2TiZ (Z =
Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is
predicted for all three compounds with only two bands crossing the Fermi energy
in the majority channel. The magnetic moments fulfill the Slater-Pauling rule
and the Curie temperatures are well above room temperature. All compounds show
a metallic like resistivity for low temperatures up to their Curie temperature,
above the resistivity changes to semiconducting like behavior. A large negative
magnetoresistance of 55% is observed for Co2TiSn at room temperature in an
applied magnetic field of 4T which is comparable to the large negative
magnetoresistances of the manganites. The Seebeck coefficients are negative for
all three compounds and reach their maximum values at their respective Curie
temperatures and stay almost constant up to 950 K. The highest value achieved
is -52muV/K m for Co2TiSn which is large for a metal. The combination of
half-metallicity and the constant large Seebeck coefficient over a wide
temperature range makes these compounds interesting materials for
thermoelectric applications and further spincaloric investigations.Comment: 4 pages 4 figure
Limitations of Near Edge X Ray Absorption Fine Structure as a tool for observing conduction bands in chalcopyrite solar cell heterojunctions
A non optimized interface band alignment in a heterojunctionbased solar cell can have negative eff ects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X ray Absorption Fine Structure spectroscopy NEXAFS as a means to measure the conduction band position, Cu In,Ga S2 chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO Buffer Cu In,Ga S2 Mo Glass. The composition dependence of the structure of the conduction bands of CuInxGa1 xS2 has been revealed for x 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band off set at the junction with the bu ffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of state
CdS/Cu(In,Ga)S2 based solar cells with efficiencies reaching 12.9% prepared by a rapid thermal process
In this letter, we report externally confirmed total area efficiencies
reaching up to 12.9% for CdS/Cu(In,Ga)S2 based solar cells. These are the
highest externally confirmed efficiencies for such cells. The absorbers were
prepared from sputtered metals subsequently sulfurized using rapid thermal
processing in sulfur vapor. Structural, compositional, and electrical
properties of one of these champion cells are presented. The correlation
between the Ga distribution profile and solar cell properties is discussed
Amélioration de la qualité microbiologique des eaux de surface dans un bassin versant, dans une zone densément peuplée : scénario des coûts et effets
Colloque avec actes et comité de lecture. Internationale.International audienc
Tuning of crystal structure and magnetic properties by exceptionally large epitaxial strains
Huge deformations of the crystal lattice can be achieved in materials with
inherent structural instability by epitaxial straining. By coherent growth on
seven different substrates the in-plane lattice constants of 50 nm thick
Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches
8,3 % relative to the fcc lattice. The in-plane lattice strain results in a
remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering
most of the Bain transformation path from fcc to bcc crystal structure. This
has dramatic consequences for the magnetic key properties. Magnetometry and
X-ray circular dichroism (XMCD) measurements show that Curie temperature,
orbital magnetic moment, and magnetocrystalline anisotropy are tuned over broad
ranges.Comment: manuscript, 3 figures, auxiliary materia
Experience in implementing harvest strategies in Australia's south-eastern fisheries
The Southern and Eastern Scalefish and Shark Fishery (SESSF) is a complex multi-species fishery, with 34 stock units under quota management, for which a harvest strategy framework was developed in 2005. The framework involves the application of a set of tier-based harvest control rules (HCR) designed to provide a precautionary approach to management. The harvest strategy framework has been applied from 2005 to 2007, resulting in substantial reductions in quotas across the fishery. The experience in implementing the framework, both positive and negative, is described, and general lessons are drawn. Key lessons include the importance of formally testing such strategies using management strategy evaluation, the impact of external management drivers on implementation of the approach, the need to define strategies for setting "bycatch quotas" in multi-species fisheries, and the need for flexibility and pragmatism in the early stages of implementing such an approach
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