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

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

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

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