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Heinemann M.D.,Helmholtz Center Berlin | Efimova V.,Institute For Komplexe Materialien | Klenk R.,Helmholtz Center Berlin | Hoepfner B.,Helmholtz Center Berlin | And 4 more authors.
Progress in Photovoltaics: Research and Applications | Year: 2015

Superstrate solar cells were prepared by thermal evaporation of Cu(In,Ga)Se2 onto ZnO coated glass substrates. For the first time, photo-conversion efficiencies above 11% were reached without the necessity of additional light soaking or forward biasing of the solar cell. This was achieved by modifying the deposition process as well as the sodium doping. Limitations of the superstrate device configuration and possible ways to overcome these were investigated by analyzing the hetero-interface with electron microscopy and X-ray photoemission spectroscopy measurements, combined with capacitance spectroscopy and device simulations. A device model was derived that explains how on the one hand the GaOx, which forms at the CIGSe/ZnO interface, reduces the interface recombination. On the other hand how it limits the efficiency by acting as an electron barrier at the hetero-interface presumably because of a high density of negatively charged acceptor states like CuGa. The addition of sodium enhances the p-type doping of the absorber but also increases the net doping within the GaOx. Hence, a trade-off between these two effects is required. The conversion efficiency was found to decrease over time, which can be explained in our model by field-induced diffusion of sodium cations out from the GaOx layer. The proposed device model is able to explain various effects frequently observed upon light soaking and forward biasing of superstrate devices. Copyright © 2014 John Wiley & Sons, Ltd.

Gegner J.,German Aerospace Center | Shuleshova O.,Institute For Komplexe Materialien | Kobold R.,German Aerospace Center | Holland-Moritz D.,German Aerospace Center | And 4 more authors.
Journal of Alloys and Compounds | Year: 2013

The phase selection of intermetallic Cu50Zr50 and of eutectic Cu46Zr54 have been investigated by in situ high energy synchrotron X-ray diffraction on electrostatically levitated samples. No change in the selected primary phase over the whole accessible undercooling range for both compositions is found. In the case of Cu50Zr 50 the primary phase is always of B2-type for undercoolings up to 310 K. Cu46Zr54 always solidifies as a combination of CuZr (B2) and CuZr2 (C11b). For Cu50Zr50 the temperature dependence of the lattice constant is reported. © 2013 Elsevier B.V. All rights reserved.

Hildebrandt S.,Umicore AG | Wiehl G.,Umicore AG | Silze F.,Institute For Komplexe Materialien
IOP Conference Series: Materials Science and Engineering | Year: 2016

For vacuum brazing applications such as in vacuum interrupter industry Hermetic Sealing Materials (HSM) with low partial pressure are widely used. AgCu28 dominates the hermetic sealing market, as it has a very good wetting behavior on copper and metallized ceramics. Within recent decades wetting on stainless steel has become more and more important. However, today the silver content of HSMs is more in focus than in the past decades, because it has the biggest impact on the material prices. Umicore Technical Materials has developed a new copper based HSM, CuAg40Ga10. The wettability on stainless steel is significantly improved compared to AgCu28 and the total silver content is reduced by almost 44%. In this article the physical properties of the alloy and its brazed joints will be presented compared to AgCu28. © Published under licence by IOP Publishing Ltd.

Wang Z.,Institute For Komplexe Materialien | Wang Z.,Tohoku University | Qu R.T.,CAS Shenyang Institute of Metal Research | Scudino S.,Institute For Komplexe Materialien | And 7 more authors.
NPG Asia Materials | Year: 2015

Methods to strengthen aluminum alloys have been employed since the discovery of the age-hardening phenomenon in 1901. The upper strength limit of bulk Al alloys is - 0.7 GPa by conventional precipitation strengthening and increases to > GPa through grain refinement and amorphization. Here we report a bulk hybrid nanostructured Al alloy with high strength at both room temperature and elevated temperatures. In addition, based on high-resolution transmission electron microscopic observations and theoretical analysis, we attribute the strengthening mechanism to the composite effect of the high-strength nanocrystalline fcc-Al and nano-sized intermetallics as well as to the confinement effect between these nano phases. We also report the plastic deformation of nano-sized intermetallics and the occurrence of a high density of stacking faults and twins in fcc-Al after low-strain-rate deformation at room and high temperatures. Our findings may be beneficial for designing highstrength materials for advanced structural applications.

Yang J.F.,Shandong University | Bian X.F.,Shandong University | Yuan M.L.,Shandong University | Bai Y.W.,Shandong University | And 4 more authors.
Journal of Sol-Gel Science and Technology | Year: 2013

The metallic glass/titanium dioxide powders (MG/TiO2) with enhanced photocatalytic oxidation activity were synthesized, which exhibit a higher efficiency in decolorizing methylene blue solutions (MB). Compared with the pure TiO2 and crystalline alloy/TiO2 (CA/TiO 2) under the same circumstances, its degradation rate was 60 % and 30 % higher, respectively. Furthermore, compared with the CA/TiO2, the MG/TiO2 photocatalytic rate was three times faster when decolorizing MB. Considering the excellent intrinsic high-performance photocatalytic degradation under visible light irradiation, these novel powders were proven to have potential applications in water purification industry. © 2013 Springer Science+Business Media New York.

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