Defects in multicrystalline silicon for photovoltaic applications and their impact on solar cell parameters have been investigated in the material research network project SolarFocus. A series of multicrystalline silicon ingots of ultrapure feedstock material were cast with intentional addition of typical transition metal impurities (Fe, Cu, Cr) and Ge as doping elements. The results of lifetime measurements, NAA and FTIR analysis, solar cell processing and microscopic investigations are presented in this study. For ingots intentionally contaminated with transition metals, the combined analysis reveals that despite the overall high impurity content, good solar cell efficiencies can be reached. A strong influence of the in-diffusion of metal impurities from the crucible as well as the back-diffusion from the top region of the ingot ca still be observed. All metals show a strong precipitation behaviour throughout the whole ingot. The solar cell efficiency is both limited by multiple recombination active defects and shunts, induced by a high metal contamination via indirect mechanisms. Solar cells with efficiencies up to 15.2% for material contaminated with 20 ppma Fe in the melt, 15.7% for 20 ppma Cu and 15.1% for 20 ppma Cr were processed. A positive effect of Cu added to the feedstock could not be found. Ge-rich ingots showed strong effects of increasing silicon carbide and silicon nitride formation with increasing Ge content larger than 0.5 wt.% thus reducing solar cell efficiency

Different compositions of galaxy types in the field in comparison to galaxy clusters as described by the morphology–density relation in the local universe are interpreted as a result of transformation processes from late‐ to early‐type galaxies. This interpretation is supported by the Butcher–Oemler effect. We investigate E+A galaxies as an intermediate state between late‐type galaxies in low‐density environments and early‐type galaxies in high‐density environment to constrain the possible transformation processes. For this purpose, we model a grid of post‐starburst galaxies by inducing a burst and/or a halting of star formation on the normal evolution of spiral galaxies with our galaxy evolution code galev. From our models, we find that the common E+A criteria exclude a significant number of post‐starburst galaxies, and propose that comparing their spectral energy distributions leads to a more sufficient method to investigate post‐starburst galaxies. We predict that a higher number of E+A galaxies in the early universe cannot be ascribed solely to a higher number of starburst, but is a result of a lower metallicity and a higher burst strength due to more gas content of the galaxies in the early universe. We find that even galaxies with a normal evolution without a starburst have an Hδ‐strong phase at early galaxy ages.

Recombination-active extended defects in semiconductors frequently occur at a low density which makes their structural and chemical analysis by transmission electron microscopy (TEM) techniques virtually impossible. Here an approach is described that uses in situ electron beam induced current (EBIC) in a focused ion beam machine to localize such defects for TEM lamella preparation. As an example, a defect complex occurring in block-cast multicrystalline silicon with a density of less than 10(4) cm(-3) has been prepared and analyzed by TEM. The chemical sensitivity of the technique is estimated to be about 10(13) atoms cm(-2) which is comparable to synchrotron-based x-ray techniques. The localization accuracy of the TEM lamella is shown to be better than 50 nm when low-energy EBIC is used.

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This contribution summarizes recent efforts to apply transmission electron microscopy (TEM) techniques to recombination-active extended defects present in a low density. In order to locate individual defects, electron beam induced current (EBIC) is applied in situ in a focused ion beam (FIB) machine combined with a scanning electron microscope. Using this approach defect densities down to about 10cm-2 are accessible while a target accuracy of better than 50nm is achieved. First applications described here include metal impurity related defects in multicrystalline silicon, recombination and charge collection at NiSi2 platelets, internal gettering of copper by NiSi2 precipitates and site-determination of copper atoms in NiSi2.