Gallium gradients in Cu(In,Ga)Se2 thin‐film solar cells

The gallium gradient in Cu(In,Ga)Se₂ (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe₂ and CuGaSe₂ were calculated using density functional theory. The migration barrier for the In_Cu antisite in CuGaSe₂ is significantly lower compared with the Ga_Cu antisite in CuInSe₂, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.     

Time‐resolved investigation of Cu(In,Ga)Se2 growth and Ga gradient formation during fast selenisation of metallic precursors

Ga segregation at the backside of Cu(In,Ga)Se₂ solar cell absorbers is a commonly observed phenomenon for a large variety of sequential fabrication processes. Here, we investigate the correlation between Se incorporation, phase formation and Ga segregation during fast selenisation of Cu–In–Ga precursor films in elemental selenium vapour. Se incorporation and phase formation are analysed by real‐time synchrotron‐based X‐ray diffraction and fluorescence analysis. Correlations between phase formation and depth distributions are gained by interrupting the process at several points and by subsequent ex situ cross‐sectional electron microscopy and Raman spectroscopy. The presented results reveal that the main share of Se incorporation takes place within a few seconds during formation of In–Se at the top part of the film, accompanied by outdiffusion of In out of a ternary Cu–In–Ga phase. Surprisingly, CuInSe₂ starts to form at the surface on top of the In–Se layer, leading to an intermediate double graded Cu depth distribution. The remaining Ga‐rich metal phase at the back is finally selenised by indiffusion of Se. On the basis of a proposed growth model, we discuss possible strategies and limitations for the avoidance of Ga segregation during fast selenisation of metallic precursors. Solar cells made from samples selenised with a total annealing time of 6.5 min reached conversion efficiencies of up to 14.2 % (total area, without anti‐reflective coating). The evolution of the Cu(In,Ga)Se₂ diffraction signals reveals that the minimum process time for high‐quality Cu(In,Ga)Se₂ absorbers is limited by cation ordering rather than Se incorporation. Copyright © 2014 John Wiley & Sons, Ltd.     

Photokatalytische Bildung von Wasserstoff aus Thiolen in Gegenwart von Vitamin B12-Modellverbindungen mit Azid als photochemischem Opferliganden

Photocatalytic Hydrogen Formation from Thioles in the Presence of Vitamin-B₁₂ Model Complexes with Azide as Photochemical Sacrificial Ligand The photolysis of [N₃Co(chelat)B] complexes ( 1–3 ) (chelat = dimethylglyoxime, dmg; N,N′-o-phynylenebis(salicylidenimine), salphen; N,N′-ethylene-bis(salicylidenimine), salen; B = pyridine) leads by homolytic cleavage of the Co–N₃ bond to both coordinatively unsaturated cobalt(II) chelates [Co(chelat)B] and N₃ ligand radicals that undergo fast decay to dinitrogen. The photolysis of the cobalt (III) complexes 1–3 in the presence of thiophenole and other thioles proceeds catalytically and yields the corresponding disulphides and dihydrogen. The mechanism of this photocatalytic generation of dihydrogen is due to the catalytic activity of the coordinatively unsaturated cobalt(II) species formed photochemically. A photocatalytic cycle is proposed describing the generation of hydrogen. Possible photochemical and thermal steps of that cycle are discussed.     

Starch-Derived Products for Detergents

Recent developments in the formulation of detergents have been driven by a strong consumer demand for natural and biodegradable products. Detergent manufacturers responded to this demand with corresponding products and advertising slogans such as “fully biodegradable”, “natural” or even “double natural” to oust their competitors. In a detergent formulation, starch- derived products can in principle be used for the following purposes: as the hydrophilic head group in surfactants, as the starting material for (poly)carboxylate co-builders and as the backbone of bleaching activators. Non-ionic classical surfactants can be replaced by alkylpolyglucosides (APGs), a class of products completely based on renewable resources such as glucose and fatty alcohols derived from natural fatty acids. Sodium tripolyphosphate (STPP), the product responsible for the eutrophication of surface waters, can be substituted by a combination of an inorganic zeolite and highly oxidised starch (dicarboxylic starch) or by citrate. Acetylated polyols derived from hydrogenated carbohydrates such as sorbitol can take over the function of the petrochemically-based tetraacetyl ethylene diamine (TAED) used as activator to allow perborate bleaching at lower washing temperatures.     

The Deubiquitinase OTUB1 Is a Key Regulator of Energy Metabolism

Dysregulated energy metabolism is a major contributor to a multitude of pathologies, including obesity and diabetes. Understanding the regulation of metabolic homeostasis is of utmost importance for the identification of therapeutic targets for the treatment of metabolically driven diseases. We previously identified the deubiquitinase OTUB1 as substrate for the cellular oxygen sensor factor-inhibiting HIF (FIH) with regulatory effects on cellular energy metabolism, but the physiological relevance of OTUB1 is unclear. Here, we report that the induced global deletion of OTUB1 in adult mice (Otub1 iKO) elevated energy expenditure, reduced age-dependent body weight gain, facilitated blood glucose clearance and lowered basal plasma insulin levels. The respiratory exchange ratio was maintained, indicating an unaltered nutrient oxidation. In addition, Otub1 deletion in cells enhanced AKT activity, leading to a larger cell size, higher ATP levels and reduced AMPK phosphorylation. AKT is an integral part of insulin-mediated signaling and Otub1 iKO mice presented with increased AKT phosphorylation following acute insulin administration combined with insulin hypersensitivity. We conclude that OTUB1 is an important regulator of metabolic homeostasis.     

Short communication: Evaluation of an automated in-house hematology analyzer for bovine blood

The objective of this study was to evaluate the suitability of the V-Sight hematology analyzer (A. Menarini Pharma GmbH, Vienna, Austria) for bovine blood by a comparison with a reference device (Advia 2120i, Siemens AG, Erlangen, Germany). In total, 97 blood samples were obtained from 75 dairy cows. Analyzed parameters included counts of white blood cells (WBC), lymphocytes, monocytes, granulocytes, red blood cells (RBC), and platelets (PLT), as well as hemoglobin concentration (HGB), hematocrit (HCT), mean corpuscular volume, mean corpuscular hemoglobin (MCH), MCH concentration (MCHC), mean platelet volume (MPV), and plateletcrit (PCT). Based on Passing-Bablok regression, the V-Sight provided accurate and precise results for MCH and MCHC only. The PCT results were comparable to the reference method, but precision was inconclusive. Significant proportional differences were detected for monocytes, granulocytes, HCT, and PLT. For all other analytes, significant proportional and systemic differences were observed. The WBC and lymphocyte results from the V-Sight were characterized by poor accuracy, poor precision, and a high number of false positive outliers. Bland-Altman analysis indicated negative biases for all WBC parameters, the erythrocyte indices, and PLT. Positive biases were observed for RBC, HGB, HCT, MPV, and PCT. Correlation coefficients of >0.9 between the V-Sight and the reference method were found only for RBC, HGB, HCT, and MPV. Intraassay precision of the V-Sight analyzer was acceptable (coefficient of variation <5%) for granulocytes, the erythrocyte indices, and MPV. It was unacceptable (coefficient of variation ≥5%) for WBC, lymphocytes, monocytes, as well as RBC, and inconclusive for HGB, HCT, PLT, and PCT. Sensitivity was high for all RBC counts and indices as well as PLT, but low for monocytes, granulocytes, and MPV. Specificity was high for monocytes and granulocytes, but low for RBC, HCT, MCH, and MCHC. With accurate and precise results for only 2 out of 13 parameters, the V-Sight cannot be recommended for analysis of bovine blood.     

Soil organic carbon changes in the cultivation of energy crops: Implications for GHG balances and soil quality for use in LCA

The environmental impact of different land-use systems for energy, up to the farm or forest “gate”, has been quantified with Life Cycle Assessment (LCA). Four representative crops are considered: OilSeed Rape (OSR), Miscanthus, Short-Rotation Coppice (SRC) willow and forest residues. The focus of the LCA is on changes in Soil Organic Carbon (SOC) but energy use, emissions of GreenHouse Gases (GHGs), acidification and eutrophication are also considered. In addition to providing an indicator of soil quality, changes in SOC are shown to have a dominant effect on total GHG emissions. Miscanthus is the best land-use option for GHG emissions and soil quality as it sequesters C at a higher rate than the other crops, but this has to be weighed against other environmental impacts where Miscanthus performs worse, such as acidification and eutrophication. OSR shows the worst performance across all categories. Because forest residues are treated as a by-product, their environmental impacts are small in all categories. The analysis highlights the need for detailed site-specific modelling of SOC changes, and for consequential LCAs of the whole fuel cycle including transport and use.