Interfacial Effects of Tin Oxide Atomic Layer Deposition in Metal Halide Perovskite Photovoltaics

Metal halide perovskites offer a wide and tunable bandgap, making them promising candidates for top‐cell absorbers in tandem photovoltaics. In this work, the authors aim to understand the atomic layer deposition (ALD) precursor–perovskite interactions of the tin oxide ALD system and the role of organic fullerenes at the perovskite–tin oxide interface while establishing a framework for developing alternative perovskite‐compatible ALD processes in the future. It is shown, in the case of tin oxide ALD growth with tetrakis(dimethylamino)tin(IV) and water on FA_0.83Cs_0.17Pb(I_0.83Br_0.17)₃ perovskite, that perovskite stability is most sensitive to metal–organic exposure at elevated temperatures with an onset near 110 °C, resulting in removal of the formamidinium cation. Transitioning from ALD to pulsed‐chemical vapor deposition tin oxide growth can minimize the degradation effects. Investigation of fullerenes at the perovskite interface shows that thin fullerene layers offer minor improvements to perovskite stability under ALD conditions, but significant enhancement in carrier extraction. Fullerene materials are undesirable due to fabrication cost and poor mechanical stability. Compositional tuning of the perovskite material can improve the fullerene‐free device performance. This method is demonstrated with a bromine‐rich perovskite phase to enable an 8.2% efficient perovskite device with all‐inorganic extraction layers.     

Microbial community differentiation between active and inactive sulfide chimneys of the Kolumbo submarine volcano,Hellenic Volcanic Arc

Over the last decades, there has been growing interest about the ecological role of hydrothermal sulfide chimneys, their microbial diversity and associated biotechnological potential. Here, we performed dual-index Illumina sequencing of bacterial and archaeal communities on active and inactive sulfide chimneys collected from the Kolumbo hydrothermal field, situated on a geodynamic convergent setting. A total of 15,701 OTUs (operational taxonomic units) were assigned to 56 bacterial and 3 archaeal phyla, 133 bacterial and 16 archaeal classes. Active chimney communities were dominated by OTUs related to thermophilic members of Epsilonproteobacteria, Aquificae and Deltaproteobacteria. Inactive chimney communities were dominated by an OTU closely related to the archaeon Nitrosopumilus sp., and by members of Gammaproteobacteria, Deltaproteobacteria, Planctomycetes and Bacteroidetes. These lineages are closely related to phylotypes typically involved in iron, sulfur, nitrogen, hydrogen and methane cycling. Overall, the inactive sulfide chimneys presented highly diverse and uniform microbial communities, in contrast to the active chimney communities, which were dominated by chemolithoautotrophic and thermophilic lineages. This study represents one of the most comprehensive investigations of microbial diversity in submarine chimneys and elucidates how the dissipation of hydrothermal activity affects the structure of microbial consortia in these extreme ecological niches.

     

Chironomid stratigraphy in the shallow and eutrophic Lake Søbygaard, Denmark: chironomid–macrophyte co-occurrence

1. A sediment core from the shallow, hypertrophic Lake Søbygaard (mean depth ∼1 m; [TP] 310 μg P L⁻¹) was analysed for subfossil remains to reconstruct chironomid community changes in relation to the succession and disappearance of aquatic macrophytes. 2. Species composition in the 1.10 m core indicates a succession from a 'naturally' eutrophic state to a hypertrophic state during recent centuries. Radiometric dating (²¹⁰Pb) of the uppermost 20 cm of the sediment core (∼1932–93) indicates that sediment accumulation rate had doubled in recent decades. 3. Changes in chironomid assemblages were in close agreement with changes in both diatoms and macrophyte remains in the same core. Distinct changes in chironomid communities reflect the eutrophication process and macrophyte succession through Chara , Ceratophyllum and Potamogeton dominance to the present state, with complete loss of submerged vegetation and dominance by phytoplankton. 4. The co-occurrence and relationship between aquatic macrophyte diversity and recent subfossil chironomid assemblages were assessed from an additional 25 Danish lakes. There was good agreement between the macrophyte and chironomid-based lake groupings. Overall, a significant difference ( P <0.001) was found in chironomid assemblages among lakes in different macrophyte classes. In a pair-wise comparison, the poorly buffered mesotrophic lakes and the alkaline eutrophic lakes had significantly different chironomid assemblages. 5. Chironomid taxa commonly reported to be associated with macrophytes ( Cricotopus , Endochironomus and Glyptotendipes ) were shown also to be indicators of highly productive lakes lacking abundant submerged vegetation.     

Steady-state kinetics of the glutaminase reaction of CTP synthase from Lactococcus lactis. The role of the allosteric activator GTP incoupling between glutamine hydrolysis and CTP synthesis.

CTP synthase catalyzes the reaction glutamine + UTP + ATP --> glutamate + CTP + ADP + Pi. The rate of the reaction is greatly enhanced by the allosteric activator GTP. We have studied the glutaminase half-reaction of CTP synthase from Lactococcus lactis and its response to the allosteric activator GTP and nucleotides that bind to the active site. In contrast to what has been found for the Escherichia coli enzyme, GTP activation of the L. lactis enzyme did not result in similar kcat values for the glutaminase activity and glutamine hydrolysis coupled to CTP synthesis. GTP activation of the glutaminase reaction never reached the levels of GTP-activated CTP synthesis, not even when the active site was saturated with UTP and the nonhydrolyzeable ATP-binding analog adenosine 5'-[gamma-thio]triphosphate. Furthermore, under conditions where the rate of glutamine hydrolysis exceeded that of CTP synthesis, GTP would stimulate CTP synthesis. These results indicate that the L. lactis enzyme differs significantly from the E. coli enzyme. For the E. coli enzyme, activation by GTP was found to stimulate glutamine hydrolysis and CTP synthesis to the same extent, suggesting that the major function of GTP binding is to activate the chemical steps of glutamine hydrolysis. An alternative mechanism for the action of GTP on L. lactis CTP synthase is suggested. Here the binding of GTP to the allosteric site promotes coordination of the phosphorylation of UTP and hydrolysis of glutamine for optimal efficiency in CTP synthesis rather than just acting to increase the rate of glutamine hydrolysis itself.     

Iridoid glucosides from Pedicularis

Pedicularis palustris contains the iridoid glucosides aucubin and gardoside methyl ester, and five hydroxy derivatives of 8-epi-deoxyloganin, together with boschnaloside and three hydroxy derivatives of boschnaloside. From P. silvatica, plantarenaloside, 8-epiloganin and euphroside have been isolated. Euphroside is also present in P. lapponica, in addition to aucubin and mussaenoside. Chemical evidence for the structure of euphroside is presented. Pedicularioside is shown to be identical with penstemoside, and the former name is thus redundant.     

Fossil pollen as a record of past biodiversity

Quaternary pollen records may contribute uniquely to the understanding of present plant diversity. Pollen assemblages can reflect diversity at community and landscape scales but the time resolution of most studies does not match that of modern ecological studies. Because of the complicating effects of differential pollen productivity and dispersal, pollen records do not directly reflect equitability aspects of vegetation diversity. Vegetation diversity indices other than S (the total number of taxa) are therefore not appropriate for pollen assemblages. As a measure of the species richness palynological richness is biased by the lack of taxonomic precision, by a possible interference on pollen dispersal from vegetation structure and by pollen representation. The nonlinear relationship between species richness and pollen-taxa richness may be used in attempts to estimate past floristic richness from fossil pollen assemblages. Using a hypothetical example the strong effect of cover shifts in the vegetation affecting taxa with different representation (R_rel) values on observed palynological richness is demonstrated. It is suggested that estimates of relative pollen productivity should be used to guide the pollen sum on which pollen-type richness is estimated by rarefaction techniques and this approach is illustrated using a paired site study of late Holocene diversity dynamics. The need for a modern training set relating pollen-type richness to species richness, pollen productivity and vegetation structure is emphasized.