Uniform selenization of crack-free films of Cu(In,Ga)Se2 nanocrystals

Crack-free films of Cu(In,Ga)Se2 (CIGS) nanocrystals were deposited with uniform thickness (>1 μm) on Mo-coated glass substrates using an ink-based, automated ultrasonic spray process, then selenized and incorporated into photovoltaic devices (PVs). The device performance depended strongly on the homogeneity of the selenized films. Cracks in the spray-deposited films resulted in uneven selenization rates and sintering by creating paths for rapid, uncontrollable selenium (Se) vapor penetration. To make crack-free films, the nanocrystals had to be completely coated with capping ligands in the ink. The selenization rate of crack-free films then depended on the thickness of the nanocrystal layer, the temperature, and duration of Se vapor exposure. Either inadequate or excessive Se exposure leads to poor device performance, generating films that were either partially sintered or exhibited significant accumulation of carbon and selenium. The deposition of uniform nanocrystal films is expected to be important for a variety of electronic and optoelectronic device applications.Fil: Harvey, Taylor B.. Texas A&M University; Estados UnidosFil: Bonafé, Franco Paúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Updegrave, Ty. University of Texas at Austin; Estados UnidosFil: Voggu, Vikas Reddy. University of Texas at Austin; Estados UnidosFil: Thomas, Cherrelle. University of Texas at Austin; Estados UnidosFil: Kamarajugadda, Sirish C.. University of Texas at Austin; Estados UnidosFil: Stolle, C. Jackson. University of Texas at Austin; Estados UnidosFil: Pernik, Douglas. University of Texas at Austin; Estados UnidosFil: Du, Jiang. University of Texas at Austin; Estados UnidosFil: Korgel, Brian A.. University of Texas at Austin; Estados Unido

The Space Weather Atmosphere Models and Indices (SWAMI) project: Overview and first results

This is the final version. Available on open access from EDP Open via the DOI in this recordSpace weather driven atmospheric density variations affect low Earth orbit (LEO) satellites during all phases of their operational lifetime. Rocket launches, re-entry events and space debris are also similarly affected. A better understanding of space weather processes and their impact on atmospheric density is thus critical for satellite operations as well as for safety issues. The Horizon 2020 project Space Weather Atmosphere Model and Indices (SWAMI) project, which started in January 2018, aims to enhance this understanding by: Developing improved neutral atmosphere and thermosphere models, and combining these models to produce a new whole atmosphere model. Developing new geomagnetic activity indices with higher time cadence to enable better representation of thermospheric variability in the models, and improving the forecast of these indices. The project stands out by providing an integrated approach to the satellite neutral environment, in which the main space weather drivers are addressed together with model improvement. The outcomes of SWAMI will provide a pathway to improved space weather services as the project will not only address the science issues, but also the transition of models into operational services. The project aims to develop a unique new whole atmosphere model, by extending and blending the Unified Model (UM), which is the Met Office weather and climate model, and the Drag Temperature Model (DTM), which is a semi-empirical model which covers the 120–1500 km altitude range. A user-focused operational tool for satellite applications shall be developed based on this. In addition, improved geomagnetic indices shall be developed and shall be used in the UM and DTM for enhanced nowcast and forecast capability. In this paper, we report on progress with SWAMI to date. The UM has been extended from its original upper boundary of 85 km to run stably and accurately with a 135 km lid. Developments to the UM radiation scheme to enable accurate performance in the mesosphere and lower thermosphere are described. These include addition of non-local thermodynamic equilibrium effects and extension to include the far ultraviolet and extreme ultraviolet. DTM has been re-developed using a more accurate neutral density observation database than has been used in the past. In addition, we describe an algorithm to develop a new version of DTM driven by geomagnetic indices with a 60 minute cadence (denoted Hp60) rather than 3-hourly Kp indices (and corresponding ap indices). The development of the Hp60 index, and the Hp30 and Hp90 indices, which are similar to Hp60 but with 30 minute and 90 minute cadences, respectively, is described, as is the development and testing of neural network and other machine learning methods applied to the forecast of geomagnetic indices.European Union Horizon 202

The genomes of two key bumblebee species with primitive eusocial organization

Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation

The first myriapod genome sequence reveals conservative arthropod gene content and genome organisation in the centipede Strigamia maritima.

Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.This work was supported by the following grants: NHGRIU54HG003273 to R.A.G; EU Marie Curie ITN #215781 “Evonet” to M.A.; a Wellcome Trust Value in People (VIP) award to C.B. and Wellcome Trust graduate studentship WT089615MA to J.E.G; Marine rhythms of Life” of the University of Vienna, an FWF (http://www.fwf.ac.at/) START award (#AY0041321) and HFSP (http://www.hfsp.org/) research grant (#RGY0082/2010) to KT-­‐R; MFPL Vienna International PostDoctoral Program for Molecular Life Sciences (funded by Austrian Ministry of Science and Research and City of Vienna, Cultural Department -­‐Science and Research to T.K; Direct Grant (4053034) of the Chinese University of Hong Kong to J.H.L.H.; NHGRI HG004164 to G.M.; Danish Research Agency (FNU), Carlsberg Foundation, and Lundbeck Foundation to C.J.P.G.; U.S. National Institutes of Health R01AI55624 to J.H.W.; Royal Society University Research fellowship to F.M.J.; P.D.E. was supported by the BBSRC via the Babraham Institute;This is the final version of the article. It first appeared from PLOS via http://dx.doi.org/10.1371/journal.pbio.100200

Efficient Carrier Multiplication in Colloidal CuInSe₂ Nanocrystals

Transient absorption spectroscopy (TAS) was used to study carrier multiplication (CM) (also called multiexciton generation (MEG)) in solvent-dispersed colloidal CuInSe₂ nanocrystals with diameters as small as 4.5 nm. Size-dependent carrier cooling rates, absorption cross sections, and Auger lifetimes were also determined. The energy threshold for CM in the CuInSe₂ nanocrystals was found to be 2.4 ± 0.2 times the nanocrystal energy gap (<i>E</i>g) and the CM efficiency was 36 ± 6% per unit <i>E</i>g. This is similar to other types of nanocrystal quantum dot materials

CuInSe₂ Quantum Dot Solar Cells with High Open-Circuit Voltage

CuInSe₂ (CISe) quantum dots (QDs) were synthesized with tunable size from less than 2 to 7 nm diameter. Nanocrystals were made using a secondary phosphine selenide as the Se source, which, compared to tertiary phosphine selenide precursors, was found to provide higher product yields and smaller nanocrystals that elicit quantum confinement with a size-dependent optical gap. Photovoltaic devices fabricated from spray-cast CISe QD films exhibited large, size-dependent, open-circuit voltages, up to 849 mV for absorber films with a 1.46 eV optical gap, suggesting that midgap trapping does not dominate the performance of these CISe QD solar cells

Multiexciton Solar Cells of CuInSe₂ Nanocrystals

Peak external quantum efficiencies (EQEs) of just over 120% were observed in photovoltaic (PV) devices of CuInSe₂ nanocrystals prepared with a photonic curing process. The extraction of more than one electron/hole pair as a result of the absorption of a single photon can occur if multiple excitons are generated and extracted. Multiexciton generation (MEG) in the nanocrystal films was substantiated by transient absorption spectroscopy. We propose that photonic curing leads to sufficient electronic coupling between nanocrystals to enable multiexciton extraction under typical solar illumination conditions. Under low light conditions, however, the EQE drops significantly, indicating that photonic curing-induced ligand desorption creates a significant amount of traps in the film that limit the overall power conversion efficiency of the device

Multiexciton Solar Cells of CuInSe₂ Nanocrystals

Peak external quantum efficiencies (EQEs) of just over 120% were observed in photovoltaic (PV) devices of CuInSe₂ nanocrystals prepared with a photonic curing process. The extraction of more than one electron/hole pair as a result of the absorption of a single photon can occur if multiple excitons are generated and extracted. Multiexciton generation (MEG) in the nanocrystal films was substantiated by transient absorption spectroscopy. We propose that photonic curing leads to sufficient electronic coupling between nanocrystals to enable multiexciton extraction under typical solar illumination conditions. Under low light conditions, however, the EQE drops significantly, indicating that photonic curing-induced ligand desorption creates a significant amount of traps in the film that limit the overall power conversion efficiency of the device

Copper Indium Gallium Selenide (CIGS) Photovoltaic Devices Made Using Multistep Selenization of Nanocrystal Films

The power conversion efficiency of photovoltaic devices made with ink-deposited Cu­(In_<i>x</i>Ga_1–<i>x</i>)­Se₂ (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 °C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 °C. Shorter selenization time alleviates excessive MoSe₂ formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process