Monolithic Perovskite/Si Tandem Solar Cells: Pathways to Over 30% Efficiency

The article commences with a review focusing on three critical aspects of the perovskite/Si tandem technology: the evolution of efficiencies to date, comparisons of Si subcell choices, and the interconnection design strategies. Building on this review, a clear route is provided for minimizing optical losses aided by optical simulations of a recently reported high‐efficiency perovskite/Si tandem system, optimizations which result in tandem current densities of ≈20 mAcm^?2 with front‐side texture. The primary focus is on electrical modeling on the Si‐subcell, in order to understand the efficiency potential of this cell under filtered light in a tandem configuration. The possibility of increasing the Si subcell efficiency by 1% absolute is offered through joint improvements to the bulk lifetime, which exceeds 4 ms, and improves surface passivation quality to saturation current densities below 10 fA cm^?2. Polycrystalline‐Si/SiO_x passivating contacts are proposed as a promising alternative to partial‐area rear contacts, with the potential for further simplifying cell fabrication and improving device performance. A combination of optical modeling of the complete tandem structure alongside electrical modeling of the Si‐subcell, both with state‐of‐the‐art modeling tools, provides the first complete picture of the practical efficiency potential of perovskite/Si tandems.     

Spatially and Spectrally Resolved Absorptivity: New Approach for Degradation Studies in Perovskite and Perovskite/Silicon Tandem Solar Cells

Instability in perovskite solar cells is the main challenge for the commercialization of this solar technology. Here, a contactless, nondestructive approach is reported to study degradation across perovskite and perovskite/silicon tandem solar cells. The technique employs spectrally and spatially resolved absorptivity at sub‐bandgap wavelengths of perovskite materials, extracted from their luminescence spectra. Parasitic absorption in other layers, carrier diffusion, and photon smearing phenomena are all demonstrated to have negligible effects on the extracted absorptivity. The absorptivity is demonstrated to reflect real degradation in the perovskite film and is much more robust and sensitive than its luminescence spectral peak position, representing its optical bandgap, and intensity. The technique is applied to study various common factors which induce and accelerate degradation in perovskite solar cells including air and heat exposure and light soaking. Finally, the technique is employed to extract the individual absorptivity component from the perovskite layer in a monolithic perovskite/silicon tandem structure. The results demonstrate the value of this approach for monitoring degradation mechanisms in perovskite and perovskite/silicon tandem cells at early stages of degradation and various fabrication stages.     

MHC class II association study in eight breeds of dog with hypoadrenocorticism

Canine hypoadrenocorticism is an endocrine disorder characterised by inadequate secretion of steroid hormones from the adrenal glands. Pathology results from immune-mediated destruction of the adrenal cortex, which is similar to that seen in the human Addison’s disease. Both the canine and human diseases have similar clinical presentation, with the diagnosis based on performing a dynamic adrenocorticotropic hormone stimulation test. MHC class II has previously been associated with the human and canine diseases. In the current study, we conducted an MHC class II association study in eight breeds of dog with diagnoses of hypoadrenocorticism. We demonstrated significant differences in dog leukocyte antigen (DLA) haplotype frequencies in six of these breeds: Cocker spaniel, Springer spaniel, Labrador, West Highland white terrier (WHWT), Bearded collie, and Standard poodle. In the Springer spaniel, the DLA-DRB1*015:01--DQA1*006:01--DQB1*023:01 haplotype was significantly associated with disease risk (p?=?0.014, odds ratio (OR)?=?5.14) and showed a similar trend in the Cocker spaniel. This haplotype is related to one associated with hypoadrenocorticism in the Nova Scotia duck tolling retriever. Similar haplotypes shared between breeds were demonstrated, with DLA-DRB1*001:01--DQA1*001:01--DQB1*002:01 more prevalent in both affected Labrador (p?=?0.0002, OR?=?3.06) and WHWT (p?=?0.01, OR?=?2.11). Other haplotypes that have not previously been associated with the disease were identified. The inter-breed differences in DLA haplotypes associated with susceptibility to canine hypoadrenocorticism could represent divergent aetiologies. This could have implications for clinical diagnosis and future comparative studies. Alternatively, it may suggest that the gene of interest is closely linked to the MHC.     

Reelin induces EphB activation

The integration of newborn neurons into functional neuronal networks requires migration of cells to their final position in the developing brain, the growth and arborization of neuronal processes and the formation of synaptic contacts with other neurons. A central player among the signals that coordinate this complex sequence of differentiation events is the secreted glycoprotein Reelin, which also modulates synaptic plasticity, learning and memory formation in the adult brain. Binding of Reelin to ApoER2 and VLDL receptor, two members of the LDL receptor family, initiates a signaling cascade involving tyrosine phosphorylation of the intracellular cytoplasmic adaptor protein Disabled-1, which targets the neuronal cytoskeleton and ultimately controls the positioning of neurons throughout the developing brain. However, it is possible that Reelin signals interact with other receptor-mediated signaling cascades to regulate different aspects of brain development and plasticity. EphB tyrosine kinases regulate cell adhesion and repulsion-dependent processes via bidirectional signaling through ephrin B transmembrane proteins. Here, we demonstrate that Reelin binds to the extracellular domains of EphB transmembrane proteins, inducing receptor clustering and activation of EphB forward signaling in neurons, independently of the ''classical'' Reelin receptors, ApoER2 and VLDLR. Accordingly, mice lacking EphB1 and EphB2 display a positioning defect of CA3 hippocampal pyramidal neurons, similar to that in Reelin-deficient mice, and this cell migration defect depends on the kinase activity of EphB proteins. Together, our data provide biochemical and functional evidence for signal integration between Reelin and EphB forward signaling.     

Species composition of skates (Rajidae) in commercial fisheries around the British Isles and their discarding patterns

Recent regulations have required European nations to report commercial landings of Rajidae (skates) to species level since 2008. Morphological similarities between some species, variability in colouration and regional differences in common names may compromise the accuracy of some of these data. An increased proportion of rajid landings reported by the U.K. (England, Wales and Northern Ireland) are now reported to species level (42% in 2008, rising to 92% in 2010). Recent landings (2007-2010) of Rajidae by the U.K. indicated that the majority of reported landings were made by otter trawl (55·9%), tangle and gillnet (18·7%) and beam trawl (15·5%). Approximately 70% of recent landings originated from four ICES Divisions: the Irish Sea (VIIa), western English Channel (VIIe), Bristol Channel (VIIf) and southern North Sea (IVc). Recent species-specific landings of Rajidae are appraised in terms of the species reported and the overall composition, and potential problems identified. Data from observer trips have been used to estimate the species composition of Rajidae taken in some of the main commercial fisheries operating around the British Isles, and these data are compared to landings. Although there was typically broad agreement between these data sets in terms of the main species landed, misidentification issues were apparent and Rajidae with highly patchy distributions may be under-represented in observer data. Data from observer trips were also used to examine the discard and retention pattern. Most rajid species were first retained from total lengths, L(T) , of 27-34 cm, with 50% retention occurring at between 49 and 51 cm and near-full retention at L(T) of 60-67 cm. Beam trawls captured a higher proportion of smaller individuals, whilst gillnets (>150 mm mesh size) caught proportionally more larger rajids.     

Replication of staphylococcal plasmid pT48

Insertion of a synthetic DNA linker into the repL gene of staphylococcal plasmid pT48 inactivates the replication system. This defect can be complemented in trans by the presence of a pT48 repL gene, but not by the rep genes of the related Staphylococcus areus plasmids pSN2 and pOX1000. Comparison of the sequences of the three replication proteins indicates that specificity may be determined by a putative helix-turn-helix region.     

Comparison of protein transduction domains in mediating cell delivery of a secreted CRE protein

Protein transduction domains (PTDs) are versatile peptide sequences that facilitate cell delivery of several cargo molecules including proteins. PTDs usually consist of short stretches of basic amino acids that can cross the plasma membrane and gain entry into cells. Traditionally, to assess PTD mediated protein delivery, PTD-fusion proteins have been used as purified proteins. To overcome the requirement for a protein purification step, we used a secretory signal peptide to allow PTD-CRE fusion proteins to be exported from transfected mammalian cells. PTD induced protein transduction into cells was assessed by a CRE-mediated recombination event that resulted in beta-galactosidase expression. Several PTDs were tested including the prototypic TAT, different TAT variants, Antp, MTS and polyarginine. A negative correlation was observed between the cationic charge on the PTD and the extent of secretion. Poor secretion was found when the PTD charge was greater than +5. One TAT-CRE protein variant had a 14-fold enhancement above CRE alone when added to cells in the presence of chloroquine. This PTD domain also enhanced gene expression after plasmid delivery. These data illustrate that some secreted PTD proteins may be useful reagents to improve protein delivery in mammalian systems and a novel approach to enhancing the response to DNA transfections.     

Stability of Metabolic Correlations under Changing Environmental Conditions in Escherichia coli – A Systems Approach

Background

Biological systems adapt to changing environments by reorganizing their cellular and physiological program with metabolites representing one important response level. Different stresses lead to both conserved and specific responses on the metabolite level which should be reflected in the underlying metabolic network.

Methodology/Principal Findings

Starting from experimental data obtained by a GC-MS based high-throughput metabolic profiling technology we here develop an approach that: (1) extracts network representations from metabolic condition-dependent data by using pairwise correlations, (2) determines the sets of stable and condition-dependent correlations based on a combination of statistical significance and homogeneity tests, and (3) can identify metabolites related to the stress response, which goes beyond simple observations about the changes of metabolic concentrations. The approach was tested with Escherichia coli as a model organism observed under four different environmental stress conditions (cold stress, heat stress, oxidative stress, lactose diauxie) and control unperturbed conditions. By constructing the stable network component, which displays a scale free topology and small-world characteristics, we demonstrated that: (1) metabolite hubs in this reconstructed correlation networks are significantly enriched for those contained in biochemical networks such as EcoCyc, (2) particular components of the stable network are enriched for functionally related biochemical pathways, and (3) independently of the response scale, based on their importance in the reorganization of the correlation network a set of metabolites can be identified which represent hypothetical candidates for adjusting to a stress-specific response.

Conclusions/Significance

Network-based tools allowed the identification of stress-dependent and general metabolic correlation networks. This correlation-network-based approach does not rely on major changes in concentration to identify metabolites important for stress adaptation, but rather on the changes in network properties with respect to metabolites. This should represent a useful complementary technique in addition to more classical approaches.