In situ observation of heat-induced degradation of perovskite solar cells

The lack of thermal stability of perovskite solar cells is hindering the progress of this technology towards adoption in the consumer market. Different pathways of thermal degradation are activated at different temperatures in these complex nanostructured hybrid composites. Thus, it is essential to explore the thermal response of the mesosuperstructured composite device to engineer materials and operating protocols. Here we produce devices according to four well-established recipes, and characterize their photovoltaic performance as they are heated within the operational range. The devices are analysed using transmission electron microscopy as they are further heated in situ, to monitor changes in morphology and chemical composition. We identify mechanisms for structural and chemical changes, such as iodine and lead migration, which appear to be correlated to the synthesis conditions. In particular, we identify a correlation between exposure of the perovskite layer to air during processing and elemental diffusion during thermal treatment. Solar cells based on lead halide perovskite composites have become increasingly popular in the past few years owing to a combination of low synthesis cost and high power conversion efficiency, with certified values in excess of 20% (refs 1,2,3,4,5). However, the stability of such devices is a concern—it is well known that heating at or above around 85 ∘C, a temperature close to those reached during normal operation in full sunlight, performance degrades rapidly, and such instability is exacerbated by exposure to moisture; systematic thermal and ageing studies are required to understand such degradation processes. Changes happen in both the organic and inorganic components of the cells; the resilience of the perovskite layer, in particular, is expected to become a limiting factor once different hole-conducting materials (or hole-conductor-free cells) are developed. To overcome this limitation, it is vital to understand the degradation pathways of the structures involved, which here are observed at nanometre-scale spatial resolution in situ, inside an analytical scanning transmission electron microscope (STEM), while the composition is monitored with elemental mapping through energy-dispersive X-ray analysis (EDX). The analysis of such devices is challenging owing to several factors. The spatial dimensions relevant to the fabrication and the operation of the cells are in the 1–100 nm range, and the materials are easily damaged by exposure to an electron beam in a TEM, requiring careful tuning of the electron dose. The system also includes organic and inorganic components in an assembly with complex chemistry and morphology. Finally, the rapid changes to the devices in air and the low degradation temperatures pose an additional challenge to the experiment, which needs to be timed appropriately and carefully executed. The monitoring of this process is made possible by combining several recent advances in TEM technology. The use of high-brightness electron guns and detectors with large collection areas allows the fast acquisition of high-quality EDX maps with limited electron dose on the sample; the signal-to-noise ratio of the maps can be further increased by applying denoising algorithms (PCA, principal components analysis) within an open-source software suite. The development of novel in situ heating holders for TEM, based on micro-heaters and featuring high stability and fast response, was also crucial—in particular, the holder used here allows very precise control (sub-degree) at values just above room temperature, as well as providing fast heating and cooling (a few seconds for the temperatures in use in this paper). The good spatial stability of the holder is crucial in acquiring EDX maps.G.D., S.C., and C.D. acknowledge funding from ERC under grant number 259619 PHOTO EM. C.D. acknowledges financial support from the EU under grant number 312483 ESTEEM2. F.M., L.C. and A.D.C. acknowledge funding from “Polo Solare Organico” Regione Lazio, the “DSSCX” MIURPRIN2010 and FP7 ITN “Destiny”. G.D and S.C. thank Dr. Francisco de la Peña and Dr. Pierre Burdet for assistance with PCA analysis.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nenergy.2015.1

The development and validation of a disease-specific quality of life measure in hyperhidrosis : the Hyperhidrosis Quality of Life Index (HidroQOL©)

This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original authors and the source are credited.PURPOSE: To develop and validate a new disease-specific quality of life measure in hyperhidrosis for use in both routine clinical practice and clinical research. METHODS: Interviews and focus group discussions with hyperhidrosis patients, reported elsewhere, provided the content for the measure validated in this study (n = 71). A panel of dermatologists (n = 5) and patients (n = 7) carried out content validation. Further, item reduction and the initial construct validation were carried out in a cross-sectional study (n = 595), using the unidimensional Rasch analysis and exploratory factor analysis. Subsequently, the construct validity, reliability and responsiveness of the revised measure were assessed in a longitudinal study (n = 260). Data collection for the item reduction and the final validation phases was entirely carried out online. RESULTS: The expert panels judged the HidroQoL as content valid. Rasch analysis supported the revision of response options from five to three. Following removal of misfitting items, a set of 15 items showed optimal fit to the model (chi-squared statistic = 159.64, p = 0.07). Three additional items were retained on consideration of their importance to patients, resulting in an 18-item instrument. The items were grouped into two subscales, daily life activities and psychosocial life domains, based on results of the factor analysis. In subsequent construct validation, the HidroQoL correlated with the DLQI (r s = 0.6, p < 0.01). Reliability was high (internal consistency, Cronbach's alpha: overall scale = 0.9; test-retest reliability, Intra-class correlation = 0.9). The HidroQoL scores were sensitive to change in patients' disease severity (score change from baseline to follow-up after 15-35 days, Cohen's ES = 0.47). CONCLUSION: This study has provided the initial evidence supporting measurement properties and the use of the HidroQoL instrument in both routine clinical practice and in research, for assessing quality of life impacts in hyperhidrosis.Peer reviewedFinal Published versio

A biohybrid synapse with neurotransmitter-mediated plasticity

Brain-inspired computing paradigms have led to substantial advances in the automation of visual and linguistic tasks by emulating the distributed information processing of biological systems1. The similarity between artificial neural networks (ANNs) and biological systems has inspired ANN implementation in biomedical interfaces including prosthetics2 and brain-machine interfaces3. While promising, these implementations rely on software to run ANN algorithms. Ultimately, it is desirable to build hardware ANNs4,5 that can both directly interface with living tissue and adapt based on biofeedback6,7. The first essential step towards biologically integrated neuromorphic systems is to achieve synaptic conditioning based on biochemical signalling activity. Here, we directly couple an organic neuromorphic device with dopaminergic cells to constitute a biohybrid synapse with neurotransmitter-mediated synaptic plasticity. By mimicking the dopamine recycling machinery of the synaptic cleft, we demonstrate both long-term conditioning and recovery of the synaptic weight, paving the way towards combining artificial neuromorphic systems with biological neural networks

How strong is the evidence for the use of perioperative β blockers in non-cardiac surgery? Systematic review and meta-analysis of randomised controlled trials

Objective To determine the effect of perioperative β blocker treatment in patients having non-cardiac surgery. Design Systematic review and meta-analysis. Data sources Seven search strategies, including searching two bibliographic databases and hand searching seven medical journals. Study selection and outcomes We included randomised controlled trials that evaluated β blocker treatment in patients having non-cardiac surgery. Perioperative outcomes within 30 days of surgery included total mortality, cardiovascular mortality, non-fatal myocardial infarction, non-fatal cardiac arrest, non-fatal stroke, congestive heart failure, hypotension needing treatment, bradycardia needing treatment, and bronchospasm. Results Twenty two trials that randomised a total of 2437 patients met the eligibility criteria. Perioperative β blockers did not show any statistically significant beneficial effects on any of the individual outcomes and the only nominally statistically significant beneficial relative risk was 0.44 (95% confidence interval 0.20 to 0.97, 99% confidence interval 0.16 to 1.24) for the composite outcome of cardiovascular mortality, non-fatal myocardial infarction, and non-fatal cardiac arrest. Methods adapted from formal interim monitoring boundaries applied to cumulative meta-analysis showed that the evidence failed, by a considerable degree, to meet standards for forgoing additional studies. The individual safety outcomes in patients treated with perioperative β blockers showed a relative risk for bradycardia needing treatment of 2.27 (95% CI 1.53 to 3.36, 99% CI 1.36 to 3.80) and a nominally statistically significant relative risk for hypotension needing treatment of 1.27 (95% CI 1.04 to 1.56, 99% CI 0.97 to 1.66). Conclusion The evidence that perioperative β blockers reduce major cardiovascular events is encouraging but too unreliable to allow definitive conclusions to be drawn