Recent advances and remaining challenges in thin-film silicon photovoltaic technology

This contribution reviews some of the latest achievements and challenges in thin-film silicon photovoltaic (PV) technology based on amorphous and nanocrystalline silicon and their alloys. We address material and device developments, including (i) improved plasma deposition processes to achieve high-quality dense absorber materials; (ii) absorber layers based on silicon tetrafluoride, which lead to enhanced absorption in the near-infrared and yield outstanding short-circuit current densities; (iii) dedicated optimization of the interfaces and device architecture, as well as (iv) enhanced light harvesting by means of multi-scale textured substrates and reduced parasitic absorption in the non-active layers. This paper will describe how, by combining all of these advances along with precise control of plasmas over large areas, key results have been achieved in recent years, at both the cell and large-area module level, with stabilized efficiencies of over 13 and 12%, respectively

Operationalising ethical challenges in dementia research:a systematic review of current evidence

BACKGROUND: the worldwide number of dementia cases is increasing, and this is a trend that is expected to continue as a growing proportion of the population ages. However, conducting research with persons suffering from dementia can be fraught due to fears surrounding research risks in vulnerable populations. This can make seeking approval for studies difficult. As research directly involving persons with dementia is key for the development of evidence-based best practice, the development of a coherent ethical strategy to perform such research feasibly and effectively is of paramount importance. OBJECTIVE: this paper aims to review and synthesise ethical challenges in performing research with persons who have dementia. METHODS: in undertaking a systematic review of the current research literature, we will identify the central issues and arguments characterising research that concerns the ethical dimensions of research participation in the dementia population. Data were analysed using both inductive and deductive content analysis. Ethical considerations in research involving persons with dementia primarily concern the representation of the interests of the person with dementia and protection of their vulnerabilities and rights. RESULTS: a total of 2,894 results were returned from initial searches, following deduplication. In total, 2,458 were excluded at title review, and following abstract review 158 papers remained; 29 papers were included for analysis after full paper review and data extraction. Papers ranged between 1995 and 2013. CONCLUSION: this review has highlighted a lack of consensus in current research and guidelines addressing these concerns; a clear stance on ethical governance of studies is important for future research and best evidence-based practice in dementia

Time evolution of surface defect states in hydrogenated amorphous silicon studied by photothermal and photocurrent spectroscopy and optical simulation

The time evolution of surface defect density and width of space charge region in thin layer of amorphous silicon is observed experimentally by Fourier transform photocurrent spectroscopy. This work reviews the assumption that photocurrent is insensitive to surface defects for samples thinner than 1500 nm. We show that correct evaluation based on simple optical model comprising layers representing surface defects and layers representing space charge region with reduced collection allows obtaining the same results as from photothermal deflection spectroscopy. Our main approach is the comparison of photocurrent or photothermal deflection spectra measured in absorptance/transmittance mode from layer and substrate side of the thin film. (C) 2011 Elsevier B.V. All rights reserved

Effects of Xrays on Perovskite Solar Cells

Synchrotron micro- and nanoprobe beamlines have demonstrated great potential to advance photovoltaic devices. Most importantly, their small X-ray spot size has enabled the direct correlation of electrical performance with elemental composition at subgrain resolution for a variety of polycrystalline solar cells. Whereas the bulk of most inorganic semiconductors is stable under the high X-ray flux of focused X-ray beams, semiconductors with organic components are prone to a variety of degradation mechanisms. This is particularly critical to evaluate for the emerging organometal halide perovskite solar cells. Here, we investigate the effects of hard X-rays on the nanoscale performance and elemental distribution of these solar cells. We show that their composition does not change during common operando and in situ measurements at synchrotron nanoprobes. However, we found a significant X-ray-induced electronic degradation of solar cells with methylammonium lead iodide absorbers. Time- and dose-dependent measurements unveiled two characteristic degradation time constants on the order of 12 and 200 s that are independent of the X-ray flux. On the basis of heat and dose simulations, we attribute the fast decay to the dose-driven creation of recombination centers, while the slow decay is compatible with the observation of compositional changes. Finally, we detail how degradation-induced measurement artifacts can be outrun and showcase the high correlation of the X-ray-beam-induced current with the iodine and lead distribution