Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).

https://science.sciencemag.org/content/sci/early/2017/02/01/science.aai9081.full.pdf

Efficient and stable solution-processed planar perovskite solar cells via contact passivation.

The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Multi-Criteria Decision Aid (MCDA) or Multi-Criteria Decision Making (MCDM) methods have received much attention from researchers and practitioners in evaluating, assessing and ranking alternatives across diverse industries. Among numerous MCDA/MCDM methods developed to solve real-world decision problems, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) continues to work satisfactorily across different application areas. In this paper, we conduct a state-of-the-art literature survey to taxonomize the research on TOPSIS applications and methodologies. The classification scheme for this review contains 266 scholarly papers from 103 journals since the year 2000, separated into nine application areas: (1) Supply Chain Management and Logistics, (2) Design, Engineering and Manufacturing Systems, (3) Business and Marketing Management, (4) Health, Safety and Environment Management, (5) Human Resources Management, (6) Energy Management, (7) Chemical Engineering, (8) Water Resources Management and (9) Other topics. Scholarly papers in the TOPSIS discipline are further interpreted based on (1) publication year, (2) publication journal, (3) authors' nationality and (4) other methods combined or compared with TOPSIS. We end our review paper with recommendations for future research in TOPSIS decision-making that is both forward-looking and practically oriented. This paper provides useful insights into the TOPSIS method and suggests a framework for future attempts in this area for academic researchers and practitioners.

Review: A state-of the-art survey of TOPSIS applications

The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

/pdf/validity-of-cubic-law-for-fluid-flow-in-a-deformable-rock-2ynq4id3hq.pdf

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Time is divided by geologists according to marked shifts in Earth's state. Recent global environmental changes suggest that Earth may have entered a new human-dominated geological epoch, the Anthropocene. Here we review the historical genesis of the idea and assess anthropogenic signatures in the geological record against the formal requirements for the recognition of a new epoch. The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964. The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.

Defining the Anthropocene

Sand and gravels are basic construction raw material globally. With increased economic activity, rate of extraction of sand and gravels has gone up three folds during last two decades reaching 40 billion tonnes per year. Critical hot spots for sand extraction are China and India. Uncontrolled illegal sand mining is common – reduction in ground water level and water transparency, increased water turbidity, adverse impact on birdlife. It is estimated that every year 10 million cubic meters of sand is extracted in Morocco by sand mafias converting large sand beaches into rocky landscape. Singapore has extended its area by 20% by importing 517 million tonnes of sand over last 20 years from neighbouring countries. Some of the countries like India and Malaysia have developed river sand mining guidelines to ensure equilibrium of river, avoid aggradation of hydraulic structures, protection of rivers against erosion, and avoid water pollution. Principal of sustainability is based on equilibrium of meeting business objectives, environmental compliance and social compliance of various stake holders. Tipple bottom line pillars for sustainability include financial stability, environmental stewardship and social equity. For minimizing environmental effect due river sand mining, many countries have adopted technology of manufacturing sand through series of crushers – primary jaw crusher, secondary cone crusher and tertiary vertical shaft impact (VSI) crusher. Japan has developed V7 dry sand manufacturing technology. Manufacturing Sand (M-Sand) has comparable gradation with river sand. Various technical specifications of aggregates and M-Sand adopted by India and US are provided in this paper. There is need of creating R&D facilities in every region for sustainability to develop specifications of M-Sand based on available resources and meet local sand requirement.

River Sand Mining Vis a Vis Manufactured Sand for Sustainability

Digital rock physics and application of high-resolution micro-CT techniques for geomaterials

The influence of discontinuities on coal measures is manifested in the form of roof and side falls, caving of the roof and sometimes in subsidence of the ground surface. This review paper is confined to roof falls due to major geological discontinuities (such as faults, joints, cleats and bedding planes) and to possible ways and means to prevent these falls. Faults with an increased frequency of joints and cleats around them, slips and slickensides play a major role in coal-mine-roof instability. Joints and cleats running parallel to roadways and thinly bedded strata in the immediate roof area also contribute to strata-instability problems. A roof-fall index has been developed relating roof instability to the presence of geological discontinuities. Significant control of such instabilities is possible by orienting roadways across the geological discontinuities and by increasing the quality and density of the supports.

Effect of discontinuities on strata-movement problems in collieries: a review

Roadways are the lifeline for any city, especially in hilly regions. The increase in population and road constructions has led to the destabilization of the slopes resulting in mass movement. Anisotropic rockmass, whose behaviour is largely dependent on the planes of weakness, was simulated using 3DEC. The three-dimensional discontinuum modelling technique provides the most rigorous analysis of the failure process and deformation in the anisotropic rock. However, due to the limited capacity of the software, it is impossible to include all the discontinuities implicitly in numerical simulation. This paper provides a methodology for the application of Ubiquitous-Joint models on a field scale to include the anisotropic behaviour of rockmass. After identifying the failure-prone area using rigorous 3DEC slope stability analysis, rockfall analysis was also carried out to identify the maximum run-out, bounce height and total kinetic energy of falling rock blocks in the same section of the slope. 3DEC results show the maximum total displacement of 2.6 cm with a maximum velocity of 0.25 m/s, which confirms the instability in the slope. The rockfall simulation reveals that the falling rock blocks can hit the vehicle on the roadway with the kinetic energy of 58.5 kJ that makes this roadway unsafe.

A case study on the rockfall assessment and stability analysis along Lengpui-Aizawl highway, Mizoram, India

We demonstrate how to establish reliable contacts to SnO2 nano-wires by growing these nano-wire on-chip on gold contacts deposited on alumina. The sensor device is used to sense the concentrations of acetone and ethanol in air and their reaction kinetics. Acetone molecules have higher adsorption and desorption rates on SnO2 nanowires than ethanol molecules which leads to a lower critical acetone concentration at which the SnO2 sensor saturates than is the case for ethanol. These differences suggest a new way of introducing selectivity to the notoriously non-selective SnO2 and other oxide-based nano-scale sensors.

Trilok Singh

Papers

River Sand Mining Vis a Vis Manufactured Sand for Sustainability

Digital rock physics and application of high-resolution micro-CT techniques for geomaterials

Effect of discontinuities on strata-movement problems in collieries: a review

A case study on the rockfall assessment and stability analysis along Lengpui-Aizawl highway, Mizoram, India

Tin dioxide nano-wire device for sensing kinetics of acetone and ethanol towards diabetes monitoring