Cooling a Band Insulator with a Metal: Fermionic Superfluid in a Dimerized Holographic Lattice

A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces aband insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal ``cools'' the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature - even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states.

Development of SnS quantum dot solar cells by SILAR method

SnS quantum dot solar cell is fabricated by Successive Ionic Layer Adsorption and Reaction (SILAR) method. SnS layer is optimized by different SILAR cycles of deposition. The particle size increased with the increase in number of SILAR cycles. Cu2S coated FTO is used as counter electrode against the conventional Platinum electrode. On comparison with a cell having a counter electrodeelectrolyte combination of Platinum-Iodine, Cu2S-polysulfide combination is found to improve both the short circuit current and fill factor of the solar cell. A maximum efficiency of 0.54% is obtained with an open circuit voltage of 311 mV and short circuit current density of 4.86 mA/cm. (C) 2014 Elsevier Ltd. All rights reserved.

ZnO/ITO core/shell nanostructure electrodes for future prototype solar cell devices

The impact of indium tin oxide (ITO) layers over vertically aligned zinc oxide nanorods (ZnO NRs) has been investigated to consider ITO nanolayers as transparent conducting oxide electrodes (TCOE) for hierarchical heteronanostructure solar cell devices that have ZnO nanostructures as branches. ZnO/ITO core/shell nanostructures were prepared in two- steps using vapor-liquid-solid and evaporation processes, and further the structures were annealed at various temperatures. Transmission electron microscopic studies show that the as-grown ZnO/ITO structures consist of an amorphous ITO shell on single crystalline ZnO cores, whereas the structures annealed above 300 degrees C consist of a single crystalline ITO shell. ITO layer deposited ZnO NRs exhibit a small red-shift in ZnO near-band-edge emission as well as optical band gap. The electrical measurements carried out on single ZnO/ITO core/shell NR under dark and UV light showed excellent thermionic transport properties. From these investigations it is emphasized that ITO nanolayers could be used as TCO electrodes for prototype ZnO based hierarchical solar cell devices.

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

Two novel triads based on a diketopyrrolopyrrole (DPP) central core and two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) units attached by thiophene rings have been synthesised having high molar extinction coefficients. These triads were characterised and used as donor materials in small molecule, solution processable organic solar cells. Both triads were blended with PC71BM as an acceptor in different ratios by wt% and their photovoltaic properties were studied. For both the triads a modest photovoltaic performance was observed, having an efficiency of 0.65%. Moreover, in order to understand the ground and excited state properties and vertical absorption profile of DPP and BODIPY units within the triads, theoretical DFT and TDDFT calculations were performed.

Heterogeneity in Dye-TiO2 Interactions Dictate Charge Transfer Efficiencies for Diketopyrrolopyrrole-Based Polymer Sensitized Solar Cells

Power conversion efficiency of a solar cell is a complex parameter which usually hides the molecular details of the charge generation process. For rationally tailoring the overall device efficiency of the dye-sensitized solar cell, detailed molecular understanding of photoinduced reactions at the dye-TiO2 interface has to be achieved. Recently, near-IR absorbing diketopyrrolopyrrole-based (DPP) low bandgap polymeric dyes with enhanced photostabilities have been used for TiO2 sensitization with moderate efficiencies. To improve the reported device performances, a critical analysis of the polymerTiO(2) interaction and electron transfer dynamics is imperative. Employing a combination of time-resolved optical measurements complemented by low temperature EPR and steady-state Raman spectroscopy on polymerTiO(2) conjugates, we provide direct evidence for photoinduced electron injection from the TDPP-BBT polymer singlet state into TiO2 through the C-O group of the DPP-core. A detailed excited state description of the electron transfer process in films reveals instrument response function (IRF) limited (<110 fs) charge injection from a minor polymer fraction followed by a picosecond recombination. The major fraction of photoexcited polymers, however, does not show injection indicating pronounced ground state heterogeneity induced due to nonspecific polymerTiO(2) interactions. Our work therefore underscores the importance of gathering molecular-level insight into the competitive pathways of ultrafast charge generation along with probing the chemical heterogeneity at the nanoscale within the polymerTiO2 films for optimizing photovoltaic device efficiencies.

Influence of dynamic operating conditions on the performance of metal hydride based solid sorption cooling systems

The performance of metal hydride based solid sorption cooling systems depends on the driving pressure differential, and the rate of hydrogen transfer between coupled metal hydride beds during cooling and regeneration processes. Conventionally, the mid-plateau pressure difference obtained from `static' equilibrium PCT data are used for the thermodynamic analysis. It is well known that the processes are `dynamic' because the pressure and temperature, and hence the concentration of the hydride beds, are continuously changing. Keeping this in mind, the pair of La0.9Ce0.1Ni5 - LaNi4.7Al0.3 metal hydrides suitable for solid sorption cooling systems were characterised using both static and dynamic methods. It was found that the PCT characteristics, and the resulting enthalpy (Delta H) and entropy (Delta S) values, were significantly different for static and dynamic modes of measurements. In the present study, the solid sorption metal hydride cooling system is analysed taking in to account the actual variation in the pressure difference (Delta P) and the dynamic enthalpy values. Compared to `static' property based analysis, significant decrease in the driving potentials and transferrable amounts of hydrogen, leading to decrease in cooling capacity by 57.8% and coefficient of performance by 31.9% are observed when dynamic PCT data at the flow rate of 80 ml/min are considered. Copyright 2014 (C) Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Narrow band gap conjugated polymer for improving the photovoltaic performance of P3HT:PCBM ternary blend bulk heterojunction solar cells

A new D-A structured conjugated polymer (PBDO-T-TDP) based on electron-rich benzo 1,2-b:4,5-b'] difuran (BDO) containing conjugated alkylthiophene side chains with an electron-deficient diketopyrrolopyrrole (DPP) derivative is designed and synthesized. The polymer shows a narrow band gap with broad UV-Visible absorption spectra, which is in contrast to that of the P3HT:PCBM binary blend. Furthermore, its energy levels can meet the energetic requirement of the cascaded energy levels of P3HT and PCBM. Therefore, PBDO-T-TDP is used as a sensitizer in P3HT: PCBM based BHJ solar cells and its effect on their photovoltaic properties was investigated by blending them together at various weight ratios. It is observed that the resulting ternary blend system exhibited a significant improvement in the device performance (similar to 3.10%) as compared with their binary ones (similar to 2.15%). Such an enhancement in the ternary blend system is ascribed to their balanced hole and electron mobility along with uniform distribution of PBDO-T-TDP in the blend system, as revealed by organic field effect transistors and AFM studies.

The Relationship Between Solar Coronal X-Ray Brightness and Active Region Magnetic Fields: A Study Using High-Resolution Hinode Observations

By using high-resolution observations of nearly co-temporal and co-spatial Solar Optical Telescope spectropolarimeter and X-Ray Telescope coronal X-ray data onboard Hinode, we revisit the problematic relationship between global magnetic quantities and coronal X-ray brightness. Co-aligned vector magnetogram and X-ray data were used for this study. The total X-ray brightness over active regions is well correlated with integrated magnetic quantities such as the total unsigned magnetic flux, the total unsigned vertical current, and the area-integrated square of the vertical and horizontal magnetic fields. On accounting for the inter-dependence of the magnetic quantities, we inferred that the total magnetic flux is the primary determinant of the observed integrated X-ray brightness. Our observations indicate that a stronger coronal X-ray flux is not related to a higher non-potentiality of active-region magnetic fields. The data even suggest a slightly negative correlation between X-ray brightness and a proxy of active-region non-potentiality. Although there are small numerical differences in the established correlations, the main conclusions are qualitatively consistent over two different X-ray filters, the Al-poly and Ti-poly filters, which confirms the strength of our conclusions and validate and extend earlier studies that used low-resolution data. We discuss the implications of our results and the constraints they set on theories of solar coronal heating.

Influence of plate length and plate cooling rate on solidification and microstructure of A356 alloy produced by oblique plate

A356 alloy melt solidifies partially when it flows down on an oblique plate cooled from bottom by counter flowing water. Columnar dendrites are continuously formed on the plate wall. Because of the forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously by producing semisolid slurry at plate exit. Plate cooling rate provides required extent/amount of solidification whereas plate length enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained is solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets are also heat-treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets are compared. The effects of plate length and plate cooling rate on solidification and microstructure of billets produced by using oblique plate are illustrated. Three different plate lengths (200 mm, 250 mm, 300 mm) associated with three different heat transfer coefficients (1000, 2000 and 2500 W/(m(2).K)) are involved. Plate length of 250 mm with heat transfer coefficient of 2000 W/(m(2).K) gives fine and globular microstructures and is the optimum as there is absolutely no possibility of sticking of slurry to plate wall.

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

The preparation of ZnO nanorod films decorated with cobalt-acetate (CoAc) electrocatalyst and its activity for photoelectrolysis of water have been demonstrated. The photochemically prepared CoAc catalyst is chemically and morphologically similar to the electrochemically prepared CoAc catalyst. The on-set potential of oxygen evolution reaction is lower on CoAc-ZnO photoanode in relation to bare ZnO photoanode. There is a three to four fold increase in photooxidation current of OER due to the presence of CoAc co-catalyst on ZnO. Thus, the photochemically prepared CoAc on ZnO is an alternative and efficient co-catalyst for photoelectrochemical oxygen evolution reaction. The enhancement in photocatalytic activity of ZnO by the CoAc catalyst photochemically deposited from acetate buffer solution is significantly greater than the cobalt-phosphate (CoPi) co-catalyst deposited from phosphate buffer solution. (C) The Author(s) 2015. Published by ECS. All rights reserved.

Fabrication of back contacts using laser writer and photolithography for inscribing textured solar cells

Semiconductor fabrication process begins with photolithography. Preparing a photo mask is the key process step in photolithography. The photo mask was fabricated by inscribing patterns directly onto a soda lime glass with the help of a laser beam, as it is easily controllable. Laser writer LW405-A was used for preparing the mask in this study. Exposure wavelength of 405 nm was used, with which 1.2 mu m feature size can be written in direct write-mode over the soda lime glass plate. The advantage of using the fabricated mask is that it can be used to design back contacts for thin film Photovoltaic (PV) solar cells. To investigate the process capability of LW405-A, same pattern with different line widths was written on soda lime glass samples at different writing speeds. The pattern was inscribed without proximity effect and stitching errors, which was characterized using optical microscope and field emission scanning electron microscope (FE-SEM). It was proven that writing speed of a mask-writer is decided according to the intended feature size and line width. As the writing speed increases, the edges of the patterns become rougher due to uneven scattering of the laser beam. From the fabricated mask, the solar cell can be developed embedding both the contacts at the bottom layer, to increase the absorption of solar radiation on the top surface effectively by increasing light absorption area.

Modeling of solar radiation management: a comparison of simulations using reduced solar constant and stratospheric sulphate aerosols

The climatic effects of Solar Radiation Management (SRM) geoengineering have been often modeled by simply reducing the solar constant. This is most likely valid only for space sunshades and not for atmosphere and surface based SRM methods. In this study, a global climate model is used to evaluate the differences in the climate response to SRM by uniform solar constant reduction and stratospheric aerosols. Our analysis shows that when global mean warming from a doubling of CO2 is nearly cancelled by both these methods, they are similar when important surface and tropospheric climate variables are considered. However, a difference of 1 K in the global mean stratospheric (61-9.8 hPa) temperature is simulated between the two SRM methods. Further, while the global mean surface diffuse radiation increases by similar to 23 % and direct radiation decreases by about 9 % in the case of sulphate aerosol SRM method, both direct and diffuse radiation decrease by similar fractional amounts (similar to 1.0 %) when solar constant is reduced. When CO2 fertilization effects from elevated CO2 concentration levels are removed, the contribution from shaded leaves to gross primary productivity (GPP) increases by 1.8 % in aerosol SRM because of increased diffuse light. However, this increase is almost offset by a 15.2 % decline in sunlit contribution due to reduced direct light. Overall both the SRM simulations show similar decrease in GPP (similar to 8 %) and net primary productivity (similar to 3 %). Based on our results we conclude that the climate states produced by a reduction in solar constant and addition of aerosols into the stratosphere can be considered almost similar except for two important aspects: stratospheric temperature change and the consequent implications for the dynamics and the chemistry of the stratosphere and the partitioning of direct versus diffuse radiation reaching the surface. Further, the likely dependence of global hydrological cycle response on aerosol particle size and the latitudinal and height distribution of aerosols is discussed.

New single-source precursor for bismuth sulfide and its use as low-cost counter electrode material for dye-sensitized solar cells

One new homoleptic Bi(dtc)(3)] (1) (dtc = 4-hydroxypiperdine dithiocarbamate) has been synthesized and characterized by microanalysis, IR, UV-Vis, H-1 and C-13 spectroscopy and X-ray crystallography. The photoluminescence spectrum for the compound in DMSO solution was recorded. The crystal structure of 1 displayed distorted octahedral geometry around the Bi(III) center bonded through sulfur atoms of the dithiocarbamate ligands. TGA indicates that the compound decomposes to a Bi and Bi-S phase system. The Bi and Bi-S obtained from decomposition of the compound have been characterized by pXRD, EDAX and SEM. Solvothermal decomposition of 1 in the absence and presence of two different capping agents yielded three morphologically different Bi2S3 systems which were deployed as counter-electrode in dye-sensitized solar cells (DSSCs). (C) 2015 Elsevier B.V. All rights reserved.

Comparison of performance of solar photovoltaics on dual axis tracker with fixed axis at 13 degrees N latitude

Tracking systems, that continually orient photovoltaic (PV) panels towards the Sun, are expected to increase the power output from the PV panels. Tremendous amount of research is being done and funds are being spent in order to increase the efficiency of PV cells to generate more power. We report the performance of two almost identical PV systems; one at a fixed latitude tilt and the other on a two-axis tracker. We observed that the fixed axis PV panels generated 336.3 kWh, and the dual-axis Sun-tracked PV panels generated 407.2 kWh during August 2012 March 2013. The tracked panels generated 21.2% more electricity than the optimum tilt angle fixed-axis panels. The cost payback calculations indicate that the additional cost of the tracker can be recovered in 450 days.

Photocatalytic inactivation of E-Coli by ZnO-Ag nanoparticles under solar radiation

Porous and fluffy ZnO photocatalysts were successfully prepared via simple solution based combustion synthesis method. The photocatalytic inactivation of Escherichia coli bacteria was studied separately for both Ag substituted and impregnated ZnO under irradiation of natural solar light. A better understanding of substitution and impregnation of Ag was obtained by Raman spectrum and X-ray photoelectron analysis. The reaction parameters such as catalyst dose, initial bacterial concentration and effect of hydroxyl radicals via H2O2 addition were also studied for ZnO catalyst. Effective inactivation was observed with 0.25 g L-1 catalyst loading having 10(9) CFU mL(-1) bacterial concentration. With an increase in molarity of H2O2, photocatalytic inactivation was enhanced. The effects of different catalysts were studied, and highest bacterial killing was observed by Ag impregnated ZnO with 1 atom% Ag compared to Ag substituted ZnO. This enhanced activity can be attributed to effective charge separation that is supported by photoluminescence studies. The kinetics of reaction in the presence of different scavengers showed that reaction is significantly influenced by the presence of hole and hydroxyl radical scavenger with high efficiency.