Department of Chemistry

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IIT Jodhpur

In the quest for indium-tin oxide (ITO)-free photovoltaics and for building integrated as well as automobile roof applications, novel transparent electrodes for both front and back electrodes are required. Here we report the fabrication and integration of submicrometer transparent silver (Ag) and gold (Au) metal network electrodes, which are invisible to the naked eye, in organic photovoltaic devices. We exploit the idea of using the spontaneous cracking of a polymer layer as template to prepare the metal network. The main challenge is to apply the cracked template approach on top of soluble organic layers and to lift off the template without damaging the photoactive layer. We demonstrate that Ag or Au back electrodes can be fabricated maintaining a transmittance of 80% for the whole visible range. These electrodes exhibit ultralow haze of approximately 5% and an excellent figure of merit value. Moreover, the ITO-free semitransparent polymer solar cell incorporating the Ag/Ag network electrodes exhibits 57% transmittance above 650nm. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

World University root node

Energy Technology

Transparent Metal Network with Low Haze and High Figure of Merit applied to Front and Back Electrodes in Semitransparent ITO-free Polymer Solar Cells

In this paper, we propose a distorted information diffusion protocol to detect diversity of different network models. The protocol is inspired by the fact that, in real social networks, the information diffusion get influenced by the property of nodes and conduct of the links. Thus, information get deformed/distorted during diffusion process and true amount of information from a spreader never reach to all the nodes in the network. We consider a single spreader which has maximum degree in the network. We divide the entire network in to different layers where the nodes in a layer are defined by the nodes having a fixed distance from the spreader. We observe that the amount of information available at every node in a layer after the diffusion process reaches to saturation, is not equal. Thus, we define density of information profile of a layer that measures the density of information available in a layer. Finally, we define a vector, which we call information diversity vector whose components are density of information of the layers. The dimension of the diversity vector is the number of layers in the entire network. We implement the protocol in standard network models which include Albert-Barabasi preferential attachment Model (ABM), Hierarchial network generation Model (HM), and Watts-Strogatz Model (WSM). We also simulate the protocol in real world networks which include ego-Face book Network, Collaboration network of ArXiv General Relativity, and Collaboration network of ArXiv High Energy Physics Theory. The simulated results show that the information diversity vectors of ABM and HM is far from reflecting the same in real world networks. However, diversity vector of WSM is similar to that of real world networks which we consider in this paper.

Measuring diversity of network models using distorted information diffusion process

A stable gel of Au nanoparticles in polydimethylsiloxane (PDMS) nanocomposite is prepared by employing the curing agent of PDMS elastomer as a reducing agent for the formation of Au nanoparticles by an in-situ process. The viscoelastic nature of these gels is very sensitive to the Au nanoparticle loading and the synthetic temperature conditions. Even a very low Au content of 0.09 wt% is sufficient enough to bring in the transition from sponge state to gel state at room temperature. Higher synthetic temperature also forms sponge formation. Infrared and ultraviolet-visible spectroscopy measurements have provided insight into PDMS crosslinking and nanoparticle formation, respectively. The optimization of the gel properties can have direct influence on the processability of Au nanoparticle-PDMS nanocomposite gels, with interesting implications in electronic, optical and microfluidic devices. © Indian Academy of Sciences.

Fulltext

Bulletin of Materials Science

Viscoelastic nature of Au nanoparticle-PDMS nanocomposite gels

Advanced Synthesis and Catalysis

Erratum: Organocatalytic Enantioselective Synthesis of Polysubstituted Spirooxindoles using a Tandem Michael-Michael Reaction (Advanced Synthesis and Catalysis (2015) 12 (2633-2638))

In the presence of bidentate 1,n-bis-diphenylphosphinoalkane-CoCl2 complexes {Cl2Co[P ∼ P]} and Me3Al or methylaluminoxane, acyclic (E)-1,3-dienes react with ethylene (1 atmosphere) to give excellent yields of hydrovinylation products. The regioselectivity (1,4- or 1,2-addition) and the alkene configuration (E- or Z-) of the resulting product depend on the nature of the ligand and temperature at which the reaction is carried out. Cobalt(ii)-complexes of 1,1-diphenylphosphinomethane and similar ligands with narrow bite angles give mostly 1,2-addition, retaining the E-geometry of the original diene. Complexes of most other ligands at low temperature (-40°C) give almost exclusively a single branched product, (Z)-3-alkylhexa-1,4-diene, which arises from a 1,4-hydrovinylation reaction. A minor product is the linear adduct, a 6-alkyl-hexa-1,4-diene, also arising from a 1,4-addition of ethylene. As the temperature is increased, a higher proportion of the major branched-1,4-adduct appears as the (E)-isomer. The unexpectedly high selectivity seen in the Co-catalysed reaction as compared to the corresponding Ni-catalysed reaction can be rationalized by invoking the intermediacy of an η4-[(diene)[P ∼ P]CoH]+-complex and its subsequent reactions. The enhanced reactivity of terminal E-1,3-dienes over the corresponding Z-dienes can also be explained on the basis of the ease of formation of this η4-complex in the former case. The lack of reactivity of the X2Co(dppb) (X = Cl, Br) complexes in the presence of Zn/ZnI2 makes the Me3Al-mediated reaction different from the previously reported hydroalkenylation of dienes. Electron-rich phospholanes, bis-oxazolines and N-heterocyclic carbenes appear to be poor ligands for the Co(ii)-catalysed hydrovinylation of 1,3-dienes. An extensive survey of chiral ligands reveals that complexes of DIOP, BDPP and Josiphos ligands are quite effective for these reactions even at -45°C and enantioselectivities in the range of 90-99% ee can be realized for a variety of 1,3-dienes. Cobalt(ii)-complex of an electron-deficient Josiphos ligand is especially active, requiring only <1 mol% catalyst to effect the reactions. © 2015 Royal Society of Chemistry.

Chemical Science

Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes

The article elaborates the development of gravity-based water filtration systems capable of removing fluoride using natural organic material. In this study, the precipitation and dissolution reaction occurring in suspension of hydroxyapatite (HAP) as addition of fluoride were investigated under well-defined condition. This process is set to occur in a quasi-static gravity-based water filter system. This system is a (pond sand, organic material (gaur seed powder, neem, sesame sawdust, and Ayurvedic waste), water, and HAP mixture) composite ceramic. This article illustrates these ceramic material systems manufactured using distinct permutations of pond sand and organic materials. HAP is introduced into the composite mix of pond sand and organic materials to manufacture some of the sintered ceramic filtration material systems tested here. The fluoride removal efficiency of these variant systems is discussed. The energy dispersive X-ray spectroscopy studies of the ceramics provided the mineral content within the system variants. At high temperatures beyond 600°C, the sintered hydroxyapatite is observed to have a microstructural transformation from amorphous to crystalline. The surface properties of these sintered as well as raw materials used in the production of the ceramic composite are also investigated. A mathematical multivariate regression model is derived providing a relationship between the effectiveness of the water filtration systems as a function of the raw material composition and properties. The Ayurvedic waste material was found to be a good substitute for HAP for fluoride removal. The proposed treatment system is appropriate and suitable approach for fluoride removal in rural areas, because of its simplicity and easy operation and handling. Since Ayurvedic and organic waste materials are easily available at low cost, the proposed method is very suitable for the people living in low-income rural areas of developing countries like India. © 2014 Balaban Desalination Publications. All rights reserved.

Department of Mechanical Engineering

Desalination and Water Treatment

Local material composite sintered systems for fluoride removal

Rotational reorientation times of a newly synthesized 2,5-bis(phenylethynyl)1,4-bis(dodecyloxy) benzene (DDPE) are experimentally determined in series of n-alkanes by employing steady state and time resolved fluorescence depolarization technique with a view to understand rotational dynamics of large non-polar solute molecule in non-polar solvents and few general solvents of different sizes and varying viscosity. It is observed that rotational reorientation times vary linearly as function of viscosity. The hydrodynamic stick condition describes the experimental results at low viscosities while the results tend to deviate significantly from it at higher viscosities. This is attributed to the possibility of long chains in solvents hosting a variety of chain defects (end-gauche, double-gauche, all-trans, kink, etc.) thereby reducing the effective length of the molecule, leading to a slightly reduced friction. The experimental results are compared with the predictions of Stokes-Einstein-Debye (SED) hydrodynamic theory as well as the quasi-hydrodynamic theories of Gierer-Wirtz (GW) and Dote-Kivelson-Shwartz (DKS). The predictions from these theories underestimate τr in the solvents employed in the study. © 2015 Springer Science+Business Media New York.

Journal of Fluorescence

Rotational Diffusion of a New Large Non Polar Dye Molecule in Alkanes

A transparent electrode is a key component of any optoelectronic or transparent device. With increasing number of large area applications, there is growing demand to replace the conventional oxide based transparent conducting films with nanomaterials, primarily to reduce the cost. This review deals with a range of materials and processes forming new generation transparent electrodes, while giving some insight into the cost. © 2015 Elsevier Ltd. All rights reserved.

Current Opinion in Chemical Engineering

Towards low cost materials and methods for transparent electrodes

Roll and spray coating methods have been employed for the fabrication of highly oxidation resistant transparent and conducting electrodes (TCEs) by a simple solution process using crackle lithography technique. We have spray-coated a crackle paint-based precursor to produce highly interconnected crackle network on PET roll mounted on a roll coater with web speed of 0.6 m/min. Ag TCE with a transmittance of 78% and sheet resistance of ∼20 Ω/□ was derived by spraying Ag precursor ink over the crackle template followed by lift-off and annealing under ambient conditions. The Ag wire mesh was stable toward bending and sonication tests but prone to oxidation in air. When electrolessly coated with Pd, its robustness toward harsh oxidation conditions was enhanced. A low-cost transparent electrode has also been realized by using only small amounts of Ag as seed layer and growing Cu wire mesh by electroless method. Thus, made Ag/Cu meshes are found to be highly stable for more than a year even under ambient atmosphere. © 2015 American Chemical Society.

ACS Applied Materials and Interfaces

Fabrication of Oxidation-Resistant Metal Wire Network-Based Transparent Electrodes by a Spray-Roll Coating Process

Flexible, semitransparent and robust heating arrays have been designed by grayscale printing as ready-to-use devices for point-of-care application. A perforated Ag mesh is first fabricated with tunable features by controllably varying the toner grayscale value during laser printer on PET. The resistance could be varied between 1 to 2Ω by tuning the Ag fill factor from 50 to 70%. The Ag/PET heater based on joule heating is able to attain highly stable temperatures upto ∼135°C maintained over long hours. Since temperature is directly related to resistance, this provides a fine temperature knob without any cumbersome processing steps. The merit of design allows individual heating elements to attain stable temperatures at low voltages (∼1.5V) without any interference from neighboring heaters of the array, thus resulting in a thermal library. A laptop USB with 5.1V output is able to power the thermal library for temperatures in the range of 30-60°C, useful in many practical applications. It is a multipurpose disposable chip for in-situ transmission microscopy that can be utilized for bioassay and point-of-care diagnostics, as demonstrated in the study. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.