Jodhpur, India
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Sharma G.D.,Randnter for Science and Engineering | Roy M.S.,Defence Laboratory | Mikroyannidis J.A.,University of Patras | Justin Thomas K.R.,Indian Institute of Technology Roorkee
Organic Electronics: physics, materials, applications | Year: 2012

A symmetrical perylene bisimide derivative (PBI) with 2-(4-nitrophenyl) acrylonitrile groups at the 1,7 bay positions of perylene and solubilizing cyclohexyl units was synthesized and characterized. The absorption spectrum of PBI was broad with the most prominent peak at 655 nm and optical band gap of 1.72 eV. The electrochemical investigation indicates that PBI has a LUMO energy level of -3.9 eV which is similar to that of PCBM or PC70BM. Bulk heterojunction solar cell fabricated using a blend of poly(3-hexylthiophene) (P3HT) and PBI (1:1 w/w) as active layer cast from THF exhibited power conversion efficiency (PCE) at 1.56%. However, the device with P3HT:PBI blend deposited from mixed solvent (DIO/THF) improved the PCE to 2.78% which further increased to 3.17% on using the thermal annealed active layer. The improvement in the PCE is attributed to the enhanced crystallinity of the blend (particularly P3HT) and increase in hole mobility leading to balanced charge transport. © 2012 Elsevier B.V. All rights reserved.

Sharma G.D.,R and nter for Engineering and Science | Singh S.P.,Indian Institute of Chemical Technology | Roy M.S.,Defence Laboratory | Mikroyannidis J.A.,University of Patras
Organic Electronics: physics, materials, applications | Year: 2012

The improvement of near infrared wavelength sensitivity in the bulk heterojunction organic polymer solar cell based on poly (3-hexylthiophene) (P3HT) and PC 70BM, by the addition of soluble DPP-CN small molecule is reported. By incorporating DPP-CN, the photosensitivity in the longer wavelength region was improved and the power conversion efficiency (PCE) has been reached to 4.37% as compared to 3.23% for the device based on P3HT:PC 70BM blend. The increase in the PCE is attributed to the increase in light harvesting property of the blend and efficient dissociation of excitons into free charge carriers due to the increased number of D-A sites. The PCE has been further enhanced to 4.70%, when mixed solvent cast P3HT:DPP-CN:PC 70BM blend is used as photoactive layer. The optical absorption spectra of the blend showed that the blend film cast from mixed solvent broadened the absorption wavelength range. This occurred as result of a large red shift of P3HT absorption peak and same time a widening and small red shift of DPP-CN absorption peak in the blend film. The improved light harvesting property of thermally annealed film is considered to the factor responsible for the improvement in the PCE. © 2012 Elsevier B.V. All rights reserved.

Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College | Suresh P.,Jai Narain Vyas University | Roy M.S.,Defence Laboratory | Mikroyannidis J.A.,University of Patras
Journal of Power Sources | Year: 2010

We report the preparation of nanoporous TiO2 electrode modified with an insulating material-BaCO3 and used as electrode for quasi solid state dye sensitized solar cells (DSSCs), with a benzothiadiazole-based dye (BTDR2) as sensitizer and PEDOT:PSS coated FTO as counter electrode. We found that the BaCO3 modification significantly increases the dye adsorption, resulting from the fact that the surface of BaCO3 is more basic than TiO2. The performance of the DSSCs with and without BaCO3 modified TiO2 electrodes were analyzed by cyclic voltammograms, optical absorption spectra, current-voltage characteristics in dark and under illumination and electrochemical impedance spectra. The photovoltaic performance has been significantly improved for the BaCO3 modified electrode as compared to bare TiO2 electrode having the same other components in the DSSCs. The value of the overall power conversion efficiency (η) improves from 2.42% to 4.38% under illumination intensity, when BaCO3 modified electrode is used instead of bare TiO2 electrode. The improvement in η has been attributed to the increased dye adsorption, reduction in recombination rate and enhancement in the electron lifetime when the modified TiO2 electrode is used. © 2009 Elsevier B.V. All rights reserved.

Sharma G.D.,Randnter for Science and Engineering | Patel K.R.,Jai Narain Vyas University | Roy M.S.,Defence Laboratory | Misra R.,Indian Institute of Technology Indore
Organic Electronics: physics, materials, applications | Year: 2014

We report the photophysical, electrochemical and theoretical properties of two dyes with same acceptor, π-linker and anchoring acceptor unit and different TPA (D1) and pyran (D2) donor central unit. The change in the central unit resulted in corresponding different photophysical and electrochemical properties. The dye sensitized solar cell fabricated using dye D1 showed the higher incident photon to current efficiency of 54%, a short circuit current (Jsc) of 11.86 mA/cm2, an open circuit voltage of 0.64 V, and fill factor (FF) of 0.68, corresponding an overall power conversion efficiency of 5.16% which is higher than that for D2 based DSSCs (4.42%). The difference in the PCE of DSSCs based on D1 and D2 is partly, due to the smaller amount of dye loading, higher dark current and charge recombination rate of D1 based DSSC. The electrochemical spectra of DSSCs demonstrated longer electron life time and charge recombination resistance and small charge transport resistance for D1 sensitized DSSC, results the higher PCE. © 2014 Elsevier B.V. All rights reserved.

Singh S.P.,Indian Institute of Chemical Technology | Kumar C.P.,Indian Institute of Chemical Technology | Sharma G.D.,R and nter for Engineering and Science | Kurchania R.,Maulana Azad National Institute of Technology | Roy M.S.,Defence Laboratory
Advanced Functional Materials | Year: 2012

A simple and effective modification of phenyl-C 70-butyric acid methyl ester (PC 70BM) is carried out in a single step after which the material is used as electron acceptor for bulk heterojunction polymer solar cells (PSCs). The modified PC 70BM, namely CN-PC 70BM, showed broader and stronger absorption in the visible region (350-550 nm) of the solar spectrum than PC 70BM because of the presence of a cyanovinylene 4-nitrophenyl segment. The lowest unoccupied molecular energy level (LUMO) of CN-PC 70BM is higher than that of PC 70BM by 0.15 eV. The PSC based on the blend (cast from tetrahydrofuran (THF) solution) consists of P3HT as the electron donor and CN-PC 70BM as the electron acceptor and shows a power conversion efficiency (PCE) of 4.88%, which is higher than that of devices based on PC 70BM as the electron acceptor (3.23%). The higher PCE of the solar cell based on P3HT:CN-PC 70BM is related to the increase in both the short circuit current (J sc) and the open circuit voltage (V oc). The increase in J sc is related to the stronger light absorption of CN-PC 70BM in the visible region of the solar spectrum as compared to that of PC 70BM. In other words, more excitons are generated in the bulk heterojunction (BHJ) active layer. On the other hand, the higher difference between the LUMO of CN-PC 70BM and the HOMO of P3HT causes an enhancement in the V oc. The addition of 2% (v/v) 1-chloronapthalene (CN) to the THF solvent during film deposition results in an overall improvement of the PCE up to 5.83%. This improvement in PCE can be attributed to the enhanced crystallinity of the blend (particularly of P3HT) and more balanced charge transport in the device. The photovoltaic properties of a bulk heterojunction based on poly(3- hexylthiophene) (P3HT):modified phenyl-C 70-butyric acid methyl ester (PC 70BM), a CN-PC 70BM blend, are studied. Polymer solar cells based on this blend demonstrate power conversion efficiencies of 5.8% with high open circuit voltages of 0.80 and short circuit current densities of 11.75 mA cm -2. These devices benefit from the high lowest unoccupied molecular orbital (LUMO) energy level of CN-PC 70BM and a more balanced charge transport. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sharma G.D.,R and nter for Engineering and Science | Roy M.S.,Defence Laboratory | Singh S.P.,Indian Institute of Chemical Technology
Journal of Materials Chemistry | Year: 2012

We have used a stepwise approach for cosensitization of a thiocyanate-free Ru(ii) sensitizer with an organic dye (TDPP) for dye sensitized solar cells. The cosensitized SPS-01 + TDPP device showed enhanced V oc and J sc relative to the individual dye sensitized solar cells. Upon the optimization, the device made of SPS-01 + TDPP dye yielded J sc = 13.7 mA cm -2, V oc = 0.70 V, FF = 0.72 and power conversion efficiency (PCE) = 6.90%. This performance is superior to that of either individual DSSC made from SPS-01 (PCE = 5.47%) and TDPP (PCE = 4.82%), fabricated under the same conditions. This journal is © The Royal Society of Chemistry.

Singh V.K.,Sejong University | Shukla A.,Defence Laboratory | Patra M.K.,Defence Laboratory | Saini L.,Defence Laboratory | And 3 more authors.
Carbon | Year: 2012

Reduced graphene oxide (RGO) with a layered and porous structure was synthesized by thermal exfoliation of graphite oxide. Synthesized RGO is very light weight and flaky. The formation of RGO was studied using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and scanning electron microscopy. Composites were prepared by dispersing 2%, 4% and 10% by weight of the synthesized RGO into nitrile butadiene rubber (NBR) matrix. Microwave absorption properties of RGO/NBR composites were investigated by measuring their complex permittivity and permeability by using waveguide method. Simulation studies show that 10 wt.% of graphene oxide in NBR matrix exhibits high values of reflection loss (>10 dB) over a wide frequency range 7.5-12 GHz and maximum loss is 57 dB at 9.6 GHz at a thickness of 3 mm. © 2011 Elsevier Ltd. All rights reserved.

Misra R.K.,Defence Laboratory | Jain S.K.,Defence Laboratory | Khatri P.K.,Defence Laboratory
Journal of Hazardous Materials | Year: 2011

Iminodiacetic acid functionality has been introduced on styrene-divinyl benzene co-polymeric beads and characterized by FT-IR in order to develop weak acid based cation exchange resin. This resin was evaluated for the removal of different heavy metal ions namely Cd(II), Cr(VI), Ni(II) and Pb(II) from their aqueous solutions. The results showed greater affinity of resin towards Cr(VI) for which 99.7% removal achieved in optimal conditions following the order Ni(II). >. Pb(II). >. Cd(II) with 65%, 59% and 28% removal. Experiments were also directed towards kinetic studies of adsorption and found to follow first order reversible kinetic model with the overall rate constants 0.3250, 0.2393, 0.4290 and 0.2968 for Cr(VI), Ni(II), Pb(II) and Cd(II) removal respectively. Detailed studies of Cr(VI) removal has been carried out to see the effect of pH, resin dose and metal ion concentration on adsorption and concluded that complexation enhanced the chromium removal efficacy of resin drastically, which is strongly pH dependent. The findings were also supported by the comparison of FT-IR spectra of neat resin with the chromium-adsorbed resin. © 2010 Elsevier B.V.

Hazra S.,Birla Institute of Technology and Science | Patra M.K.,Defence Laboratory | Vadera S.R.,Defence Laboratory | Ghosh N.N.,Birla Institute of Technology and Science
Journal of the American Ceramic Society | Year: 2012

A novel "one-pot" synthetic method has been reported for the preparation of (NiFe 2O 4) x-(BaFe 12O 19) 1-x composites. The synthesized composites were characterized using thermogravimetric analysis, differential scanning calorimetric analysis, X-ray diffraction, dynamic light scattering technique, scanning electron microscopy, and vibrating sample magnetometer. The (NiFe 2O 4) x-(BaFe 12O 19) 1-x composites prepared by this method showed crystallographically two phase behavior, but magnetically a good single phase exchange spring-coupled behavior with high saturation magnetization as well as high coercivity. © 2011 The American Ceramic Society.

Sarangi P.P.,Birla Institute of Technology and Science | Vadera S.R.,Defence Laboratory | Patra M.K.,Defence Laboratory | Ghosh N.N.,Birla Institute of Technology and Science
Powder Technology | Year: 2010

Series of single-phase Ni1-xZnxFe2O4 (x=0.20, 0.35, 0.50 and 0.60) nanopowders with average particle size of ∼35nm have been synthesized by using oxalate based precursor method. Precursor powders were synthesized by reacting aqueous solutions of metal nitrates and oxalic acid by using different total metal ions: oxalic acid molar ratios and then evaporating them to dryness. Pure, single-phase Ni-Zn ferrite nanopowder was formed by calcining the precursor with total metal ion: oxalic acid ratio of 1:0.125 at a temperature of 850°C. The synthesized nanopowders were characterized by using X-ray diffraction, Thermo-gravimetric and Differential Scanning Calorimetric analysis, Transmission Electron Microscope and Scanning Electron Microscope. Room temperature DC resistivity of the nanopowders was measured with respect to temperature by the two-probe method and was of the order of ∼107Ωcm. Room temperature saturation magnetization was measured by using Vibrating Sample Magnetometer and it varied between 34-49emu/g depending on the composition. This aqueous solution based method provides a simple and cost-effective route to synthesize single phase, Ni-Zn ferrite nanopowders. © 2010 Elsevier B.V.

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