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Mikroyannidis J.A.,University of Patras | Tsagkournos D.V.,University of Patras | Balraju P.,Jai Narain Vyas University | Balraju P.,Molecular Electronics Laboratory | And 2 more authors.
Journal of Power Sources | Year: 2011

A new series of low band gap dyes, C1, C2 and S, based on 2-styryl-5-phenylazo-pyrrole was synthesized. These dyes contain one carboxy, two carboxy and one sulfonic acid anchoring groups, respectively. They were soluble in common organic solvents, showed long-wavelength absorption maximum at ∼620 nm and optical band gap of 1.66-1.68 eV. The photophysical and electrochemical properties of these dyes were investigated and found to be suitable as photosensitizers for dye sensitized solar cells (DSSCs). The quasi solid state DSSCs with dye S showed a maximum monochromatic incident photon to current efficiency (IPCE) of 78% and an overall power conversion efficiency (PCE) of 4.17% under illumination intensity of 100 mW cm -2 (1.5 AM), which is higher than the other dyes (3.26% for C2 and 2.59% for C1). Even though dye S contains one sulfonic acid anchoring group, the higher PCE for the DSSCs based on this dye has been attributed to the higher dye loading at the TiO 2 surface and enhanced electron lifetime in the device, as indicated by absorption spectra and electrochemical impedance spectra measurements. Finally, by increasing the molecular weight of poly(ethylene oxide) (PEO) in electrolyte, the PCE also increases up to 4.8% for the electrolyte with PEO molecular weight of 2.0 × 10 6. This improvement has been attributed to the enhancement in iodide ions diffusion due to the increase in free volume of polymer gel electrolyte. © 2010 Elsevier B.V. All rights reserved. Source


Sharma G.D.,University of Rajasthan | Sharma G.D.,Randnter for Science and Engineering | Mikroyannidis J.A.,University of Patras | Singh S.P.,Indian Institute of Chemical Technology
Materials Chemistry and Physics | Year: 2012

Two low band gap conjugated polymers P1 (alternating phenylenevinylene containing thiophene and pyrrole rings) and P2 (alternating phenylenevinylene with dithenyl (thienothiadiazole) segments) having optical band gap 1.65 eV and 1.74 eV, respectively, were used as electron donor along with the PC 70BM as electron acceptor for the fabrication of bulk heterojunction solar cells. The power conversion efficiency (PCE) of BHJ devices based on P1:PC 70BM and P2:PC 70BM cast from THF solvent is about 2.84% and 2.34%, respectively, which is higher than the BHJ based on PCBM as electron acceptor. We have investigated the effect of mixed (1-chloronaphthalene (CN)/THF) solvent, modification of PEDOT:PSS layer and inserting of TiO 2 layer, on the photovoltaic performance of polymer solar cell. We have achieved power conversion efficiency of 5.07% for the polymer solar cells having structure ITO/PEDOT:PSS (modified)/P1:PC 70BM (CN/THF cast)/TiO 2/Al. The effect of solvent used for spin coating, modification of PEDOT:PSS layer and inclusion of TiO 2 layer has been discussed in detail. © 2012 Elsevier B.V. All rights reserved. Source


Singh S.P.,Indian Institute of Chemical Technology | Roy M.S.,Defence Laboratory | Thomas A.,Indian Institute of Chemical Technology | Bhanuprakash K.,Indian Institute of Chemical Technology | Sharma G.D.,Randnter for Science and Engineering
Organic Electronics: physics, materials, applications | Year: 2012

Two novel D-A-π-A metal free dyes with triphenylamine as donor, dithiophene-diketo-pyrrolo-pyrrole as acceptor unit, thiophene and phenyl π-conjugated bridges and a cyanoacetic acid as electron acceptor (TDPP1 and TDPP2 were denoted for thiophene and phenyl π-conjugated bridge, respectively) have been designed and used as sensitizers for DSSCs. Incorporation of dithiophene-diketo-pyrrolo-pyrrole, reduces the band gap significantly. The influence of π-conjugated bridge on optical and electrochemical properties were investigated. Results demonstrated that the absorption band of TDPP with thiophene π-conjugated bridge has red shifted due to the enhancement of electron donating ability of π-conjugated bridge. The DSSC based on TDPP1 shows prominent power conversion efficiency about 4.81%, which is higher that for TDPP2 (3.42%). The electrochemical impedance spectroscopy analysis reveal that the charge recombination resistance at the TiO2/dye/electrolyte interface for the DSSC based on TDPP1 is higher than that for TDPP2, which improves both Jsc and Voc. The PCE of the DSSC based on TDPP1 is further improved up to 6.34%, when deoxycholic acid (DCA) was employed as coadsorbant. © 2012 Elsevier B.V. All rights reserved. Source


Thomas K.R.J.,Indian Institute of Technology Roorkee | Kapoor N.,Indian Institute of Technology Roorkee | Roy M.S.,Defence Laboratory | Sharma G.D.,Randnter for Science and Engineering
Organic Electronics: physics, materials, applications | Year: 2012

Two new small molecules based on tetrasubstituted pyrene derivatives F4P and DF4P were used as electron donor along with PC60BM or PC70BM as electron acceptor for the fabrication of solution processed bulk heterojunction (BHJ) solar cells. The optimized BHJ device with F4P:PC70BM at weight ratio of 1:2 delivered a power conversion efficiency (PCE) of 2.06%, with short circuit current (Jsc) of 5.9 mA/cm2, open circuit voltage (Voc) of 0.92 V and fill factor (FF) of 0.38. In contrast DF4P:PC70BM produced better PCE of 2.70%, with Jsc of 7.3 mA/cm2, Voc of 0.84 V and FF of 0.44. The PCE of the device based on thermally annealed DF4P:PC70BM blend has been further improved up to 3.63%, which may be attributed to the better charge transport due to the increase in the hole mobility upon thermal annealing. © 2012 Elsevier B.V. All rights reserved. Source


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. Source

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