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Mikroyannidis J.A.,University of Patras | Tsagkournos D.V.,University of Patras | Balraju P.,Molecular Electronics Laboratory | Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College
Journal of Power Sources | Year: 2011

We have fabricated bulk heterojunction (BHJ) photovoltaic devices based on the as cast and thermally annealed P:[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) blends and found that these devices gave power conversion efficiency (PCE) of about 1.15 and 1.60% respectively. P is a novel alternating phenylenevinylene copolymer which contains 2-cyano-3-(4-(diphenylamino)phenyl) acrylic acid units along the backbone and was synthesized by Heck coupling. This copolymer was soluble in common organic solvents and showed long-wavelength absorption maximum at 390-420 nm with optical band gap of 1.94 eV. The improvement of PCE after thermal annealing of the device based on the P:PCBM blend was attributed to the increase in hole mobility due to the enhanced crystallinity of P induced by thermal treatment. In addition, we have fabricated BHJ photovoltaic devices based on the as cast and thermally annealed PB:P:PCBM ternary blend. PB is a low band gap alternating phenylenevinylene copolymer with BF 2-azopyrrole complex units, which has been previously synthesized in our laboratory. We found that the device based on this ternary blend exhibited higher PCE (2.56%) as compared to either P:PCBM (1.15%) or PB:PCBM (1.57%) blend. This feature was associated with the well energy level alignment of P, PB and PCBM, the higher donor-acceptor interfaces for the exciton dissociation and the improved light harvesting property of the ternary blend. The further increase in the PCE with thermally annealed ternary blend (3.48%) has been correlated with the increase in the crystallinity of both P and PB. Finally, we used copolymer P as sensitizer for quasi solid state dye-sensitized solar cell and we achieved PCE of approximately 3.78%. © 2010 Elsevier B.V.


Mikroyannidis J.A.,University of Patras | Kabanakis A.N.,University of Patras | Tsagkournos D.V.,University of Patras | Balraju P.,Jai Narain Vyas University | And 3 more authors.
Journal of Materials Chemistry | Year: 2010

The diazonium salt derived from 4-(hexyloxy)benzamine reacted with half an equivalent of pyrrole to afford 2,5-bis(4-hexyloxyphenylazo)-1H-pyrrole (A). The reaction of the latter with BF3·Et2O gave the corresponding BF2-azopyrrole complex (B). The thin film absorption spectra of A and B were broad and extended into the near infrared region with optical band gaps of 1.54 and 1.49 eV, respectively. The photovoltaic properties have been investigated using blends of A or B with PCBM, and it was found that the device based on B:PCBM showed higher power conversion efficiency (PCE) in comparison to that for the device with A:PCBM blend. This has been attributed to the higher hole mobility and lower band gap of B relative to A. The effect of different thermal annealing on the photovoltaic response of the devices has been investigated and it was found that the contact annealed device displayed PCE of approximately 2.7% and 3.15% for A:PCBM and B:PCBM blends, respectively. The increase in the PCE for the contact annealed device has been interpreted in terms of more balanced charge transport. © 2010 The Royal Society of Chemistry.


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.
Organic Electronics: physics, materials, applications | Year: 2010

Two simple dyes D1 and D2 based on 4-nitro-a-cyanostilbene were conveniently synthesized from a one-step reaction. These dyes were prepared from the condensation of 4-carboxybenzaldehyde or 4-hydroxybenzaldehyde with 4-nitrobenzyl cyanide to afford 4-nitro-40-carboxy-a-cyanostilbene (D1) and 4-nitro-40-hydroxy-a-cyanostilbene (D2) respectively. Photophysical and electrochemical properties of the dyes were investigated by UV-vis spectroscopy and cyclic voltammetry. Their absorption spectra were broad with long-wavelength absorption maximum at 617-655 nm and optical band gap of 1.63 eV. These two dyes were used as sensitizers in quasi solid state dye-sensitized solar cells (DSSCs). Photovoltaic devices with D1 showed a maximum monochromatic incident photon to current efficiency (IPCE) of 70% and overall power conversion efficiency (PCE) of 4.8%, under illumination intensity 100 mW/cm2. The photovoltaic performance of the cell with D2 was lower because of less dye loading on the TiO2 surface, since it has OH anchoring group, and lower electron lifetime. Additionally, we have investigated the photovoltaic response of the DSSCs with nitrogen doped TiO2 photoanode and found that the PCE has been enhanced. The enhancement in PCE has been attributed to the increase in open circuit voltage and fill factor. © 2010 Elsevier B.V. All rights reserved.


Mikroyannidis J.A.,University of Patras | Kabanakis A.,University of Patras | Balraju P.,Jai Narain Vyas University | Balraju P.,Jaipur Engineering College | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

Three new organic sensitizers D1, D2, and D3 with carboxy, acid anhydride, and hydroxy anchoring groups, respectively, and terminal cyanovinylene 4-nitrophenyl segments were synthesized. Their absorption spectra were broad with long wavelength absorption maximum approximately at 620 nm and optical band gap of 1.64-1.73 eV. We have fabricated the quasi-solid-state dye-sensitized solar cells (DSSCs) using these dyes and found that the power conversion efficiency (PCE) is of the order D1 > D2 > D3. The maximum PCE is about 4.58% with D1, which is further improved up to 5.80% when chenodeoxyacholic acid (CDCA) coadsorbent is added in the dye solution. The superior PCE for the DSSC with D1 has been attributed to the higher energy gap between the LUMO level of D1 and the conduction band of the TiO 2 as compared to the other two dyes. The further improvement in the PCE with the addition of the coadsorbent has been attributed to the longer electron lifetime, which leads to reduction in back recombination of injected electrons with electrolyte. The PCE of the DSSC based on D1 has been improved up to 6.9% with the incorporation of poly(vinylidene fluoride) (PVDF) in the polymer gel electrolyte. This has been correlated with the ionic conductivity of the polymer electrolyte blend. © 2010 American Chemical Society.


Mikroyannidis J.A.,University of Patras | Kabanakis A.N.,University of Patras | Balraju P.,Jai Narain Vyas University | Balraju P.,Molecular Electronics Laboratory | And 2 more authors.
Macromolecules | Year: 2010

Two novel low band gap soluble copolymers, P1 and P2, were synthesized and characterized. P1 consisted of alternating dihexyloxyphenylene and α-[[4-(diphenylamino) phenyl]methylene]-4-nitro-ben-zeneacetonitrile. P2 consisted of alternating dihexyloxyphenylene and α,α'-[(1,4- phenylene)dimethy-lidyne]bis(αZ,α'Z)-4-nitrobenzeneacetonitrile. These copolymers showed broad absorption curves with long-wavelength absorption maximum around 620 nm and optical band of 1.68 and 1.64 eV for P1 and P2, respectively. Both P1 and P2 were blended with PCBM to study the photovoltaic response of bulk heterojunction (BHJ) solar cells. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of both P1 and P2 are well aligned with those of PCBM acceptor. This allows efficient photoinduced charge transfer and high open circuit voltage, leading to an overall power conversion efficiency (PCE) of 3.15% and 2.60% for the as cast P1:PCBM-and P2:PCBM-based devices, respectively. The PCE of the devices has been further improved up to 4.06% and 3.35% for the devices based on thermally annealed P1:PCBM and P2:PCBM blends, respectively. © 2010 American Chemical Society.

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