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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 | Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College | Sharma S.S.,Rajsthan University | Vijay Y.K.,Rajsthan University
Journal of Physical Chemistry C | Year: 2010

An alternating phenylenevinylene copolymer (P) was synthesized by Heck coupling of 2,5-bis[2-(4-bromophenyl)diazeny]-1H-pyrrole with 1,4-divinyl-2,5-bis(hexyloxy)-benzene. The subsequent reaction of P with boron trifluoride diethyl etherate afforded the corresponding BF2- azopyrrole complex (PB) which was used for bulk heterojunction solar cells. A thin film of PB showed a broad absorption band with a longwave absorption maximum at 511 nm and an optical band gap of 1.63 eV. We have used a solvent mixture consisting of THF with various contents of acetone, in order to prepare the PB:PCBM blend films for polymer bulk heterojunction (BHJ) photovoltaic (PV) Devices. Since the vapor pressure of the solvent mixture is lower compared to neat THF, the blend films dried slowly and nanoparticles of PB are formed, as indicated by the XRD pattern. The correlation of PB nanoparticles with PV properties of the PB:PCBM BHJ Devices was investigated. It was found that the optical absorption and hole transport in the resulting PB:PCBM blend films increase with increasing content of acetone in the THF solution of PB, which is responsible for the enhancement in the power Conversion efficiency (PCE). The effect of thermal annealing on the PV response was also investigated. The overall PCE for the BHJ PV Devices was 3.54%. This was achieved for the thermally annealed Device which was fabricated with a mixture of 2.5% acetone in the THF solution of PB. Copyright © 2010 American Chemical Society.

Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College | Suresh P.,Jai Narain Vyas University | Mikroyannidis J.A.,University of Patras | Stylianakis M.M.,University of Patras
Journal of Materials Chemistry | Year: 2010

We report the fabrication and characterization of photovoltaic devices using a bulk heterojunction (BHJ) photoactive layer consisting of a small molecule (T), which contains a central p-phenylenevinylene unit, intermediate thiophene moieties, and terminal cyano-vinylene 4-nitrophenyls as the donor and a perylene-pyrene bisimide (PPI) as the acceptor. The difference in the LUMO levels (0.5 eV) of these materials is sufficient for the photoinduced charge transfer in the bulk heterojunction active layer. The optimum blend ratio (by weight) between T and PPI is 1:3.5 with a power conversion efficiency (PCE) of about 1.87%, beyond that the PCE starts to decrease. The incorporation of a thin ZnO layer between the organic BHJ layer and the top Al electrode increases the PCE to 2.46%, which is attributed to the enhanced light absorption due to the optical interference between incident light and reflected light from the Al electrode. It is also attributed to the improved electron transport in the device, since the conduction band of ZnO closely matches the work function of the Al electrode. The PCE is further increased to 3.17% when the device with the ZnO layer is annealed at a temperature of 100 °C for 5 min. This PCE is among the highest values reported to date for solar cells using solution processable small molecules. © The Royal Society of Chemistry 2010.

Kanimozhi C.,Indian Institute of Science | Balraju P.,Jai Narain Vyas University | Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College | Patil S.,Indian Institute of Science
Journal of Physical Chemistry B | Year: 2010

The diketopyrrolopyrrole-based copolymers PDPP-BBT and TDPP-BBT were synthesized and used as a donor for bulk heterojunction photovoltaic devices. The photophysical properties of these polymers showed absorption in the range 500-600 nm with a maximum peak around 563 nm, while TDPP-BBT showed broadband absorption in the range 620 - 800 nm with a peak around 656 nm. The power conversion efficiencies (PCE) of the polymer solar cells based on these copolymers and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were 0.68% (as cast PDPP-BBT:PCBM), 1.51% (annealed PDPP-BBT:PCBM), 1.57% (as cast TDPPBBT:PCBM), and 2.78% (annealed TDPP-BBT:PCBM), under illumination of AM 1.5 (100 mW/cm2). The higher PCE for TDPP-BBT-based polymer solar cells has been attributed to the low band gap of this copolymer as compared to PDPP-BBT, which increases the numbers of photogenerated excitons and corresponding photocurrent of the device. These results indicate that PDPP-BBT and TDPP-BBT act as excellent electron donors for bulk heterojunction devices. © 2010 American Chemical Society.

Mikroyannidis J.A.,University of Patras | Suresh P.,Jai Narain Vyas University | Sharma G.D.,Jai Narain Vyas University | Sharma G.D.,Jaipur Engineering College
Organic Electronics: physics, materials, applications | Year: 2010

A new low-band gap small molecule (Se-SM), which contains dithyenyl-benzoselenadiazole as central unit and terminal cyanovinylene 4-nitrophenyls, was synthesized. In addition, a new phenylenevinylene copolymer (P) containing dithyenyl-dinitrobenzothiadiazole moieties was synthesized by Heck coupling. Se-SM showed broad absorption band with long-wavelength absorption maximum (λa,max) at ∼640 nm and optical band gap (Eg opt) of 1.67 eV. Copolymer P had λa,max around 420 nm and Eg opt of 2.31 eV. The dark current-voltage characteristics and incident photon to current efficiency spectra of the devices based on copolymer P and Se-SM indicates that both materials behave as p-type organic semiconductors. The power conversion efficiency (PCE) of the photovoltaic devices based on these materials is low. However, the PCE of the devices fabricated with the blends of copolymer P or Se-SM with PCBM, was improved significantly. The increase is attributed to the formation of bulk heterojunction with increased interfacial area. The effect of the incorporation of Se-SM molecule on the photovoltaic properties of copolymer P:PCBM blend has been also investigated. The overall PCE of the copolymer P:PCBM:Se-SM device is approximately 2.24%, which is further enhanced up to 3.16%, when the thermally annealed blend is used. Therefore, we conclude that the Se-SM molecule increases the light harvesting property of the blend and also provides efficient path for holes and electron in copolymer and PCBM phases, respectively. © 2009 Elsevier B.V. All rights reserved.

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