ana charas - Academia.edu (original) (raw)
Papers by ana charas
Advanced Functional Materials, 2008
ABSTRACT Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suz... more ABSTRACT Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suzuki coupling, but their high polarity and ionic nature limit the potential applications of these materials. Here, we demonstrate three methods for transforming these polar polyelectrolytes into nonpolar lipophilic insulated molecular wires. A water-soluble polyfluorene-alt-biphenylene β-cyclodextrin (CD) polyrotaxane was converted into nonpolar derivatives by methylation of the carboxylic acid groups with diazomethane and conversion of the hydroxyl groups of the CDs to benzyl ethers, trihexylsilyl ethers, benzoyl esters, and butanoate esters to yield polyrotaxanes that are soluble in organic solvents such as chloroform and cyclohexane. Elemental analysis, NMR spectroscopy, and gel permeation chromatography (GPC) data support the proposed structures of the organic-soluble polyrotaxanes. The extents of reaction of the polyrotaxane CD hydroxyl groups were 55% for trihexylsilyl chloride/imidazole; 81% for benzyl chloride/sodium hydride; 72% for benzoyl chloride/pyridine/4-dimethylaminopyridine; and 98% butanoic anhydride/pyridine/4-dimethylaminopyridine. Alkylation, silylation, and esterification increase the bulk of the encapsulating sheath, preventing interstrand aggregation, increasing the photoluminescence efficiency in the solid state and simplifying the time-resolved fluorescence decay. The organic-soluble polyrotaxanes were processed into polymer light-emitting diodes (PLEDs) from solution in nonpolar organic solvents, thereby excluding ionic impurities from the active layer.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
book, Solar Cells 2016. 1 IMPROVING ORGANIC SOLAR CELLS THROUGH USING TERNARY SYSTEMS Ana CHARAS,... more book, Solar Cells 2016. 1 IMPROVING ORGANIC SOLAR CELLS THROUGH USING TERNARY SYSTEMS Ana CHARAS, Joana FARINHAS, Ricardo OLIVEIRA, Jorge MORGADO Instituto de Telecomunicações, IST, Av. Rovisco Pais, 1049-001, Lisbon, Portugal ana.charas@lx.it.pt Bulk heterojunctions based on ternary blends of materials of complementary properties have been explored as an approach to improve organic photovoltaic cells through the improvement of the photon-absorption and/or charge transport within the devices. 1 Nevertheless, the mechanisms sustaining such device optimizations are often difficult to unveil due to the more complex nature of the ternary system, i.e. in diversity of materials properties and in morphologic features. Here, two efficient ternary blends are reported: One is a dual polymer donor blend composed of poly[9,9’-dioctyl-fluorene-alt-bithiophene (F8T2) and poly[[4,8-bis[(2ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2ethylhexyl)carbonyl]thieno[3,4-b]thio...
Frontiers in Nanotechnology
Photovoltaic (PV) devices based on organic heterojunctions have recently achieved remarkable powe... more Photovoltaic (PV) devices based on organic heterojunctions have recently achieved remarkable power conversion efficiency (PCE) values. However, photodegradation is often a cause of dramatic drops in device performance. The use of ultraviolet (UV)-absorbing luminescent downshifting (LDS) layers can be a mitigation strategy to simultaneously filter UV radiation reaching the device and reemit it with lower energy in the visible spectral range, matching the maximum spectral response of the PV cells and thus enabling the increase of the photocurrent generated by the cell. In this work, we report the use of a Eu3+-doped siliceous-based organic–inorganic hybrid as a coating on organic solar cells based on the PTB7-Th:ITIC bulk heterojunction with the purpose of increasing their performance. We found that the applied coatings yield a PCE enhancement of ∼22% (from 3.1 to 3.8%) in solar cells with spin-coated layers, compared with the bare solar cells, which is among the highest performance e...
Dalton Transactions
A gold bisdithiolene complex with a unique crystal structure displays high electrical conductivit... more A gold bisdithiolene complex with a unique crystal structure displays high electrical conductivity at room temperature.
Proceedings of 2nd International Online-Conference on Nanomaterials
Conducting films comprising conducting polymers and carbon nanomaterials have gained a lot of int... more Conducting films comprising conducting polymers and carbon nanomaterials have gained a lot of interest for applications in several fields, including transparent electrodes, supercapacitors, light-emitting diodes (LEDs), polymer solar cells (PSCs), etc. One of the main motivations is the replacement of costly oxides and degradable materials, like indium tin oxide (ITO). On the other hand, graphene oxide (GO) has emerged as an ideal filler to reinforce polymeric matrices owing to its large specific surface area, transparency, flexibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, the potential of polymer nanocomposites based on hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) for use as active layers (ALs) or interfacial layers (IFLs) in PSCs has been assessed. Conventional deposition...
Organic Electronics
Abstract The molecular design of conjugated polymers for efficient organic photovoltaic devices (... more Abstract The molecular design of conjugated polymers for efficient organic photovoltaic devices (OPVs) providing advantageous processing properties, namely solubility in low toxic solvents as ethanol, is an important issue for the progress of OPV technology. In this work, the pattern substitution and chemical nature of the side chain, either n-alkoxy or oligo(ethylene oxide) groups, in alternating thiophene-quinoxaline copolymers is varied and their effect in polymer chain grow, solubility and optical spectra is thoroughly analyzed in light of quantum mechanical calculations. Although the polymer with oligo(ethylene oxide) groups exhibited good solubility in ethanol, it was found that substituting in both meta- and para-positions of the peripheral phenyl rings attached to the quinoxaline groups causes smaller molecular weight, lower solubility in chlorinated solvents and poorer performance in photovoltaic devices. The theoretical studies revealed differences in the most energetically favored conformers for each case of the polymers'substitution pattern that can justify the observed results.
Dyes and Pigments
Abstract Perylenediimides (PDIs) are among the most promising non-fullerene electron-acceptors fo... more Abstract Perylenediimides (PDIs) are among the most promising non-fullerene electron-acceptors for applications in organic photovoltaics (PV), providing a large scope for structural modifications. PDI-based dimers have shown the highest performances in PV devices owing to their characteristic twisted conformations that reduce their tendency to form large aggregates which are detrimental for PV operation. In this work, two fluorene-bridged perylenediimide (PDI) dimers with oligo(ethylene oxide) or alkyl chains anchored to the C9 position of the fluorene unit were synthesized and investigated in solution-processed organic bulk heterojunction (BHJ) photovoltaic cells as electron acceptors. The PDI dimer substituted with oligo(ethylene oxide) chains resulted in improved power conversion efficiencies (in 20%–53%) in solution processed bulk heterojunction (BHJ) cells with two different polymer donors, PTB7 and PffBT4T-2OD. Nevertheless, the replacement of alkyl chains by oligo(ethylene oxide) chains did not significantly affect the geometric characteristics of the PDI dimers and the optical and electrochemical properties were only marginally modified. Increased exciton dissociation and enhanced charge transport derived from a more densely packed π-π stacking in the solid state caused by ethylene oxide groups are pointed out as possible causes for the improved PV performance. The influence of 1,8-diiodooctane as solvent additive in the blend films was also investigated and allowed to further increase the efficiencies of the cells with PTB7. Overall, the results show that the simple replacement of alkyl chains by oligo(ethylene oxide) chains in PDI dimers is an efficient way to improve the PV performance without compromising the optoelectronic properties of the PDI acceptor.
![Research paper thumbnail of Band-Gap Tunable Thiadiazolo[3,4-g]quinoxaline Derivatives as Non-Fullerene Acceptors in Organic Photovoltaic Cells Processed from Low Toxic Ethanol/Anisole Mixtures](https://attachments.academia-assets.com/75728635/thumbnails/1.jpg)
](New Journal of Chemistry
The synthesis, characterisation and application in organic photovoltaic cells as electron-accepto... more The synthesis, characterisation and application in organic photovoltaic cells as electron-acceptors of new [1,2,5]thiadiazolo[3,4-g]quinoxaline-based small molecules with oligo(ethylene oxide) solubilising groups and exhibiting tunable optical bandgaps are reported. A new...
Sensors
This paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) c... more This paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) connected to a DC–DC converter, designed in a 130 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology, with a quasi- maximum power point tracking (MPPT) algorithm to maximize the system efficiency, for indoor applications. OPVs are an emerging technology with potential for low cost indoor light energy harvesting. The OPV current-voltage curves (I-V) under an irradiance of solar simulator Oriel Sol 3A, at room temperature, are obtained and an accurate electrical model is derived. The energy harvesting system is subjected to four different indoor light sources: 35 W halogen, 3.5 W LED, 5 W LED, and 7 W LED, positioned at three different heights (0.45 m, 0.26 m, and 0.11 m), to evaluate the potential of the system for indoor applications. The measurements showed maximum efficiencies of 60% for 35 W halogen and 45% for 7 W LED at the highest distance (0.45 m) and between 60% (5 W LED...
New Journal of Chemistry
Two new molecules, TQT1 and TQT2, and a polymer, PTQT, with a core based on [1,2,5]thiadiazolo[3,... more Two new molecules, TQT1 and TQT2, and a polymer, PTQT, with a core based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) with oligoether-substituted phenyl groups as acceptor and thiophene (T) or bithiophene (T2) as...
Journal of Materials Research
Sensors (Basel, Switzerland), Jan 3, 2017
Conjugated polymers (CPs) have proved to be promising chemosensory materials for detecting nitroa... more Conjugated polymers (CPs) have proved to be promising chemosensory materials for detecting nitroaromatic explosives vapors, as they quickly convert a chemical interaction into an easily-measured high-sensitivity optical output. The nitroaromatic analytes are strongly electron-deficient, whereas the conjugated polymer sensing materials are electron-rich. As a result, the photoexcitation of the CP is followed by electron transfer to the nitroaromatic analyte, resulting in a quenching of the light-emission from the conjugated polymer. The best CP in our studies was found to be poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2). It is photostable, has a good absorption between 400 and 450 nm, and a strong and structured fluorescence around 550 nm. Our studies indicate up to 96% quenching of light-emission, accompanied by a marked decrease in the fluorescence lifetime, upon exposure of the films of F8T2 in ethyl cellulose to nitrobenzene (NB) and 1,3-dinitrobenzene (DNB) vapors ...
International Journal of Photoenergy
Ternary blend polymer solar cells combining two electron-donor polymers, poly[4,8-bis[(2-ethylhex... more Ternary blend polymer solar cells combining two electron-donor polymers, poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (pBTTT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), as electron-acceptor, were fabricated. The power conversion efficiency of the ternary cells was enhanced by 18%, with respect to the reference binary cells, for a blend composition with 25% (wt%) of pBTTT in the polymers content. The optimized device performance was related to the blend morphology, nonrevealing pBTTT aggregates, and improved charge extraction within the device.
Dalton Trans., 2016
New fluorescent aromatic ring-fused 2-iminopyrrolyl diphenyl boron complexes are emitters in the ... more New fluorescent aromatic ring-fused 2-iminopyrrolyl diphenyl boron complexes are emitters in the range blue to orange.
1-Novel plastic optical fibers (POF) based on polymethylmethacrylate, PMMA, doped with luminescen... more 1-Novel plastic optical fibers (POF) based on polymethylmethacrylate, PMMA, doped with luminescent conjugated polymers and oligomers were fabricated. Our innovative approach is based on the chemical binding between the PMMA matrix and the dopant material as an alternative to the blending approach (mixture) of PMMA and the active material. We aimed at controlling load and dispersion of the luminescent polymer in the PMMA matrix, which are crucial for the optimisation of these optical media, while reducing the possibility of dopant segregation during the fiber drawing. Stimulated emission and optical switching inside the fiber were observed in some of the new materials, indicating that they can represent possible routes to plastic optical media, namely POFs, exhibiting gain and ultrafast switching.
Journal of Physics D Applied Physics 36 434 434, Feb 13, 2003
We study the effect of indium-tin oxide surface modification by self assembling of highly polar m... more We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.
1-At variance with a high stability of the inorganic materials for electronics under normal atmos... more 1-At variance with a high stability of the inorganic materials for electronics under normal atmospheric conditions, organic materials are more sensitive, due to charge transfer doping by oxygen and water and degradation when exposed to the ultraviolet radiation. Here we show that the chemical structure of the conjugated polymer used as active semiconducting material of polymer field-effect transistors has a drastic effect on their stability. These results show that, by chemical manipulation, some of the above limitations, when envisaging the use of organic materials for electronics, can be reduced.
Advanced Functional Materials, 2008
ABSTRACT Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suz... more ABSTRACT Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suzuki coupling, but their high polarity and ionic nature limit the potential applications of these materials. Here, we demonstrate three methods for transforming these polar polyelectrolytes into nonpolar lipophilic insulated molecular wires. A water-soluble polyfluorene-alt-biphenylene β-cyclodextrin (CD) polyrotaxane was converted into nonpolar derivatives by methylation of the carboxylic acid groups with diazomethane and conversion of the hydroxyl groups of the CDs to benzyl ethers, trihexylsilyl ethers, benzoyl esters, and butanoate esters to yield polyrotaxanes that are soluble in organic solvents such as chloroform and cyclohexane. Elemental analysis, NMR spectroscopy, and gel permeation chromatography (GPC) data support the proposed structures of the organic-soluble polyrotaxanes. The extents of reaction of the polyrotaxane CD hydroxyl groups were 55% for trihexylsilyl chloride/imidazole; 81% for benzyl chloride/sodium hydride; 72% for benzoyl chloride/pyridine/4-dimethylaminopyridine; and 98% butanoic anhydride/pyridine/4-dimethylaminopyridine. Alkylation, silylation, and esterification increase the bulk of the encapsulating sheath, preventing interstrand aggregation, increasing the photoluminescence efficiency in the solid state and simplifying the time-resolved fluorescence decay. The organic-soluble polyrotaxanes were processed into polymer light-emitting diodes (PLEDs) from solution in nonpolar organic solvents, thereby excluding ionic impurities from the active layer.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
book, Solar Cells 2016. 1 IMPROVING ORGANIC SOLAR CELLS THROUGH USING TERNARY SYSTEMS Ana CHARAS,... more book, Solar Cells 2016. 1 IMPROVING ORGANIC SOLAR CELLS THROUGH USING TERNARY SYSTEMS Ana CHARAS, Joana FARINHAS, Ricardo OLIVEIRA, Jorge MORGADO Instituto de Telecomunicações, IST, Av. Rovisco Pais, 1049-001, Lisbon, Portugal ana.charas@lx.it.pt Bulk heterojunctions based on ternary blends of materials of complementary properties have been explored as an approach to improve organic photovoltaic cells through the improvement of the photon-absorption and/or charge transport within the devices. 1 Nevertheless, the mechanisms sustaining such device optimizations are often difficult to unveil due to the more complex nature of the ternary system, i.e. in diversity of materials properties and in morphologic features. Here, two efficient ternary blends are reported: One is a dual polymer donor blend composed of poly[9,9’-dioctyl-fluorene-alt-bithiophene (F8T2) and poly[[4,8-bis[(2ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2ethylhexyl)carbonyl]thieno[3,4-b]thio...
Frontiers in Nanotechnology
Photovoltaic (PV) devices based on organic heterojunctions have recently achieved remarkable powe... more Photovoltaic (PV) devices based on organic heterojunctions have recently achieved remarkable power conversion efficiency (PCE) values. However, photodegradation is often a cause of dramatic drops in device performance. The use of ultraviolet (UV)-absorbing luminescent downshifting (LDS) layers can be a mitigation strategy to simultaneously filter UV radiation reaching the device and reemit it with lower energy in the visible spectral range, matching the maximum spectral response of the PV cells and thus enabling the increase of the photocurrent generated by the cell. In this work, we report the use of a Eu3+-doped siliceous-based organic–inorganic hybrid as a coating on organic solar cells based on the PTB7-Th:ITIC bulk heterojunction with the purpose of increasing their performance. We found that the applied coatings yield a PCE enhancement of ∼22% (from 3.1 to 3.8%) in solar cells with spin-coated layers, compared with the bare solar cells, which is among the highest performance e...
Dalton Transactions
A gold bisdithiolene complex with a unique crystal structure displays high electrical conductivit... more A gold bisdithiolene complex with a unique crystal structure displays high electrical conductivity at room temperature.
Proceedings of 2nd International Online-Conference on Nanomaterials
Conducting films comprising conducting polymers and carbon nanomaterials have gained a lot of int... more Conducting films comprising conducting polymers and carbon nanomaterials have gained a lot of interest for applications in several fields, including transparent electrodes, supercapacitors, light-emitting diodes (LEDs), polymer solar cells (PSCs), etc. One of the main motivations is the replacement of costly oxides and degradable materials, like indium tin oxide (ITO). On the other hand, graphene oxide (GO) has emerged as an ideal filler to reinforce polymeric matrices owing to its large specific surface area, transparency, flexibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, the potential of polymer nanocomposites based on hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) for use as active layers (ALs) or interfacial layers (IFLs) in PSCs has been assessed. Conventional deposition...
Organic Electronics
Abstract The molecular design of conjugated polymers for efficient organic photovoltaic devices (... more Abstract The molecular design of conjugated polymers for efficient organic photovoltaic devices (OPVs) providing advantageous processing properties, namely solubility in low toxic solvents as ethanol, is an important issue for the progress of OPV technology. In this work, the pattern substitution and chemical nature of the side chain, either n-alkoxy or oligo(ethylene oxide) groups, in alternating thiophene-quinoxaline copolymers is varied and their effect in polymer chain grow, solubility and optical spectra is thoroughly analyzed in light of quantum mechanical calculations. Although the polymer with oligo(ethylene oxide) groups exhibited good solubility in ethanol, it was found that substituting in both meta- and para-positions of the peripheral phenyl rings attached to the quinoxaline groups causes smaller molecular weight, lower solubility in chlorinated solvents and poorer performance in photovoltaic devices. The theoretical studies revealed differences in the most energetically favored conformers for each case of the polymers'substitution pattern that can justify the observed results.
Dyes and Pigments
Abstract Perylenediimides (PDIs) are among the most promising non-fullerene electron-acceptors fo... more Abstract Perylenediimides (PDIs) are among the most promising non-fullerene electron-acceptors for applications in organic photovoltaics (PV), providing a large scope for structural modifications. PDI-based dimers have shown the highest performances in PV devices owing to their characteristic twisted conformations that reduce their tendency to form large aggregates which are detrimental for PV operation. In this work, two fluorene-bridged perylenediimide (PDI) dimers with oligo(ethylene oxide) or alkyl chains anchored to the C9 position of the fluorene unit were synthesized and investigated in solution-processed organic bulk heterojunction (BHJ) photovoltaic cells as electron acceptors. The PDI dimer substituted with oligo(ethylene oxide) chains resulted in improved power conversion efficiencies (in 20%–53%) in solution processed bulk heterojunction (BHJ) cells with two different polymer donors, PTB7 and PffBT4T-2OD. Nevertheless, the replacement of alkyl chains by oligo(ethylene oxide) chains did not significantly affect the geometric characteristics of the PDI dimers and the optical and electrochemical properties were only marginally modified. Increased exciton dissociation and enhanced charge transport derived from a more densely packed π-π stacking in the solid state caused by ethylene oxide groups are pointed out as possible causes for the improved PV performance. The influence of 1,8-diiodooctane as solvent additive in the blend films was also investigated and allowed to further increase the efficiencies of the cells with PTB7. Overall, the results show that the simple replacement of alkyl chains by oligo(ethylene oxide) chains in PDI dimers is an efficient way to improve the PV performance without compromising the optoelectronic properties of the PDI acceptor.
New Journal of Chemistry
The synthesis, characterisation and application in organic photovoltaic cells as electron-accepto... more The synthesis, characterisation and application in organic photovoltaic cells as electron-acceptors of new [1,2,5]thiadiazolo[3,4-g]quinoxaline-based small molecules with oligo(ethylene oxide) solubilising groups and exhibiting tunable optical bandgaps are reported. A new...
Sensors
This paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) c... more This paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) connected to a DC–DC converter, designed in a 130 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology, with a quasi- maximum power point tracking (MPPT) algorithm to maximize the system efficiency, for indoor applications. OPVs are an emerging technology with potential for low cost indoor light energy harvesting. The OPV current-voltage curves (I-V) under an irradiance of solar simulator Oriel Sol 3A, at room temperature, are obtained and an accurate electrical model is derived. The energy harvesting system is subjected to four different indoor light sources: 35 W halogen, 3.5 W LED, 5 W LED, and 7 W LED, positioned at three different heights (0.45 m, 0.26 m, and 0.11 m), to evaluate the potential of the system for indoor applications. The measurements showed maximum efficiencies of 60% for 35 W halogen and 45% for 7 W LED at the highest distance (0.45 m) and between 60% (5 W LED...
New Journal of Chemistry
Two new molecules, TQT1 and TQT2, and a polymer, PTQT, with a core based on [1,2,5]thiadiazolo[3,... more Two new molecules, TQT1 and TQT2, and a polymer, PTQT, with a core based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) with oligoether-substituted phenyl groups as acceptor and thiophene (T) or bithiophene (T2) as...
Journal of Materials Research
Sensors (Basel, Switzerland), Jan 3, 2017
Conjugated polymers (CPs) have proved to be promising chemosensory materials for detecting nitroa... more Conjugated polymers (CPs) have proved to be promising chemosensory materials for detecting nitroaromatic explosives vapors, as they quickly convert a chemical interaction into an easily-measured high-sensitivity optical output. The nitroaromatic analytes are strongly electron-deficient, whereas the conjugated polymer sensing materials are electron-rich. As a result, the photoexcitation of the CP is followed by electron transfer to the nitroaromatic analyte, resulting in a quenching of the light-emission from the conjugated polymer. The best CP in our studies was found to be poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2). It is photostable, has a good absorption between 400 and 450 nm, and a strong and structured fluorescence around 550 nm. Our studies indicate up to 96% quenching of light-emission, accompanied by a marked decrease in the fluorescence lifetime, upon exposure of the films of F8T2 in ethyl cellulose to nitrobenzene (NB) and 1,3-dinitrobenzene (DNB) vapors ...
International Journal of Photoenergy
Ternary blend polymer solar cells combining two electron-donor polymers, poly[4,8-bis[(2-ethylhex... more Ternary blend polymer solar cells combining two electron-donor polymers, poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (pBTTT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), as electron-acceptor, were fabricated. The power conversion efficiency of the ternary cells was enhanced by 18%, with respect to the reference binary cells, for a blend composition with 25% (wt%) of pBTTT in the polymers content. The optimized device performance was related to the blend morphology, nonrevealing pBTTT aggregates, and improved charge extraction within the device.
Dalton Trans., 2016
New fluorescent aromatic ring-fused 2-iminopyrrolyl diphenyl boron complexes are emitters in the ... more New fluorescent aromatic ring-fused 2-iminopyrrolyl diphenyl boron complexes are emitters in the range blue to orange.
1-Novel plastic optical fibers (POF) based on polymethylmethacrylate, PMMA, doped with luminescen... more 1-Novel plastic optical fibers (POF) based on polymethylmethacrylate, PMMA, doped with luminescent conjugated polymers and oligomers were fabricated. Our innovative approach is based on the chemical binding between the PMMA matrix and the dopant material as an alternative to the blending approach (mixture) of PMMA and the active material. We aimed at controlling load and dispersion of the luminescent polymer in the PMMA matrix, which are crucial for the optimisation of these optical media, while reducing the possibility of dopant segregation during the fiber drawing. Stimulated emission and optical switching inside the fiber were observed in some of the new materials, indicating that they can represent possible routes to plastic optical media, namely POFs, exhibiting gain and ultrafast switching.
Journal of Physics D Applied Physics 36 434 434, Feb 13, 2003
We study the effect of indium-tin oxide surface modification by self assembling of highly polar m... more We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.
1-At variance with a high stability of the inorganic materials for electronics under normal atmos... more 1-At variance with a high stability of the inorganic materials for electronics under normal atmospheric conditions, organic materials are more sensitive, due to charge transfer doping by oxygen and water and degradation when exposed to the ultraviolet radiation. Here we show that the chemical structure of the conjugated polymer used as active semiconducting material of polymer field-effect transistors has a drastic effect on their stability. These results show that, by chemical manipulation, some of the above limitations, when envisaging the use of organic materials for electronics, can be reduced.