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Research paper thumbnail of Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices

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Research paper thumbnail of Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/ PC 71 BM devices OPEN

We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the pre... more We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the preparation of a bulk-heterojunction photovoltaic device increases its power conversion efficiency by 20%, through a mechanism of transient plasticisation. We follow the removal of 1,8-diiodooctane directly after spin-coating using ellipsometry and ion beam analysis, while using small angle neutron scattering to characterise the morphological nanostructure evolution of the film. In PffBT4T-2OD/ PC 71 BM devices, the power conversion efficiency increases from 7.2% to above 8.7% as a result of the coarsening of the phase domains. This coarsening process is assisted by thermal annealing and the slow evaporation of 1,8-diiodooctane, which we suggest, acts as a plasticiser to promote molecular mobility. Our results show that 1,8-diiodooctane can be completely removed from the film by a thermal annealing process at temperatures ≤100 °C and that there is an interplay between the evaporation rate of 1,8-diiodooctane and the rate of domain coarsening in the plasticized film which helps elucidate the mechanism by which additives improve device efficiency. Organic photovoltaic solar cells (OPVs) represent a promising approach to generate renewable energy 1–3. Compared to silicon-based solar cells, OPVs can be processed via solution over much larger areas and using flexible substrates, suggesting possible reductions in module fabrication cost together with the potential to reduce the energy payback time 3–6. In the last decade, bulk heterojunction (BHJ) OPVs based on low band gap copolymers as electron donor and fullerene derivatives as the electron acceptor have developed rapidly, attaining power conversion efficiencies (PCEs) > 10% for single layer devices 7,8. The photovoltaic effect in a BHJ commences with the generation of an exciton resulting from the absorption of a photon. Such excitons must be rapidly dissociated at a donor-acceptor interface to avoid recombination, with the charges generated being extracted through a bicontinuous and inter-penetrating network of phase-separated fullerene and polymer-rich domains. The typical diffusion length of a singlet-exciton in conjugated polymers is as low as ca. 10 nm 9,10 ; a length-scale that necessarily defines the size of phase-separation for optimal device efficiency. Different processing methodologies to optimize the morphology of BHJ films and increase device performance (including the use of thermal annealing 11–15 and the use of solvent additives 16–19) are now widely established in the OPV field. Thermal annealing (TA) was the first of these strategies to be explored as it proved most effective when used with crystalline polymers such as P3HT. For example annealing P3HT:PCBM blends at around 150 °C was used to improve the degree of crystallinity of the polymer and thus enhance device efficiency 11–15. This is in contrast with less crystalline or amorphous polymers such as PCDTBT 20,21 in which anneal-ing at temperatures < 100 °C has a limited benefit on device PCE mainly through removal of residual solvent rather than by causing a change in film nanostructure 20 , with annealing at higher temperatures causing a drastic decrease in PCE 21. The use of solvent additives 16,17,19 such as 1,8-diiodooctane (DIO) is an alternative strategy

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Research paper thumbnail of Impact of Fullerenes on the Thermal Stability of Melt Processed Polystyrene and Poly(Methyl-Methacrylate) Composites

Polymer Testing, 2015

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Research paper thumbnail of Phase behavior of blends of PCBM with amorphous polymers with different aromaticity

Journal of Polymer Science Part B: Polymer Physics, 2016

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Research paper thumbnail of Melt Processed Polyethylene/Fullerene Nanocomposites with Highly Improved Thermo-Oxidative Stability

Polymer Testing, 2015

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Research paper thumbnail of Enhanced thermal stability of poly(methyl methacrylate) composites with fullerenes

Polymer Bulletin, 2015

ABSTRACT The thermal stability of poly(methyl methacrylate) (PMMA) composites with the two fuller... more ABSTRACT The thermal stability of poly(methyl methacrylate) (PMMA) composites with the two fullerenes C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), was studied over the whole composition range under nitrogen (N2) and air atmosphere using dynamic thermogravimetric analysis (TGA). The aim of this study was to compare the thermal stabilization effect of both fullerenes on PMMA. When compared with pure PMMA, both C60 and PCBM increase substantially the thermal degradation temperature of the corresponding composites, both in nitrogen and air atmospheres. The amounts of C60 and PCBM in the PMMA composites can be successfully determined along the whole composition range using TGA. The initial amounts of fullerene present in the composites correlates linearly with the residual mass values obtained above 450 °C in nitrogen and with the residual mass values observed at the temperatures of transition from the first to the second decomposition steps in air. There are no significant differences between the thermal stabilization effects of C60 and PCBM in both atmospheres (nitrogen and air).

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Research paper thumbnail of The Adsorption of Acetylene and Ethylene on Transition Metal Surfaces

Progress in Theoretical Chemistry and Physics, 2001

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Research paper thumbnail of The adsorption of ethylene on the (100) surfaces of platinum, palladium and nickel: A DFT study

Journal of Molecular Structure: THEOCHEM, 2001

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Research paper thumbnail of The adsorption of ethylene on the (110) surfaces of copper, silver and platinum: A DFT study

Journal of Molecular Structure: THEOCHEM, 2002

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Research paper thumbnail of Cluster model DFT study of acetylene adsorption on the Cu (100) surface

Journal of Molecular Structure: THEOCHEM, 2003

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Research paper thumbnail of Recent Progress in the Understanding and Manipulation of Morphology in Polymer: Fullerene Photovoltaic Cells

Optoelectronics - Advanced Materials and Devices, 2013

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Research paper thumbnail of Synergistic effect on the efficiency of polymer light-emitting diodes upon blending of two green-emitting polymers

Journal of Applied Physics, 2010

Light-emitting diodes based on blends of the two green-emitting polymers, poly(9,9-dioctylfluoren... more Light-emitting diodes based on blends of the two green-emitting polymers, poly(9,9-dioctylfluorene-alt-benzothiadiazole), F8BT, and poly(9,9-dioctylfluorene-alt-bithiophene), F8T2, show efficiencies that lie in between those of the devices based on the neat polymers (with a maximum efficiency of approximately 4 cd/A for the devices with magnesium cathodes based on F8BT), except for the blend with 5% by weight of F8T2, which is more

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Research paper thumbnail of Improving polymer light-emitting diodes efficiency using interlayers based on cross-linkable polymers

Applied Physics Letters, 2007

ABSTRACT The efficiency of light-emitting diodes based on poly[(2-methoxy)-5-(2&#39;-ethyl-he... more ABSTRACT The efficiency of light-emitting diodes based on poly[(2-methoxy)-5-(2&#39;-ethyl-hexyloxy)-1,4-phenylenevinylene] increases upon formation of interlayers, on top of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS), made of acid-initiated cross-linkable polyfluorenes. The use of this type of polymers allows for the formation of thicker interlayers leading to higher efficiencies when comparing with similar devices with interlayers formed by the parent non-cross-linkable polymers. This efficiency increase is attributed to a combination of electron and exciton confinement away from PEDOT:PSS.

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Research paper thumbnail of Impact of composition and morphology on the optical properties of Si-NC/P3HT thin films processed from solution

Applied Physics A, 2013

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Research paper thumbnail of Thermal stability of P3HT and P3HT:PCBM blends in the molten state

Polymer Testing, 2013

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Research paper thumbnail of Solid-state low-temperature extrusion of P3HT ribbons

Applied Physics A, 2014

ABSTRACT Ribbons of poly(3-hexylthiophene) (P3HT) 0.15 and 0.30 mm thickness were extruded at the... more ABSTRACT Ribbons of poly(3-hexylthiophene) (P3HT) 0.15 and 0.30 mm thickness were extruded at the temperatures of 200 and 250 °C, i.e., below and above the melting temperature of P3HT (∼240 °C), using a small home-made extrusion device. The ribbons produced by this method are continuous and freestanding. WAXS results show that all the extruded samples are more crystalline than the original powder, and the different processing conditions cause different variations in the crystal unit cell dimensions of P3HT. In terms of the degree of orientation, the ribbons extruded in the solid state (T T m ), which is fully isotropic.

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Research paper thumbnail of Phase Morphology and Molecular Structure Correlations in Model Fullerene-Polymer Nanocomposites

Materials Science Forum, 2012

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Research paper thumbnail of Low temperature solid state processing of pure P3HT fibers

AIP Advances, 2013

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Research paper thumbnail of Morphology Control of Thin P3HT-Si-NCs Composite Films for Hybrid Photovoltaic Cells

Materials Science Forum, 2012

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Research paper thumbnail of Tailoring kappa/iota-hybrid carrageenan from Mastocarpus stellatus with desired gel quality through pre-extraction alkali treatment

Food Hydrocolloids, 2013

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Research paper thumbnail of Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices

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Research paper thumbnail of Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/ PC 71 BM devices OPEN

We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the pre... more We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the preparation of a bulk-heterojunction photovoltaic device increases its power conversion efficiency by 20%, through a mechanism of transient plasticisation. We follow the removal of 1,8-diiodooctane directly after spin-coating using ellipsometry and ion beam analysis, while using small angle neutron scattering to characterise the morphological nanostructure evolution of the film. In PffBT4T-2OD/ PC 71 BM devices, the power conversion efficiency increases from 7.2% to above 8.7% as a result of the coarsening of the phase domains. This coarsening process is assisted by thermal annealing and the slow evaporation of 1,8-diiodooctane, which we suggest, acts as a plasticiser to promote molecular mobility. Our results show that 1,8-diiodooctane can be completely removed from the film by a thermal annealing process at temperatures ≤100 °C and that there is an interplay between the evaporation rate of 1,8-diiodooctane and the rate of domain coarsening in the plasticized film which helps elucidate the mechanism by which additives improve device efficiency. Organic photovoltaic solar cells (OPVs) represent a promising approach to generate renewable energy 1–3. Compared to silicon-based solar cells, OPVs can be processed via solution over much larger areas and using flexible substrates, suggesting possible reductions in module fabrication cost together with the potential to reduce the energy payback time 3–6. In the last decade, bulk heterojunction (BHJ) OPVs based on low band gap copolymers as electron donor and fullerene derivatives as the electron acceptor have developed rapidly, attaining power conversion efficiencies (PCEs) > 10% for single layer devices 7,8. The photovoltaic effect in a BHJ commences with the generation of an exciton resulting from the absorption of a photon. Such excitons must be rapidly dissociated at a donor-acceptor interface to avoid recombination, with the charges generated being extracted through a bicontinuous and inter-penetrating network of phase-separated fullerene and polymer-rich domains. The typical diffusion length of a singlet-exciton in conjugated polymers is as low as ca. 10 nm 9,10 ; a length-scale that necessarily defines the size of phase-separation for optimal device efficiency. Different processing methodologies to optimize the morphology of BHJ films and increase device performance (including the use of thermal annealing 11–15 and the use of solvent additives 16–19) are now widely established in the OPV field. Thermal annealing (TA) was the first of these strategies to be explored as it proved most effective when used with crystalline polymers such as P3HT. For example annealing P3HT:PCBM blends at around 150 °C was used to improve the degree of crystallinity of the polymer and thus enhance device efficiency 11–15. This is in contrast with less crystalline or amorphous polymers such as PCDTBT 20,21 in which anneal-ing at temperatures < 100 °C has a limited benefit on device PCE mainly through removal of residual solvent rather than by causing a change in film nanostructure 20 , with annealing at higher temperatures causing a drastic decrease in PCE 21. The use of solvent additives 16,17,19 such as 1,8-diiodooctane (DIO) is an alternative strategy

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Research paper thumbnail of Impact of Fullerenes on the Thermal Stability of Melt Processed Polystyrene and Poly(Methyl-Methacrylate) Composites

Polymer Testing, 2015

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Research paper thumbnail of Phase behavior of blends of PCBM with amorphous polymers with different aromaticity

Journal of Polymer Science Part B: Polymer Physics, 2016

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Research paper thumbnail of Melt Processed Polyethylene/Fullerene Nanocomposites with Highly Improved Thermo-Oxidative Stability

Polymer Testing, 2015

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Research paper thumbnail of Enhanced thermal stability of poly(methyl methacrylate) composites with fullerenes

Polymer Bulletin, 2015

ABSTRACT The thermal stability of poly(methyl methacrylate) (PMMA) composites with the two fuller... more ABSTRACT The thermal stability of poly(methyl methacrylate) (PMMA) composites with the two fullerenes C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), was studied over the whole composition range under nitrogen (N2) and air atmosphere using dynamic thermogravimetric analysis (TGA). The aim of this study was to compare the thermal stabilization effect of both fullerenes on PMMA. When compared with pure PMMA, both C60 and PCBM increase substantially the thermal degradation temperature of the corresponding composites, both in nitrogen and air atmospheres. The amounts of C60 and PCBM in the PMMA composites can be successfully determined along the whole composition range using TGA. The initial amounts of fullerene present in the composites correlates linearly with the residual mass values obtained above 450 °C in nitrogen and with the residual mass values observed at the temperatures of transition from the first to the second decomposition steps in air. There are no significant differences between the thermal stabilization effects of C60 and PCBM in both atmospheres (nitrogen and air).

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Research paper thumbnail of The Adsorption of Acetylene and Ethylene on Transition Metal Surfaces

Progress in Theoretical Chemistry and Physics, 2001

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Research paper thumbnail of The adsorption of ethylene on the (100) surfaces of platinum, palladium and nickel: A DFT study

Journal of Molecular Structure: THEOCHEM, 2001

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Research paper thumbnail of The adsorption of ethylene on the (110) surfaces of copper, silver and platinum: A DFT study

Journal of Molecular Structure: THEOCHEM, 2002

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Research paper thumbnail of Cluster model DFT study of acetylene adsorption on the Cu (100) surface

Journal of Molecular Structure: THEOCHEM, 2003

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Research paper thumbnail of Recent Progress in the Understanding and Manipulation of Morphology in Polymer: Fullerene Photovoltaic Cells

Optoelectronics - Advanced Materials and Devices, 2013

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Research paper thumbnail of Synergistic effect on the efficiency of polymer light-emitting diodes upon blending of two green-emitting polymers

Journal of Applied Physics, 2010

Light-emitting diodes based on blends of the two green-emitting polymers, poly(9,9-dioctylfluoren... more Light-emitting diodes based on blends of the two green-emitting polymers, poly(9,9-dioctylfluorene-alt-benzothiadiazole), F8BT, and poly(9,9-dioctylfluorene-alt-bithiophene), F8T2, show efficiencies that lie in between those of the devices based on the neat polymers (with a maximum efficiency of approximately 4 cd/A for the devices with magnesium cathodes based on F8BT), except for the blend with 5% by weight of F8T2, which is more

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Research paper thumbnail of Improving polymer light-emitting diodes efficiency using interlayers based on cross-linkable polymers

Applied Physics Letters, 2007

ABSTRACT The efficiency of light-emitting diodes based on poly[(2-methoxy)-5-(2&#39;-ethyl-he... more ABSTRACT The efficiency of light-emitting diodes based on poly[(2-methoxy)-5-(2&#39;-ethyl-hexyloxy)-1,4-phenylenevinylene] increases upon formation of interlayers, on top of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS), made of acid-initiated cross-linkable polyfluorenes. The use of this type of polymers allows for the formation of thicker interlayers leading to higher efficiencies when comparing with similar devices with interlayers formed by the parent non-cross-linkable polymers. This efficiency increase is attributed to a combination of electron and exciton confinement away from PEDOT:PSS.

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Research paper thumbnail of Impact of composition and morphology on the optical properties of Si-NC/P3HT thin films processed from solution

Applied Physics A, 2013

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Research paper thumbnail of Thermal stability of P3HT and P3HT:PCBM blends in the molten state

Polymer Testing, 2013

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Research paper thumbnail of Solid-state low-temperature extrusion of P3HT ribbons

Applied Physics A, 2014

ABSTRACT Ribbons of poly(3-hexylthiophene) (P3HT) 0.15 and 0.30 mm thickness were extruded at the... more ABSTRACT Ribbons of poly(3-hexylthiophene) (P3HT) 0.15 and 0.30 mm thickness were extruded at the temperatures of 200 and 250 °C, i.e., below and above the melting temperature of P3HT (∼240 °C), using a small home-made extrusion device. The ribbons produced by this method are continuous and freestanding. WAXS results show that all the extruded samples are more crystalline than the original powder, and the different processing conditions cause different variations in the crystal unit cell dimensions of P3HT. In terms of the degree of orientation, the ribbons extruded in the solid state (T T m ), which is fully isotropic.

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Research paper thumbnail of Phase Morphology and Molecular Structure Correlations in Model Fullerene-Polymer Nanocomposites

Materials Science Forum, 2012

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Research paper thumbnail of Low temperature solid state processing of pure P3HT fibers

AIP Advances, 2013

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Research paper thumbnail of Morphology Control of Thin P3HT-Si-NCs Composite Films for Hybrid Photovoltaic Cells

Materials Science Forum, 2012

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Research paper thumbnail of Tailoring kappa/iota-hybrid carrageenan from Mastocarpus stellatus with desired gel quality through pre-extraction alkali treatment

Food Hydrocolloids, 2013

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