Roberto Pacios | IKERLAN Technological Research Center (original) (raw)
Papers by Roberto Pacios
Quantum dots (QDs) are inorganic semiconductor particles that exhibit size and shape dependent op... more Quantum dots (QDs) are inorganic semiconductor particles that exhibit size and shape dependent optical and electronic properties. Due to the typical dimension in the range of 1-100 nm, the surface-to-volume ratios of the materials become large and their electronic states become discrete. Moreover, due to the fact that the size of the semiconductor nanocrystal is smaller than the size of the exciton, charge carriers become spatially confined, which raises their energy (quantum confinement). Thus, the size and shape-dependent optoelectronic properties are attributed to the quantum confinement effect. Because of this effect, light emission from these particles can be tuned, throughout the ultraviolet, visible and near infrared spectral ranges. Quantum dots possess many advantages that make them interesting for several applications: They show symmetrical and narrow emission spectra and broad absorption spectra, enabling that a single light source can be used to excite multicolour quantu...
We present a simple, low-cost, pioneering technique for the metallization of polymeric substrates... more We present a simple, low-cost, pioneering technique for the metallization of polymeric substrates that allows manufacturing of 3D-PCBs for fully encapsulated Smart Systems. This 3D packaging approach provides a compact solution to integrate MEMs with fluidics in a durable substrate, opening the door to adapting Smart Systems to harsh environments of vibration and temperature
Nanoscale
Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot syn... more Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists of using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.
Journal of Photonics for Energy, 2015
In spite of the impressive development achieved by organic photovoltaics throughout the last deca... more In spite of the impressive development achieved by organic photovoltaics throughout the last decades, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and then fullerene derivatives, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once and for all. The potential and the expectation raised by this technology is such that it is very difficult to keep track of the most significant progresses being now published in different and even monographic journals. In this paper, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. We separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% power conversion efficiency: active materials, strategies-fabrication/processing procedures-that can mainly modify the active film morphology, and all the different cell layout/architectures that have been used in order to extract as high a photocurrent as possible from the Sun. The synthesis of new donors, the use of additives and postprocessing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are reviewed in detail in this paper. All have equally contributed to develop this technology and bring it at the doors of commercialization.
Organic Electronics, 2015
Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive develo... more Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and fullerene derivatives then, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once for all. Nowadays, the promise of printing solar cells by low-cost and high throughput mass production techniques still stands. However, the potential and the expectation raised by this technology is such that it is considerably difficult to keep track of the most significant progresses being now published in different and even monographic journals. There is therefore the need to compile the most remarkable advances in well-documented reviews than can be used as a reference for future ideas and works. In this letter, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. After analyzing their fundamental limits, we separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% http://dx.power conversion efficiency: Active materials, strategies -fabrication/processing procedures-that can mainly modify the active film morphology and result in improved efficiencies for the same starting materials, and all the different cell layout/architectures that have been used in order to extract as high photocurrent as possible from the Sun. The synthesis of new donors and acceptors, the use of additives and post-processing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are in detailed reviewed in this letter. All have equally contributed to develop this technology and leave it at doors of commercialization.
2009 Spanish Conference on Electron Devices, 2009
![Research paper thumbnail of Charge recombination studies in polyfluorene:[6, 6]-phenyl c~ 6~ 1-butyric acid methyl ester blend photovoltaic cells [5215-47]](https://attachments.academia-assets.com/39918625/thumbnails/1.jpg)
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Organic Electronics, 2014
In this work we compare the photovoltaic performance of different cell designs, standard and inve... more In this work we compare the photovoltaic performance of different cell designs, standard and inverted, for one of the most promising systems to achieve power conversion efficiencies over 10% in polymer:fullerene single cells, namely PTB7:PC70BM. Impedance spectroscopy, charge extraction and transient photovoltage are used in order to assign the electrical losses initially observed in the current density-voltage curve and understand the main limitation of every design. While inverted devices show competitive performance in terms of charge generation, transport of carriers and also for charge collection at electrodes, standard devices present additional resistive losses that are assigned to charge transfer issues at the active layer/anode interface. This additional resistance increase the overall series resistance of devices, lowers the fill factor and it is the ultimate responsible for the observed reduced device performance of standard cells in comparison to inverted ones. In this way, devices over 7.2% are reported with ZnO and MoO 3 as interlayer electrodes that act as improved highly selective and extracting contacts in comparison to standard PED-OT:PSS and Ca/Ag. Contacts are thus electrically optimized. Additional improvement of device performance must consider enhancement of intrinsic recombination properties of the blend. Lower molecular weights and/or any residual catalyst impurities with respect to other batches are the only limitation to reach record efficiencies as those shown in recent works.
Solar Energy Materials and Solar Cells, 2012
We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a t... more We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a transparent conducting electrode. Current limitations to achieve high conversion efficiencies are overcome with the combination of Ag NW and specifically designed ZnO nanoparticles (NP). The new transparent electrode presents improved optoelectronic properties with respect to the most widely used ITO-indium tin oxide. We demonstrate that there are non-conducting void spaces left between neighboring nanowires onto the holding substrate as a consequence of processing the Ag NW film from a solvent dispersion. Moreover, the fabrication of efficient ITO-free organic solar cells (OSC) based on Ag NW relies on filling the resulting void spaces with a highly selective and conductive supporting thin layer. This slight modification of the Ag NW film enables the great majority of photogenerated charge carriers -that would otherwise be recombined at voids -to be efficiently collected by the nanowires. In this way, we report -to our knowledge -one of the highest ITO-free OSC (3.8%) also fabricated onto flexible substrates (3.2%) with commercially available Poly (3-Hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). This breakthrough could once and for all bring the potential of flexible low-cost organic photovoltaics into reality.
Organic Electronics, 2009
We present a detailed study and experimental recipes to tune the outcoming light of single layer ... more We present a detailed study and experimental recipes to tune the outcoming light of single layer polymeric diodes fabricated with commercially available polyfluorene. The standard blue emission peaking at 440 nm can be tuned to obtain even white emission by controlling the deliberate oxidation of the material. Furthermore, with the addition of inorganic quantum dots was not only possible to redshift the emission as a function of the blend composition but also a fine tuning of the emitted light as a function of the external applied voltage. Merging these two effects we fabricated PFO and PFO:QD light emitting diodes that practically cover the entire visible spectrum. The same device exhibits emission from blue to red depending on the applied bias, from blue to green depending on the oxidation degree of the polymer and from white to blue and/or red combining both. The door is already open to cover the whole color gamut with solely one device.
Thin Solid Films, 2012
Energetics and kinetics of defects in the effective band gap of organic bulk heterojunctions are ... more Energetics and kinetics of defects in the effective band gap of organic bulk heterojunctions are determined by means of capacitance methods. The technique consists of calculating the junction capacitance derivative with respect to the angular frequency of the small voltage perturbation applied to thin film poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C 61 -butyric acid methyl ester solar cells, varying the temperature. The analysis reveals the presence of defect bands (shallow acceptors) centered at E 0 =35 meV above the highest-occupied molecular orbital level of P3HT. The total density of defects results of order 10 16 cm − 3 . Characteristic frequency is obtained to be situated within the range of 1-10 Hz. Defect bands acting as negatively charged levels are responsible for the p-doping of the active layer and the band-bending near the cathode contact, as derived from Mott-Schottky capacitance-voltage analysis.
Synthetic Metals, 2002
The photosensitivity of semiconducting polymers can be enhanced by blending donor (D) and accepto... more The photosensitivity of semiconducting polymers can be enhanced by blending donor (D) and acceptor (A) polymers to optimise photoinduced charge separation. The photoluminescence of two such polymers, an acceptor poly(9,9-dioctyl¯uorene-co-benzothidiadiozole) (BT) and a donor poly(9,9-dioctyl¯uorene-co-bis-N,N H -(4-butylphenyl)-bis-N,N H -phenylbenzidine) (BFB) are quenched in their mutual blend indicative of rapid and ef®cient separation of photogenerated electron±hole pairs with electrons in the BT acceptor and holes in the BFB donor. In order to be useful for photovoltaic applications, the excitons have to reach a D/A interface before they decay radiatively or non-radiatively. Whereas charge separation seems to be ef®cient in these polymer networks, charge transport still remains a limiting factor due to the imperfect network structures and low charge carrier mobilities. This charge transport can be improved by controlling the morphology of the blend. Although the initial power conversion ef®ciency (PCE) was low for our composites (0.12%), the blends show promising photovoltaic characteristics; the ef®ciency is 220 times higher than for diodes made with pure BFB. We report work aimed at improving the ef®ciency via control of the blend morphology and the use of polymeric anodes. #
Solar Energy Materials and Solar Cells, 2006
We present a study of dark air-exposure degradation of organic solar cells based on photoactive b... more We present a study of dark air-exposure degradation of organic solar cells based on photoactive blends of the conjugated polymer, poly[2-methoxy-5-(3 0 ,7 0 -dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM). Photovoltaic devices were fabricated on indium tin oxide (ITO) glass with or without a layer of poly (3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS), and were studied without encapsulation. Photovoltaic performance characteristics were measured as a function of time for different ambient conditions (under white light irradiation and in the dark, and under air, dry oxygen and humid nitrogen atmospheres). It was found that a key cause of degradation under air exposure is light independent and results from water adsorption by the hygroscopic PEDOT:PSS layer. Measurements of the charge mobility and hole injection after air exposure showed that the degradation increases the resistance of the PEDOT:PSS/blend layer interface. r
Physical Chemistry Chemical Physics, 2009
Since the demonstration of efficient hybrid photovoltaic devices using CdSe/P3HT, a number of dif... more Since the demonstration of efficient hybrid photovoltaic devices using CdSe/P3HT, a number of different QD/polymer molecular solar cells have been investigated. However, considerably less attention has been paid to the photo-induced processes occurring in these devices, in particular the strong dependence that device efficiencies show upon QD concentration. This study aims to shed more light on this dependence by monitoring these processes occurring at the QD/polymer interface, namely, exciton formation, charge separation and undesired charge recombination.
Physical Chemistry Chemical Physics, 2011
Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective ele... more Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective electrodes for electron collection. The interfacial charge transfer reactions, under working conditions, that limit the energy conversion efficiency of these devices have been measured and compared to the standard OPSC geometry which collects the electrons through a low work function metal contact.
physica status solidi (a), 2008
ABSTRACT In this paper, a new method for obtaining poly(3,4-ethylenedioxythiophene) (PEDOT/PSS)/g... more ABSTRACT In this paper, a new method for obtaining poly(3,4-ethylenedioxythiophene) (PEDOT/PSS)/gold nanocomposites is described. In a first step, PEDOT/PSS gold nanoparticle aqueous dispersions were obtained by simultaneous chemical synthesis of PEDOT and gold nanoparticles in the presence of PSS that acts as a stabilizer. In a second step, these PEDOT/PSS gold nanoparticle dispersions were used to formulate nanocomposites by mixing the initial dispersion with commercially available PEDOT/PSS aqueous dispersion. Nanocomposite thin films, obtained by casting these dispersions, present an intimate contact between the inorganic and organic components. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Organic Electronics, 2011
We have measured the charge transfer processes on near IR small molecule solution processes solar... more We have measured the charge transfer processes on near IR small molecule solution processes solar cells under working conditions. The results show that there are two different behavior, for the device under working conditions, controlled by the intrinsic properties of the organic bulk-heterojunction phase to store charges at the different organic materials. Furthermore, our recombination kinetic studies show the origin of the photovoltage on these thin organic devices (80 nm thick) and the reason for the difference between the observed open circuit cell potential and the theoretical expected value based on the LUM-OPCBM-HOMO phthalocyanine difference.
Organic Electronics, 2013
and sharing with colleagues.
Quantum dots (QDs) are inorganic semiconductor particles that exhibit size and shape dependent op... more Quantum dots (QDs) are inorganic semiconductor particles that exhibit size and shape dependent optical and electronic properties. Due to the typical dimension in the range of 1-100 nm, the surface-to-volume ratios of the materials become large and their electronic states become discrete. Moreover, due to the fact that the size of the semiconductor nanocrystal is smaller than the size of the exciton, charge carriers become spatially confined, which raises their energy (quantum confinement). Thus, the size and shape-dependent optoelectronic properties are attributed to the quantum confinement effect. Because of this effect, light emission from these particles can be tuned, throughout the ultraviolet, visible and near infrared spectral ranges. Quantum dots possess many advantages that make them interesting for several applications: They show symmetrical and narrow emission spectra and broad absorption spectra, enabling that a single light source can be used to excite multicolour quantu...
We present a simple, low-cost, pioneering technique for the metallization of polymeric substrates... more We present a simple, low-cost, pioneering technique for the metallization of polymeric substrates that allows manufacturing of 3D-PCBs for fully encapsulated Smart Systems. This 3D packaging approach provides a compact solution to integrate MEMs with fluidics in a durable substrate, opening the door to adapting Smart Systems to harsh environments of vibration and temperature
Nanoscale
Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot syn... more Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists of using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.
Journal of Photonics for Energy, 2015
In spite of the impressive development achieved by organic photovoltaics throughout the last deca... more In spite of the impressive development achieved by organic photovoltaics throughout the last decades, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and then fullerene derivatives, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once and for all. The potential and the expectation raised by this technology is such that it is very difficult to keep track of the most significant progresses being now published in different and even monographic journals. In this paper, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. We separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% power conversion efficiency: active materials, strategies-fabrication/processing procedures-that can mainly modify the active film morphology, and all the different cell layout/architectures that have been used in order to extract as high a photocurrent as possible from the Sun. The synthesis of new donors, the use of additives and postprocessing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are reviewed in detail in this paper. All have equally contributed to develop this technology and bring it at the doors of commercialization.
Organic Electronics, 2015
Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive develo... more Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and fullerene derivatives then, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once for all. Nowadays, the promise of printing solar cells by low-cost and high throughput mass production techniques still stands. However, the potential and the expectation raised by this technology is such that it is considerably difficult to keep track of the most significant progresses being now published in different and even monographic journals. There is therefore the need to compile the most remarkable advances in well-documented reviews than can be used as a reference for future ideas and works. In this letter, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. After analyzing their fundamental limits, we separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% http://dx.power conversion efficiency: Active materials, strategies -fabrication/processing procedures-that can mainly modify the active film morphology and result in improved efficiencies for the same starting materials, and all the different cell layout/architectures that have been used in order to extract as high photocurrent as possible from the Sun. The synthesis of new donors and acceptors, the use of additives and post-processing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are in detailed reviewed in this letter. All have equally contributed to develop this technology and leave it at doors of commercialization.
2009 Spanish Conference on Electron Devices, 2009
Organic Electronics, 2014
In this work we compare the photovoltaic performance of different cell designs, standard and inve... more In this work we compare the photovoltaic performance of different cell designs, standard and inverted, for one of the most promising systems to achieve power conversion efficiencies over 10% in polymer:fullerene single cells, namely PTB7:PC70BM. Impedance spectroscopy, charge extraction and transient photovoltage are used in order to assign the electrical losses initially observed in the current density-voltage curve and understand the main limitation of every design. While inverted devices show competitive performance in terms of charge generation, transport of carriers and also for charge collection at electrodes, standard devices present additional resistive losses that are assigned to charge transfer issues at the active layer/anode interface. This additional resistance increase the overall series resistance of devices, lowers the fill factor and it is the ultimate responsible for the observed reduced device performance of standard cells in comparison to inverted ones. In this way, devices over 7.2% are reported with ZnO and MoO 3 as interlayer electrodes that act as improved highly selective and extracting contacts in comparison to standard PED-OT:PSS and Ca/Ag. Contacts are thus electrically optimized. Additional improvement of device performance must consider enhancement of intrinsic recombination properties of the blend. Lower molecular weights and/or any residual catalyst impurities with respect to other batches are the only limitation to reach record efficiencies as those shown in recent works.
Solar Energy Materials and Solar Cells, 2012
We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a t... more We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a transparent conducting electrode. Current limitations to achieve high conversion efficiencies are overcome with the combination of Ag NW and specifically designed ZnO nanoparticles (NP). The new transparent electrode presents improved optoelectronic properties with respect to the most widely used ITO-indium tin oxide. We demonstrate that there are non-conducting void spaces left between neighboring nanowires onto the holding substrate as a consequence of processing the Ag NW film from a solvent dispersion. Moreover, the fabrication of efficient ITO-free organic solar cells (OSC) based on Ag NW relies on filling the resulting void spaces with a highly selective and conductive supporting thin layer. This slight modification of the Ag NW film enables the great majority of photogenerated charge carriers -that would otherwise be recombined at voids -to be efficiently collected by the nanowires. In this way, we report -to our knowledge -one of the highest ITO-free OSC (3.8%) also fabricated onto flexible substrates (3.2%) with commercially available Poly (3-Hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). This breakthrough could once and for all bring the potential of flexible low-cost organic photovoltaics into reality.
Organic Electronics, 2009
We present a detailed study and experimental recipes to tune the outcoming light of single layer ... more We present a detailed study and experimental recipes to tune the outcoming light of single layer polymeric diodes fabricated with commercially available polyfluorene. The standard blue emission peaking at 440 nm can be tuned to obtain even white emission by controlling the deliberate oxidation of the material. Furthermore, with the addition of inorganic quantum dots was not only possible to redshift the emission as a function of the blend composition but also a fine tuning of the emitted light as a function of the external applied voltage. Merging these two effects we fabricated PFO and PFO:QD light emitting diodes that practically cover the entire visible spectrum. The same device exhibits emission from blue to red depending on the applied bias, from blue to green depending on the oxidation degree of the polymer and from white to blue and/or red combining both. The door is already open to cover the whole color gamut with solely one device.
Thin Solid Films, 2012
Energetics and kinetics of defects in the effective band gap of organic bulk heterojunctions are ... more Energetics and kinetics of defects in the effective band gap of organic bulk heterojunctions are determined by means of capacitance methods. The technique consists of calculating the junction capacitance derivative with respect to the angular frequency of the small voltage perturbation applied to thin film poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C 61 -butyric acid methyl ester solar cells, varying the temperature. The analysis reveals the presence of defect bands (shallow acceptors) centered at E 0 =35 meV above the highest-occupied molecular orbital level of P3HT. The total density of defects results of order 10 16 cm − 3 . Characteristic frequency is obtained to be situated within the range of 1-10 Hz. Defect bands acting as negatively charged levels are responsible for the p-doping of the active layer and the band-bending near the cathode contact, as derived from Mott-Schottky capacitance-voltage analysis.
Synthetic Metals, 2002
The photosensitivity of semiconducting polymers can be enhanced by blending donor (D) and accepto... more The photosensitivity of semiconducting polymers can be enhanced by blending donor (D) and acceptor (A) polymers to optimise photoinduced charge separation. The photoluminescence of two such polymers, an acceptor poly(9,9-dioctyl¯uorene-co-benzothidiadiozole) (BT) and a donor poly(9,9-dioctyl¯uorene-co-bis-N,N H -(4-butylphenyl)-bis-N,N H -phenylbenzidine) (BFB) are quenched in their mutual blend indicative of rapid and ef®cient separation of photogenerated electron±hole pairs with electrons in the BT acceptor and holes in the BFB donor. In order to be useful for photovoltaic applications, the excitons have to reach a D/A interface before they decay radiatively or non-radiatively. Whereas charge separation seems to be ef®cient in these polymer networks, charge transport still remains a limiting factor due to the imperfect network structures and low charge carrier mobilities. This charge transport can be improved by controlling the morphology of the blend. Although the initial power conversion ef®ciency (PCE) was low for our composites (0.12%), the blends show promising photovoltaic characteristics; the ef®ciency is 220 times higher than for diodes made with pure BFB. We report work aimed at improving the ef®ciency via control of the blend morphology and the use of polymeric anodes. #
Solar Energy Materials and Solar Cells, 2006
We present a study of dark air-exposure degradation of organic solar cells based on photoactive b... more We present a study of dark air-exposure degradation of organic solar cells based on photoactive blends of the conjugated polymer, poly[2-methoxy-5-(3 0 ,7 0 -dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM). Photovoltaic devices were fabricated on indium tin oxide (ITO) glass with or without a layer of poly (3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS), and were studied without encapsulation. Photovoltaic performance characteristics were measured as a function of time for different ambient conditions (under white light irradiation and in the dark, and under air, dry oxygen and humid nitrogen atmospheres). It was found that a key cause of degradation under air exposure is light independent and results from water adsorption by the hygroscopic PEDOT:PSS layer. Measurements of the charge mobility and hole injection after air exposure showed that the degradation increases the resistance of the PEDOT:PSS/blend layer interface. r
Physical Chemistry Chemical Physics, 2009
Since the demonstration of efficient hybrid photovoltaic devices using CdSe/P3HT, a number of dif... more Since the demonstration of efficient hybrid photovoltaic devices using CdSe/P3HT, a number of different QD/polymer molecular solar cells have been investigated. However, considerably less attention has been paid to the photo-induced processes occurring in these devices, in particular the strong dependence that device efficiencies show upon QD concentration. This study aims to shed more light on this dependence by monitoring these processes occurring at the QD/polymer interface, namely, exciton formation, charge separation and undesired charge recombination.
Physical Chemistry Chemical Physics, 2011
Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective ele... more Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective electrodes for electron collection. The interfacial charge transfer reactions, under working conditions, that limit the energy conversion efficiency of these devices have been measured and compared to the standard OPSC geometry which collects the electrons through a low work function metal contact.
physica status solidi (a), 2008
ABSTRACT In this paper, a new method for obtaining poly(3,4-ethylenedioxythiophene) (PEDOT/PSS)/g... more ABSTRACT In this paper, a new method for obtaining poly(3,4-ethylenedioxythiophene) (PEDOT/PSS)/gold nanocomposites is described. In a first step, PEDOT/PSS gold nanoparticle aqueous dispersions were obtained by simultaneous chemical synthesis of PEDOT and gold nanoparticles in the presence of PSS that acts as a stabilizer. In a second step, these PEDOT/PSS gold nanoparticle dispersions were used to formulate nanocomposites by mixing the initial dispersion with commercially available PEDOT/PSS aqueous dispersion. Nanocomposite thin films, obtained by casting these dispersions, present an intimate contact between the inorganic and organic components. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Organic Electronics, 2011
We have measured the charge transfer processes on near IR small molecule solution processes solar... more We have measured the charge transfer processes on near IR small molecule solution processes solar cells under working conditions. The results show that there are two different behavior, for the device under working conditions, controlled by the intrinsic properties of the organic bulk-heterojunction phase to store charges at the different organic materials. Furthermore, our recombination kinetic studies show the origin of the photovoltage on these thin organic devices (80 nm thick) and the reason for the difference between the observed open circuit cell potential and the theoretical expected value based on the LUM-OPCBM-HOMO phthalocyanine difference.
Organic Electronics, 2013
and sharing with colleagues.