Terahertz Time-Domain Spectroscopy of Thermoresponsive Polymers in Aqueous Solution

The behavior of highly concentrated aqueous solutions of two thermoresponsive polymers poly(N-isopropylacrylamide) (PNIPAm) and poly(N-vinylcaprolactam) (PVCL) have been investigated by terahertz time-domain spectroscopy (THz-TDS). Measurements have been performed for concentrations up to 20 wt %, over a frequency range from 0.3 to 1.5 THz and for temperatures from 20 to 45 °C including the zone for lower critical solution temperature (LCST). THz-TDS enables the study of the behavior of water present in the solution (i.e., free or bound to the polymer). From these measurements, in addition to phase transition temperature, thermodynamic data such as variation of enthalpy and entropy can be inferred. Thanks to these data, further insights upon the mechanism involved during the dehydration phenomenon were obtained. These results were compared to the ones issued from dynamic light scattering, spectroscopy, or microscopy techniques to underline the interest to use THz-TDS as a powerful tool to characterize the behavior of thermoresponsive polymers in highly concentrated solutions

CASPワークショップ参加記

The nanostructure of the active layer in polymer/fullerene bulk heterojunction solar cells is known to have a strong impact on the device performances. Controlling the polymer/fullerene blend morphology is therefore particularly important. In this work, a rod-coil block copolymer, based on a regioregular poly(3-hexylthiophene) electron-donor rod block and a C-60-grafted coil block, is used as compatibilizer and its influences on the thin film morphology as well as the photovoltaic performances are investigated. It is shown that a small fraction of compatibilizer can enhance the device performances in an otherwise non-optimized process. At higher fractions or long annealing times however, the fullerene-grafted copolymer is found to behave as a nucleation center and triggers the formation of fullerene crystals

Utilisation de copolymères à blocs dans les cellules solaires organiques : morphologie, transport de charges et conversion photovoltaïque

Polymer/fullerene bulk heterojunction (BHJ) solar cells use an interpenetrating network of TT-conjugated electron-donor polymers and electron-acceptor C60 as photo-active layer. Currently, the most investigated blends are constituted of regioregular poly(3-hexylthiophene) (rr-P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The nanostructured active layer determines to great extend the overall performance of the devices.First of all, we introduced rod-coil block copolymers as compatibilizer into P3HT:PCBM blends and investigate their influence on the blend morphology and the related photovoltaic performance. Two P3HT-based block copolymer families have been studied. The first one has a C60-grafted polybutylacrylate coil block and the second one is based on poly(4-vinylpyridine) (P4VP) coil block. The film morphology and device efficiencies are investigated as a function of copolymer content, P3HT/PCBM mass ratio and coil nature.A second possible route to obtain a stable donor/acceptor nanostructure consists of using semiconductor block copolymers as photoactive layer, since these materials are able to self-assemble into donor/acceptor BHJ by microphase separation. We explored P3HT-P4VP rod-coil block copolymers blended with PCBM in view of their utilization in photovoltaic devices. The copolymer selfassembles into nano-domains rich in either P3HT or P4VP, while the strong chemical affinity of P4VP with PCBM leads to an accumulation of the latter in the P4VP domains, providing them an acceptorcharacter. It is found that organized and thermally stable thin films, that exhibit ambipolar field effect mobilities, can be achieved for a specific rod/coil ratio.Les matériaux les plus répandus dans le domaine du photovoltaïque (PV) organique à base de polymères sont le poly(3-hexylthiophène) régiorégulier (rr-P3HT) et le [6,6]-phenyl-C61-butyric acide methyl ester (PCBM). La couche active est une hétérojonction en volume (BHJ) de nanodomaines interpénétrés accepteur d’électron (le PCBM) et donneur d’électron (le P3HT). Le contrôle de la morphologie de la couche active et de sa stabilité est un défi majeur pour le développement des cellules organiques et est au centre de ce travail de thèse.Dans un premier temps, nous avons cherché à contrôler la morphologie du mélange P3HT:PCBM via l’utilisation de compatibilisants. Deux familles de copolymères à blocs rigide et souple ont été étudiées. Elles ont en commun leur bloc rigide à base de P3HT et diffèrent par leur bloc souple. Pourla première famille, le bloc souple poly-butylacrylate est greffé de C60, ce qui lui confère une affinité chimique avec les domaines de PCBM, et la seconde famille a un bloc souple poly(4-vinylpiridine) (P4VP) non greffé en C60. De par son affinité chimique avec le C60, le PCBM se localisera préférentiellement au voisinage des domaines P4VP.Dans un deuxième temps, nous avons exploité les propriétés d’auto-assemblages des copolymères à blocs afin de les étudier en tant que matériaux photo-actifs. Nous avons cherché à appréhender l’influence de la nature du bloc flexible let de a taille des blocs souple et rigide sur l’organisation des copolymères ainsi que sur les propriétés de transport de charge et sur les performances PV

Use of block copolymers in organic solar cells : morphology, charge transport and photovoltaic performances

Les matériaux les plus répandus dans le domaine du photovoltaïque (PV) organique à base de polymères sont le poly(3-hexylthiophène) régiorégulier (rr-P3HT) et le [6,6]-phenyl-C61-butyric acide methyl ester (PCBM). La couche active est une hétérojonction en volume (BHJ) de nanodomaines interpénétrés accepteur d’électron (le PCBM) et donneur d’électron (le P3HT). Le contrôle de la morphologie de la couche active et de sa stabilité est un défi majeur pour le développement des cellules organiques et est au centre de ce travail de thèse.Dans un premier temps, nous avons cherché à contrôler la morphologie du mélange P3HT:PCBM via l’utilisation de compatibilisants. Deux familles de copolymères à blocs rigide et souple ont été étudiées. Elles ont en commun leur bloc rigide à base de P3HT et diffèrent par leur bloc souple. Pourla première famille, le bloc souple poly-butylacrylate est greffé de C60, ce qui lui confère une affinité chimique avec les domaines de PCBM, et la seconde famille a un bloc souple poly(4-vinylpiridine) (P4VP) non greffé en C60. De par son affinité chimique avec le C60, le PCBM se localisera préférentiellement au voisinage des domaines P4VP.Dans un deuxième temps, nous avons exploité les propriétés d’auto-assemblages des copolymères à blocs afin de les étudier en tant que matériaux photo-actifs. Nous avons cherché à appréhender l’influence de la nature du bloc flexible let de a taille des blocs souple et rigide sur l’organisation des copolymères ainsi que sur les propriétés de transport de charge et sur les performances PV.Polymer/fullerene bulk heterojunction (BHJ) solar cells use an interpenetrating network of TT-conjugated electron-donor polymers and electron-acceptor C60 as photo-active layer. Currently, the most investigated blends are constituted of regioregular poly(3-hexylthiophene) (rr-P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The nanostructured active layer determines to great extend the overall performance of the devices.First of all, we introduced rod-coil block copolymers as compatibilizer into P3HT:PCBM blends and investigate their influence on the blend morphology and the related photovoltaic performance. Two P3HT-based block copolymer families have been studied. The first one has a C60-grafted polybutylacrylate coil block and the second one is based on poly(4-vinylpyridine) (P4VP) coil block. The film morphology and device efficiencies are investigated as a function of copolymer content, P3HT/PCBM mass ratio and coil nature.A second possible route to obtain a stable donor/acceptor nanostructure consists of using semiconductor block copolymers as photoactive layer, since these materials are able to self-assemble into donor/acceptor BHJ by microphase separation. We explored P3HT-P4VP rod-coil block copolymers blended with PCBM in view of their utilization in photovoltaic devices. The copolymer selfassembles into nano-domains rich in either P3HT or P4VP, while the strong chemical affinity of P4VP with PCBM leads to an accumulation of the latter in the P4VP domains, providing them an acceptorcharacter. It is found that organized and thermally stable thin films, that exhibit ambipolar field effect mobilities, can be achieved for a specific rod/coil ratio

Use of block copolymers in organic solar cells : morphology, charge transport and photovoltaic performances

Les matériaux les plus répandus dans le domaine du photovoltaïque (PV) organique à base de polymères sont le poly(3-hexylthiophène) régiorégulier (rr-P3HT) et le [6,6]-phenyl-C61-butyric acide methyl ester (PCBM). La couche active est une hétérojonction en volume (BHJ) de nanodomaines interpénétrés accepteur d’électron (le PCBM) et donneur d’électron (le P3HT). Le contrôle de la morphologie de la couche active et de sa stabilité est un défi majeur pour le développement des cellules organiques et est au centre de ce travail de thèse.Dans un premier temps, nous avons cherché à contrôler la morphologie du mélange P3HT:PCBM via l’utilisation de compatibilisants. Deux familles de copolymères à blocs rigide et souple ont été étudiées. Elles ont en commun leur bloc rigide à base de P3HT et diffèrent par leur bloc souple. Pourla première famille, le bloc souple poly-butylacrylate est greffé de C60, ce qui lui confère une affinité chimique avec les domaines de PCBM, et la seconde famille a un bloc souple poly(4-vinylpiridine) (P4VP) non greffé en C60. De par son affinité chimique avec le C60, le PCBM se localisera préférentiellement au voisinage des domaines P4VP.Dans un deuxième temps, nous avons exploité les propriétés d’auto-assemblages des copolymères à blocs afin de les étudier en tant que matériaux photo-actifs. Nous avons cherché à appréhender l’influence de la nature du bloc flexible let de a taille des blocs souple et rigide sur l’organisation des copolymères ainsi que sur les propriétés de transport de charge et sur les performances PV.Polymer/fullerene bulk heterojunction (BHJ) solar cells use an interpenetrating network of TT-conjugated electron-donor polymers and electron-acceptor C60 as photo-active layer. Currently, the most investigated blends are constituted of regioregular poly(3-hexylthiophene) (rr-P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The nanostructured active layer determines to great extend the overall performance of the devices.First of all, we introduced rod-coil block copolymers as compatibilizer into P3HT:PCBM blends and investigate their influence on the blend morphology and the related photovoltaic performance. Two P3HT-based block copolymer families have been studied. The first one has a C60-grafted polybutylacrylate coil block and the second one is based on poly(4-vinylpyridine) (P4VP) coil block. The film morphology and device efficiencies are investigated as a function of copolymer content, P3HT/PCBM mass ratio and coil nature.A second possible route to obtain a stable donor/acceptor nanostructure consists of using semiconductor block copolymers as photoactive layer, since these materials are able to self-assemble into donor/acceptor BHJ by microphase separation. We explored P3HT-P4VP rod-coil block copolymers blended with PCBM in view of their utilization in photovoltaic devices. The copolymer selfassembles into nano-domains rich in either P3HT or P4VP, while the strong chemical affinity of P4VP with PCBM leads to an accumulation of the latter in the P4VP domains, providing them an acceptorcharacter. It is found that organized and thermally stable thin films, that exhibit ambipolar field effect mobilities, can be achieved for a specific rod/coil ratio

Surface plasmon effect on metallic nanoparticles integrated in organic solar cells

Experimental results concerning the influence of plasmon effect from silver nanoparticles on the organic photovoltaic device performance are presented. The metallic nanoparticles (NPs) are placed on top of ITO layer using a physical vapor deposition technique. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) followed by an interpenetrated poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend layer are then spin-coated. The aluminum electrode is finally evaporated on. Photovoltaic properties compared to devices without NPs are shown. A spectrophotometric characterization is carried on. Moreover, a ToF-SIMS measurement is performed in order to obtain the depth chemical profiles of solar cell containing such NPs. Silver NPs diffusion inside other layers of the cell is investigated

Pluronic and beta-cyclodextrin in water: from swollen micelles to self-assembled crystalline platelets

Cyclodextrin (CD) and copolymers of polyethylene oxide (PEO)-b-polypropylene oxide (PPO)-b-polyethylene oxide (PEO) (pluronics) form inclusion complexes (ICs) in water. A solution of native unmodified beta-CD was mixed with a dilute solution of pluronic F-68 at 70 degrees C. The temperature was then quickly cooled down below the critical micellization temperature (CMT) of the triblock-copolymer. The mixture was left ageing at controlled temperature until turbidity, opalescence and finally sedimentation occurred. The self-organization behaviour of the system was investigated by small angle neutron scattering (SANS) in D(2)O. At high temperature the formation of stable, beta-CD-swollen micelles was observed. ICs were formed while the mixture was thermally quenched. Their subsequent aggregation was studied by SANS, and the resulting structures were observed by atomic force microscopy (AFM) after film deposition. With time, we evidenced the formation of thin platelets (17 nm) having large planar dimensions (about 1 mu m at 20 degrees C to 4 mu m at 40 degrees C) and a crystallographic angle of 105.4 degrees. Fitting the SANS data, a model was proposed where the growth of a platelet occurred through association of IC bundles in a characteristic time of 190 min. Each bundle (2.4 nm in radius and 17 nm in length) of well-organized IC molecules is formed in a characteristic time of 17 min at 20 degrees C. The platelets are original because of their crystalline nature with well-defined angles, and their very flat and rigid shape. Moreover they form effortlessly through self-assembling in water

Microstructure and Optoelectronic Properties of P3HT-b-P4VP/PCBM Blends: Impact of PCBM on the Copolymer Self-Assembly

Block copolymers have been widely investigated over the past decades for their ability to microphase separate into well-defined nanostructured thin films with tailored physical properties. The aim of the present study is to investigate the thin film properties of rod coil block copolymer/phenyl-C-61-butyric acid methyl ester (PCBM) blends as a function of the blend weight ratio, using a copolymer which is based on a poly(3-hexylthiophene) (P3HT) rod block and poly(4-vinylpyridine) (P4VP) coil block. Atomic force microscopy, transmission electron microscopy and grazing incidence X-ray diffraction analysis are used to study the influence of PCBM on the copolymer self-assembling. UV-visible absorption and photoluminescence spectroscopies as well as field-effect mobility measurements are performed in order to get further insight into the blend optoelectronic properties. It is found that the block copolymer phase-separated morphology and charge carrier mobilities strongly depend on the PCBM loading and thermal annealing. In particular, the results point out that PCBM enhances the block copolymer microphase separation within a narrow range of the polymer:PCBM weight ratio. In addition, clear evidence for PCBM accumulation within the P4VP domains is found by monitoring the P3HT fluorescence and charge carrier mobilities

Microstructure and Optoelectronic Properties of P3HT- b

International audienceBlock copolymers have been widely investigated over the past decades for their ability to microphase separate into well-defined nanostructured thin films with tailored physical properties. The aim of the present study is to investigate the thin film properties of rod coil block copolymer/phenyl-C-61-butyric acid methyl ester (PCBM) blends as a function of the blend weight ratio, using a copolymer which is based on a poly(3-hexylthiophene) (P3HT) rod block and poly(4-vinylpyridine) (P4VP) coil block. Atomic force microscopy, transmission electron microscopy and grazing incidence X-ray diffraction analysis are used to study the influence of PCBM on the copolymer self-assembling. UV-visible absorption and photoluminescence spectroscopies as well as field-effect mobility measurements are performed in order to get further insight into the blend optoelectronic properties. It is found that the block copolymer phase-separated morphology and charge carrier mobilities strongly depend on the PCBM loading and thermal annealing. In particular, the results point out that PCBM enhances the block copolymer microphase separation within a narrow range of the polymer:PCBM weight ratio. In addition, clear evidence for PCBM accumulation within the P4VP domains is found by monitoring the P3HT fluorescence and charge carrier mobilities