1,721,120 research outputs found
New regioregular polythiophenes functionalized with sulfur-containing substituents for bulk heterojunction solar cells
No full textOrganic photovoltaic devices fabricated with polythiophenic derivatives and single-walled carbon nanotubes
(SWCNT)s have been assembled and tested. For this purpose, some new regioregular polythiophenes
with different sulfur-containing groups in the terminal position of a hexamethylenic side chain
were prepared using direct and indirect polymerization routes. The optical features of the synthesized
polymers were examined and compared by registering their UV–Vis spectra in different solvent/non-solvent
systems and in film; their thermal stability, electrical conductivity, cyclic voltammetry and photovoltaic
properties were carefully analyzed. In particular, the two samples bearing the sulfinyl group in
side chain showed better chromic responses, enhanced self-assembling capabilities, more extended conjugation
length, higher electrical conductivity and very promising photovoltaic performances, when compared
to those of analogous systems reported on up to now
Effect of Electron-Acceptor Content on the Efficiency of Regioregular Double-Cable Thiophene Copolymers in Single-Material Organic Solar Cells
No full textABSTRACT: Three regioregular thiophenic copolymers, characterized by a bromine atom or a C60-fullerene group at different molar ratios at the end of a decamethylenic plastifying side chain, have been successfully synthesized using a straightforward postpolymerization functionalization procedure based on a Grignard coupling reaction. Owing to their good solubility in common organic solvents, the products were fully characterized using chromatographic, spectroscopic, thermal, and morphological techniques and used as single materials in the photoactive layers of organic solar cells. The photoconversion efficiencies obtained with copolymers were compared with those of a reference cell prepared using a physical blend of the precursor homopolymer and [6,6]-phenyl-C61- butyric acid methyl ester. The best results were obtained with COP2, the copolymer with a 21% molar content of C60- functionalized side chains. The use of the double-cable polymer made possible an enhanced control on the nanomorphology of the active blend, thus reducing phase-segregation phenomena as well as the macroscale separation between the electronacceptor and -donor components, yielding a power conversion efficiency higher than that of the reference cell (4.05 vs 3.68%). Moreover, the presence of the halogen group was exploited for the photo-cross-linking of the active layer immediately after the thermal annealing procedure. The cross-linked samples showed an increased stability over time, leading to good efficiencies even after 120 h of accelerated aging: this was a key feature for the widespread practical applicability of the prepared devices
EncapsysEnFinit®PCM28 and viscoelastic polyurethane foams: what is the winning combination?
No full textEffect of the incorporation of an Ag nanoparticle interlayer on the photovoltaic performance of green bulk heterojunction water-soluble polythiophene solar cells
No full textTwo water-soluble regioregular poly(3-alkylthiophene)s, incorporating aminic groups at the end of the side chains, have been synthesized using a post-polymerization functionalization procedure on a ω-bromine substituted polyalkylthiophene. The high solubility of the obtained polymers in water allowed for the preparation of “green” bulk heterojunction solar cells which reached a power conversion efficiency of 4.85% when PC61BM was used as electron-acceptor material. Improved optical absorption and photocurrent have been obtained by interposing a layer of Ag nanoparticles between the buffer and the photoactive layer, leading to a final power conversion efficiency of 5.51%
Effects of polar additives on the anionic polymerization of 1,3-butadiene and styrene
No full textThe homopolymerization of butadiene and copolymerization
of styrene with butadiene were performed
using n-butyllithium as the initiator, cyclohexane as a solvent
and some new ethers (σ-ligands) as active centers
modifiers. The modifiers were synthesized using an elegant
synthetic route starting from a commercial precursor,
and high yields were obtained. Their addition in the
homopolymerization of butadiene strongly influences the
vinyl content and reduces the polydispersity of the obtained
polymer. The modifiers are also able to change the
reactivity ratios in the styrene-butadiene copolymerization,
leading to an appreciable randomizing effect. The
modifiers also show a high activity, since their addition
in a very low amount is able to strongly modify the progress
in the reaction of anionic polymerization
Straightforward synthesis of well-defined poly(vinyl acetate) and its block copolymers by atom transfer radical polymerization
No full textA facile Atom Transfer Radical Polymerization (ATRP) method based on the use of the complex obtained with CuCl, CuCl2 and the very active ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6CyClam) as catalytic system, was successfully employed for the first time to polymerize vinyl acetate (VAc) with a good control over the polymerization, which showed a living character and monomer conversion up to 90%. The use of such an active ligand allows to maintain a particularly low concentration of propagating species once very reactive radicals, from such monomers, are formed, hence establishing a fast and dynamic ATRP equilibrium. Several kinetic studies on the ATRP of VAc were carried out with the aim to identify the optimized conditions allowing a good control over the process attaining materials with well-defined structure and low polydispersity. The livingness of the macromolecular system was confirmed, among the others, by using the obtained PVAc as ATRP macroinitiator for the synthesis of several block copolymers. Furthermore, the possibility to hydrolyse the VAc block thus attaining amphiphilic materials was studied
Fluorecence Microscopy Study of CdS quantum dots Obtained by Laser Irradiation from a Single Source Precursor in Polymeric Film
No full textRecently the quantum dots (QDs) synthesis from single source precursors (SSPs) showed a potential interest for patterning formation of nano-composites. In this approach the SSPs have to be mixed with a matrix that afterwards is treated selectively to obtain the desired nanocomposite. The study of the generation of the QDs from the SSPs is, therefore, crucial for the definition of its behaviour within the polymeric matrix. The formation of the CdS QDs via thermolysis of the cadmium diethyldithiocarbamate (CdDDTC) was performed and studied in the presence of a non coordinating solvent such as octadecene (ODE) in presence of myristic acid (MA) as ligand. The precursor is then studied in combination with the poly(methyl methacrylate) (PMMA) polymer for the generation of the CdS QDs under the laser irradiation within a film. The effect of the laser has been studied both on neat PMMA and on the polymer/precursor blend film with the aid of the fluorescence microscope. The results are used to identify the optimal laser parameters to obtain the decomposition of the precursor and to evaluate the effect of the laser irradiation on the polymer
Chirality on Amorphous High-Tg Polymeric Nanofilms: Optical Activity Amplification by Thermal Annealing
No full textThe chiroptical properties of amorphous chiral polymers functionalized with conjugated trans-azoaromatic chromophore linked to the backbone through a chiral cyclic pyrrolidine moiety of one single configuration at the solid state, as thin films, were investigated. For the first time nanometric thin films of amorphous polymers (not liquid crystals) showed a remarkable chiral amplification upon thermal treatment at a temperature close to their Tg. The side-chain azobenzene chromophores rearrangement driven by the enhanced chain mobility seems to favor the formation of nanodomains of conformationally ordered macromolecular chains with one prevailing helical handedness whose optical activity depends on the configuration of the intrinsic chirality of the monomeric units and which as a result are stable at room temperature for a long time
Electrospun Polyaniline-Based Composite Nanofibers: Tuning the Electrical Conductivity by Tailoring the Structure of Thiol-Protected Metal Nanoparticles
Full text linkComposite nanofibers made of a polyaniline-based polymer blend and different thiol-capped metal nanoparticles were prepared using ex situ synthesis and electrospinning technique. The effects of the nanoparticle composition and chemical structure on the electrical properties of the nanocomposites were investigated. This study confirmed that Brust’s procedure is an effective method for the synthesis of sub-10 nm silver, gold, and silver-gold alloy nanoparticles protected with different types of thiols. Electron microscopy results demonstrated that electrospinning is a valuable technique for the production of composite nanofibers with similar morphology and revealed that nanofillers are well-dispersed into the polymer matrix. X-ray diffraction tests proved the lack of a significant influence of the nanoparticle chemical structure on the polyaniline chain arrangement. However, the introduction of conductive nanofillers in the polymer matrix influences the charge transport noticeably improving electrical conductivity. The enhancement of electrical properties is mediated by the nanoparticle capping layer structure. The metal nanoparticle core composition is a key parameter, which exerted a significant influence on the conductivity of the nanocomposites. These results prove that the proposed method can be used to tune the electrical properties of nanocomposites.</jats:p
π-Stacking signature in nmr solution spectra of thiophene-based conjugated polymers
No full textStudies on conjugated polymers seldom report on their NMR characterization in solution. This paper shows how NMR experiments, both 1H NMR and routine 2D NMR spectra, can help in gaining a further insight into the aggregation behavior of conjugated polymers and could be used to flank the more employed solid-state NMR and other spectroscopy and microscopy techniques in the understanding of the aggregation processes. NMR spectroscopy allows distinguishing, within the class of poorly solvatochromic conjugated polymers, those highly prone to form π-stacked aggregates from the ones that have a low tendency toward π-stacking
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