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Ambrogi V.,University of Naples | Gentile G.,CNR Institute of Polymer Chemistry and Technology | Ducati C.,University of Cambridge | Oliva M.C.,University of Naples | Carfagna C.,University of Naples

Ball milling was used to graft maleated polypropylene (MAPP) on the surface of multiwalled carbon nanotubes (MWCNTs), with a view to preparing MWCNT/polypropylene composites with improved matrix/nanotube compatibility. The occurrence of the grafting reaction was evaluated by FTIR spectroscopy and the yield was quantified by thermogravimetric analysis, as a function of the milling time. Dispersion experiments confirmed the nanotube surface modification of the nanotubes since functionalized MWCNTs remained stably dispersed in an ethanol/xylene solution for more than 48 h after sonication. No evidences of significant structural damage after the mechano-chemical treatment were shown by Raman spectroscopy. Moreover, a layer attributable to the presence of grafted MAPP chains on MWCNT walls was clearly detected by transmission electron microscopy. The average thickness of this amorphous layer was evaluated and compared with quantitative TGA data. © 2011 Elsevier Ltd. All rights reserved. Source

Abate A.,University of Oxford | Saliba M.,University of Oxford | Hollman D.J.,University of Oxford | Stranks S.D.,University of Oxford | And 5 more authors.
Nano Letters

Organic-inorganic halide perovskites, such as CH3NH 3PbX3 (X = I-, Br-, Cl-), are attracting growing interest to prepare low-cost solar cells that are capable of converting sunlight to electricity at the highest efficiencies. Despite negligible effort on enhancing materials' purity or passivation of surfaces, high efficiencies have already been achieved. Here, we show that trap states at the perovskite surface generate charge accumulation and consequent recombination losses in working solar cells. We identify that undercoordinated iodine ions within the perovskite structure are responsible and make use of supramolecular halogen bond complexation to successfully passivate these sites. Following this strategy, we demonstrate solar cells with maximum power conversion efficiency of 15.7% and stable power output over 15% under constant 0.81 V forward bias in simulated full sunlight. The surface passivation introduces an important direction for future progress in perovskite solar cells. © 2014 American Chemical Society. Source

Avolio R.,University of Naples Federico II | Gentile G.,CNR Institute of Polymer Chemistry and Technology | Avella M.,CNR Institute of Polymer Chemistry and Technology | Capitani D.,National Research Council Italy | Errico M.E.,CNR Institute of Polymer Chemistry and Technology
Journal of Polymer Science, Part A: Polymer Chemistry

Organic/inorganic nanocomposites were synthesized from poly(methylmethacrylate) (PMMA) and properly modified silica nanoparticles by in situ polymerization. Methacryloylpropyltrimethoxysilane was selected as nanoparticle surface modifier because it is characterized by unsaturated end groups available to radical reactions, making possible to suppose their participation in the acrylic monomer polymerization. As a result of the above hypothesized reactions, a phase constituted by polyacrylic chains grafted onto modified silica surface was isolated. 29Si and 13C solid-state nuclear magnetic resonance experiments permitted to analyze this phase in terms of composition and chain mobility as well as to highlight interaction mechanisms occurring between growing PMMA oligoradicals and functional groups onto silica surface. It was demonstrated that this PMMA grafted onto silica surface acts as an effective coupling agent and assures a good dispersion of nanoparticles as well as a strong nanoparticle/matrix interfacial adhesion. As a result of strong interactions occurring between phases, a significant increase of the glass transition temperature was recorded. Finally, the abrasion resistance of PMMA in the hybrids was significantly improved as a result of a different abrasion propagation mechanism induced by silica particles thus overcoming one of the most serious PMMA drawback. © 2010 Wiley Periodicals, Inc. Source

Abate A.,University of Oxford | Leijtens T.,University of Oxford | Pathak S.,University of Oxford | Teuscher J.,University of Oxford | And 7 more authors.
Physical Chemistry Chemical Physics

Lithium salts have been shown to dramatically increase the conductivity in a broad range of polymeric and small molecule organic semiconductors (OSs). Here we demonstrate and identify the mechanism by which Li+ p-dopes OSs in the presence of oxygen. After we established the lithium doping mechanism, we re-evaluate the role of lithium bis(trifluoromethylsulfonyl)-imide (Li-TFSI) in 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′- Spirobifluorene (Spiro-OMeTAD) based solid-state dye-sensitized solar cells (ss-DSSCs). The doping mechanism consumes Li+ during the device operation, which poses a problem, since the lithium salt is required at the dye-sensitized heterojunction to enhance charge generation. This compromise highlights that new additives are required to maximize the performance and the long-term stability of ss-DSSCs. © 2013 the Owner Societies. Source

Abate A.,University of Oxford | Hollman D.J.,University of Oxford | Teuscher J.,University of Oxford | Teuscher J.,Ecole Polytechnique Federale de Lausanne | And 6 more authors.
Journal of the American Chemical Society

Chemical doping is a powerful method to improve the charge transport and to control the conductivity in organic semiconductors (OSs) for a wide range of electronic devices. We demonstrate protic ionic liquids (PILs) as effective p-dopant in both polymeric and small molecule OSs. In particular, we show that PILs promote single electron oxidation, which increases the hole concentration in the semiconducting film. The illustrated PIL-doping mechanism is compatible with materials processed by solution and is stable in air. We report the use of PIL-doping in hybrid solar cells based on triarylamine hole transporting materials, such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (spiro-OMeTAD). We show improved power conversion efficiency by replacing lithium salts, typical p-dopants for spiro-OMeTAD, with PILs. We use photovoltage-photocurrent decay and photoinduced absorption spectroscopy to establish that significantly improved device performance is mainly due to reduced charge transport resistance in the hole-transporting layer, as potentiated by PIL-doping. © 2013 American Chemical Society. Source

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