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24 results on '"Latini, Gianluca"'

1. Charge separation by photoexcitation in semicrystalline polymeric semiconductors: An intrinsic or extrinsic mechanism?

Author

Paquin, Francis, Latini, Gianluca, Sakowicz, Maciej, Karsenti, Paul-Ludovic, Wang, Linjun, Beljonne, David, Stingelin, Natalie, and Silva, Carlos

Subjects
Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

We probe charge photogeneration and subsequent recombination dynamics in neat regioregular poly(3-hexylthiophene) films over six decades in time by means of time-resolved photoluminescence spectroscopy. Exciton dissociation at 10K occurs extrinsically at interfaces between molecularly ordered and disordered domains. Polaron pairs thus produced recombine by tunnelling with distributed rates governed by the distribution of electron-hole radii. Quantum-chemical calculations suggest that hot-exciton dissociation at such interfaces results from a high charge-transfer character., Comment: 10 pages, 3 figures

Published
2011
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2. Background-free quasi-steady-state photoinduced absorption spectroscopy by dual optical modulation

Author

Kallel, Houssem, Latini, Gianluca, Paquin, Francis, Rinfret, Robert, Stingelin, Natalie, and Silva, Carlos

Subjects
Condensed Matter - Materials Science, Physics - Optics
Abstract

We present a simple and inexpensive means to measure background-free photoinduced absorption spectra by implementing a dual optical modulation scheme. Our objective is to measure quasi-steady-state absorption spectra of long-lived photoexcitations, such as polarons and triplet excitons in organic semiconductors, when the photoluminescence of the sample is strong compared to the photoinduced absorption signal. In our instrument, we modulate a continuous-wave laser at a frequency $f_{pu}$ with a mechanical chopper before exciting the material. We measure the fractional change of transmission of the sample with a tuneable monochromatic probe source modulated at a frequency $f_{pr}$, and with a digital lockin amplifier at a reference frequency $f_{ref} = f_{pu} + f_{pr}$. We generate the reference sinusoidal wave for the lockin amplifier using a simple home-built electronic circuit that generates their sum-frequency signal. This scheme allows measurement of the fractional change of transmittance of the sample induced by the pump laser at a frequency $f_{pu} + f_{pr}$ without parasitic signal at a frequency $f_{pu}$, such as photoluminescence of the sample or pump-laser scatter. We demonstrate the power of this approach by measuring cleanly the photoinduced absorption spectrum of a highly luminescent semiconductor polymer, poly(9,9-dioctylfluorene-co-benzothiadiazole), at 10\,K. We compare this measurement favourably with that obtained by simple modulation of the pump laser after subtraction of the dominant photoluminescence background., Comment: 17 pages, 5 figures

Published
2010

9. Enhanced luminescence properties of highly threaded conjugated polyelectrolytes with potassium counter-ions upon blending with poly(ethylene oxide).

Author

Latini, Gianluca, Winroth, Gustaf, Brovelli, Sergio, McDonnell, Shane O., Anderson, Harry L., Mativetsky, Jeffrey M., Samorí, Paolo, and Cacialli, Franco

Subjects
*THIN films, *CYCLODEXTRINS, *POTASSIUM, *PHOTOLUMINESCENCE, *ROTAXANES
Abstract

The photophysics and electroluminescence (EL) of thin films of unthreaded and cyclodextrin-encapsulated poly(4,4′-diphenylenevinylene) (PDV) with potassium countercations, blended with poly(ethylene oxide) (PEO) are investigated as a function of the PEO concentration. We show that three main factors contribute to increasing the photoluminescence (PL) quantum efficiency as a result of suppressed intermolecular interactions, namely: the high degree of encapsulation of the polyrotaxanes, the relatively large countercation (e.g., compared to lithium), and the complexation of the rotaxanes with PEO. By facilitating cationic transport to the negative electrodes, PEO also leads to devices with enhanced electron injection and improved charge balance, whose operation therefore resembles that of “virtually unipolar” light-emitting electrochemical cells. This effect, together with the enhanced PL efficiency, leads to higher EL efficiency for both polyrotaxanes and unthreaded polymers, upon addition of the PEO. We show that the concurrent exploitation of the various strategies above lead to an overall EL efficiency that is approximately twice the value previously reported for Li-based PDV. A blueshift of the EL spectrum during the devices turn-on is also reported and analyzed in terms of interference and doping effects. [ABSTRACT FROM AUTHOR]

Published
2010
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15. Synthesis and Optoelectronic Properties of Nonpolar Polyrotaxane Insulated Molecular Wires with High Solubility in Organic Solvents

Author

Frampton, Michael J., primary, Sforazzini, Giuseppe, additional, Brovelli, Sergio, additional, Latini, Gianluca, additional, Townsend, Emily, additional, Williams, Charlotte C., additional, Charas, Ana, additional, Zalewski, Leszek, additional, Kaka, Naeem S., additional, Sirish, Mallena, additional, Parrott, Lisa J., additional, Wilson, Joanne S., additional, Cacialli, Franco, additional, and Anderson, Harry L., additional

Published
2008
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23. Modelling topographical artifacts in scanning near-field optical microscopy

Author

Fenwick, Oliver, Latini, Gianluca, and Cacialli, Franco

Subjects
*NEAR-field microscopy, *SCANNING probe microscopy, *ATOMIC force microscopy, *MICROSCOPY
Abstract

Abstract: Scanning probe techniques such as atomic force microscopy and scanning tunnelling microscopy have been used extensively for the study of surface properties on the nanoscale. A valuable, but less commonly used technique is scanning near-field optical microscopy (SNOM). This scanning probe technique allows the optical properties of supramolecular structures to be probed at resolutions better than allowed by the diffraction limit. This means that resolution better than 100nm is achievable even with visible radiation. However, the geometry of the SNOM probe causes images obtained by this method to contain a mixture of optical and topographical information. Where there is no optical contrast on a surface, topography can introduce contrast to the image, which is obviously undesirable. Additionally, the topographical artifacts can cause apparent distortion or displacement of features in the optical image. To have confidence in results obtained by SNOM, the nature of topographical artifacts must be fully understood. Here we present one-dimensional numerical simulations of SNOM images and an investigation into several observable effects. In addition to the occurrence of topography-induced optical contrast we show that a low topographical feature near a higher one can be visible in an image but with low intensity and can appear displaced and distorted if it is approximately a probe diameter from the larger feature. [Copyright &y& Elsevier]

Published
2004
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24. Graded vertical phase separation of donor/acceptor species for polymer solar cells

Author

Concetta Nobile, Milena De Giorgi, Anna Loiudice, Gianluca Latini, Aurora Rizzo, Giuseppe Gigli, Loiudice, Anna, Rizzo, Aurora, Latini, Gianluca, Nobile, Concetta, de Giorgi, Milena, and Gigli, Giuseppe

Subjects
Fabrication, Materials science, Analytical chemistry, 02 engineering and technology, 010402 general chemistry, 01 natural sciences, Polymer solar cell, THIN-FILMS, Phase (matter), COMPOSITES, Renewable Energy, Sustainability and the Environment, business.industry, Open-circuit voltage, Bilayer, POLY(3-HEXYLTHIOPHENE), Energy conversion efficiency, PERFORMANCE, 021001 nanoscience & nanotechnology, Acceptor, MORPHOLOGY EVOLUTION, 0104 chemical sciences, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Amorphous solid, INTERNAL QUANTUM EFFICIENCY, Optoelectronics, 0210 nano-technology, business
Abstract

The donor/acceptor inter-mixing in bulk heterojunction (BHJ) solar cells is a critical parameter, often leading to irreproducible performance of the finished device. An alternative solution-processed device fabrication strategy towards a better control of the micro/nano-structured morphology consists of a sequential coating of the donor (e.g., poly-(3-hexylthiophene), P3HT) and the acceptor (e.g., [6,6]-phenyl-C61-butyric acid methyl ester, PCBM) from orthogonal solvents. We demonstrate that, in spite of the solvent orthogonality, this technique does not lead to a well-defined bilayer with a sharp interface, but it rather results in a graded vertical phase-separated junction, resulting from the diffusion of the PCBM in the P3HT bottom layer. We are able to control the diffusion of PCBM, which occurs preferentially in the amorphous P3HT domains, by easily varying the ratio between crystalline/amorphous domains in the P3HT. Such a ratio can be simply modified by changing the solvent for P3HT. We show that the donor–acceptor diffused bilayer (DB) junction is an intermediate structure which combines both advantages of the well-defined bilayer and conventional BHJ configurations. Indeed, the DB device geometry ensures the good reproducibility and charge percolation, like the well-defined bilayer, while preserving the interpenetration of the donor and acceptor species, resulting in an efficient charge separation, characteristic of the BHJ. Overall the annealed DB device geometry can be assimilated to a graded BHJ with an improved reproducibility and mean power conversion efficiency (PCE) of 3.45%, higher than that of the standard BHJ devices of 3.07%. Furthermore, we demonstrate the highest performance for the as-cast DB device with a PCE of 2.58%. It is worthy to note that our DB device exhibits improved open circuit voltage, fill factor, series and shunt resistances, which denote that the vertically phase separated DB junction ensures improved charge percolation.

Published
2012
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