Enhanced crystallinity and film retention of P3HT thin-films for efficient organic solar cells by use of preformed nanofibers in solution

We report the preparation of films of poly(3-hexylthiophene) nanofibers suitable for fabrication of efficient multilayer solar cells by successive deposition of donor and acceptor layers from the same solvent. The nanofibers are obtained by addition of di-tert-butyl peroxide (DTBP) to a solution of P3HT in chlorobenzene. Interestingly, by varying the concentration of DTBP we are able to control both crystallinity and film retention of the spin-cast films. We also investigate the influence of the DTBP-induced crystallization on charge transport by thin-film transistor measurements, and find a more than five-fold increase in the hole mobility of nanofiber films compared to pure P3HT. We attribute this effect to the synergistic effects of increased crystallinity of the fibers and the formation of micrometer-sized fiber networks. We further demonstrate how it is possible to make use of the high film retention to fabricate photovoltaic devices by subsequent deposition of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) from a chlorobenzene solution on top of the nanofiber film. The presence of a relatively large crystalline phase strongly affects the diffusion behavior of PCBM into the P3HT film, resulting in a morphology which is different from that of common bulk heterojunction solar cells and resembles a bilayer structure, as can be inferred from comparison of the external quantum efficiency spectra. However, a high power conversion efficiency of 2.3% suggests that there is still a significant intermixing of the two materials taking place

Traceable atomic force microscopy of high-quality solvent-free crystals of [6,6]-phenyl-C61-butyric acid methyl ester

We report high-resolution, traceable atomic force microscopymeasurements of high-quality, solvent-free single crystals of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These were grown by drop-casting PCBM solutions onto the spectrosil substrates and by removing the residual solvent in a vacuum. A home-built atomic force microscope featuring a plane mirror differential optical interferometer, fiber-fed from a frequency-stabilized laser (emitting at 632.8 nm), was used to measure the crystals' height. The optical interferometer together with the stabilized laser provides traceability (via the laser wavelength) of the vertical measurements made with the atomic force microscope. We find that the crystals can conform to the surface topography, thanks to their height being significantly smaller compared to their lateral dimensions (namely, heights between about 50 nm and 140 nm, for the crystals analysed, vs. several tens of microns lateral dimensions). The vast majority of the crystals are flat, but an isolated, non-flat crystal provides insights into the growth mechanism and allows identification of “molecular terraces” whose height corresponds to one of the lattice constants of the single PCBM crystal (1.4 nm) as measured with X-ray diffraction

Traceable atomic force microscopy of high-quality solvent-free crystals of [6,6]-phenyl-C-61-butyric acid methyl ester

We report high-resolution, traceable atomic force microscopymeasurements of high-quality, solvent-free single crystals of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These were grown by drop-casting PCBM solutions onto the spectrosil substrates and by removing the residual solvent in a vacuum. A home-built atomic force microscope featuring a plane mirror differential optical interferometer, fiber-fed from a frequency-stabilized laser (emitting at 632.8 nm), was used to measure the crystals' height. The optical interferometer together with the stabilized laser provides traceability (via the laser wavelength) of the vertical measurements made with the atomic force microscope. We find that the crystals can conform to the surface topography, thanks to their height being significantly smaller compared to their lateral dimensions (namely, heights between about 50 nm and 140 nm, for the crystals analysed, vs. several tens of microns lateral dimensions). The vast majority of the crystals are flat, but an isolated, non-flat crystal provides insights into the growth mechanism and allows identification of “molecular terraces” whose height corresponds to one of the lattice constants of the single PCBM crystal (1.4 nm) as measured with X-ray diffraction

An artificial neural network approach to laser-induced breakdown spectroscopy quantitative analysis

The usual approach to laser-induced breakdown spectroscopy (LIBS) quantitative analysis is based on the use of calibration curves, suitably built using appropriate reference standards. More recently, statistical methods relying on the principles of artificial neural networks (ANN) are increasingly used. However, ANN analysis is often used as a 'black box' system and the peculiarities of the LIBS spectra are not exploited fully. An a priori exploration of the raw data contained in the LIBS spectra, carried out by a neural network to learn what are the significant areas of the spectrum to be used for a subsequent neural network delegated to the calibration, is able to throw light upon important information initially unknown, although already contained within the spectrum. This communication will demonstrate that an approach based on neural networks specially taylored for dealing with LIBS spectra would provide a viable, fast and robust method for LIBS quantitative analysis. This would allow the use of a relatively limited number of reference samples for the training of the network, with respect to the current approaches, and provide a fully automatizable approach for the analysis of a large number of samples

Evaluation of macular pigment optical density following femtosecond laser-assisted cataract surgery

Background: To evaluate macular pigment optical density (MPOD) after bimanual femtosecond laser-assisted cataract surgery (FLACS) compared to standard bimanual phacoemulsification (B-MICS). Methods: Aprospective, casematched, comparative cohort study conducted at theInstitute of Ophthalmology, University of Modena and Reggio Emilia (Italy); 30 eyes under wentbimanual FLACS with low-energy Ziemer LDV Z8 (FLACS) and 30 underwent B-MICS standard technique (B-MICS). All interventions were conducted by the same expert surgeon. MPOD using the Macular Pigment Screener II (MPS II) was evaluated at baseline, 7 and 30 days after surgery. As secondary outcomes, we considered best corrected visual acuity (BCVA) and central macular thickness (CMT) obtained using optical coherence tomography. Results: In all cases, a BunnyLens AF IOL was safely implanted in the capsular bag through a1.4 mm incision. We found asignificant reductionin MPOD in both groups at 7 and 30 days; 0.16 ±0.14 and 0.10±0.12 (FLACS) and 0.18±0.13 and 0.15±0.14 (B-MICS), respectively (P<0.05). However, there was no significant difference between the two groups at either 7 (P=0.52) or 30 days (P=0.18). BCVA improved significantly in both groups and CMT increased in both groups (P<0.001, P<0.001, respectively). BCVA and CMT were similar between the groups with a significant difference in CMT in favor of the FLACS group at 30 days (P=0.017). Conclusions: MPOD was reduced in both groups without any significant difference between the FLACS and B-MICS cataract interventions. FLACS is associated with a significantly higher increase of macular thickness at 30 days compared to B-MICS

C-Si hybrid photonic structures by full infiltration of conjugated polymers into porous silicon rugate filters

Loading of one-dimensional (1-D) porous silicon photonic crystals (PS-PhCs), known as rugate filters, with luminescent materials is generally limited by the potential for (undesired) "pore clogging," in relation to the size of the nanoparticles (e.g. quantum dots) or molecular species, and so far mainly restricted to small molecular weight materials or small nanocrystals, or in situ polymerized dyes. Here we report the infiltration 1-D PS-PhCs with a green-emitting commercial luminescent polymer (F8BT, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[ 2,1,3]thiadiazol-4,8-diyl)]), with a molecular weight of approximately 46 kDa across their whole depth (approximately 7.5 mu m), thereby showing that pore clogging is not a concern for these structures. We also characterize the modification of the photoluminescence (PL) and decay rates, and investigate the detailed inner morphology of the filters with the help of (scanning) transmission electron microscopy. We observe both suppression (in the stop-band) and enhancement (at the high-energy band-edge) of the PL. We also find that the photonic stop-band is red-shifted after polymer infiltration, due to the increased effective refractive index of the polymer-infiltrated nanostructured system. The presence of just one unbroadened peak in the reflectance spectra after infiltration confirms that infiltration extends for the whole depth of the rugate filters

Effects of systemic glucocorticosteroids on peripheral neutrophil functions in asthmatic subjects: an ex vivo study

In 21 asthmatic subjects, several functions of isolated peripheral neutrophils (chemokinesis and chemotaxis toward 10% E. coli; superoxide anion generation after PMA; leukotriene B4 (LTB4) release from whole blood and isolated neutrophtls, before and after different stimuli) were evaluated during an acute exacerbation of asthma, and after 14 – 54 days of treatment with systemic glucocorticosteroids (GCS). During acute exacerbation, superoxide anion generation was higher in asthmatics than in eleven normal subjects (39.2 ± 14.1 vs. 25.2 ± 7.3 nmol, p < 0.05); there was a significant correlation between FEV1 (% of predicted) and neutrophil chemotaxis (r = −0.52, p = 0.04). After treatment, there was no significant change in all neutrophil functions, except for a decrease in neutrophil chemotaxis in subjects who showed an FEV1 increase > 20% after GCS treatment (from 131 ± 18 to 117 ± 21 μm, p = 0.005). Chemokinesis sicantly decreased in all subjects, and the changes significantly correlated with an arbitrary score of the total administered dose of GCS (r = 0.57, p < 0.05). These data suggest that neutrophil activation plays a minor role in asthma, and that treatment with GCS is not able to modify most functions of peripheral neutrophils in asthmatic subjects; chemotaxis seems to be related only to the severity of the asthma and it could reflect the improvement of the disease

C-Si hybrid photonic structures by full infiltration of conjugated polymers into porous silicon rugate filters

Loading of one-dimensional (1-D) porous silicon photonic crystals (PS-PhCs), known as rugate filters, with luminescent materials is generally limited by the potential for (undesired) “pore clogging,” in relation to the size of the nanoparticles (e.g. quantum dots) or molecular species, and so far mainly restricted to small molecular weight materials or small nanocrystals, or in situ polymerized dyes. Here we report the infiltration 1-D PS-PhCs with a green-emitting commercial luminescent polymer (F8BT, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)]), with a molecular weight of approximately 46 kDa across their whole depth (approximately 7.5 μm), thereby showing that pore clogging is not a concern for these structures. We also characterize the modification of the photoluminescence (PL) and decay rates, and investigate the detailed inner morphology of the filters with the help of (scanning) transmission electron microscopy. We observe both suppression (in the stop-band) and enhancement (at the high-energy band-edge) of the PL. We also find that the photonic stop-band is red-shifted after polymer infiltration, due to the increased effective refractive index of the polymer-infiltrated nanostructured system. The presence of just one unbroadened peak in the reflectance spectra after infiltration confirms that infiltration extends for the whole depth of the rugate filters