81 research outputs found
Innovative solution in organic photovoltaic devices
No full textNew technologies for photovoltaic energy generation can contribute to environmentally friendly, renewable energy production and may lead to the reduction of carbon dioxide liberated by burning fossil fuels and biomasses. Besides the established silicon based solar cells new photovoltaic technology has gained a lot of interest during the last decade. Among them organic solar cells (OSC) based on conjugated molecules or polymers are promising candidates for the manufacturing of environmentally safe, flexible, lightweight, and inexpensive photovoltaic devices which can be used in low cost applications. Particularly attractives are in photovoltaic (PV) elements based on thin plastic films. The flexibility offered through the chemical tailoring of desired properties, as well as the cheap technology already well developed for all kinds of plastic thin film applications would make such an approach widely adopted. Unfortunately a
main bottleneck is to be solved before industrial production could become economically viable, particularly represented by the still low conversion efficiency. In organic semiconductors the primary photo-excitations do not directly and quantitatively lead to free charge carriers but to coulombically bound electron-hole pairs, called excitons, that need strong electric fields to generated free charge carriers, present for example at the discontinuous potential drops at the interfaces between donors and acceptors as well as between semiconductors and metals. The exciton diffusion lengths in polymers and in organic semiconductors is usually around 10-20 nm: for efficient photovoltaic devices, the excitons have to split before recombining and the free electrons and holes must be transported towards the electrodes to produce the photocurrent.
Major problem derives from loss mechanism, such as exciton decay, charge recombination and low mobility, resulting in reduced photocurrent extraction at the electrodes and low power conversion efficiency. The improvement of the efficiency is one of the most important aspect in which is concentrated the research in OSC, our too. Two different routes going towards this objective focalized in this aspect have been explored, in order to contribute to realize a novel
and effective technology in the photovoltaic field. The first concerns the development of a novel light trapping system bases on microlenses, The second, on which we are still working, regards the fabrication of nanostructured solar cells by top-down techniques, particularly nanoimprinting (NIL).Il problema energetico sta destando negli ultimi anni sempre maggior interesse e preoccupazione, per il ridursi delle risorse fossili e dal conseguente acuirsi dei problemi d’inquinamento derivanti dal loro quasi esclusivo utilizzo per la produzione di energia elettrica. Non è sorprendente quindi che dal mondo della ricerca un grande sforzo sia dedicato allo sviluppo della tecnologia fotovoltaica. Attualmente, il silicio possiede una posizione centrale nel panorama delle celle fotovoltaiche: l’elevato costo di questo tipo di tecnologia, derivato dall’alto costo del materiale e dei processi fabbricativi, ha incoraggiato lo sviluppo di soluzioni alternative che si basino su materiali innovativi. Tra queste, grande risalto è stato dato negli ultimi anni alle cosiddette "organic solar cell", basate sull’impiego di semiconduttori organici. Il loro vantaggio risiede nel fatto che questi possono essere depositati, su larghe aree e a costi molto ridotti, in fase liquida, utilizzando quindi metodi tipici dell’industria della stampa nel campo del fotovoltaico ed eliminando così alti costi di materiale e di processo tipici dell’industria a semiconduttore inorganico. L’impiego di film sottili e conseguentemente di poco materiale, contribuisce a rendere il fotovoltaico organico uno dei più quotati candidati per lo sviluppo di una tecnologia solare a basso costo. Una tipologia di celle solari organiche utilizza come materiali
foto attivi i polimeri coniugati; evidenti progressi sono stati compiuti, col raggiungimento di efficienze ragguardevoli, dell’ordine del 4-5%. Purtroppo però, questo non è ancora sufficiente perché la tecnologia possa essere trasferita su scala industriale. Molti sforzi si stanno facendo nell’ambito della ricerca per migliorare l’efficienza di queste celle. Sullo sviluppo e l’impiego di soluzioni alternative e innovative applicabili al campo del fotovoltaico organico, e in particolare polimerico, è concentrata la nostra attività di ricerca. Due percorsi in particolare sono stati investigati, basate sull’impiego di un nuovo sistema per l’intrappolamento in cavità della luce e sull’impiego delle nanotecnologie fabbricative
Nanostructured P3HT layers fabricated by self-assembly as promising gas sensors
No full textPoly(3-hexylthiophene) (P3HT) nanofibers fabricated by self-assemby have been used as active sensing layers in chemiresistive gas sensors for acetone, ammonia and water. Their response has been compared to that of analogous devices in which P3HT was present as a plain, nonnanostructured layer. The results of this comparison show that nanofiber-based sensors have faster signal decay times and complete baseline recovery even after being exposed to saturated vapors of the analytes. Moreover, the current response of nanofiber-based devices increases by one order of magnitude or more upon exposure to the analyte, while for plain layers this increase is about 50% at maximum. Finally, on the basis of the
collected data, a correlation between the analyte polarizability and the 90% baseline recovery times seems to exist, likely due to the occurrence of just physical adsorption (and not also of vapor penetration) of the analyte onto the polymer surface
Low-cost and Fast Wet-based Technique to Generate Nanostructured Organic Materials Layers and its Application to Chemiresistive Gas-sensing Devices
No full textAbstractNanostructured materials for sensors and transducers are of great interest to the scientific community due to several advantages that these materials can provide (e.g., integration with large scale manufacturing technologies, enhanced performances, etc.). Nonetheless, large-area, low-cost and fast processing technologies for creating effective sensing nanostructures are still sought for. In this work, a recently described technique called Auxiliary Solvent-Based Sublimation-Aided NanoStructuring (ASB-SANS) has been used to generate poly(3-hexylthiophene) (P3HT, a well known semiconducting polymer) nanofilamentary structures onto interdigitated electrodes. These have been tested as gas sensing layers for volatile organic compounds, delivering promising results
Metaoptics for the spin-controlled generation of orbital angular momentum vector beams
No full textMoving from diffractive optics to metalenses, novel tools for structuring light are provided for the integration in compact optical layouts. Here we propose new metaoptics designed for light shaping into structured beams implementing on-demand vectorial configurations. Different optical layouts are achieved in order to generate orbital angular momentum (OAM) vector beams with different shape and peculiarities
Controlled self-organization of polymer nanopatterns over large areas
No full textSelf-assembly methods allow to obtain ordered patterns on surfaces with exquisite precision, but
often lack in effectiveness over large areas. Here we report on the realization of hierarchically ordered
polymethylmethacrylate (PMMA) nanofibres and nanodots over large areas from solution via a fast,
easy and low-cost method named ASB-SANS, based on a ternary solution that is cast on the substrate.
Simple changes to the ternary solution composition allow to control the transition from nanofibres to
nanodots, via a wide range of intermediate topologies. The ternary solution includes the material to
be patterned, a liquid solvent and a solid substance able to sublimate. The analysis of the fibres/dots
width and inter-pattern distance variations with respect to the ratio between the solution components
suggests that the macromolecular chains mobility in the solidified sublimating substance follows
Zimm-like models (mobility of macromolecules in diluted liquid solutions). A qualitative explanation
of the self-assembly phenomena originating the observed nanopatterns is given. Finally, ASB-SANSgenerated
PMMA nanodots arrays have been used as lithographic masks for a silicon substrate and
submitted to Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE). As a result, nanopillars with
remarkably high aspect ratios have been achieved over areas as large as several millimeters square,
highlighting an interesting potential of ASB-SANS in practical applications like photon trapping in
photovoltaic cells, surface-enhanced sensors, plasmonics
Frequency Modulated Raman Spectroscopy
No full textThe coupling of plasmonic and mechanical properties at the nanoscale is of great potential for the development of next generation devices capable to detect weak forces, mass changes, minute displacements and temperature-induced effects. Both the transduction of mechanical motion to the scattered light fields in term of polarization or intensity modulation and plasmon-driven mechanical oscillations have already been demonstrated. Quasi static tunable hot spots have recently been designed and applied to surface-enhanced Raman spectroscopy (SERS). Here we fabricated a plasmomechanical device, with a plasmonic hot spot modulated at the oscillator eigenfrequency, and demonstrated that the nonlinear modulation of polarization-dependent SERS signal from a synthetic dye can be analyzed with lock-in techniques, thus, realizing frequency modulated Raman spectroscopy
Nanostructured P3HT as a Promising SensingElement for Real-Time, Dynamic Detection ofGaseous Acetone
No full textThe dynamic response of gas sensors based on poly(3-hexylthiophene) (P3HT) nanofibers (NFs) to gaseous acetone was assessed using a setup based on flow-injection analysis, aimed at emulating actual breath exhalation. The setup was validated by using a commercially available sensor. The P3HT NFs sensors tested in dynamic flow conditions showed satisfactory reproducibility down to about 3.5 ppm acetone concentration, a linear response over a clinically relevant concentration range (3.5-35 ppm), excellent baseline recovery and reversibility upon repeated exposures to the analyte, short pulse rise and fall times (less than 1 s and about 2 s, respectively) and low power consumption (few nW), with no relevant response to water. Comparable responses’ decay times under either nitrogen or dry air suggest that the mechanisms at work is mainly attributable to specific analyte-semiconducting polymer interactions. These results open the way to the use of P3HT NFs-based sensing elements for the realization of portable, real-time electronic noses for on-the-fly exhaled breath analysis
High-efficiency generation of OAM-independent perfect vector vortices using multifocal phase-only silicon metalenses
No full textPerfect vortices have garnered significant attention due to their role as orbital angular momentum (OAM) beams with tunable ring-like intensity distributions. More recently, the non-separable combination of perfect vortices with opposite OAM and spin, known as perfect vector vortices, has extended their applicability in optical manipulation, high-resolution lithography, imaging, and telecommunications. The generation of perfect vector vortices with a size that remains constant regardless of the encoded topological charge typically requires both phase and amplitude modulation. In this study, we propose an efficient and innovative solution that leverages a multifocal approach encoded on phase-only silicon metalenses. A simultaneous control over dynamic and geometric phases was achieved through the careful design and fabrication of the individual meta-atoms comprising the metalens. This meta-atom engineering approach, modulating both phase components, enabled the generation and characterization of orbital angular momentum-independent perfect vector beams with an improved depth of focus. These devices represent a crucial step toward developing integrated optical architectures for information and communication technologies, with potential applications in both classical and quantum domains
Spin-decoupled metasurfaces for the generation of self-accelerating vector beams
No full textThe ability to generate structured light with arbitrary controlled polarization in a compact optical path has been challenging for the last few years in the optics and photonics fields. In this regard, for the first time in our knowledge, this work proposes the design, fabrication, and characterization of spin-decoupled metasurfaces able to generate self-accelerating orbital angular momentum beams having variant topological charges. Illuminated such metasurfaces with a linearly polarized light we are able to generate vector beams and, depending on the polarization angle it is possible to explore different states of the Hybrid Poincaré Sphere (HPS). Our metaoptics are designed as an array of periodic subwavelength metastructures (the so-called meta-atoms) composed of silicon nanofins on a silicon substrate. Each meta-atom acts like a half-wave plate that exploits both the geometrical and dynamical phases in a different way depending on its position on the entire optical element. This design solution offers both compactness of the optical path and easy integration with other optical elements. In particular, the proposed metaoptics are suitable for telecommunications, imaging, particle manipulation, and quantum applications
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