P. Delli Veneri

Self-organized broadband light trapping in thin film amorphous silicon solar cells.

Nanostructured glass substrates endowed with high aspect ratio one-dimensional corrugations are prepared by defocused ion beam erosion through a self-organized gold (Au) stencil mask. The shielding action of the stencil mask is amplified by co-deposition of gold atoms during ion bombardment. The resulting glass nanostructures enable broadband anti-reflection functionality and at the same time ensure a high efficiency for diffuse light scattering (Haze). It is demonstrated that the patterned glass substrates exhibit a better photon harvesting than the flat glass substrate in p-i-n type thin film a-Si:H solar cells.

Light trapping efficiency of periodic and quasiperiodic back-reflectors for thin film solar cells: A comparative study

Recently, great efforts have been carried out to design optimized metallic nano-grating back-reflectors to improve the light absorption in thin film solar cells. In this work, we compare the performances of deterministic aperiodic backreflectors in the form of 1-D nanogratings based on the generalized Fibonacci deterministic aperiodic sequence with a standard periodic one. The case of study here analyzed relies on a realistic solar cell model, where light absorption is evaluated only in the intrinsic region of an amorphous silicon P-I-N junction. We found that the results of comparison are strongly influenced by the amorphous silicon extinction coefficient within the near-infrared wavelength range, where most photonic-plasmonic modes (responsible for the light absorption enhancement typically observed when structured metal nanogratings are employed) are excited. In particular, with device-grade hydrogenated amorphous silicon, we demonstrate that Fibonacci-like backreflectors are able to provide an absorpt...

Changes of hydrogen evolution thermodynamics induced by He and H2 dilution in PECVD a-Si:H films: influence on thermal crystallization

Abstract Intrinsic and n-type amorphous silicon films were deposited by plasma-enhanced chemical vapour deposition on Qz (fused silica), crystalline silicon and aluminium substrates. Different substrate temperatures (200°C and 300°C) and 50% diluted SiH 4 in He or H 2 process gas were used to change hydrogen content and microstructure of deposited amorphous material. The hydrogen evolution thermodynamics of a-Si:H films was investigated using differential scanning calorimetry to obtain the entropy change and the activation energy of hydrogen evolution process. Crystallization of a-Si:H was obtained by an isothermal annealing performed at a pressure of 30 mTorr, at 650°C, using different annealing times (30–480 s). Different entropy variations are observed in the a-Si:H films. The hydrogen evolution affects the crystallization kinetics; in fact, crystallization was delayed in the samples with a greater disorder after hydrogen evolution.

Laser-assisted chemical vapor deposition of thick poly-Si layers for solar cells

Abstract The growth of polycrystalline silicon on glass by laser-assisted chemical vapor deposition has been studied with the aim of identifying a light absorber layer for solar cells, with superior material quality compared to other technologies available for low-temperature substrates. One-dimensional calculations of the thermal wave produced by laser irradiation have been used to elucidate the complex interaction of the molten silicon surface layer with the substrate during the growth. The experiments show the relevant role played by the seed layer used as the growth initiator. The morphology of the laser-crystallized films has been analysed by scanning electron microscopy and X-ray diffraction. Polysilicon films, 2 μm thick, with a compact structure consisting of 1–2-μm grains that are almost monocrystalline, have been obtained.

Dynamic multivariate regression for on-field calibration of high speed air quality chemical multi-sensor systems

In the last few years, the interest in the development of new pervasive or mobile implementations of air quality multi-sensor devices, has significantly grown. New application opportunities appeared together with new challenges due to limitations in dealing with rapid pollutants concentrations transients. In this work, we propose a Dynamic Neural Network (DNN) approach to the stochastic prediction of air pollutants concentrations by means of chemical multi-sensor devices. DNN architectures have been devised and tested in order to tackle the cross sensitivities issues and sensors inherent dynamic limitations. Testing have been performed using an on-field recorded dataset from a pervasive deployment in Cambridge (UK), encompassing several weeks. Results have been compared with those obtainable by static models showing the performance advantages of on-field dynamic multivariate calibration in a real world air quality monitoring scenario.

Application of Nd:YLF laser to amorphous silicon crystallization process

Abstract Polysilicon thin films have been obtained by Laser Induced Crystallization utilizing a Q-switched diode pumped, frequency-doubled Nd:YLF laser at 523-nm wavelength. Intrinsic and n-doped amorphous materials, of different thickness, have been deposited on Corning 1737 by LPCVD technique. The irradiation conditions have been varied in order to study their influence on crystallized material properties. Electrical and optical properties of as-deposited and crystallized films have been determined. Structural characterization has been performed to evaluate average grain size and distribution. Larger grain size has been observed in intrinsic materials compared to n-doped materials and the largest grain size (≈1 μm) has been obtained on materials having thickness of 50 nm. Critical role of doping in the crystallization process has been pointed out.

Nanosphere lithography for advanced all fiber Sers probes

In this work, we report a straightforward and cost-effective fabrication route for the development of nano-patterned optical fiber tips. The technique is based on self-assembling polystyrene microspheres at the air/water interface and on their successive transferring on the fiber tip of single mode optical fiber. By applying to the fiber further treatments like particle size reduction, metal coating and sphere removal, different periodic structures have been conveniently realized. The morphological analysis reveals indeed the successful creation on the optical fiber tip of regular metallic-dielectric spheres’ arrays as well as metallic patterns with dimensional features down to a submicron scale. Finally, as proof of concept, we demonstrated the capability of the realized patterns to work as efficient Surface Enhanced Raman Spectroscopy (SERS) fiber probes.

Reproducible SERS substrates on optical fiber tips by nanosphere lithography

This paper reports on the assessment of a simple and economical self-assembly methodology to obtain reproducible substrates onto the optical fiber tip for surface-enhanced Raman spectroscopy (SERS) applications. The method relies on the use of the nanosphere lithography of the optical fiber end facet. A careful analysis has been carried out to investigate the capability of the proposed procedure to realize repeatable pattern on the optical fiber tip. Finally, we demonstrate the effective application of the patterned OFTs as SERS nanoprobes.

A Distributed Sensor Network for Waste Water Management Plant Protection

Waste water management process has a significant role in guarantee sea and surface water bodies water quality with direct impact on tourism based economy and public health. Protection of this critical infrastructure form illicit discharges is hence paramount for the whole society. Here, We propose a pervasive monitoring centered approach to the protection of wastewater management plant. An hybrid sensor network is actually deployed along the wastewater network including several different transducers. Incepted data are harmonized and processed with an integrated SWMM model and machine learning based approach in order to forecast water qualitative and quantitative aspects, detect and localize anomalies. An advanced WEBGIS-SOS based interface conveys relevant information to the management entity allowing it to take appropriate actions in a timely way, reducing and mitigating the impacts of illicit discharges.

Relevance Of TCO workfunction in n-silicon oxide emitter - c-Si (p) heterojunction solar cell

The amorphous /crystalline silicon heterojunction solar cells have largely demonstrated their usefulness to reach high efficiency. We have adopted a different and wider bandgap emitter based on silicon oxide, n-SiOx. A central role in this type of structure is played from the TCO workfunction whose value affects strongly the heterojunctions band structure at the emitter interface. RF magnetron sputtered TCO obtained with different deposition parameters, have been made in order to optimize their use in our heterojunction solar cell. Numerical simulation on the SiOx HJ, with TCO having proper workfunction value, show potential efficiency conversion well over the 23%. New Roman Bold font. An example is shown next.