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The quaternary chalcopyrite semiconductor alloy Cu(In,Ga)Se2 (CIGS) is nowadays commonly considered one of the most suitable materials to fabricate cost-effective and high-efficiency photovoltaic cells. Thanks to the optical and structural properties of the absorber layer and to the tunable bandgap, thin-film CIGS cells have reached efficiencies around 20%, not far from the maximum values of traditional crystalline silicon cells. This high efficiency, together with the conceivable low fabrication costs, makes CIGS cells a promising alternative to silicon technology for large-scale production. In order to further improve the cells performance, in a previous work we have already proposed a simple structure having a linear graded carrier concentration absorber profile, which allows to induce a quasi-electrical field directed towards the back-contact, like CIGS cells with a Ga back-graded profile. Thanks to the increase of Ec and Ev towards the backcontact, while keeping the energy gap constant along the depth, the generation process is even more efficient in our structure, thus improving cells performance (efficiency over 21%). Herein, we investigate on other non-uniform doping concentration profiles that can be technologically easily realised, still maintaining the already demonstrated high-efficiency values.

Despite the technical difficulties in developing efficient and compact sources and detectors for Terahertz (THz) radiation, this region of the electromagnetic spectrum is attracting an ever-increasing interest, due to its peculiar and high-potential applications in several fields, such as wideband communications, medicine, biology, non-destructive testing, security and defense. Within such contexts, the most widespread approach aiming to deal with THz pulses is based on the THz Time-Domain Spectroscopy (THz-TDS) system. In this work, we present our experimental results obtained by means of a THz-TDS set-up based on photoconductive antennas for both the generation and detection stage. It is composed by i) a mode-locked Ti:Sapphire femtosecond laser (Mai-Tai SP - Spectra Physics, (800±20 nm, 120 fs, 84 MHz); ii) two LT-GaAs photoconductive antennas, acting as THz emitter and detector; iii) an optical delay line.

An interesting phenomenon occurring in Dye Sensitized Solar Cells (DSSCs) when exposed to an uninterrupted period of illumination is the so-called light soaking effect, which consists in the increase of the main electrical parameters of the cell, such as the photocurrent and the efficiency. Studying such an effect has noteworthy practical implications, ranging from the optimization of the manufacturing process to stability tests of DSSCs. In this paper, we present an experimental investigation on the performance variation, due to light soaking, of Ruthenium-based DSSCs.

In this work, we present a cost-effective technique to produce CIGS thin films for solar cells by means of a single-step electrodeposition. In fact, electrodeposition is known as an easy technique for building low cost materials for photovoltaic device processing. Morphological, structural and optical characterization of these films has been performed.

The aim of this study is to understand the photoresponse of a Ruthenium-complex/graphene heterostructure. Early work demonstrated that light detection by graphene field effect devices was enhanced by dropcasting Ruthenium Complex molecules. Here we proposed to fabricate a new class of devices where the Ruthenium-complex molecules are embedded between two layer of CVD monolayer graphene.

Nowadays, a growing demand for free and clean energy requires the study and the development of new low-cost solar photovoltaic (PV) cells. Among them, Dye Sensitized Solar Cells (DSSCs) based on ruthenium complexes as sensitizers are assuming a great importance. The DSSCs under study are composed placing in succession a transparent conductive glass on which is screen-printed a mesoporous TiO2 thin film sensitized by a ruthenium based dye (N719) , an electrolytic solution containing a redox couple (I-/I3-) and another conductive glass covered by a thin transparent catalyst platinum film. In this work, we have measured the main photoelectrochemical parameters of the above mentioned DSSCs at different irradiance levels, incident wavelengths, temperatures and hours of light soaking.

In this paper, we measure the main photoelectrical parameters of Dye Sensitized Solar Cells (DSSCs) based on ruthenium complexes at different irradiance levels, incident wavelengths, temperatures and hours of light soaking

In this work, the electrical and optical characterization of CIG(S, Se)2 sub-modules using both a solar simulator equipment and the Laser Beam Induced Current (LBIC) technique is presented. By using the solar simulator and a proper set-up, the electrical parameters of the modules at varying irradiance and temperatures are determined. In addition, the LBIC measurements are carried out to analyze the 2D photocurrent uniformity of the modules at two different wavelengths. Dispersion values of extracted parameters can be very useful for practically tuning the modelling stage at device/module level.

The aim of this study is to understand the photoresponse of a Ruthenium-complex/graphene heterostructure. Early work demonstrated that light detection by graphene field effect devices was enhanced by dropcasting Ruthenium Complex molecules. Here we proposed to fabricate a new class of devices where the Ruthenium-complex molecules are embedded between two layer of CVD monolayer graphene.

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice. This peculiarity is responsible of extraordinary physical properties. Graphene exhibits a strong ambipolar field effect and thanks to its huge charge carrier mobility, graphene is a suitable material for high frequency Electronics. Graphene field effect transistors (GFET) for high frequency applications have recently received much attention and significant progress has been achieved in this area. GFETs have been already made by using pre-patterned metal or graphene nanoribbon (GNR) back-gates and hexagonal boron nitride as a dielectric spacer. Among the most employed techniques for the graphene transfer, i.e. mechanical exfoliation, chemical exfoliation and chemical vapor deposition (CVD) growth, the latter has the advantage to produce several devices on the same chip with a very high yield. In this work, we focus on the characterization of a novel generation of GFETs, in which a graphene sheet, grown via CVD, is used as channel material.

Nowadays, a growing demand for free and clean energy requires the study and the development of new low-cost solar photovoltaic (PV) cells. Among them, Dye Sensitized Solar Cells (DSSCs) based on ruthenium complexes as sensitizers are assuming a great importance. The DSSCs under study are composed placing in succession a transparent conductive glass on which is screen-printed a mesoporous TiO2 thin film sensitized by a ruthenium based dye (N719), an electrolytic solution containing a redox couple (I-/I3-) and another conductive glass covered by a thin transparent catalyst platinum film. In this work, we have measured the main photoelectrochemical parameters of the above mentioned DSSCs at different irradiance levels, incident wavelengths, temperatures and hours of light soaking.

In this paper, we measure the main photoelectrical parameters of Dye Sensitized Solar Cells (DSSCs) based on ruthenium complexes at different irradiance levels, incident wavelengths, temperatures and hours of light soaking.

Electrodeposition is a convenient technique for the development of low cost materials for photovoltaic (PV) device processing. Using a single step electrodeposition route, several groups have fabricated CIS (CuInSe) and CIGS (CuInGaSe) films. One of the most important requirements for successful application of one-step electrodeposition film formation is the ability to control composition of the deposited films and to develop polycrystalline microstructures with a low surface roughness and high sintered density.

In this work, we are reporting results on the electrodeposition of the CuInSe2 thin films on molybdenum thin foil substrates. We have used an aqueous non-buffered electrolyte and a careful choice of deposition parameters to ensure a good quality and composition of the deposited films. In addition, CdS was replaced in the buffer layer with a wider bandgap Zn(S,O,OH) film obtained by chemical bath deposition. The deposited films were annealed in inert atmosphere at different temperatures. The influence of annealing temperature on the properties of the films is briefly discussed. Films were also characterized by photoelectrochemical and I-V measurements. Structural characterization was carried out by XRD and Raman spectroscopy. Results show the growth of good quality films with very uniform morphology and good chemical composition.

Among the next-generation solar cells, a predominant role is played by Dye sensitized solar cells (DSSC) based on ruthenium complexes as sensitizers. They take advantage of a photoelectrochemical system to transform solar radiation into electric energy. In fact, DSSCs represent a cost-effective alternative to traditional silicon-based photovoltaic devices and they do not require expensive and sophisticated apparatus for their fabrication. In this work, we have produced and tested ruthenium DSSCs. In particular, we have measured the main parameters of these cells, such as the electrical and power performances and the efficiency levels, at different irradiance levels and at different incident wavelengths. Our results show a maximum conversion efficiency between 11% and 12% in the range within 540 and 550 nm. The results are in a fairly good agreement with theoretical predictions, especially with regard to the dependence of the parameters on the irradiance levels. Nevertheless, there are some aspects that suggest the need for further and more detailed studies on the deterioration mechanisms and fabrication processes.

Electrodeposition is a convenient technique for the development of low cost materials for photovoltaic (PV) device processing. Using a single step electrodeposition route, several groups have fabricated CIS (CuInSe) and CIGS (CuInGaSe) films [1]. One of the most important requirements for successful application of one-step electrodeposition film formation, is the ability to control composition of the deposited films and to develop polycrystalline microstructures with a low surface roughness and high sintered density. In this preliminary work, CIS films were produced by single bath electrodeposition finding the optimal conditions in order to achieve a dense film with high crystallinity and uniform, flat surfaces, which are of critical importance for photovoltaic applications. Electrodeposition was carried out in the potentiostatic mode using a conventional three-electrode configuration.

We present an analytical model describing the full electromagnetic propagation in a THz Time Domain Spectroscopy (THz-TDS) laser based system. We pay particular attention to the modelling of the time-frequency behavior of all the stages, which compose our experimental set-up. In particular, our model takes into account the following features: pump beam focusing into the generation crystal; phase-matching between pump and THz pulses inside both the generation and detection crystals; chromatic dispersion and absorption inside the materials; Fabry-Perot effect in both the crystals; diffraction along the propagation, focalization and overlapping between THz and probe beams; Electro-Optic Sampling. The data obtained from our experimental set-up are in optimum agreement with simulations, so proving the effectiveness of our model.

We report on backward second-harmonic generation using picosecond laser pulses in congruent lithium niobate with 3.2 µm periodic poling. By tuning both the pump wavelength and the sample temperature, we observed three resonant peaks in the range 1530-1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders, respectively. A maximum conversion efficiency of 0.475% was achieved at the 16th order with a 10 kW peak pump power. The latter is the highest conversion reported in bulk to date, for the backward configuration, with an improvement greater than 50% with respect to those previously achieved with nanosecond pulses for the same order of resonance.

An analytical model describing a laser based set-up for wideband THz generation and detection is presented. Particular attention is focused on the main broadband phenomena, which occur when THz radiations have to be handled.

Content synopsis of the following paper: Matteo Cherchi, Alberto Taormina, Alessandro C. Busacca, Roberto L. Oliveri, Saverio Bivona, Alfonso C. Cino, Salvatore Stivala, Stefano Riva Sanseverino, and Claudio Leone, "Exploiting the Optical Quadratic Nonlinearity of Zinc-Blende Semiconductors for Guided-Wave Terahertz Generation: A Material Comparison", IEEE Journal of Quantum Electronics, Vol. 46, N. 3, March 2010

DFG TeraHertz generation can approach the quantum efficiency limit with much lower peak powers than bulk experiments. We give details on the model and on the waveguide geometry.

Nella memoria si presentano i risultati preliminari su un processo di crescita elettrochimica di materiali nanostrutturati mediante l’impiego di stampi nanoporosi. Vengono quindi analizzate le possibili applicazioni del processo alla fabbricazione di semiconduttori nanostrutturati di interesse nel settore fotovoltaico, quali il CIGS, e le implicazioni dal punto di vista delle tecniche di caratterizzazione e di modellazione per dispositivi basati su tale tecnologia.

Some of the most severe problems in the replacement of galvanic treatment with PVD coatings reside, first of all, in the higher costs of vacuum processes and in the difficulty to coat many 3D small samples. This work describes the results obtained by using energetic deposition vacuum processes, of the family of Ion Plating Plasma Assisted (IPPA), using both thermal and sputtering sources, able to reduce dramatically the duration of deposition process and to eliminate the substrate heating and their pre-cleaning. Regarding the small 3D samples, an innovative structure, named "Ionic Rotarybarrel" is presented. The realised treatments are in the fields of decorative, protective and tribological coatings. Special decorative treatments were realised by using interferential effect produced by dielectric films. Metal, plastic, glass and natural shell substrates were coated with the proposed treatments. A typical duration of 15 minutes of the whole deposition cycle was obtained. The good mechanical and environmental characteristics of the treatments are also described.

We report on first experimental results on UltraViolet second-harmonic generation by first-order quasiphase-matching in a surface periodically poled proton exchanged Lithium Tantalate waveguide. We have achieved a good compatibility with alpha phase proton exchanged channel waveguides in Lithium Tantalate. We held the sample in a temperature controlled oven kept at a constant temperature of 250 °C, to reduce photorefractive damage. The pump source was a Ti-Sapphire laser with a tunability range of 700 - 980 nm and a 40-GHz linewidth. Continuous wave UV light at 365.4 nm was produced with a conversion efficiency of 6.6% W-1cm-2.