Study of heterostructures of Cu3BiS3–buffer layer measured by Kelvin probe force microscopy measurements (KPFM)

The interface formed between Cu3BiS3 thin films and the buffer layer is a potentially limiting factor to the performance of solar cells based on Al/Cu3BiS3/buffer heterojunctions. The buffer layers of ZnS and In2S3 were grown by coevaporation, and tested as an alternative to the traditional CdS deposited by chemical bath deposition. From the Kelvin probe force microscopy measurements, we found the values of the work function of ZnS, In2S3, and CdS, layers deposited into Cu3BiS3. Additionally, different electronic activity was found for different grain boundaries (GBs), from studies under illumination, we also found the net doping concentration and the density of charged GB states for Cu3BiS3 and Cu3BiS3/CdS.

First-Principles Calculations of the Electronic and Structural Properties of GaSb

In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects ofexchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew– Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B0); while for the cohesive energy (Ecoh), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.

Assessment of PV Systems Performance in the Madeira Island Using Typical Meteorological Year Data

This paper focus on the development of an algorithm using Matlab to generate Typical Meteorological Years from weather data of eight locations in the Madeira Island and to predict the energy generation of photovoltaic systems based on solar cells modelling. Solar cells model includes the effect of ambient temperature and wind speed. The analysis of the PV system performance is carried out through the Weather Corrected Performance Ratio and the PV system yield for the entire island is estimated using spatial interpolation tools.

A finite element framework for the interplay between delamination and buckling of rubber-like bi-material systems and stretchable electronics

In this study, a finite element (FE) framework for the analysis of the interplay between buckling and delamination of thin layers bonded to soft substrates is proposed. The current framework incorporates the following modeling features: (i) geometrically nonlinear solid shell elements, (ii) geometrically nonlinear cohesive interface elements, and (iii) hyperelastic material constitutive response for the bodies that compose the system. A fully implicit Newton–Raphson solution strategy is adopted to deal with the complex simultaneous presence of geometrical and material nonlinearities through the derivation of the consistent FE formulation. Applications to a rubber-like bi-material system under finite bending and to patterned stiff islands resting on soft substrate for stretchable solar cells subjected to tensile loading are proposed. The results obtained are in good agreement with benchmark results available in the literature, confirming the accuracy and the capabilities of the proposed numerical method for the analysis of complex three-dimensional fracture mechanics problems under finite deformations.

New functional polythiophene based materials: fine-tuning of photovoltaic or chiroptical properties

There is a remarkable level of interest in the development of π-conjugated polymers (ICPs) which have been employed, thanks to their promising optical and electronic properties, in numerous applications including photovoltaic cells, light emitting diodes and thin-film transistors. Although high power conversion efficiency can be reached using poly(3-alkylthiophenes) (P3ATs) as electron-donating materials in polymeric solar cells of the Bulk-Heterojunction type (BHJ), their relatively large band gap limits the solar spectrum fraction that can be utilized. The research work described in this dissertation thus concerns the synthesis, characterization and study of the optical and photoactivity properties of new organic semiconducting materials based on polythiophenes. In detail, various narrow band gap polymers and copolymers were developed through different approaches and were characterized by several complementary techniques, such as gel permeation chromatography (GPC), NMR spectroscopy, thermal analyses (DSC, TGA), UV-Vis/PL spectroscopy and cyclic voltammetry (CV), in order to investigate their structural and chemical/photophysical properties. Moreover, the polymeric derivatives were tested as active material in air-processed organic solar cells. The activity has also been devoted to investigate the behavior of polythiophenes with chiral side chain, that are fascinating materials capable to assume helix supramolecular structures, exhibiting optical activity in the aggregated state.

Sintesi e caratterizzazione di materiali polimerici water-soluble per applicazioni nel campo del fotovoltaico organico

The need to use renewable energy sources, due to the massive production of pollution for the energy production, has led to the development of new technologies for the use of solar energy. The purpose of this thesis project is to synthesize and characterize new thiophene-based polymeric materials processable in water, a green solvent, for the construction of organic solar cells, promising and versatile devices used for the production of electric energy. For this, a highly regioregular polymer was synthesized through GRIM polymerization (Grignard Metathesis Polymerization) on which a study was performed to identify the optimal reaction time.

Sintesi, caratterizzazione e nano-strutturazione di politiofeni e loro applicazione in celle solari

Negli ultimi decenni i polimeri coniugati, grazie alla loro peculiarità di essere dei semiconduttori organici, hanno attirato l’attenzione della ricerca scientifica, e tra questi composti rientrano i politiofeni. Versatilità, robustezza chimica strutturale e fluorescenza sono alcune delle proprietà che caratterizzano tali composti e che hanno permesso di esplorare nuovi materiali da un punto di vista scientifico e tecnologico. Recentemente molto interessanti sono risultate essere le nanoparticelle politiofeniche poiché permettono di modulare le proprietà chimico-fisiche dei relativi polimeri, ampliandone le potenzialità a trovare applicazione in molteplici dispositivi elettronici, tra cui le celle solari (CS) organiche. Infatti, molto attivo è l’interesse della comunità scientifica per ottimizzare questi dispositivi ricercando nuovi prodotti che soddisfino diversi requisiti, come riduzione dell’impatto ambientale, la facilità di preparazione e compatibilità con substrati flessibili. In tale contesto, uno degli obiettivi della ricerca attualmente si focalizza sulla preparazione di nuovi accettori da usare in CS organiche alternativi ai derivati fullerenici, i quali presentano diversi svantaggi. Alla luce dei più recenti risultati si è visto che i politiofeni push-pull, caratterizzati dall’alternanza di gruppi accettori (A) e gruppi donatori (D), hanno una notevole potenzialità a rimpiazzare tali materiali e ad essere usati come accettori non-fullerenici. Infatti, questi hanno permesso di ottenere buoni risultati in termini di conversioni ed efficienze delle celle fotovoltaiche. Lo scopo di questo lavoro di tesi è sintetizzare sei nuovi polimeri a base tiofenica (quattro con sequenza A-D e due con sequenza A-A) per studiarne le possibili applicazioni come materiali accettori non-fullerenici e la loro organizzazione in strutture ordinate di nanoparticelle.

Molecular modelling of organic functional materials

The investigation of the mechanisms lying behind the (photo-)chemical processes is fundamental to address and improve the design of new organic functional materials. In many cases, dynamics simulations represent the only tool to capture the system properties emerging from complex interactions between many molecules. Despite the outstanding progresses in calculation power, the only way to carry out such computational studies is to introduce several approximations with respect to a fully quantum mechanical (QM) description. This thesis presents an approach that combines QM calculations with a classical Molecular Dynamics (MD) approach by means of accurate QM-derived force fields. It is based on a careful selection of the most relevant molecular degrees of freedom, whose potential energy surface is calculated at QM level and reproduced by the analytic functions of the force field, as well as by an accurate tuning of the approximations introduced in the model of the process to be simulated. This is made possible by some tools developed purposely, that allow to obtain and test the FF parameters through comparison with the QM frequencies and normal modes. These tools were applied in the modelling of three processes: the npi* photoisomerisation of azobenzene, where the FF description was extended to the excited state too and the non-adiabatic events were treated stochastically with Tully fewest switching algorithm; the charge separation in donors-acceptors bulk heterojunction organic solar cells, where a tight-binding Hamiltonian was carefully parametrised and solved by means of a code, also written specifically; the effect of the protonation state on the photoisomerisation quantum yield of the aryl-azoimidazolium unit of the axle molecule of a rotaxane molecular shuttle. In each case, the QM-based MD models that were specifically developed gave noteworthy information about the investigated phenomena, proving to be a fundamental key for a deeper comprehension of several experimental evidences.

Optoelectronic investigation of defects in hybrid metal halide perovskites

The growing demand for flexible and low-cost electronics has driven research towards the study of novel semiconducting materials to replace traditional semiconductors like silicon and germanium, which are limited by mechanical rigidity and high production cost. Some of the most promising semiconductors in this sense are metal halide perovskites (MHPs), which combine low-cost fabrication and solution processability with exceptional optoelectronic properties like high absorption coefficient, long charge carrier lifetime, and high mobility. These properties, combined with an impressive effort by many research groups around the world, have enabled the fabrication of solar cells with record-breaking efficiencies, and photodetectors with better performance than commercial ones. However, MHP devices are still affected by issues that are hindering their commercialization, such as degradation under humidity and illumination, ion migration, electronic defects, and limited resistance to mechanical stress. The aim of this thesis work is the experimental characterization of these phenomena. We investigated the effects of several factors, such as X-ray irradiation, exposure to environmental gases, and atmosphere during synthesis, on the optoelectronic properties of MHP single crystals. We achieved this by means of optical spectroscopy, electrical measurements, and chemical analyses. We identified the cause of mechanical delamination in MHP/silicon tandem solar cells by atomic force microscopy measurements. We characterized electronic defects and ion migration in MHP single crystals by applying for the first time the photo-induced current transient spectroscopy technique to this class of materials. This research allowed to gain insight into both intrinsic defects, like ion migration and electron trapping, and extrinsic defects, induced by X-ray irradiation, mechanical stress, and exposure to humidity. This research paves the way to the development of methods that heal and passivate these defects, enabling improved performance and stability of MHP optoelectronic devices.

Characterization of innovative kerfless cutting of monocrystalline silicon wafers for photovoltaic applications

Nowadays renewable energies are a hot research topic, and the goal is to improve cell efficiency and reduce production costs, aiming to make the use of photovoltaics increasingly widespread and convenient. Monocrystalline silicon solar cells are leaders in the photovoltaic market. However, market-established cutting techniques produce a consistent amount of material waste when cutting ingots into wafers. The“Stress-induced LIft-Off Method” (SLIM) is emerging in recent years as an alternative, more sustainable separation technique, which reduces material loss and can lead to obtaining increasingly thinner wafers, further reducing the required amount of silicon. This thesis presents the micro-characterization of the separated wafers with the SLIM technique. The wafers were obtained with a two-step procedure. First, a layer of defects was induced in the silicon using ultra-short medium-infrared laser pulses. Then, the material was deposited on one of the sides and induced stress in the silicon, such as to further weaken it. In this way, only rapid cooling is required for detachment to occur. The obtained results indicate that the SLIM-cut technique halves the minority carriers’ lifetime. There is no amorphization, crystal disorder or high-pressure phases. However, changes in the Raman spectra suggest that tensile stress may have been produced on these surface layers by the separation process. The AFM topography highlights surface irregularities, which may be removed with a polishing step. The surface also shows laser-modified regions, which are evident in SEM images, but not in AFM topographies, suggesting a charging effect due to electron bombardment. Lastly, the electrical characterization by conductive AFM lacks any changes in the conductive behaviour of the material where the laser-modified areas should be located. In conclusion, these preliminary results are promising to carry out a systematic characterization of this technique of this innovative SLIM technique.

Ovariectomized OVA-sensitized mice display increased frequency of CD4+Foxp3+ T regulatory cells in the periphery

It is well established that female sex hormones have a pivotal role in inflammation. For instance, our group has previously reported that estradiol has proinflammatory actions during allergic lung response in animal models. Based on these findings, we have decided to further investigate whether T regulatory cells are affected by female sex hormones absence after ovariectomy. We evaluated by flow cytometry the frequencies of CD4+Foxp3+ T regulatory cells (Tregs) in central and peripheral lymphoid organs, such as the thymus, spleen and lymph nodes. Moreover, we have also used the murine model of allergic lung inflammation a to evaluate how female sex hormones would affect the immune response in vivo. To address that, ovariectomized or sham operated female Balb/c mice were sensitized or not with ovalbumin 7 and 14 days later and subsequently challenged twice by aerosolized ovalbumin on day 21. Besides the frequency of CD4+Foxp3+ T regulatory cells, we also measured the cytokines IL-4, IL-5, IL-10, IL-13 and IL-17 in the bronchoalveolar lavage from lungs of ovalbumine challenged groups. Our results demonstrate that the absence of female sex hormones after ovariectomy is able to increase the frequency of Tregs in the periphery. As we did not observe differences in the thymus-derived natural occurring Tregs, our data may indicate expansion or conversion of peripheral adaptive Tregs. In accordance with Treg suppressive activity, ovariectomized and ovalbumine-sensitized and challenged animals had significantly reduced lung inflammation. This was observed after cytokine analysis of lung explants showing significant reduction of pro-inflammatory cytokines, such as IL-4, IL-5, IL-13 and IL-17, associated to increased amount of IL-10. In summary, our data clearly demonstrates that OVA sensitization 7 days after ovariectomy culminates in reduced lung inflammation, which may be directly correlated with the expansion of Tregs in the periphery and further higher IL-10 secretion in the lungs.

Mutagenic specificity of solar UV light in nucleotide excision repair-deficient rodent cells.

To investigate the role of nucleotide excision repair (NER) in the cellular processing of carcinogenic DNA photoproducts induced by defined, environmentally relevant portions of the solar wavelength spectrum, we have determined the mutagenic specificity of simulated sunlight (310-1100 nm), UVA (350-400 nm), and UVB (290-320 nm), as well as of the "nonsolar" model mutagen 254-nm UVC, at the adenine phosphoribosyltransferase (aprt) locus in NER-deficient (ERCC1) Chinese hamster ovary (CHO) cells. The frequency distributions of mutational classes induced by UVB and by simulated sunlight in repair-deficient CHO cells were virtually identical, each showing a marked increase in tandem CC-->TT transitions relative to NER-proficient cells. A striking increase in CC-->TT events was also previously documented for mutated p53 tumor-suppressor genes from nonmelanoma tumors of NER-deficient, skin cancer-prone xeroderma pigmentosum patients, compared to normal individuals. The data therefore indicate that the aprt gene in NER-deficient cultured rodent cells irradiated with artificial solar light generates the same distinctive "fingerprint" for sunlight mutagenesis as the p53 locus in NER-deficient humans exposed to natural sunlight in vivo. Moreover, in strong contrast to the situation for repair-component CHO cells, where a significant role for UVA was previously noted, the mutagenic specificity of simulated sunlight in NER-deficient CHO cells and of natural sunlight in humans afflicted with xeroderma pigmentosum can be entirely accounted for by the UVB portion of the solar wavelength spectrum.

T cells signaled by NF-kappa B- dendritic cells are sensitized not anergic to subsequent activation

Paradoxically, while peripheral self-tolerance exists for constitutively presented somatic self Ag, self-peptide recognized in the context of MHC class II has been shown to sensitize T cells for subsequent activation. We have shown that MHC class II(+)CD86(+)CD40(-) DC, which can be generated from bone marrow in the presence of an NF-kappaB inhibitor, and which constitutively populate peripheral tissues and lymphoid organs in naive animals, can induce Ag-specific tolerance. In this study, we show that CD40(-) human monocyte-derived dendritic cells (DC), generated in the presence of an NF-kappaB inhibitor, signal phosphorylation of TCRzeta, but little proliferation or IFN-gamma in vitro. Proliferation is arrested in the G(1)/G(0) phase of the cell cycle. Surprisingly, responding T cells are neither anergic nor regulatory, but are sensitized for subsequent IFN-gamma production. The data indicate that signaling through NF-kappaB determines the capacity of DC to stimulate T cell proliferation. Functionally, NF-kappaB(-)CD40(-)class II+ DC may either tolerize or sensitize T cells. Thus, while CD40(-) DC appear to prime or prepare T cells, the data imply that signals derived from other cells drive the generation either of Ag-specific regulatory or effector cells in vivo.

Proteasome Inhibition Represses Unfolded Protein Response and Nox4, Sensitizing Vascular Cells to Endoplasmic Reticulum Stress-Induced Death

Background: Endoplasmic reticulum (ER) stress has pathophysiological relevance in vascular diseases and merges with proteasome function. Proteasome inhibition induces cell stress and may have therapeutic implications. However, whether proteasome inhibition potentiates ER stress-induced apoptosis and the possible mechanisms involved in this process are unclear. Methodology/Principal Findings: Here we show that proteasome inhibition with MG132, per se at non-lethal levels, sensitized vascular smooth muscle cells to caspase-3 activation and cell death during ER stress induced by tunicamycin (Tn). This effect was accompanied by suppression of both proadaptive (KDEL chaperones) and proapoptotic (CHOP/GADD153) unfolded protein response markers, although, intriguingly, the splicing of XBP1 was markedly enhanced and sustained. In parallel, proteasome inhibition completely prevented ER stress-induced increase in NADPH oxidase activity, as well as increases in Nox4 isoform and protein disulfide isomerase mRNA expression. Increased Akt phosphorylation due to proteasome inhibition partially offset the proapoptotic effect of Tn or MG132. Although proteasome inhibition enhanced oxidative stress, reactive oxygen species scavenging had no net effect on sensitization to Tn or MG132-induced cell death. Conclusion/Relevance: These data indicate unfolded protein response-independent pathways whereby proteasome inhibition sensitizes vascular smooth muscle to ER stress-mediated cell death. This may be relevant to understand the therapeutic potential of such compounds in vascular disease associated with increased neointimal hyperplasia.

Sensitized formation of oxidatively generated damage to cellular DNA by UVA radiation

The survey is aimed at critically reviewing information on the UVA-mediated oxidative reactions to cellular components with emphasis on DNA as the result of mostly photosensitized pathways. It appears clearly that UVA radiation is relatively much more efficient than UVB photons in inducing oxidative processes. The main UVA-induced oxidative degradation pathways of DNA are reported and discussed mechanistically. They are mostly rationalized in terms of a major contribution of singlet molecular oxygen ((1)O(2)) and to a lesser extent of hydroxyl radical ((center dot)OH), that in the latter case originates from Fenton-type reactions. This leads to the predominant formation of 8-oxo-7,8-dihydroguanine together with smaller amounts of oxidized pyrimidine bases and DNA strand breaks in UVA-irradiated cells.