Photoelectrochemical and photophysical characterization of new molecular photosensitizers and electron transfer mediators for Dye-Sensitized Solar Cells

Solar energy is one of the most promising future energy resources. The direct conversion of sunlight into electricity by solar cells is of particular interest because has relevant advantages over most of the presently used electrical power generation methods: indeed, electricity is produced without the exhaust of greenhouse gases and without nuclear waste byproducts. Due to their high efficiencies and their potentially low production costs, dye sensitized solar cells (DSSC) have attracted much attention during the last few years : this technology is based on a layer of mesoscopic TiO2 film (sintered on a conductive glass) which significantly increases the optical path for light harvesting by surface anchored sensitizer molecules whilst keeping an efficient contact with the electrolytic solution. These sensitizers molecules are often based on ruthenium polypyridyl complexes which couple intense visible region absorption bands to favourable ground and excited state electronic and thermodynamic properties (of their excited states) which allow, in the most favorable cases, for an almost quantitative photon to electron conversion. The standard DSSC usually contains, as electron mediator, the iodide/triiodide couple which posseses nearly ideal properties in terms of fast regeneration of the oxidized dye, very slow conduction band electron recapture and high diffusion coefficient in many solvents commonly used in the DSSCs. The main drawback of the I-/I- 3 couple arises from its high corrosivity towards most of the common higly conductive metals and poses a serious problem for the insertion in the DSSCs of metal grids necessary to increase the electron collection efficiency. It is known that transparent conductive glass exhibit large ohmic losses that are apparent when constructing cells of area exceeding few square centimeters and the only way to overcome the problem, when large surfaces are required and transparency is an issue, is to collect the electrons via metallic fingers deposited on the photoelectrode and on the counter electrode. The work presented here is largely focused on finding efficient non corrosive alternative redox couple for DSSCs based on polipyridyl Co(II) complexes and polypyridyl and pyridylquinoline Cu(I) complexes: these compounds, generally characterized by a very low visible extinction coefficient, minimize the competition with the light harvesting dye and exhibit a quasi-reversible electrochemical behaviour markedly dependent on the nature of the electrodic surface. Gold was found to be the most appropriate material to catalyze the heterogeneous electron transfer reaction at the counter electrode of the solar cells, but interesting results were also obtained with carbon coated electrodes. The best performing of these mediators when used with the best sensitizers gave photon to current conversion yields variable from 50 % to 70 %. Since the dye regeneration was found to limit the Co(II) electron mediator efficiency, Co(II) electrolyte performance has been improved by mixing kinetically fast couples and exploiting a cascade of electron transfer events. It has also been observed that copper complexes with a distorted tetragonal geometry show promise for developing alternative low cost mediators for photoelectrochemical cells. The transport of the electroactive ions is expected to play a significant role in determining DSSC efficiency: this is particularly true under strong illumination when a large number of photooxidized dye molecules are simultaneously generated at the photoanode and an efficient turnover of electron donating species is required to sustain the photocurrent. The search for suitable solid materials that can replace the liquid electrolyte is an additional interesting and active area of research. In a solid state DSSC the solid hole conducting material captures the holes and closes the circuit with the counter electrode. Conducting polymers have been studied and have shown promising results as hole conducting materials for their application to regenerative photoelectrochemical cells. In particular it has been reported that the presence of ionic liquids may improve the charge transporting capabilities of the heterointerface through screening of space charge effects. In the last part of the thesis some efforts towards the modification of the counter electrode with inexpensive and transparent materials have been described: interest in such materials is boosted by the possible realization of stacked cells, either serially or in parallel connected, in which two spectrally complementary dyes can work in their optimal absorption region, improving the spectral responsivity of the modules. In these studies it has been found that osmium complexes as well as electrodeposited conductive polymers like PEDOP an\ud PEDOT are effective in enhancing the electrochemical response of Co(II) electron mediators at surface modified FTO. The study of Ru(II) sensitizers based on 4-4’-pyrrol (or pyrrolidine)-2,2’bipyridine have been carried out both in liquid and quasi-solid state solar cells. Sensitization of the TiO2 to the near IR region and photon to current conversion efficiencies close to 90% can be obtained with a proper synthetic design of these dyes and with a careful choice of the hole transporting electrolyte. Research on dye sensitizers has been mainly focused on transition metal complexes, but a considerable work has also been directed towards the study of organic natural sensitizers extracted from fruits and vegetables. In particular families of anthocyanin and betalain dyes have been deeply investigated as natural sensitizers for dye sensitized solar cell and, with properly engineered titania photoelectrodes, photon to current conversion efficiencies close to 70% have been reached

Opendata, liberazione dei dati e partecipazione nei nativi digitali. Autoregolazione intelligente delle tecnologie E-partecipation and smart citizens in education.

Democracy encourages the participation of individuals to the common interest in order to relate one\u2019s action to that of the other\u2019s and takes into consideration the action by the other to give meaning to his own thus overcoming the barriers of social class, race and territory. A mobile society spreading the continuous changes taking place all over the world by means of its media channels must ensure that all its members are educated to be flexible and encouraged to take up personal initiative. If not, they would be overwhelmed by the changes they would experience, changes whose full meanings and connections would not be able to understand. A confusing situation would arise in which a small number of people would take possession of the results of the activities by the others. The present work has been inspired by such an assumption based on the concerns involved due to the gradual loss of representativeness of the institutions that traditionally took charge of giving voice to social issues. Parties and associations have made the synthesis between state and society up to the time when this was possible. Populist and techno-populist movements and personalized leaderships of these social formations show the declining phase of such model of representation. To overcome the crisis of traditionally conceived representation some of the potentialities of the web and of the new communication technology have been investigated. The argument is based on the need to educate future generations to democratic participation through the introduction of the Open Data included in a teaching unit to be proposed in secondary schools. The possibility of accessing and manipulating the rough data or doing citizen participative journalism activities on data still disregarded by the tame information is based on the positive feedback coming from the educational experiences of partecipa.net and Citizenship and Constitution whose main target is participation. The work ends by underlining the value of the use of open data in teaching on account of the chance that the data released may be used in school activities of citizen participative journalism in continuity with the experience of participatory journalism which gave birth to the North American telematic agor\ue0 of the 1990s. The intelligent self-disciplined awareness in the use of technology is to support the net surfing by the digital natives. Such approach would help them to establish \u201cwho is what\u201d, as to say, to be able to recognize and deal with the positive aspects of the Internet. For this purpose the contribution of teachers choosing the educational dimension of the mandate instead of the content of the discipline is essential

CONTRATTAZIONE COLLETTIVA E DIRITTO DELLA CONCORRENZA ( il contributo della giurisprudenza comunitaria al delinearsi progressivo di un sistema di relazioni tra due famiglie in conflitto)

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Local similarity discriminant analysis

We propose a local, generative model for similarity-based classification. The method is applicable to the case that only pairwise similarities between samples are available. The classifier models the local class-conditional distribution using a maximum entropy estimate and empirical moment constraints. The resulting exponential class conditionaldistributions are combined with class prior probabilities and misclassification costs to form the local similarity discriminant analysis (local SDA) classifier. We compare the performance of local SDA to a non-local version, to the local nearest centroid classifier, the nearest centroid classifier, k-NN, and to the recently-developed potential support vector machine (PSVM). Results show that local SDA is competitive with k-NN and the computationally-demanding PSVM while offering the advantages of a generative classifier. 1. Similarity-based Classification Similarity-based learning methods make inferences based only on pairwise similarities or dissimilarities between a test sample and training samples and between pairs of training samples [Bicego et al., 2006,Pekalska et al., 2001, Jacobs et al., 2000, Hochreiter & Obermayer, 2006]. The term similarity-based learning is used whether the pairwise relationship is a similarity or a dissimilarity. The similarity/dissimilarity function is not constrained to satisfy the properties of a metric. Similarity-based learning can be applied when the test and training samples are not described as point

TECHNIQUES AND INSTRUMENTS OF REGULATION OF SOCIAL POLICY: EVOLUTION AND PERSPESCTIVES

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