1,721,200 research outputs found
Design of Experiments (DoE): a multivariate approach to dye-sensitized solar cells comprehension and optimization
No full textNowadays, modern science proposes and optimizes new materials and technologies, whose characteristics and performances are governed by many factors. However, the scientific community rarely adopts multivariate strategies for the comprehension of what is proposed. As a striking example, a standard dye-sensitized solar cell (DSSC) is a typical complex system assembled with different and heterogeneous layers (FTO/nanocrystalline semiconductor/sensitizer/electrolyte/Pt-FTO), each one affected by intrinsic variability; moreover the layers influence each other and this increases the number of variables involved at the same time in the photoconversion process. The idea of the present work started from the need to identify all the factors by which the photoconversion processes may be influenced. In order to obtain a significant improvement of photovoltaic performances, particularly in reproducibility, long-term stability and efficiency, a chemometric design of experiments (DoE) approach is here presented for four case studies: the formulation of a UV-cured polymer electrolyte membrane, the composition of a cellulose-based gel-polymer electrolyte, the proper sensitization of a ZnO photoanode and the photostability optimization of a series of NIR dyes under different dipping conditions. We are firmly convinced that this approach will make possible to find the optimal experimental conditions to achieve, within a good reproducibility, optimized performances, both in term of efficiency and long term stabilit
Synthesis and crystal structure of Bis(2-phenylpyridine-C,N’)-bis(acetonitrile) iridium(III)hexafluorophosphate showing three anion/cation couples in the asymmetric unit
Full text linkThe title compound bis(2-phenylpyridine-C,N’)-bis(acetonitrile)iridium(III)hexafluorophosphate, a six-coordinate iridium(III) complex, crystallizes in the P-1 space group. Iridium is in a distorted octahedral (n = 6) coordination with the N,C’ atoms of two phenylpyridine and the N atoms of two acetonitrile ligands. The peculiarity of this structure is that three independent moieties of the title compound and three PF6− anions, to counterbalance the charge, are observed in the asymmetric unit and this is a rather uncommon fact among the Cambridge Crystallographic Database (CSD) entries. The three couples are almost identical conformers with very similar torsional angles. The packing, symmetry, and space group were accurately analyzed and described also by means of Hirshfeld surface analysis, which is able to underline subtle differences among the three anion/cation couples in the asymmetric unit. The driving force of the packing is the clustering of the aromatic rings and the maximization of acetonitrile:PF6− interactions. The asymmetry of the cluster is the cause of the unusual number of moieties in the asymmetric unit
Water-based electrolytes in hybrid solar cells: from liquid to gel formulations
No full textDye sensitized solar cells (DSSCs) with high performances have been fabricated mainly with organic solvent-based liquid electrolytes. However, these solvents not only have high vapor pressure, but they are often toxic and flammable. In the last few years, the idea of moving towards a water-based system clearly emerged. DSSCs fabricated with water-based electrolytes may offer reduced costs, non-flammability and environmental compatibility, but the presence of water in the cell may reduce the long term stability as well as the photovoltaic performance. For this reason, in recent years, an increasing number of research articles has been published in this direction and new dyes, electrodes and electrolyte components are continuously proposed. In this work, the study of different truly aqueous electrolytes is presented and a chemometric approach, useful to investigate and optimize their efficiency and stability, is effectively demonstrated. A few curious and anomalous behaviors observed in the literature and in our laboratories are investigated for this class of electrolytes. Moreover the development of a series of novel aqueous gel electrolytes based on natural polymers is also discussed as well as their interesting photovoltaic characteristic
Fotovoltaico acquoso: una nuova frontiera nel campo del solare
No full textL'energia solare rappresenta, per abbondanza e distribuzione geografica, la principale fonte rinnovabile. Per soddisfare la domanda energetica sempre più crescente, l'uomo ha sviluppato molteplici tecnologie fotovoltaiche negli ultimi decenni. La tecnologia al silicio ha aperto la strada del fotovoltaico, seguita dalla generazione di celle a film sottile, fino all'attuale terza generazione basata su materiali organici o ibridi organico/inorganico. Le celle sensibilizzate a colorante (dye-sensitized solar cells, DSSCs) rappresentano al giorno d'oggi, a 25 anni dalla loro invenzione, una tecnologia altamente promettente quando sono richieste, allo stesso tempo, buone efficienze e costi contenuti. Il dispositivo DSSC è costituito da materiali facilmente reperibili, quali vetri conduttivi, diossido di titanio, coppie redox, solventi organici, catalizzatori di riduzione. L'ingegnerizzazione dei materiali e delle interfacce di questa cella solare ha portato ad un recente record di efficienza, pari al 14.3%. Uno dei limiti del dispositivo DSSC è la presenza di un elettrolita liquido costituito da una coppia redox disciolta in un solvente organico. Quest'ultimo è solitamente acetonitrile, e rende la cella solare infiammabile, nonché caratterizzata da aspetti di tossicità non trascurabili qualora l'elettrolita fuoriesca dalla cella. Come soluzione al problema, la comunità scientifica ha recentemente iniziato a studiare DSSC acquose, ovvero celle solari dove l'unico solvente presente nell'elettrolita è l'acqua. Nonostante a primo impatto possa sembrare semplice sostituire il solvente di una DSSC, specialmente se si considera che non è un componente partecipe al meccanismo di funzionamento, l'introduzione dell'acqua nell'elettrolita comporta notevoli variazioni rispetto alla cella tradizionale. Innanzitutto, non è possibile utilizzare i tradizionali coloranti basati su complessi del rutenio, in quanto il loro legame con il diossido di titanio verrebbe istantaneamente idrolizzato dall'acqua. In secondo luogo, l'acqua è un solvente in grado di sciogliere quantità di sali molto maggiori rispetto all'acetonitrile, quindi occorre rivisitare completamente le formulazioni dei mediatori redox a base iodio oppure cobalto. Infine, la stabilità delle DSSCs rappresenta un aspetto cruciale, che in presenza di un elettrolita acquoso deve essere accuratamente studiata. In questo contributo, i recenti sviluppi nel campo delle DSSC acquose studiate presso il Politecnico di Torino e l'Università degli Studi di Torino vengono propost
Aqueous electrolytes: a possible breakthrough toward DSSCs widespread commercialization
No full textDye sensitized solar cells (DSSCs) with high performances (PCE > 14%) have been fabricated mainly with organic solvent-based liquid electrolytes, i.e. acetonitrile and methoxypropionitrile. However, these solvents have high vapor pressure and are often toxic and flammable. In recent years, the idea of creating an efficient, inexpensive and safe system moved the attention of scientific community towards alternative solvent-based systems. Above all, DSSCs fabricated with water-based electrolytes may offer reduced costs, non-flammability and environmental compatibility, but the same water present in the cell may reduce the long term stability as well as the photovoltaic performances. In order to reduce these drawbacks, an increasing number of research articles has been published in this direction and several sensitizers, electrodes and electrolyte components are continuously proposed and investigated. In this contribution, the study of iodine-based 100% aqueous electrolytes and their interaction with different selected dyes are presented. Moreover, a chemometric approach, useful to perform a multivariate investigation (DoE) and to optimize DSSCS efficiency and stability, is effectively demonstrated. Finally, the development of a series of novel aqueous gel electrolytes based on bio-derived polymers is also discussed as well as their interesting photovoltaic characteristic
Aqueous photovoltaics: a new era in third generation devices
No full textA key aspect still to be addressed in the DSSC community is the presence of water in the cell, either in the electrolyte or at the electrode/electrolyte interface. While it has been considered strongly harmful for a long time, in the last few years the scientific community suddenly turned the efforts in the direction of using water as a solvent, as demonstrated by the increasing number of research articles being published in the literature. Indeed, by means of DSSCs fabricated with water-based electrolytes, reduced costs, non-flammability, reduced volatility and improved environmental compatibility could be easily achieved. As a result, an increasing number of novel electrodes, dyes and electrolytes components are continuously proposed, being highly challenging from the materials science viewpoint and with the golden tread of producing truly water-based DSSCs. If the initial purpose of DSSCs was the construction of an artificial photosynthetic system able to convert solar light into electricity, the use of water as key component may represent a great step forward towards their widespread diffusion in the market. A starting point in this direction is given in this work, and a few curious and anomalous behaviours observed in the literature and in our laboratories are presented for this class of electrolytes. After a brief discussion of the current state of the art, this contribution proposes the investigation of both the stability of different classes of dyes (Ru complexes, squaraines, indolenines, carbazoles) in fully a aqueous environment, and the effect of the concentration of different iodine salts on the cell parameters and their stabilit
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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