1,720,991 research outputs found
DEVELOPMENT AND CHARACTERIZATION OF NANOSTRUCTURED MATERIALS FOR ORGANIC AND HYBRID SOLAR CELLS
Full text linkIn the last years, the massive evolution of modern technologies has gradually created an alarming gap between the production and the consumption of energy. Traditional energy resources are no longer sufficient to satisfy the demand of energy without spoiling earth environment. Solar photovoltaics represents a highly promising technology to tackle this global energy issue. The thorough scientific discussion on this fundamental topic gave rise to interesting results and the organic solar cells (OSCs) are one of these achievements.
One major reason of the development and the increasing interest in this new technology is its eco-friendliness and the potentially low-cost production of solar modules on flexible (plastic) substrates. Furthermore, new applications are expected by flexible or semitransparent organic solar cells. Nevertheless, two main problems must be overcome before this promising technology replaces the long-established silicon solar cells: the low power conversion efficiency and the scarce stability. In order to tackle these fundamental issues the research efforts must be focused towards both the development of new materials and their detailed photophysical and morphological characterization.
Recently the application of nanostructured architectures within the active layers of OSCs has demonstrated to be an efficient alternative to boost solar cell efficiency. Indeed, the nanometric miniaturization of materials opened a huge amount of possibilities to tune and bolster their optical and electrical properties.
In this thesis work, the potentialities of the nanostructured architectures are explored. In particular, the attention of this work is addressed towards the development and the photophysical characterization of new hybrid nanostructured photoactive materials. Three different families of nanostructures, colloidal Quantum Dots, Carbon Dots, and hybrid organic/inorganic perovskite nanoparticles, are blended with organic photovoltaic materials. The thorough investigation of the photo-physical and morphological interactions between the nanostructures and the organic materials aims to investigate these nanocomposite as new photoactive materials for next-generation solar cells.
The first step of the work focuses on the investigation of a prototypical active layer consisting in binary blends of the fullerene derivative PCBM and CdSe/CdS core-shell Quantum Dots (QDs) capped with different ligands (namely, oleylamine, octadecanethiol, and propanethiol). The double purpose is both to demonstrate that QDs do not influence only the morphology of the active layers, as it is often reported in literature, but also its photophysics and to unravel the pivotal role of QDs ligands on the electron transfer process, which is fundamental for organic solar cells. Through the combined use of steady-state, time resolved and pulsed electron paramagnetic resonance (EPR) techniques the photophysical role of QDs in OSCs is clarified and the possibility to tailor the electron transfer process through the proper choice of QDs ligands is demonstrated.
The second part of the work aims at promoting the application of carbon dots (CDs) as electron donor materials for OSCs. CDs seem to be a good alternative to colloidal QDs, thanks to their low toxicity, good biocompatibility and peculiar photo-physical properties, however their poor solubility in organic solvents and mediocre electron-donor properties hampered their photovoltaic application. To tackle these critical issues, the synthesis and photo-physical characterization of N-doped CDs functionalized with two different thiophene-containing groups is carried out in this work. The functionalization intends to enhance the electron donating properties of the CDs and improve their solubility in organic solvents. The increased solubility allows to investigate the photoinduced interactions of functionalized CDs with the PCBM in solution and in solid blends. Through the combined cyclic voltammetry, optical and EPR analysis the enhanced electron donor capabilities of the functionalized CDs are demonstrated and the electron transfer process is characterized in detail.
Finally, the last part of the work concentrates on the hybrid organic inorganic perovskite nanostructures. These recent nanostructures are definitely the best candidate to compete with silicon solar cells since their bulk counterpart has already provided record photovoltaic efficiencies in less than five years. However, the application of perovskite nanoparticles (PNPs) in organic solar cells has been scarcely investigated so far. Therefore, in this thesis work the synthesis of PNPs and the investigation of their interaction with both the PCBM and the semiconducting polymer P3HT is carried out. After the confirmation of the obtained synthesis through optical spectroscopy, X-ray diffraction and XPS analysis, the electron transfer from PNPs to PCBM is investigated. In particular, the effect of the ligand length on the electron transfer is examined, probing the process with two different PNPs ligands: octylamine and oleylamine. Successively, the role of the PNPs in blend with P3HT is studied. A triple effect of PNPs on the polymer properties is observed: (1) an increment of the dimension of P3HT crystalline domains, (2) a p-doping of the P3HT, and (3) an enhanced interchain order.
The results of this work underpin the relevance of applying nanostructured architectures in organic photovoltaic materials, highlighting their beneficial role not only in morphology, but also in the main photo-physical processes that take place in solar cells. Additionally, the relevant role of the tailored surface engineering of nanostructures in the process of solar energy conversion is evidenced. All these observations aim at providing guidelines for the design and the fabrication of highly efficient solar cells
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
Azetidinium as Cation in Lead Mixed Halide Perovskite Nanocrystals of Optoelectronic Quality
No full textThe dataset is part of the research work submitted for publication titled "Azetidinium as Cation in Lead Mixed Halide Perovskite Nanocrystals of Optoelectronic Quality
The central role of ligands in electron transfer from perovskite nanocrystals
No full textThe nanoscale miniaturization of hybrid organic-inorganic perovskite has given rise to new functionalities, but the full understanding of the multifaceted properties of perovskite nanostructures is still incomplete. Using a combination of optical and magnetic resonance (EPR) spectroscopies, we focused our investigation on the photoinduced electron transfer process taking place in perovskite nanocrystals blended with the fullerene derivative PCBM. In particular we analyzed the different effect of two types of nanocrystal ligands, namely octylamine and oleylamine, on the photoinduced processes. The electron transfer process resulted in efficient fluorescence quenching in a mixed solution and in the formation of charges (PCBM anions) detected by EPR in the blends. Both the optical and EPR techniques revealed a stronger effect when the shorter ligand is present. Finally, pulsed EPR demonstrated the stabilization of the photogenerated charges in proximity of perovskite nanocrystals
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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