1,720,974 research outputs found
Vibrational Response of Methylammonium Lead Iodide: From Cation Dynamics to Phonon–Phonon Interactions
No full textThe dynamic evolution of the vibrational interactions in the prototypical CH3NH3PbI3 was studied through a comprehensive experimental and theoretical investigation with a focus on the interactions between the organic cations and the inorganic cage. To date, no clear picture has emerged on the critical and fundamental interactions between the two perovskite components, despite the relevance of phonons to the electronic properties of several classes of perovskites. For the first time, we have monitored the IR and nonresonant Raman response in the broad frequency range 30–3400 cm−1 and in the temperature interval 80–360 K. Strong changes in the energies of different vibrational modes with temperature are observed and examined in the framework of phonon–phonon interactions considering a significant anharmonic contribution to the phonon relaxation process. The vibrational relaxation of the bending modes and their reorientation activation energies identify that such mechanisms are governed by medium-to-strong hydrogen bonds in the orthorhombic phase; however, any ferroelectric ordering in the orthorhombic phase is governed mostly by dipole interactions. These changes imply that charge localization mechanisms play a primary role, and our study enriches the fundamental knowledge of phonon interactions and charge transport in CH3NH3PbI3 for the further development of optoelectronic applications
Direct deposition of magnetite thin films on organic semiconductors
No full textTechnological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10 nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3
Long-Lived Photoinduced Polarons in Organohalide Perovskites
No full textThe long diffusion length of charge carriers in the CH3NH3PbI3 perovskite is one of the most relevant properties for explaining the high photovoltaic efficiency of perovskite solar cells. As a possible mechanism for the large diffusion length of electrons and holes, several authors suggested a reduced coulomb attraction of the carriers due to the formation of polarons. Here we performed continuous wave far-infrared photoinduced absorption (PIA) experiments on CH3NH3PbI3; spectral changes are associated with local deformation of the lattice around the photogenerated long-lived charges, a typical signature of photoinduced polarons. Ab initio calculations show confinement of charge carriers at the interface between structural domains characterized by a different tilting of the PbI6 octahedra. The differential IR spectrum between unperturbed and perturbed simulated structures shows a close pattern to the experimental PIA. Positive and negative charges are confined in different varieties of the perovskites coherent with the low recombination and long diffusion length of photogenerated carriers
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
Efficient and Versatile Interconnection Layer by Solvent Treatment of PEDOT:PSS Interlayer for Air-Processed Organic Tandem Solar Cells
No full textA robust and efficient interconnection layer (ICL) based on low conductive
poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and
ZnO nanoparticles is implemented in a solution-air-processed, blade coated
inverted polymer tandem solar cell. The commercial PEDOT:PSS (Heraeus
Clevios P VP Al 4083) is modified with a fluorosurfactant to allow its deposition
onto any hydrophobic active layer surface. However, this method alters
the electrical and energetic properties of the PEDOT:PSS thus affecting the
interface with the ZnO layer, responsible for an inefficient ICL and poorly
performing tandem devices. The ohmic contact at the PEDOT:PSS/ZnO
interface is successfully optimized through a simple solvent treatment of the
PEDOT:PSS film surface, leading to tandem devices with power conversion
efficiencies (PCEs) improved by more than 50% compared to the untreated
reference system. The reported method is an easy and versatile approach to
optimize the functionality of the PEDOT:PSS/ZnO ICL of inverted multijunction
devices, applicable onto any organic active layer and compatible with a
roll-to-roll production line
Integration of a silk fibroin based film as a luminescent down-shifting layer in ITO-free organic solar cells
No full textWe report here a study on the integration of the silk fibroin (SF) protein in organic solar cells. The intrinsic low toxicity, natural availability, biodegradability, water processing, good film forming properties and capability to be doped with functional molecules of SF biopolymer inspired us to integrate it as a transparent and inert or functional bottom layer in organic solar cells. Water stable, optically transparent, smooth and homogeneous SF thin films (thickness ∼400 nm) were successfully prepared on glass and characterized. Then ITO-free bulk heterojunction (BHJ) solar cells employing P3HT:PC61BM as a standard active layer and a highly conductive PEDOT:PSS formulation as a semi-transparent anode were deposited over the SF films. As a result, the power conversion efficiency (PCE) of all silk-integrated BHJ solar cells was comparable to the references on bare glass. The ability of SF to act as a host matrix for functional moieties was exploited to give to the SF layer the functionality of a Luminescent Down-shifting film (LDS), as confirmed by the spectral response measurements, by using a water soluble stilbene derivative (Stb). The photovoltaic performance of all SF-based devices was significantly stable over time, overcoming the problems of the ITO-based reference cells after 70 days. Finally, flexible SF-integrated ITO-free solar cells were successfully fabricated on PET substrates
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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