1,720,972 research outputs found
Semitransparent Design of Planar n-i-p Perovskite Solar Cells using a Cost-Effective, Perovskite-Compatible DMD Structure as the Top Electrode
No full textIn recent years, a significant emphasis has been placed on developing multi-functional solar cells that integrate new features such as color and transparency, thereby opening up the possibility of unconventional photovoltaic (PV) applications, including building-integrated PV (BIPV) systems, tandem solar cells, and wearable electronics. In particular, the integration of semitransparent (ST) solar cells into buildings as power-generating windows, facades or other aesthetic architectural elements constitutes one of the most intriguing perspectives [1]. Since silicon-based panels are generally opaque and unaesthetic, there has been a growing research interest in emerging thin-film solar cells that can be made truly semitransparent, display different colors, and be easily adapted to any type and surface of buildings. Among third-generation PVs, perovskite solar cells (PSCs) are particularly attractive for these applications owing to their superior performances. Over the past few years, tremendous efforts have been applied to develop esthetic semitransparent perovskite solar cells (ST-PSCs) by exploring various kinds of transparent electrodes, controlling the morphology, and engineering the bandgap of the perovskite absorber [2].
Here, a novel multilayer dielectric/metal/dielectric (DMD) transparent electrode based on non-precious copper (Cu) and molybdenum suboxide (MoOx) is manufactured via thermal evaporation and successfully incorporated as top anode in semitransparent planar n-i-p PSCs. Continuous and percolative Cu films as thin as 9.5 nm are grown onto the oxide surface by means of a pre-deposited ultra-thin Au seed layer, which also acts as an effective Cu diffusion barrier. The final MoOx/Au-seed/Cu/MoOx DMD structure shows a very good trade-off between optical transparency and electrical conductivity as well as a great thermal and mechanical stability. Whilst silver and gold are typically used in such DMD structures [3], their replacement with copper allows for a substantial cost reduction without sacrificing the device performance and stability. Through this strategy, PCEs as high as 12.5%, along with acceptable transparency levels, are successfully achieved. It is also demonstrated that the performance of the fabricated devices can be further improved by introducing specific interfacial layers as well as by incorporating appropriate solvent additives into the perovskite precursor solution.
References
[1] C. J. Traverse, R. Pandey, M. C. Barr, R. R. Lunt, Nat. Energy 2017, 2, 849.
[2] Q. Xue, R. Xia, C. J. Brabec, H.-L. Yip, Energy Environ. Sci. 2018, 11 (7), 1688.
[3] E. Della Gaspera, Y. Peng, Q. Hou, L. Spiccia, U. Bach, J. J. Jasieniak, Y.-B. Cheng, Nano Energy 2015, 13, 249.
[4] G. Giuliano, S. Cataldo, M. Scopelliti, F. Principato, D. Chillura Martino, T. Fiore, B. Pignataro, Adv. Mater. Technol. 2019, 4 (5), 1800688
Improved performance in flexible organic solar cells by using copolymeric phase-separation modulators
Full text linkOne of the main problems related to the low performance of the organic solar cells (OSCs), concerns the low mobility of the materials constituting the heterojunction. Indeed, the poor charge transport in the active layer is the principal cause of a competition between separation and recombination of the photogenerated carriers. In this regard, a major obstacle to enhance OSCs efficiency is developing strategies to optimize the exciton dissociation and, consequently, the charge collection at the electrodes. Donor and acceptor systems must be well mixed on the length scale of 5 – 20 nm (exciton diffusion length) to meet the criteria for efficient exciton dissociation. In addition, the network structure should involve continuous donor-acceptor pathways for efficient carrier transport. The most common practice to achieve this goal is by thermal or solvent annealing of active layer.[1] However, this approach often leads to an unwanted phase segregation with formation of large domains where only a small fraction of excitons could diffuse to the donor-acceptor interface.[2] In this work, we show how this challenge is achievable by incorporating phase-separation modulators into bulk heterojunction (BHJ). In particular, three copolymers based on polythiophene and C60 units have been designed, easily synthesized, characterized, and employed as additive in P3HT:PCBM devices. The effect of the thienyl spacer length between C60 monomers on optoelectronic properties, morphology, and structure of heterojunction has been examined using several techniques (NMR, FTIR, XPS, XRD and AFM). We observed that small quantities of these systems can play a critical role in tuning the device morphology by improving the phase separation in thin film heterojunction.[3] In particular, these copolymers act as phase separation modulators by controlling the growth of donor/acceptor domains in the heterojunction, during the thermal annealing process. Indeed, by employing copolymers containing oligothiophenic chains with size of about 8 nm, a large number of domains with a size comparable to the length scale of exciton diffusion are generated, resulting in the highest power conversion efficiency (PCE) (4.46 %) and short current density (JSC) (16.15 mA cm-2) values reported so far for P3HT:PCBM solar cells on plastic substrates. Moreover, the results obtained in preliminary investigations on the other devices containing different fullerene acceptors seem to show the effectiveness and the generality of our approach. Finally, bending tests showed that OSCs with copolymers maintain higher level of performance than reference devices, thus giving new perspectives to applications of flexible photovoltaics
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
Carbon nanotubes and Organic Solar Cells
No full textThe use of carbon nanotubes in photovoltaics is still challenging due to different issues connected to
their synthesis, purification, functionalization, processing and device integration. From this perspective
at first we review on selected contributions dealing with the above issues; then we focus on the
advantages and limitations of carbon nanotubes for the development of organic solar cells
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
Inkjet Printing Quasi-Miscible Droplets for Pseudo-Planar Organic Heterojunctions
No full textThe control of droplet mixing is of great interest for fundamental science (e.g. biomolecular
analysis, molecular diffusion, analytes separation) and emerging technologies in lab-on-chip devices (e.g. multiplexed biochips, micrototal analysis systems, Point-of-care) [1]. In this scenario, printing methodologies are a scalable and versatile approach for droplets production, resulting in
bespoke life-inspired platforms applicable to a vast range of disciplines [2], e.g. materials sciences, sensors, flexible electronics, and biotechnologies. Based on the rapid development of printing
techniques for the fabrication of photovoltaic devices [3], this work shows an innovative platform involving inkjet printing to fabricate pseudo-planar heterojunction (PHJ) organic solar cells (OSC)
on ITO/PET [4]. The process is based on the sequential deposition of two quasi-miscible inks
containing poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), the model donor/acceptor couple for OSCs. The optimization of printing process consists in finding
a suitable ink formulation (chlorobenzene based for P3HT and chlorobenzene:dichlorometane in the
ratio 1:1 for PCBM), droplet velocity (about 7-8 m/s), droplet spacing ȝP, ultimately leading
to satellites-free spherical picolitre-scale droplets resulting in a continuous film on the ITO/PET
support. The chemical analysis of the PCBM-on-P3HT printed film is realized by atomic force
microscopy, X-ray photoelectron spectroscopy and fluorescence spectroscopy. The morphology is
characterized by a continuous and low roughness surface at the center of a printed droplet (average
roughness is about 1.3 nm), whereas nanometric aggregates at the droplet border are observed, as a
result of Marangoni flows mainly involving PCBM molecules. Such instabilities bringing molecular
recirculation to the droplet border agree with models developed for bisolvent droplets evaporation
[5]. XPS depth profile under mild sputtering (1 kV) permits to analyze the two printed layers,
demonstrating the lack of the separation of the P3HT and PCBM layers due the occurrence of
complete mixing. The almost complete quenching of the P3HT fluorescence emission band at about
655 nm due to the PCBM layer printed on top of P3HT confirms the effective formation of an
interface between the two films. The characterization of the solar cell device allows demonstrating
the goodness of the proposed approach, since the extracted parameters are quite similar (in
particular the power conversion efficiency) to those realized in a previous reference study which
employs spin coating deposition of the same materials in a glove box under inert nitrogen
atmosphere [6]. In conclusion, this study is a first step towards the analysis of functional interfaces
for the realization of a new class of inkjet printed PHJs and, in general, printed mixing interfaces
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