1,720,983 research outputs found
Replication Data for: Role of Water in Suppressing Recombination Pathways in CH3NH3PbI3 Perovskite Solar Cells
No full textMoisture degradation of halide perovskites is the Achilles heel of perovskite solar cells. A surprising revelation in 2014 about the beneficial effects of controlled humidity in enhancing device efficiencies overthrew established paradigms on perovskite solar cell fabrication. Despite the extensive studies on water additives in perovskite solar cell processing that followed, detailed understanding of the role of water from the photophysical perspective remains lacking; specifically, the interplay between the induced morphological effects and the intrinsic recombination pathways. Through ultrafast optical spectroscopy, we show that both the monomolecular and bimolecular recombination rate constants decrease by approximately 1 order with the addition of an optimal 1% H2O by volume in CH3NH3PbI3 as compared to the reference (without the H2O additive). Correspondingly, the trap density reduces from 4.8 × 1017 cm–3 (reference) to 3.2 × 1017 cm–3 with 1% H2O. We obtained an efficiency of 12.3% for the champion inverted CH3NH3PbI3 perovskite solar cell (1% H2O additive) as compared to the 10% efficiency for the reference cell. Increasing the H2O content further is deleterious for the device. Trace amounts of H2O afford the benefits of surface trap passivation and suppression of trap-mediated recombination, whereas higher concentrations result in a preferential dissolution of methylammonium iodide during fabrication that increases the trap density (MA vacancies). Importantly, our study reveals the effects of trace H2O additives on the photophysical properties of CH3NH3PbI3 films. DOI: 10.1021/acsami.9b0079
Replication Data for: Cation influence on carrier dynamics in perovskite solar cells
No full textRubidium and Cesium cations (Rb+ and Cs+) incorporation recently emerged as a viable strategy to enhance perovskite solar cells (PSCs) efficiency. However, a clear understanding of the impact of these cations on the structure-function relationship in relation to the device performance is severely lacking. Here, we systematically investigate the influence of Rb+ and Cs+ on the carrier dynamics using transient optical spectroscopy and correlate with solar cell performance. Unlike Rb+, Cs+ integrates well with methylammonium (MA+) and formamidinium (FA+) yielding increased perovskite grain size, longer charge carrier lifetimes and improved power conversion efficiency (PCE). Concomitant incorporation of Cs+/Rb+ cooperatively retards radiative recombination by ~60% in the quaternary-cation based perovskite system (RbCsMAFA) compared to the dual-cation MAFA samples. By suppressing the defect density, PCEs around 20% are obtained along with more balanced charge carrier diffusion length and comparable photoluminescence quantum yield in quaternary-cation perovskites. While the synergistic addition of Rb+ and Cs+ is attractive for controlling defects and recombination losses in efficient solar cells development, sole incorporation of Rb+ is still an engineering challenge. Importantly, our study explicates the underlying mechanisms behind the synergistic combination of cations to minimize the charge carrier losses and achieve high efficiency perovskite solar cells
Replication Data for: Interfacial Mechanism for Efficient Resistive Switching in Ruddlesden-Popper Perovskites for Non-Volatile Memories
No full textIon migration, one origin of current–voltage hysteresis, is the bane of halide perovskite optoelectronics. Herein, we leverage this unwelcome trait to unlock new opportunities for resistive switching using layered Ruddlesdsen–Popper perovskites (RPPs) and explicate the underlying mechanisms. The ON/OFF ratio of RPP-based devices is strongly dependent on the layers and peaks at n̅ = 5, demonstrating the highest ON/OFF ratio of ∼104 and minimal operation voltage in 1.0 mm2 devices. Long data retention even in 60% relative humidity and stable write/erase capabilities exemplify their potential for memory applications. Impedance spectroscopy reveals a chemical reaction between migrating ions and the external contacts to modify the charge transfer barrier at the interface to control the resistive states. Our findings explore a new family of facile materials and the necessity of ionic population, migration, and their reactivity with external contacts in devices for switching and memory applications
Replication Data for: Heavy Water Additive in Formamidinium: A Novel Approach to Enhance Perovskite Solar Cell Efficiency
No full textHeavy water or deuterium oxide (D2O) comprises of deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, we herein divulge the serendipitous effect of D2O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple-A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from approximately 19.2% (reference) to 20.8% (using 1 vol% D2O) with higher stability. Ultrafast optical spectroscopy confirms trap states passivation increased carrier recombination lifetimes and enhanced charge carrier diffusion lengths in our deuterated samples. Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy validate the N-H2 group as the preferential isotope exchange site. Furthermore, NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photo-physical properties. First-principles density functional theory calculations reveal a decrease in PbI6 phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI6 structures and weakens the electron-LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, our findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties
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
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
- …
