1,721,013 research outputs found
White light emission in low-dimensional perovskites
No full textLow-dimensional perovskites are rapidly emerging due to their distinctive emission properties, consisting of ultrabroad and highly Stokes shifted luminescence with pure white light chromaticity, which makes them very attractive for solution-processed light-emitting devices and scintillators. To foster the design of new materials and their device applications, it is timely to review the relation between perovskite structural properties and the photophysical phenomena underlying their unique light emission characteristics. From a number of recent studies, it has emerged that broadband emission properties in metal halide frameworks are very common, stemming from the self-localization of small polaron species at specific sites of the inorganic lattice, with a wide energy distribution. This review aims to provide an account of the current understanding of the photophysical processes underpinning luminescence broadening and highly efficient emission in various classes of low-dimensional metal-halide frameworks, and to highlight their potential for solution-processed optoelectronic device applications. The discussion will additionally establish a wider perspective on the role of intrinsic and extrinsic self-trapping, formation of polarons and their effect on charge generation and transport in low-dimensional perovskites
Lead iodide perovskite light-emitting field-effect transistor
No full textDespite the widespread use of solution-processable hybrid organic-inorganic perovskites in photovoltaic and light-emitting applications, determination of their intrinsic charge transport parameters has been elusive due to the variability of film preparation and history-dependent device performance. Here we show that screening effects associated to ionic transport can be effectively eliminated by lowering the operating temperature of methylammonium lead iodide perovskite (CH3NH3PbI3) field-effect transistors. Field-effect carrier mobility is found to increase by almost two orders of magnitude below 200 K, consistent with phonon scattering-limited transport. Under balanced ambipolar carrier injection, gate-dependent electroluminescence is also observed from the transistor channel, with spectra revealing the tetragonal to orthorhombic phase transition. This demonstration of CH3NH3PbI3 light-emitting field-effect transistors provides intrinsic transport parameters to guide materials and solar cell optimization, and will drive the development of new electro-optic device concepts, such as gated light-emitting diodes and lasers operating at room temperature
CH3NH3PbI3 perovskite light emitting field-effect transistor
No full textHybrid organic-inorganic perovskites have emerged as excellent solution-processable materials for photovoltaic applications [1]. Recently, their light emission properties have also attracted considerable attention for light-emitting devices [2,3]. Here we demonstrate CH3NH3PbI3 light emitting field-effect transistor (LE-FET), a new device concept in perovskite-based optoelectron
AC-driven perovskite light-emitting field-effect transistors
No full textSummary form only given. In recent years, hybrid organic-inorganic perovskites has drawn great attention towards applications in light-emitting devices such as light-emitting diodes [1], X-ray scintillators [2] and lasers [3]. Recently we have demonstrated a perovskite light-emitting field-effect transistors (PeLEFETs) [4] operating at low temperatures, with gate-controlled carrier injection and recombination zone. Despite the balanced carrier injection provided by the FET configuration, the performance of these devices is strongly affected by ionic transport effects which cause large hysteresis and hinder operation at room temperature.In this work we present an improved CH3NH3PbI3 PeLEFET with bottom gate, top contact configuration (Fig. 1a), which, compared to the previously reported bottom gate bottom contact configuration [4], yields a tenfold improvement of the field-effect electron mobility, up to 0.1 cm2V-1s-1 and 0.01 cm2V-1s-1 for holes. Furthermore, we show that AC-driven gate bias modulation, allows minimizing the ionic drift within the perovskite channel, hence reducing the effects of the ionic screening and increasing the brightness of electroluminescence compared to its DC-driven counterpart at comparable voltages
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
Optical Gain of Lead Halide Perovskites Measured via the Variable Stripe Length Method: What We Can Learn and How to Avoid Pitfalls
Full text linkIn the search for novel photonic materials, the recent focus on metal halide perovskites (MHPs) has revealed their promise to become groundbreaking low-threshold, tunable coherent light sources. An accurate determination of the optical gain coefficient (g) would help to screen for materials and design highly efficient perovskite lasers. Nevertheless, contradictory numbers are continuously reported, making this figure of merit unreliable. To address this issue, the present work outlines a meticulous analysis to retrieve g of MAPbI3, based on the variable stripe-length (VSL) method. This method is often preferred due to its apparent simplicity; however, one can arrive at incorrect conclusions without the adequate considerations. Therefore, here the experimental implementation and numerical treatment of the data are thoroughly discussed to establish a robust VSL methodology. The obtained power dependence and spectral gain evolution point to the role of electron–hole bimolecular recombination dictating the stimulated emission properties of MAPbI3, with a behavior resembling that of bulk GaAs. Beyond providing further knowledge on the procedure to carry out pertinent VSL measurements, this work also outlines a meticulous methodology to study the underlying photophysical gain properties of MHPs and consequently, to obtain a deeper understanding of the lasing properties of these complex materials
Defect Engineering in 2D Perovskite by Mn(II) Doping for Light-Emitting Applications
No full textLow-dimensional perovskites are considered good candidates for light-emitting applications given their high exciton binding energy. Yet, single-layered two-dimensional (2D) perovskites are strongly limited by trap-assisted recombination and suffer from low luminescence yields, hampering their application in electroluminescence devices. Here, we use synthetic and defect engineering strategies to overcome such issues. We employ metallic doping (Mn2+ and Eu3+) to introduce luminescent impurities in the 2D perovskite NMA2PbX4 (NMA = 1-naphtylmethylammonium). By means of temperature-dependent and time-resolved spectroscopy, we demonstrate efficient energy transfer to Mn2+ centers. This avoids funneling of photo-excited species in inefficient recombination channels, enhancing photoluminescence and giving a quantum yield surpassing 20% in doped films. Eventually, we embody Mn-doped NMA2PbBr4 in a light-emitting diode architecture and show electroluminescence from the Mn2+ 4T1 → 6A1 transition. This proof-of-concept demonstration shows the potential of doping in layered perovskites and prompts the study of a wider range of host-guest structures. Metal halide perovskites have emerged for light-emitting applications, such as light-emitting diodes (LEDs). While intensive research has focused on three-dimensional (3D) perovskites, layered perovskites are also gaining interest for their peculiar light-emitting properties. The higher exciton binding energy of low-dimensional perovskites is considered beneficial to improve the radiative recombination efficiency. However, the luminescence yield of single-layered two-dimensional (2D) perovskites is severely lowered by trap-assisted recombination. By including Mn2+ and Eu3+ in a 2D perovskite, we show that metallic doping can be exploited to enhance and tune its luminescence. Efficient energy transfer from the perovskite to the dopant is achieved, provided that a suitable energy level alignment of the host-guest system is realized. We show that such a mechanism can be exploited to tune the material's electroluminescence in a proof-of-concept LED based on a Mn-doped 2D perovskite. Cortecchia et al. report the use of metallic dopants to overcome the detrimental trap-mediated non-radiative recombination processes, lowering the luminescence yield in two-dimensional perovskites. This results in tuning and enhancement of the perovskite's luminescence properties. In particular, efficient energy transfer and high luminescence yield are obtained with manganese doping. This strategy is shown to be suitable for application in light-emitting diodes
Self-Powered Edible Defrosting Sensor
Full text linkImproper freezing of food causes food waste and negatively impacts the environment. In this work, we propose a device that can detect defrosting events by coupling a temperature-activated galvanic cell with an ionochromic cell, which is activated by the release of ions during current flow. Both the components of the sensor are fabricated through simple and low-energy-consuming procedures from edible materials. The galvanic cell operates with an aqueous electrolyte solution, producing current only at temperatures above the freezing point of the solution. The ionochromic cell exploits the current generated during the defrosting to release tin ions, which form complexes with natural dyes, causing the color change. Therefore, this sensor provides information about defrosting events. The temperature at which the sensor reacts can be tuned between 0 and -50 °C. The device can thus be flexibly used in the supply chain: as a sensor, it can measure the length of exposure to above-the-threshold temperatures, while as a detector, it can provide a signal that there was exposure to above-the-threshold temperatures. Such a device can ensure that frozen food is handled correctly and is safe for consumption. As a sensor, it could be used by the workers in the supply chain, while as a detector, it could be useful for end consumers, ensuring that the food was properly frozen during the whole supply chain
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
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