Metal halide perovskites have excellent optical and electrical properties and can be easily processed
via
low-cost solution-based techniques like blade-coating and inkjet printing, promising a bright ...future for various optoelectronic applications. Recently, encouraging progress has been made in perovskite light-emitting diodes (PeLEDs). Green, red, and near-infrared PeLEDs have achieved high external quantum efficiencies of more than 20%. However, as historically blue electroluminescence remains challenging in all previous LED technologies, we are witnessing a similar case with the development of blue PeLEDs, an essential part of displays and solid-state lighting, which lag far behind those of their counterparts. Herein, we review the recent progress of blue PeLEDs and discuss the main challenges including colour instability, poor photoluminescence efficiency and emission quenching by interlayers. Future directions are provided to facilitate the development of efficient blue PeLEDs.
We report on the progress, challenges and future directions of blue perovskite light-emitting diodes to facilitate their further development.
Nearly 100% triplet harvesting in conventional fluorophor‐based organic light‐emitting devices is realized through energy transfer from exciplex. The best C545T‐doped device using the exciplex host ...exhibits a maximum current efficiency of 44.0 cd A‐1, a maximum power efficiency of 46.1 lm W‐1, and a maximum external quantum efficiency of 14.5%.
A high‐performance hybrid white organic light‐emitting device (WOLED) is demonstrated based on an efficient novel thermally activated delayed fluorescence (TADF) blue exciplex system. This device ...shows a low turn‐on voltage of 2.5 V and maximum forward‐viewing external quantum efficiency of 25.5%, which opens a new avenue for achieving high‐performance hybrid WOLEDs with simple structures.
High‐efficiency, thermally activated delayed‐fluorescence organic light‐emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high ...external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high‐efficiency organic light‐emitting diodes, for future use in displays and lighting applications.
Perovskite light‐emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure‐red (620−660 nm) light emission, ...an essential part for full‐color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden–Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge‐transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP‐based pure‐red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure‐red or even pure‐blue PeLEDs with high performance.
A simple and general strategy of spacer cation alloying is developed to modulate the thickness distribution of quantum wells in Ruddlesden–Popper perovskite films. Based on this method, efficient perovskite light‐emitting diodes with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak external quantum efficiencies up to 11.5%.
Recently, Ruddlesden–Popper perovskites (RPPs) have attracted increasing interests due to their promising stability. However, the efficiency of solar cells based on RPPs is much lower than that based ...on 3D perovskites, mainly attributed to their poor charge transport. Herein, a simple yet universal method for controlling the quality of RPP films by a synergistic effect of two additives in the precursor solution is presented. RPP films achieved by this method show (a) high quality with uniform morphology, enhanced crystallinity, and reduced density of sub‐bandgap states, (b) vertically oriented perovskite frameworks that facilitate efficient charge transport, and (c) type‐II band alignment that favors self‐driven charge separation. Consequently, a hysteresis‐free RPP solar cell with a power conversion efficiency exceeding 12%, which is much higher than that of the control device (1.5%), is achieved. The findings will spur new developments in the fabrication of high‐quality, aligned, and graded RPP films essential for realizing efficient and stable perovskite solar cells.
A simple and universal method involving the use of two synergistic additives (dimethylsulfoxide and methylammonium chloride) into precursor solution is reported for growing high‐quality Ruddlesden–Popper perovskite films. Based on this method, hysteresis‐free solar cells with power conversion efficiencies over 12% and excellent reproducibility are achieved.
Metal halide perovskites have shown promising optoelectronic properties suitable for light-emitting applications. The development of perovskite light-emitting diodes (PeLEDs) has progressed rapidly ...over the past several years, reaching high external quantum efficiencies of over 20%. In this Review, we focus on the key requirements for high-performance PeLEDs, highlight recent advances on materials and devices, and emphasize the importance of reliable characterization of PeLEDs. We discuss possible approaches to improve the performance of blue and red PeLEDs, increase the long-term operational stability and reduce toxicity hazards. We also provide an overview of the application space made possible by recent developments in high-efficiency PeLEDs.
Studies of novel coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have reported varying estimates of epidemiological parameters, ...including serial interval distributions-i.e., the time between illness onset in successive cases in a transmission chain-and reproduction numbers. By compiling a line-list database of transmission pairs in mainland China, we show that mean serial intervals of COVID-19 shortened substantially from 7.8 to 2.6 days within a month (9 January to 13 February 2020). This change was driven by enhanced nonpharmaceutical interventions, particularly case isolation. We also show that using real-time estimation of serial intervals allowing for variation over time provides more accurate estimates of reproduction numbers than using conventionally fixed serial interval distributions. These findings could improve our ability to assess transmission dynamics, forecast future incidence, and estimate the impact of control measures.
Ship detection from synthetic aperture radar (SAR) imagery is a fundamental and significant marine mission. It plays an important role in marine traffic control, marine fishery management, and marine ...rescue. Nevertheless, there are still some challenges hindering accuracy improvements of SAR ship detection, e.g., complex background interferences, multi-scale ship feature differences, and indistinctive small ship features. Therefore, to address these problems, a novel quad feature pyramid network (Quad-FPN) is proposed for SAR ship detection in this paper. Quad-FPN consists of four unique FPNs, i.e., a DEformable COnvolutional FPN (DE-CO-FPN), a Content-Aware Feature Reassembly FPN (CA-FR-FPN), a Path Aggregation Space Attention FPN (PA-SA-FPN), and a Balance Scale Global Attention FPN (BS-GA-FPN). To confirm the effectiveness of each FPN, extensive ablation studies are conducted. We conduct experiments on five open SAR ship detection datasets, i.e., SAR ship detection dataset (SSDD), Gaofen-SSDD, Sentinel-SSDD, SAR-Ship-Dataset, and high-resolution SAR images dataset (HRSID). Qualitative and quantitative experimental results jointly reveal Quad-FPN’s optimal SAR ship detection performance compared with the other 12 competitive state-of-the-art convolutional neural network (CNN)-based SAR ship detectors. To confirm the excellent migration application capability of Quad-FPN, the actual ship detection in another two large-scene Sentinel-1 SAR images is conducted. Their satisfactory detection results indicate the practical application value of Quad-FPN in marine surveillance.
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