Query: perovskite light-emitting diodes， MAAc

title: Ionic liquid induced enhanced performance of perovskite light emitting diodes
abstract: Organic inorganic hybrid perovskites (OIHP) have attained a fantastic vigilance as promising light emitting materials because of their low cost production via facile solution processing, high color purity and easily tunable bandgaps. Nevertheless, the fabrication of OIHP films for light emitting diodes generally requires complicated post treatments, such as anti solvent dropping process, owing to poor film formation property of the solvent being used for film deposition. In this work, we employed an ionic liquid, methylammonium acetate (MAAc) as additive to optimize the growth of FAPbBr3 perovskite films via an anti solvent free approach. The influence of MAAc on the crystallization kinetics of FAPbBr3 phase and optoelectronic properties of the resulting perovskite films is systematically investigated. Our results demonstrate that MAAc is an effective modifier to attain perovskite films with reduced grain size, homogeneous grain distribution and smooth surface thereby leading to enhanced average lifetime of the excitons. Perovskite light emitting diodes (PeLEDs) containing FAPbBr3 films obtained via incorporating 10 vol% MAAc as additive exhibited considerably suppressed leakage current with a significant enhancement in the current efficiency (CE) from 0.027 cd/A to 4.85 cd/A. These findings reveal that the incorporation of a suitable additive could play a beneficial role in the formation of well optimized perovskite films which would ultimately lead to the realization of PeLEDs with improved performance.

title: Rational molecular passivation for high performance perovskite light emitting diodes
abstract: A major efficiency limit for solution processed perovskite optoelectronic devices, for example light emitting diodes, is trap mediated non radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non radiative recombination losses. Consequently, we achieve exceptionally high performance near infrared perovskite light emitting diodes with a record external quantum efficiency of 21.6% In addition, our passivated perovskite light emitting diodes maintain a high external quantum efficiency of 20.1% and a wall plug efficiency of 11.0% at a high current density of 200 mA cm 2, making them more attractive than the most efficient organic and quantum dot light emitting diodes at high excitations.Improved understanding of passivation leads to near infrared perovskite light emitting diodes with 21.6% external quantum efficiency.

title: Modulation of recombination zone position for quasi two dimensional blue perovskite light emitting diodes with efficiency exceeding 5%
abstract: In recent years, substantial progress has been made in developing perovskite light emitting diodes with near infrared, red and green emissions and over 20% external quantum efficiency. However, the development of perovskite light emitting diodes with blue emission remains a great challenge, which retards further development of full color displays and white light illumination based on perovskite emissive materials. Here, firstly, through composition and dimensional engineering, we prepare quasi two dimensional perovskite thin films with improved blue emission, taking advantages of reduced trap density and enhanced photoluminescence quantum yield. Secondly, we find a vertically non uniform distribution of perovskite crystals in the PEDOT:PSS/perovskite hybrid film. Through modulating the position of the recombination zone, we activate the majority of quasi two dimensional perovskite crystals, and thus demonstrate the most efficient blue perovskite light emitting diode to date with emission peak at 480 nm, record luminance of 3780 cd m 2 and record external quantum efficiency of 5.7%.Halide perovskite based light emitting diodes attracted intensive research interest recently but the efficiency of blue diodes is much lower than the green and red ones. Here Li et al. push up the efficiency of blue diodes through composition engineering and vertical morphology control.

title: Spectra stable blue perovskite light emitting diodes
abstract: Device performance and in particular device stability for blue perovskite light emitting diodes (PeLEDs) remain considerable challenges for the whole community. In this manuscript, we conceive an approach by tuning the 'A site' cation composition of perovskites to develop blue emitters. We herein report a Rubidium Cesium alloyed, quasi two dimensional perovskite and demonstrate its great potential for pure blue PeLED applications. Composition engineering and in situ passivation are conducted to further improve the material's emission property and stabilities. Consequently, we get a prominent film photoluminescence quantum yield of around 82% under low excitation density. Encouraged by these findings, we finally achieve a spectra stable blue PeLED with the peak external quantum efficiency of 1.35% and a half lifetime of 14.5 min, representing the most efficient and stable pure blue PeLEDs reported so far. The strategy is also demonstrated to be able to generate efficient perovskite blue emitters and PeLEDs in the whole blue spectral region (from 454 to 492 nm).Besides device operational stability, the color stability is also an important challenge for the perovskite light emitting diodes, especially the blue ones. Here Jiang et al. report the most efficient and color stable pure blue perovskite LEDs so far, with a half lifetime of 14.5 minutes.

title: Efficient metal halide perovskite light emitting diodes with significantly improved light extraction on nanophotonic substrates
abstract: Metal halide perovskite has emerged as a promising material for light emitting diodes. In the past, the performance of devices has been improved mainly by optimizing the active and charge injection layers. However, the large refractive index difference among different materials limits the overall light extraction. Herein, we fabricate efficient methylammonium lead bromide light emitting diodes on nanophotonic substrates with an optimal device external quantum efficiency of 17.5% which is around twice of the record for the planar device based on this material system. Furthermore, optical modelling shows that a high light extraction efficiency of 73.6% can be achieved as a result of a two step light extraction process involving nanodome light couplers and nanowire optical antennas on the nanophotonic substrate. These results suggest that utilization of nanophotonic structures can be an effective approach to achieve high performance perovskite light emitting diodes.The rapid development of halide perovskite light emitting diodes mainly relies on the optimization of the active layer and charge injection layers. Here Zhang et al. incorporate three dimensional nanophotonic substrates to enhance light out coupling and achieve high external quantum efficiency of 17.5%

title: High Efficiency Perovskite Light Emitting Diodes with Synergetic Outcoupling Enhancement.
abstract: Perovskite light emitting diodes (PeLEDs) show great application potential in high quality flat panel displays and solid state lighting due to their steadily improved efficiency, tunable colors, narrow emission peak, and easy solution processing capability. However, because of high optical confinement and nonradiative charge recombination during electron photon conversion, the highest reported efficiency of PeLEDs remains far behind that of their conventional counterparts, such as inorganic LEDs, organic LEDs, and quantum dot LEDs. Here a facile route is demonstrated by adopting bioinspired moth eye nanostructures at the front electrode/perovskite interface to enhance the outcoupling efficiency of waveguided light in PeLEDs. As a result, the maximum external quantum efficiency and current efficiency of the modified cesium lead bromide (CsPbBr3 green emitting PeLEDs are improved to 20.3% and 61.9 cd A 1 while retaining spectral and angular independence. Further reducing light loss in the substrate mode using a half ball lens, efficiencies of 28.2% and 88.7 cd A 1 are achieved, which represent the highest values reported to date for PeLEDs. These results represent a substantial step toward achieving practical applications of PeLEDs.

title: Blue perovskite light emitting diodes: progress, challenges and future directions
abstract: We report on the progress, challenges and future directions of blue perovskite light emitting diodes to facilitate their further development.

title: Improved Outcoupling Efficiency and Stability of Perovskite Light Emitting Diodes using Thin Emitting Layers.
abstract: Hybrid organic inorganic perovskite semiconductors have shown potential to develop into a new generation of light emitting diode (LED) technology. Herein, an important design principle for perovskite LEDs is elucidated regarding optimal perovskite thickness. Adopting a thin perovskite layer in the range of 35 40 nm is shown to be critical for both device efficiency and stability improvements. Maximum external quantum efficiencies (EQEs) of 17.6% for Cs0.2 FA0.8 PbI2.8 Br0.2 14.3% for CH3 NH3 PbI3 (MAPbI3 10.1% for formamidinium lead iodide (FAPbI3 and 11.3% for formamidinium lead bromide (FAPbBr3 based LEDs are demonstrated with optimized perovskite layer thickness. Optical simulations show that the improved EQEs source from improved light outcoupling. Furthermore, elevated device temperature caused by Joule heating is shown as an important factor contributing to device degradation, and that thin perovskite emitting layers maintain lower junction temperature during operation and thus demonstrate increased stability.

title: Efficient sky blue perovskite light emitting diodes via photoluminescence enhancement
abstract: The efficiencies of green and red perovskite light emitting diodes (PeLEDs) have been increased close to their theoretical upper limit, while the efficiency of blue PeLEDs is lagging far behind. Here we report enhancing the efficiency of sky blue PeLEDs by overcoming a major hurdle of low photoluminescence quantum efficiency in wide bandgap perovskites. Blending phenylethylammonium chloride into cesium lead halide perovskites yields a mixture of two dimensional and three dimensional perovskites, which enhances photoluminescence quantum efficiency from 1.1% to 19.8% Adding yttrium (III) chloride into the mixture further enhances photoluminescence quantum efficiency to 49.7% Yttrium is found to incorporate into the three dimensional perovskite grain, while it is still rich at grain boundaries and surfaces. The yttrium on grain surface increases the bandgap of grain shell, which confines the charge carriers inside grains for efficient radiative recombination. Record efficiencies of 11.0% and 4.8% were obtained in sky blue and blue PeLEDs, respectively. Despite the rapid progress on perovskite light emitting diodes (PeLEDs) the efficiency of blue PeLEDs is lagging behind. Here Wang et al. employ yttrium (III) chloride additive to yield enhanced photoluminescence in the perovskite materials and thus record high device efficiencies for sky blue and blue PeLEDs.

title: Efficient blue light emitting diodes based on quantum confined bromide perovskite nanostructures
abstract: The emergence of inorganic organic hybrid perovskites, a unique class of solution processable crystalline semiconductors, provides new opportunities for large area, low cost and colour saturated light emitting diodes (LEDs) ideal for display and solid state lighting applications1. However, the performance of blue perovskite LEDs (PeLEDs)2 11 is far inferior to that of their near infrared, red and green counterparts12 19, strongly limiting the practicality of the PeLED technology. Here, we demonstrate blue PeLEDs emitting at 483 nm with colour coordinates of (0.094, 0.184) and operating with a peak external quantum efficiency of up to 9.5% at a luminance of 54 cd m 2. The devices have a T50 lifetime of 250 s for an initial brightness of 100 cd m 2. The efficient blue electroluminescence originates from a structure of quantum confined perovskite nanoparticles embedded within quasi two dimensional phases with higher bandgaps, prepared by an antisolvent processing scheme. Our work paves the way towards high performance PeLEDs in the blue region. Blue light emitting diodes based on perovskite nanostructures embedded within quasi two dimensional phases show highly effective charge injection and suppressed non radiative recombination.