Metal halide perovskites (MHPs) have numerous advantages as light emitters such as high photoluminescence quantum efficiency with a direct bandgap, very narrow emission linewidth, high charge‐carrier ...mobility, low energetic disorder, solution processability, simple color tuning, and low material cost. Based on these advantages, MHPs have recently shown unprecedented radical progress (maximum current efficiency from 0.3 to 42.9 cd A−1) in the field of light‐emitting diodes. However, perovskite light‐emitting diodes (PeLEDs) suffer from intrinsic instability of MHP materials and instability arising from the operation of the PeLEDs. Recently, many researchers have devoted efforts to overcome these instabilities. Here, the origins of the instability in PeLEDs are reviewed by categorizing it into two types: instability of (i) the MHP materials and (ii) the constituent layers and interfaces in PeLED devices. Then, the strategies to improve the stability of MHP materials and PeLEDs are critically reviewed, such as A‐site cation engineering, Ruddlesden–Popper phase, suppression of ion migration with additives and blocking layers, fabrication of uniform bulk polycrystalline MHP layers, and fabrication of stable MHP nanoparticles. Based on this review of recent advances, future research directions and an outlook of PeLEDs for display applications are suggested.
Recent progress in understanding the origins of the low stability of metal halide perovskite (MHP) materials and light‐emitting diodes (PeLEDs) is reviewed. Various strategies to overcome the low stability are discussed with a special focus on the MHP material stability and operational stability of the PeLEDs. Future research directions to improve the stability are also suggested.
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2.
Metal halide perovskite light emitters Kim, Young-Hoon; Cho, Himchan; Lee, Tae-Woo
Proceedings of the National Academy of Sciences - PNAS,
10/2016, Volume:
113, Issue:
42
Journal Article
Peer reviewed
Open access
Twenty years after layer-type metal halide perovskites were successfully developed, 3D metal halide perovskites (shortly, perovskites) were recently rediscovered and are attracting multidisciplinary ...interest from physicists, chemists, and material engineers. Perovskites have a crystal structure composed of five atoms per unit cell (ABX₃) with cation A positioned at a corner, metal cation B at the center, and halide anion X at the center of six planes and unique optoelectronic properties determined by the crystal structure. Because of very narrow spectra (full width at half-maximum ≤20 nm), which are insensitive to the crystallite/grain/particle dimension and wide wavelength range (400 nm ≤ λ ≤ 780 nm), perovskites are expected to be promising high-color purity light emitters that overcome inherent problems of conventional organic and inorganic quantum dot emitters. Within the last 2 y, perovskites have already demonstrated their great potential in light-emitting diodes by showing high electroluminescence efficiency comparable to those of organic and quantum dot light-emitting diodes. This article reviews the progress of perovskite emitters in two directions of bulk perovskite polycrystalline films and perovskite nanoparticles, describes current challenges, and suggests future research directions for researchers to encourage them to collaborate and to make a synergetic effect in this rapidly emerging multidisciplinary field.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of ...perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr₃ nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr₃ nanograin layers.
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Bright organic/inorganic hybrid perovskite light‐emitting diodes (PrLEDs) are realized by using CH3NH3PbBr3 as an emitting layer and self‐organized buffer hole‐injection layer (Buf‐HIL). The PrLEDs ...show high luminance, current efficiency, and EQE of 417 cd m−2, 0.577 cd A−1, and 0.125%, respectively. Buf‐HIL can facilitate hole injection into CH3NH3PbBr3 as well as block exciton quenching.
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Colloidal metal–halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter D B (quantum size regime) emerged as promising light emitters due to their spectrally narrow ...light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > D B (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than D B show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic–inorganic metal–halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.
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Electron‐injecting interlayers (ILs) which are stable in air, inject electrons efficiently, block holes, and block quenching of excitons, are very important to realize efficient inverted polymer ...light‐emitting diodes (IPLEDs). Two air‐stable polymer electron‐injecting interlayers (ILs), branched polyethyleneimine (PEI) and polyethyleneimine ethoxylated (PEIE) for use in IPLEDs are introduced, and the roles of the ILs in IPLEDs comparing these with a conventional Cs2CO3 IL are elucidated. These polymer ILs can reduce the electron injection barrier between ZnO and emitting layer by decreasing the work function (WF) of underlying ZnO, thereby effectively facilitating electron injection into the emitting layer. WF of ZnO covered by PEI is found to be lower than that covered by PEIE due to higher N+/C ratio of PEI. Furthermore, they can block the quenching of excitons and increase the luminous efficiency of devices. Thus, IPLEDs with PEI IL of optimum thickness (8 nm) show current efficiency (13.5 cd A–1), which is dramatically higher than that of IPLEDs with a Cs2CO3 IL (8 cd A‐1).
Efficient and air‐stable inverted polymer‐light emitting diodes (IPLEDs) can be realized by using insulating polymer electron‐injecting interlayers (ILs), branched polyethyleneimine (PEI), and polyethyleneimine ethoxylated (PEIE), giving highest current efficiencies of 13.5 cd A‐1 and 12 cd A‐1, respectively. Polymer ILs can facilitate electron injection into emitting layer as well as block the exciton quenching.
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In patients with acute myocardial infarction receiving potent antiplatelet therapy, the bleeding risk remains high during the maintenance phase. We sought data on a uniform unguided de-escalation ...strategy of dual antiplatelet therapy (DAPT) from ticagrelor to clopidogrel after acute myocardial infarction.
In this open-label, assessor-masked, multicentre, non-inferiority, randomised trial (TALOS-AMI), patients at 32 institutes in South Korea with acute myocardial infarction receiving aspirin and ticagrelor without major ischaemic or bleeding events during the first month after index percutaneous coronary intervention (PCI) were randomly assigned in a 1:1 ratio to a de-escalation (clopidogrel plus aspirin) or active control (ticagrelor plus aspirin) group. Unguided de-escalation without a loading dose of clopidogrel was adopted when switching from ticagrelor to clopidogrel. The primary endpoint was a composite of cardiovascular death, myocardial infarction, stroke, or bleeding type 2, 3, or 5 according to Bleeding Academic Research Consortium (BARC) criteria from 1 to 12 months. A non-inferiority test was done to assess the safety and efficacy of de-escalation DAPT compared with standard treatment. The hazard ratio (HR) for de-escalation versus active control group in a stratified Cox proportional hazards model was assessed for non-inferiority by means of an HR margin of 1·34, which equates to an absolute difference of 3·0% in the intention-to-treat population and, if significant, a superiority test was done subsequently. To ensure statistical robustness, additional analyses were also done in the per-protocol population. This trial is registered at ClinicalTrials.gov, NCT02018055.
From Feb 26, 2014, to Dec 31, 2018, from 2901 patients screened, 2697 patients were randomly assigned: 1349 patients to de-escalation and 1348 to active control groups. At 12 months, the primary endpoints occurred in 59 (4·6%) in the de-escalation group and 104 (8·2%) patients in the active control group (pnon-inferiority<0·001; HR 0·55 95% CI 0·40–0·76, psuperiority=0·0001). There was no significant difference in composite of cardiovascular death, myocardial infarction, or stroke between de-escalation (2·1%) and the active control group (3·1%; HR 0·69; 95% CI 0·42–1·14, p=0·15). Composite of BARC 2, 3, or 5 bleeding occurred less frequently in the de-escalation group (3·0% vs 5·6%, HR 0·52; 95% CI 0·35–0·77, p=0·0012).
In stabilised patients with acute myocardial infarction after index PCI, a uniform unguided de-escalation strategy significantly reduced the risk of net clinical events up to 12 months, mainly by reducing the bleeding events.
ChongKunDang Pharm, Medtronic, Abbott, and Boston Scientific.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Ruddlesden–Popper phase (RP‐phase) perovskites that consist of 2D perovskite slabs interleaved with bulky organic ammonium (OA) are favorable for light‐emitting diodes (LEDs). The critical limitation ...of LED applications is that the insulating OA arranged in a preferred orientation limits charge transport. Therefore, the ideal solution is to achieve a randomly connected structure that can improve charge transport without hampering the confinement of the electron–hole pair. Here, a structurally modulated RP‐phase metal halide perovskite (MHP), (PEA)2(CH3NH3)m−1PbmBr3m+1 is introduced to make the randomly oriented RP‐phase unit and ensure good connection between them by applying modified nanocrystal pinning, which leads to an increase in the efficiency of perovskite LEDs (PeLEDs). The randomly connected RP‐phase MHP forces contact between inorganic layers and thereby yields efficient charge transport and radiative recombination. Combined with an optimal dimensionality, (PEA)2(CH3NH3)2Pb3Br10, the structurally modulated RP‐phase MHP exhibits increased photoluminescence quantum efficiency, from 0.35% to 30.3%, and their PeLEDs show a 2,018 times higher current efficiency (20.18 cd A−1) than in the 2D PeLED (0.01 cd A−1) and 673 times than in the 3D PeLED (0.03 cd A−1) using the same film formation process. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs.
Ruddlesden–Popper phase (RP‐phase) perovskites are promising materials for optoelectronic devices. Efficient RP‐phase perovskite light‐emitting diodes (PeLEDs) are developed by introducing a structurally modulated RP‐phase metal halide perovskite (MHP) emitter to increase the charge transport ability without hampering the confinement of the electron–hole pair. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs.
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Highly efficient, simplified, solution‐processed thermally activated delayed‐fluorescence organic light‐emitting diodes can be realized by using pure‐organic thermally activated delayed fluorescence ...emitters and a multifunctional buffer hole‐injection layer, in which high EQE (≈24%) and current efficiency (≈73 cd A−1) are demonstrated. High‐efficiency fluorescence red‐emitting and blue‐emitting devices can also be fabricated in this manner.
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In this work, a series of mixed matrix membranes (MMMs) consisting of Pebax® 1657 as the main polymer matrix, poly(ethylene glycol) (PEG) derivatives with low molecular weights as additives, and ...graphene oxide (GO) with different loadings as a nanofiller, were prepared for CO2/N2 separation. Changes in the amorphous and crystalline regions of Pebax®/PEG blend membranes and in the free volume of GO-embedded MMMs were estimated based on differential scanning calorimetry (DSC) thermograms. The fractional free volume and density of the Pebax®/PEG blend membranes were investigated according to additive models. Particularly, blending poly(ethylene glycol) methyl ethyl acrylate (PEG-MEA) with the Pebax® matrix significantly improved CO2 permeability without sacrificing high CO2/N2 selectivity. Incorporating GO nanosheets up to 0.3 wt% into the Pebax®/PEG-MEA matrix was found to have a considerable impact on increasing CO2/N2 selectivity, due to largely in part to an increase in the CO2 solubility coefficients. Upon a further increase in GO loading, both CO2 permeability and CO2/N2 selectivity decreased as a result of increasing tortuosity for gas diffusion and also GO aggregation at high GO loading content. More importantly, the Pebax®/PEG-MEA blend membrane with the optimized loading of GO, i.e., 0.3 wt% indicated outstanding anti-CO2 plasticization resistance up to 10 bar as well as long-term stability over 100 days without significant deterioration of CO2/N2 separation performance.
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•Graphene Oxide (GO)-embedded mixed matrix membranes (MMMs) were systematically designed with two additives.•GO-embedded MMMs show both higher CO2 permeability and CO2/N2 selectivity beyond the upper bound.•The effect of GO on transport property of MMMs was explained using solution-diffusion model.•Incorporating GO nanosheets in MMMs play a significant role against CO2-induced plasticization.
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