The use of CRISPR-Cas9 as a therapeutic reagent is hampered by its off-target effects. Although rationally designed S. pyogenes Cas9 (SpCas9) variants that display higher specificities than the ...wild-type SpCas9 protein are available, these attenuated Cas9 variants are often poorly efficient in human cells. Here, we develop a directed evolution approach in E. coli to obtain Sniper-Cas9, which shows high specificities without killing on-target activities in human cells. Unlike other engineered Cas9 variants, Sniper-Cas9 shows WT-level on-target activities with extended or truncated sgRNAs with further reduced off-target activities and works well in a preassembled ribonucleoprotein (RNP) format to allow DNA-free genome editing.
Photonic synapses combine sensing and processing in a single device, so they are promising candidates to emulate visual perception of a biological retina. However, photonic synapses with wavelength ...selectivity, which is a key property for visual perception, have not been developed so far. Herein, organic photonic synapses that selectively detect UV rays and process various optical stimuli are presented. The photonic synapses use carbon nitride (C3N4) as an UV‐responsive floating‐gate layer in transistor geometry. C3N4 nanodots dominantly absorb UV light; this trait is the basis of UV selectivity in these photonic synapses. The presented devices consume only 18.06 fJ per synaptic event, which is comparable to the energy consumption of biological synapses. Furthermore, in situ modulation of exposure to UV light is demonstrated by integrating the devices with UV transmittance modulators. These smart systems can be further developed to combine detection and dose‐calculation to determine how and when to decrease UV transmittance for preventive health care.
To selectively detect and process UV exposure information, photonic synapses that emulate functions of a retina are demonstrated by using UV‐responsive 2D C3N4 nanodot layers. Depending on the degree of UV exposure, in situ modulation of exposure to UV light is demonstrated by integrating C3N4‐based photonic synapses with UV‐transmittance modulators.
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.
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.
Metal‐halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely ...tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light‐emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted efforts to increase the LE of MHP emitters and PeLEDs. Within three and half years, PeLEDs have shown rapidly increased LE from external quantum efficiency ≈0.1% to ≈14.36%. Herein, the factors that limit the LE of PeLEDs are reviewed; the factors are characterized into the following groups: i) photophysical properties of MHP crystals, ii) morphological factors of MHP layers, and iii) problems caused by device architectures. Then, the strategies to overcome those luminescence‐limiting factors in MHP emitters and PeLEDs are critically evaluated. Finally, research directions to further increase the LE of MHP emitters and the potential of MHPs as a core component in next‐generation displays and solid‐state lightings are suggested.
The factors that limit the luminescence efficiency (LE) of metal halide perovskite (MHP) light‐emitting diodes (PeLEDs) are reviewed by categorizing them into i) photophysical properties of MHPs, ii) morphological factors, and iii) problems caused by device architectures. Various strategies to overcome those LE‐limiting factors in MHPs and PeLEDs, and research directions to further increase the LE of MHPs are discussed.
Metal halide perovskite light emitters Kim, Young-Hoon; Cho, Himchan; Lee, Tae-Woo
Proceedings of the National Academy of Sciences - PNAS,
10/2016, Letnik:
113, Številka:
42
Journal Article
Recenzirano
Odprti dostop
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.
Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge ...carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd A−1 (external quantum efficiency of 23.4%), which rises to 205 cd A−1 (external quantum efficiency of 45.5%) with a hemispherical lens.Guanidinium doping is shown to enhance the operation of perovskite nanocrystal light-emitting diodes.
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.
Although several transparent conducting materials such as carbon nanotubes, graphene, and conducting polymers have been intensively explored as flexible electrodes in optoelectronic devices, their ...insufficient electrical conductivity, low work function, and complicated electrode fabrication processes have limited their practical use. Herein, a 2D titanium carbide (Ti3C2) MXene film with transparent conducting electrode (TCE) properties, including high electrical conductivity (≈11 670 S cm−1) and high work function (≈5.1 eV), which are achieved by combining a simple solution processing with modulation of surface composition, is described. A chemical neutralization strategy of a conducting‐polymer hole‐injection layer is used to prevent detrimental surface oxidation and resulting degradation of the electrode film. Use of the MXene electrode in an organic light‐emitting diode leads to a current efficiency of ≈102.0 cd A−1 and an external quantum efficiency of ≈28.5% ph/el, which agree well with the theoretical maximum values from optical simulations. The results demonstrate the strong potential of MXene as a solution‐processable electrode in optoelectronic devices and provide a guideline for use of MXenes as TCEs in low‐cost flexible optoelectronic devices.
A solution‐processed transparent conducting electrode with desirable properties including high electrical conductivity (≈11 668 S cm−1) and work function (≈5.1 eV) is achieved by using a 2D titanium carbide (Ti3C2) MXene thin film. Precise control of the surface chemical composition and a neutralized hole‐injection layer prevent detrimental surface/interface oxidation of the MXene and enable a high‐efficiency organic light‐emitting diode that uses the solution‐processed MXene electrode.
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