Matched Electron Transport Materials Enabling Efficient and Stable Perovskite Quantum Dot-based Light-Emitting Diodes.

Here, we report 2,4,6-Tris(3'-(pyridine-3-yl) biphenyl-3-yl)-1,3,5-triazine (TmPPPyTz, 3P) with strong electron-withdrawing moieties of pyridine and triazine to modulate the performance of P-QLEDs. Compared with commonly used 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), the pyridine in 3P have a strong interaction with perovskites, which can effectively suppress the interface non-radiative recombination caused by the·Pb2+ defects on the surface of QDs. In addition, 3P have deep highest occupied molecular orbital (HOMO) (enhancing hole-blocking properties), matched lowest unoccupied molecular orbital (LUMO) and excellent electron mobility (enhancing electron transport properties), realizing the carrier balance and maximizing the exciton recombination. Furthermore, high thermal resistance of·3P obviously improves the stability of QDs under variable temperature, continuous UV illumination, and electric field excitation. Resultantly, the P-QLEDs using the 3P as ETM achieved an outstanding performance with a champion EQE of 30.2%·and an operational lifetime T50·of 3220 hours at an initial luminance of 100 cd m-2, which is 151% and about 11-fold improvement compared to control devices (EQE = 20%, T50 = 297 hours), respectively. These results provide a new concept for constructing the efficient and stable P-QLEDs from the perspective of selective ETM.

Boosting External Quantum Efficiency of Blue Perovskite QLEDs Exceeding 23% by Trifluoroacetate Passivation and Mixed Hole Transportation Design.

Perovskite quantum dot-based light-emitting diodes (QLEDs) have been considered a promising display technology due to their wide color gamut for authentic color expression. Currently, the external quantum efficiency (EQE) for state-of-the-art blue perovskite QLEDs is about 15%, which still lags behind its green and red counterparts (>25%) and blue film-based LEDs. Here, blue perovskite QLEDs that achieve an EQE of 23.5% at 490 nm is presented, to the best knowledge, which is the highest value reported among blue perovskite-based LED fields. This impressive efficiency is achieved through a combination of quantum dot (QD) passivation and optimal device design. First, blue mixed halide perovskite CsPbCl3- xBrx QDs passivated by trifluoroacetate exhibit excellent exciton recombination behavior with a photoluminescence quantum yield of 84% due to reducing uncoordinated Pb surface defects. Furthermore, the device is designed by introducing a mixed hole-transport layer (M-HTL) to increase hole injection and transportation capacity and improve carrier balance. It is further found that M-HTL can decrease carrier leakage and increase radiative recombination in the device, evidenced by the visual electroluminescence spectrum at 2.0 V. The work breaks through the EQE gap of 20% for blue perovskite-based QLEDs and significantly promotes their commercialization process.

Polymer-Surface-Mediated Mechanochemical Reaction for Rapid and Scalable Manufacture of Perovskite QD Phosphors.

Perovskite quantum dots (QDs) have been considered new-generation emitters for lighting and displays due to their high photoluminescence (PL) efficiency, and pure color. However, their commercialization process is currently hindered by the challenge of mass production in a quick and environmentally friendly manner. In this study, a polymer-surface-mediated mechanochemical reaction (PMR) is proposed to prepare perovskite QDs using a high-speed multifunction grinder for the first time. PMR possesses two distinctive features: i) The ultra-high rotating speed (>15 000 rpm) of the grinder facilitates the rapid conversion of the precursor to perovskite; ii) The surface-rich polymer particulate ensures QDs with high dispersity, avoiding QD aggregation-induced PL quenching. Therefore, PMR can successfully manufacture green perovskite QDs with a high PL quantum yield (PLQY) exceeding 90% in a highly material- (100% yield), time- (1 kg min-1), and effort- (solvent-free) efficient manner. Moreover, the PMR demonstrates remarkable versatility, including synthesizing by various polymers and producing diverse colored and Pb-free phosphors. Importantly, these phosphors featuring a combination of polymer and perovskite, are facilely processed into various solid emitters. The proposed rapid, green, and scalable approach has great potential to accelerate the commercialization of perovskite QDs.

A ligand strategy retarding monovalent copper oxidation toward achieving Cs3Cu2I5 perovskite emitters with enhanced stability for lighting.

0D copper-based perovskites (Cs3Cu2I5) have fascinating optical properties, such as strong exciton binding energy, high photoluminescence quantum yield (PLQY) and large Stokes shifts from self-trapped excitons (STEs), which make them highly considerable candidates in the field of lighting. However, the stability of Cs3Cu2I5 is compromised by the oxidation of Cu+ to Cu2+ during the storage or operation process. Here, we proposed a ligand engineering strategy to improve the stability of Cs3Cu2I5via an organic molecule (ethylenediaminetetraacetic acid, EDTA) with multiple functional groups. The strong interaction between carboxyl groups and Cu+ was evidenced through FTIR and XPS, and it could retard monovalent copper oxidation. After storing for 90 days, the EDTA-engineered Cs3Cu2I5 (EDTA-Cs3Cu2I5) maintained its original crystalline structure, while the control Cs3Cu2I5 exhibited an impurity phase. Through quantitative analysis, the content of Cu2+ in EDTA-Cs3Cu2I5 was found to be 83.9% lower than that in control Cs3Cu2I5. Benefiting from the inhibition of Cu+ oxidation, EDTA-Cs3Cu2I5 exhibited improved light emission stability. For example, the optimized EDTA-Cs3Cu2I5 retained 74.7% of the initial photoluminescence (PL) intensity after 90-day storage under ambient conditions, while the pure Cs3Cu2I5 retained only 41.7%. Furthermore, EDTA could passivate defects and enhance the PL properties of the optimized Cs3Cu2I5, which showed a PLQY of 94.7%, much higher than that of 71.4% for pure Cs3Cu2I5. We further constructed a WLED based on the EDTA-engineered Cs3Cu2I5, which showed CIE at (0.3238, 0.3354), a CRI of 91.7, and a T50 of 361 h. The proposed EDTA ligand strategy provides a new way to regulate the light-emitting properties and stabilities of Cs3Cu2I5 for future industrialization.

Fiber Optic Plate Coupled Pb-Free Perovskite X-ray Camera Featuring Low-Dose-Rate Imaging toward Dental Diagnosis.

Copper-based halide perovskites have been considered as promising scintillators. However, they still cannot meet the requirement of low-dose-rate X-ray imaging in medical diagnosis. Herein, we design a fiber optic plate (FOP) coupled perovskite X-ray camera to reduce the dose rate toward dental X-ray imaging. Tl doped Cs3Cu2I5 prepared via molten salt reaction has a high light yield of 72,000 photons/MeV, resulting from Tl10/Tl20-self-trapped hole emissions. After FOP coupling, the pulp cavity, root canal, dentin and root canal file can be clearly observed under a low dose rate as low as 3 µGyair s-1, which is absolutely lower than the required 5.5 µGyair s-1 for commercial intraoral dental sensors. The realization of such a low dose rate is attributed to the high coupling efficiency of 75% for the FOP and the high brightness of 262 lm m-2 for the scintillation screen. This designed portable X-ray camera shows its huge potential in intraoral dental X-ray imaging.

Recent progress of single-halide perovskite nanocrystals for advanced displays.

Light-emitting diodes based on lead halide perovskite nanocrystals (LHP NCs) have shown an astonishing increase in efficiency in just several years of academic research, reaching high external quantum efficiencies exceeding 20%. The extensive color-tunability and narrow emission bandwidth of LHP NCs, in particular, are of great importance in the creation of the next generation of ultra-high-definition displays, as defined by the Rec. 2020 standard recommendation. In fact, whereas the colour of LHP NCs can be easily tuned by the compositions of halogens, the ion migration in mixed-halide perovskites under the electric field will seriously affect the spectral stability and operational lifetimes of perovskite light-emitting diodes (PeLEDs). Therefore, it is essential to realize efficient colour-saturated PeLEDs based on single-halide perovskite NCs. In this review, we focus on the recent progress in LHP NC-based PeLEDs and highlight the strategy of tuning the spectral emission based on quantum confinement or cation alloying/doping in single-halide perovskite NCs. Finally, we will give an outlook on future research avenues for preparing high-efficiency pure green, red and blue PeLEDs based on single-halide perovskite NCs.

Perovskite light-emitting/detecting bifunctional fibres for wearable LiFi communication.

Light fidelity (LiFi), which is emerging as a compelling technology paradigm shifting the common means of high-capacity wireless communication technologies, requires wearable and full-duplex compact design because of its great significance in smart wearables as well as the 'Internet of Things'. However, the construction of the key component of wearable full-duplex LiFi, light-emitting/detecting bifunctional fibres, is still challenging because of the conflicting process between carrier separation and recombination, as well as the highly dynamic film-forming process. Here, we demonstrate light-emitting/detecting bifunctional fibres enabled by perovskite QDs with hybrid components. The hybrid perovskite inks endow fibres with super-smooth QD films. This, combined with the small exciton binding energy and high carrier mobility of perovskite QDs, enables successful integration of electroluminescence and photodetection into monofilaments. The bifunctional fibres possess the narrowest electroluminescence full width at half maximum of ~19 nm and, more importantly, the capability for simultaneously transmitting and receiving information. The successful fabrication of narrow emission full-duplex LiFi fibres paves the way for the fabrication and integration of low crosstalk interoperable smart wearables.

A bilateral interfacial passivation strategy promoting efficiency and stability of perovskite quantum dot light-emitting diodes.

Perovskite quantum-dot-based light-emitting diodes (QLEDs) possess the features of wide gamut and real color expression, which have been considered as candidates for high-quality lightings and displays. However, massive defects are prone to be reproduced during the quantum dot (QD) film assembly, which would sorely affect carrier injection, transportation and recombination, and finally degrade QLED performances. Here, we propose a bilateral passivation strategy through passivating both top and bottom interfaces of QD film with organic molecules, which has drastically enhanced the efficiency and stability of perovskite QLEDs. Various molecules were applied, and comparison experiments were conducted to verify the necessity of passivation on both interfaces. Eventually, the passivated device achieves a maximum external quantum efficiency (EQE) of 18.7% and current efficiency of 75 cd A-1. Moreover, the operational lifetime of QLEDs is enhanced by 20-fold, reaching 15.8 h. These findings highlight the importance of interface passivation for efficient and stable QD-based optoelectronic devices.

Histone-induced thrombotic thrombocytopenic purpura in adamts13 -/- zebrafish depends on von Willebrand factor.

Thrombotic thrombocytopenic purpura (TTP) is caused by severe deficiency of ADAMTS13 (A13), a plasma metalloprotease that cleaves endothelium-derived von Willebrand factor (VWF). However, severe A13 deficiency alone is often not sufficient to cause an acute TTP; additional factors may be required to trigger the disease. Using CRISPR/Cas9, we created and characterized several novel zebrafish lines carrying a null mutation in a13-/- , vwf, and both. We further used these zebrafish lines to test the hypothesis that inflammation that results in neutrophil activation and release of histone/DNA complexes may trigger TTP. As shown, a13-/- zebrafish exhibit increased levels of plasma VWF antigen, multimer size, and ability of thrombocytes to adhere to a fibrillar collagen-coated surface under flow. The a13-/- zebrafish also show an increased rate of occlusive thrombus formation in the caudal venules after FeCl3 injury. More interestingly, a13-/- zebrafish exhibit ~30% reduction in the number of total, immature, and mature thrombocytes with increased fragmentation of erythrocytes. Administration of a lysine-rich histone results in more severe and persistent thrombocytopenia and a significantly increased mortality rate in a13-/- zebrafish than in wildtype (wt) ones. However, both spontaneous and histone-induced TTP in a13-/- zebrafish are rescued by the deletion of vwf These results demonstrate a potentially mechanistic link between inflammation and the onset of TTP in light of severe A13 deficiency; the novel zebrafish models of TTP may help accelerate our understanding of pathogenic mechanisms and the discoveries of novel therapeutics for TTP and perhaps other arterial thrombotic disorders.

Self-template Synthesis of Metal Halide Perovskite Nanotubes as Functional Cavities for Tailored Optoelectronic Devices.

Intriguing optoelectronic features of low-dimensional perovskites drive researchers to develop novel nanostructures for exploring new photophysical properties and meeting the requirements of future practical applications. Here, we report the facile and universal synthesis of metal halide perovskite nanotubes (NTs) in a micro alkylammonium emulsion system for the first time. The [PbBr6]4--based NTs with a diameter of 300 nm and length of 100 µm were synthesized through the reaction of PbBr2 and long-chain bromide in advance, which can be controllably converted into general metal halide perovskite APbBr3 (A = Cs, FA, MA) with preserved tubular morphology by introducing the Cs+, MA+, and FA+ cations. Importantly, the NTs can readily couple with other nanofillers exhibiting tunable and novel optoelectronic properties demonstrated by the photodetectors. The device performance can be significantly improved and broadened to infrared photoresponse through the introduction of Au nanocrystal (NC) plasma and PbS NCs, respectively. These results demonstrate that the metal halide perovskite NTs are expected to enrich the diversity of nanostructures and have a huge potential in the fabrication of integrated, light-manipulated, and miniaturized electronic and photonic devices.

Synthesis of stable and phase-adjustable CsPbBr3@Cs4PbBr6 nanocrystals via novel anion-cation reactions.

All-inorganic cesium lead halide perovskites have emerged as promising semiconductor materials due to their preeminent performance in lighting, display, light detecting, and laser fields. However, the applications of lead halide perovskites are limited by the dissatisfactory stability owing to their fragile ionic crystal characteristics and highly dynamic surface-coordinated states. The in situ diphase structure passivation possessing the same chemical constituents (such as passivating CsPbBr3 with Cs4PbBr6) has been proven to be an effective way to improve the stabilities and simultaneously maintain the highly efficient luminescence properties. Herein, for the first time, we report a novel anion-cation reaction method to synthesize the lead halide perovskite NCs with diphase CsPbBr3@Cs4PbBr6 structure. Moreover, we have found that the phase transformation between CsPbBr3 and Cs4PbBr6 is temperature dependent. Thus, we could control the relative composition of the diphase CsPbBr3@Cs4PbBr6 composite by adjusting the temperature. The optimized CsPbBr3@Cs4PbBr6 composite NCs achieve highly light emissive performance and stabilities against atmosphere, moisture and heating. Furthermore, we could obtain 135% of the NTSC color gamut through anion exchange. These highly emissive composite NCs with improved stabilities exhibit great potential in future optoelectronic fields.

Narrowband Perovskite Photodetector-Based Image Array for Potential Application in Artificial Vision.

Image sensor arrays are widely used in digital cameras, smartphones, and biorobots. However, most commercial image arrays rely on the dichroic prisms or a set of interference filters to distinguish characteristic color spectrum, which significantly increases the cost and fabrication processing complexity. In this work, an ultranarrow response photodetector with full-width at half-maximum being ∼12 nm and specific detectivity over 1011 Jones at 545 nm are successfully achieved in CsPbBr3 polycrystalline films using freeze-drying casting method to adjust the surface-charge recombination. To our best knowledge, this is the narrowest spectrum response for perovskite photodetectors in the visible light waveband. More importantly, a series of narrowband photodetectors are developed to enhance diverse selectivity for target signals covering from blue light to red light via bandgap tuning in CsPbX3 by tailoring the halide component. Finally, an integrated sensing array with CsPbX3 (X = Cl, Br, I) narrowband photodetectors acting as color recognition cones is constructed, which presents clear color and shape recognition paving the way for commercialization of perovskite photodetector in artificial vision.

Organic-Inorganic Hybrid Passivation Enables Perovskite QLEDs with an EQE of 16.48.

Perovskite quantum dots (QDs) with high photoluminescence quantum yields (PLQYs) and narrow emission peak hold promise for next-generation flexible and high-definition displays. However, perovskite QD films often suffer from low PLQYs due to the dynamic characteristics between the QD's surface and organic ligands and inefficient electrical transportation resulting from long hydrocarbon organic ligands as highly insulating barrier, which impair the ensuing device performance. Here, a general organic-inorganic hybrid ligand (OIHL) strategy is reported on to passivate perovskite QDs for highly efficient electroluminescent devices. Films based on QDs through OIHLs exhibit enhanced radiative recombination and effective electrical transportation properties compared to the primal QDs. After the OIHL passivation, QD-based light-emitting diodes (QLEDs) exhibit a maximum peak external quantum efficiency (EQE) of 16.48%, which is the most efficient electroluminescent device in the field of perovskite-based LEDs up to date. The proposed OIHL passivation strategy positions perovskite QDs as an extremely promising prospect in future applications of high-definition displays, high-quality lightings, as well as solar cells.

Room-Temperature Triple-Ligand Surface Engineering Synergistically Boosts Ink Stability, Recombination Dynamics, and Charge Injection toward EQE-11.6% Perovskite QLEDs.

Developing low-cost and high-quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light-emitting diodes (LEDs) is crucial for the next-generation ultra-high-definition flexible displays. Here, there is a report on a room-temperature triple-ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward "ideal" perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD-based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A-site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr3 QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W-1 , respectively, which are the most-efficient perovskite QLEDs with colloidal CsPbBr3 QDs as emitters up to now. These results demonstrate that the as-obtained QD inks have a wide range application in future high-definition QD displays and high-quality lightings.

High Performance Metal Halide Perovskite Light-Emitting Diode: From Material Design to Device Optimization.

Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovskite LEDs are inadequate for practical application. Strategies to optimize the emitting layer and the device structure, with respect to material design, synthesis, surface passivation, and device optimization, are reviewed and highlighted. The long-term stability of perovskite LEDs is evaluated as well. Meanwhile, several challenges and prospects for future development of perovskite materials and LEDs are identified.

Double-Protected All-Inorganic Perovskite Nanocrystals by Crystalline Matrix and Silica for Triple-Modal Anti-Counterfeiting Codes.

Novel fluorescence with highly covert and reliable features is quite desirable to combat the sophisticated counterfeiters. Herein, we report a simultaneously triple-modal fluorescent characteristic of CsPbBr3@Cs4PbBr6/SiO2 by the excitation of thermal, ultraviolet (UV) and infrared (IR) light for the first time, which can be applied for the multiple modal anti-counterfeiting codes. The diphasic structure CsPbBr3@Cs4PbBr6 nanocrystals (NCs) was synthesized via the typical reprecipitation method followed by uniformly encapsulation into silica microspheres. Cubic CsPbBr3 is responsible for the functions of anti-counterfeiting, while Cs4PbBr6 crystalline and SiO2 are mainly to protect unstable CsPbBr3 NCs from being destroyed by ambient conditions. The as-prepared CsPbBr3@Cs4PbBr6/SiO2 NCs possess improved stability and are capable of forming printable ink with organic binders for patterns. Interestingly, the fluorescence of diphasic CsPbBr3@Cs4PbBr6/SiO2 capsule patterns can be reversibly switched by the heating, UV, and IR light irradiation, which has been applied as triple-modal fluorescent anti-counterfeiting codes. The results demonstrate that the perovskite@silica capsules are highly promising for myriad applications in areas such as fluorescent anti-counterfeiting, optoelectronic devices, medical diagnosis, and biological imaging.

An all-inkjet-printed flexible UV photodetector.

In this work, a novel concept of the all-inkjet-printed flexible photodetectors based on ZnO nanocrystals with high performance was proposed and demonstrated with emphasis on the influence of different post-treatments including UV light irradiation and high temperature annealing. The photodetectors based on UV-treated ZnO nanocrystal films exhibit a responsivity and an on/off ratio as high as 0.14 A W-1 and >103, respectively, which are better than the thermally treated devices. The high performance of ZnO nanocrystal-based photodetectors originates from unique band-edge modulation among the nanoparticles, where the existence of Schottky barriers leads to a low dark current and gives rise to a fast photoelectric response. The photodetector is capable of 500 bending cycles, and almost no degradation is observed. The as-obtained all-printable devices open up the possibility of fabricating a low-cost, solution processed, flexible, and large-area integrated optoelectronic sensor circuitry for future practical applications.

Constructing Mie-Scattering Porous Interface-Fused Perovskite Films to Synergistically Boost Light Harvesting and Carrier Transport.

Light harvesting (LH) and carrier transport abilities of a photoactive layer, which are both crucial for optoelectronic devices such as solar cells and photodetectors (PDs), are typically hard to be synergistically improved. Taking perovskite as an example, a freeze-drying recrystallization method is used to construct porous films with improvements of both LH and carrier transport ability. During the freeze-drying casting process, the rapid solvent evaporation produces massive pores, the sizes of which can be adjusted to exploit the Mie scattering for enhancement of the LH ability. Meanwhile, owing to the strong iconicity, the interface between perovskite nanocrystals fused during recrystallization, which favors carrier transport. Subsequently, PDs based on these Mie porous and interface-fused films show a high on/off ratio of more than 104 and an external quantum efficiency value of 658 % under 9 V bias and 520 nm light irradiation.

Nanowire-based transparent conductors for flexible electronics and optoelectronics.

As the necessary components for various modern electronic and optoelectronic devices, novel transparent electrodes (TEs) with the low cost, abundance features, and comparable performance of indium tin oxide (ITO) are inquired materials. Metal nanowires (NWs) with the excellent photoelectric properties as next-generation TE candidates have widely applications in smart optoelectronic devices such as electronic skins, wearable electronics, robotic skins, flexible and stretchable displays. This review describes the synthetic strategies for the preparation of metal NWs, the assemble process for metal NW films, and the practical aspects of metal NW films with the desired properties in various low-cost, flexible, and solution-based photoelectric devices.

50-Fold EQE Improvement up to 6.27% of Solution-Processed All-Inorganic Perovskite CsPbBr3 QLEDs via Surface Ligand Density Control.

Solution-processed CsPbBr3 quantum-dot light-emitting diodes with a 50-fold external quantum efficiency improvement (up to 6.27%) are achieved through balancing surface passivation and carrier injection via ligand density control (treating with hexane/ethyl acetate mixed solvent), which induces the coexistence of high levels of ink stability, photoluminescence quantum yields, thin-film uniformity, and carrier-injection efficiency.