Ultrastable Photodetectors Based on Blue CsPbBr3 Perovskite Nanoplatelets via a Surface Engineering Strategy.

Recently, photodetectors based on perovskite nanoplatelets (NPLs) have attracted considerable attention in the visible spectral region owing to their large absorption cross-section, high exciton binding energy, excellent charge transfer properties, and appropriate flexibility. However, their stability and performance are still challenging for perovskite NPL photodetectors. Here, a surface engineering strategy to enhance the optical stability of blue-light CsPbBr3 NPLs by acetylenedicarboxylic acid (ATDA) treatment has been developed. ATDA has strong binding capacity and a short chain length, which can effectively passivate defects and significantly improve the photoluminescence quantum efficiency, stability, and carrier mobility of NPLs. As a result, ATDA-treated CsPbBr3 NPLs exhibit improved optical properties in both solutions and films. The NPL solution maintains high PL performance even after being heated at 80 °C for 2 h, and the NPL film remains nondegradable after 4 h of exposure to ultraviolet irradiation. Especially, photodetectors based on the treated CsPbBr3 NPL films demonstrate exceptional performance, especially when the detectivity approaches up to 9.36 × 1012 Jones, which can be comparable to the best CsPbBr3 NPL photodetectors ever reported. More importantly, the assembled devices demonstrated high stability (stored in an air environment for more than 30 days), significantly exceeding that of untreated NPLs.

Exciton-to-Dopant Energy Transfer Dynamics in Mn2+ Doped CsPbBr3 Nanowires Synthesized by Diffusion Doping.

Mn2+ doped perovskite nanocrystals have garnered significant attention in optoelectronic applications. However, the synthesis of Mn2+ doped perovskite nanowires (NWs) poses challenges, and the dynamics of energy transfer from the exciton to Mn2+ remains unexplored, which is crucial for optimizing Mn2+ luminescence efficiency. Herein, we present a method to synthesize Mn2+ doped CsPbBr3 NWs with a photoluminescence quantum yield of 52% by diffusing Mn2+ into seed CsPbBr3 NWs grown via a hot injection method. We control the solution and lattice chemical potentials of Pb2+ and Mn2+ to enable Mn2+ to diffuse into the CsPbBr3 NWs while minimizing Ostwald ripening. Variable temperature photoluminescence spectroscopy reveals that the energy transfer from the exciton to Mn2+ in Mn2+ doped CsPbBr3 NWs is temperature dependent. A dynamic competition is observed between energy transfer and backward energy transfer, resulting in stronger Mn2+ photoluminescence at 80 K. This work provides a specific synthesis pathway for Mn2+ doped CsPbBr3 NWs and sheds light on their exciton-to-Mn2+ energy transfer dynamics.

Enhanced Hygrothermal Stability of In-Situ-Grown MAPbBr3 Nanocrystals in Polymer with Suppressed Desorption of Ligands.

Currently, the intrinsic instability of organic-inorganic hybrid perovskite nanocrystals (PNCs) at high temperature and high humidity still stands as a big barrier to hinder their potential applications in optoelectronic devices. Herein, we report the controllable in-situ-grown PNCs in polyvinylidene fluoride (PVDF) polymer with profoundly enhanced hygrothermal stability. It is found that the introduced tetradecylphosphonic acid (TDPA) ligand enables significantly improved binding to the surface of PNCs via a strong covalently coordinated P-O-Pb bond, as evidenced by density functional theory calculations and X-ray photoelectron spectroscopy analyses. Accordingly, such enhanced binding could not only make efficient passivation of the surface defects of PNCs but also enable the remarkably suppressed desorption of the ligand from the PNCs under high-temperature environments. Consequently, the photoluminescence quantum yield (PL QY) of the as-fabricated MAPbBr3-PNCs@PVDF film exhibits almost no decay after exposure to air at 333 K over 1800 h. Once the temperatures are increased from 293 to 353 K, their PL intensity can be kept as 88.6% of the initial value, much higher than that without the TDPA ligand (i.e., 42.4%). Moreover, their PL QY can be maintained above 50% over 1560 h (65 days) under harsh working conditions of 333 K and 90% humidity. As a proof of concept, the as-assembled white light-emitting diodes display a large color gamut of 125% National Television System Committee standard, suggesting their promising applications in backlight devices.

Dimethyl Ferrocene-Induced Ambient-Processed High-Quality Films toward Efficient Perovskite Solar Cells for Industrial Application.

Metal halide perovskite solar cells (PSCs) have recently made significant progress with power conversion efficiencies (PCEs) boosted from 3.8% to a certified one over 26.1%, partially benefiting from the high-quality perovskite film enabled by the effective one-step spin-coating route. However, an extra antisolvent step with poor controllability and producibility is often involved in such a process, and some intrinsic defects are generated inevitably, especially in ambient atmospheric conditions, thus fundamentally limiting the commercialization of PSCs. Here, we introduce 1,1'dimethyl ferrocene into methylammonium lead halide precursor, which could not only recover the defects within perovskite film but also simplify the process without the extra antisolvent step. Accordingly, a dense and uniform perovskite film with large grains has been obtained under ambient conditions, which has much lower defect density, better stability against moisture penetration, and enhanced thermal tolerance than the control one, delivering a champion PCE of 16.92%. Current work sheds light on the simplified air-processed strategy for high-quality perovskite films, which might pave the way for exploring efficient and stable PSCs toward industrial applications.

Reducing Emission Linewidth of Pure-Blue ZnSeTe Quantum Dots through Shell Engineering toward High Color Purity Light-Emitting Diodes.

High color purity blue quantum dot light-emitting diodes (QLEDs) have great potential applications in the field of ultra-high-definition display. However, the realization of eco-friendly pure-blue QLEDs with a narrow emission linewidth for high color purity remains a significant challenge. Herein, a strategy for fabricating high color purity and efficient pure-blue QLEDs based on ZnSeTe/ZnSe/ZnS quantum dots (QDs) is presented. It is found that by finely controlling the internal ZnSe shell thickness of the QDs, the emission linewidth can be narrowed by reducing the exciton-longitudinal optical phonon coupling and trap states in the QDs. Additionally, the regulation of the QD shell thickness can suppress the Förster energy transfer between QDs in the QLED emission layer, which will help to reduce the emission linewidth of the device. As a result, the fabricated pure-blue (452 nm) ZnSeTe QLED with ultra-narrow electroluminescence linewidth (22 nm) exhibit high color purity with the Commission Internationale de l'Eclairage chromatic coordinates of (0.148, 0.042) and considerable external quantum efficiency (18%). This work provides a demonstration of the preparation of pure-blue eco-friendly QLEDs with both high color purity and efficiency, and it is believed that it will accelerate the application process of eco-friendly QLEDs in ultra-high-definition displays.

Photo- and Thermal-Induced Ion Migration and Phase Separation in Mn-Doped Two-Dimensional PEA2PbX4 Perovskite.

Ion migration and phase separation in perovskite materials have negatively affected the solid-state lighting and display. Studying photo- and thermal-induced degradation is considered as a promising approach to understanding the luminescence mechanism and promoting practical applications. Herein, the Mn-doped two-dimensional PEA2PbX4 (X = Cl, Br, I) microcrystals with changing halogen composition were synthesized by an acid-assisted post-processing strategy. Then, photo- and thermal-induced degradation was studied by using steady-state and time-resolved photoluminescence (PL) spectroscopy. The band edge exciton PL peak of Mn-doped 2D PEA2PbX4 microcrystals was adjusted from 397 to 500 nm. The reduced Mn PL lifetime (1.37 to 0.21 ms) was monitored under ion exchange from Cl to Br to I. The degradation mechanism could be divided into two cases: (i) The halide ion migration in Mn-doped 2D perovskite under continuous illumination was revealed, suggesting that the migration of Cl ions was more accessible than that of Br and I. (ii) The PL redshift and lifetime reduction were observed after annealing at 420 K, which means that thermally induced aggregation of Mn ions resulted in the formation of Mn2+-Mn2+ dimers. In addition, the experimental results indicated that the induced B-site phase separation at high temperature annealing made the mixed perovskite phase of Pb and Mn ultimately transform into pure PEA2PbBr4 and PEA2MnBr4.

The role of FoxM1 in immune cells.

Forkhead box M1 (FoxM1), a proliferation specific transcriptional modulator, plays a principal role in many physiological and pathological processes. FoxM1-mediated oncogenic processes have been well addressed. However, functions of FoxM1 in immune cells are less summarized. The literatures about the expression of FoxM1 and its regulation on immune cells were searched on PubMed and Google Scholar. In this review, we provide an overview on the roles of FoxM1 in regulating functions of immune cells, including T cells, B cells, monocytes, macrophages, and dendritic cells, and discuss their contributions to diseases.

In situ preparation of Mn-doped perovskite nanocrystalline films and application to white light emitting devices.

Mn-doped perovskite nanocrystals have promised new optoelectronic applications due to their unique material properties. In the present study, Mn-doped perovskite nanocrystalline films were prepared in situ in a polymer matrix. The Mn-doped perovskite nanocrystals (PNCs) had good crystallinity and uniform size/spatial distributions in the polymer film. Bright dual-color emission and the long lifetime of the excited state of the dopant were observed from the host exciton and the Mn2+ dopant, respectively. Furthermore, magnetism was observed in the optimal Mn2+ concentration, implying that magnetic coupling was achieved in the Mn-doped perovskite lattice. The Mn-doped perovskite films also showed superior stability against moisture. To demonstrate the practicality of this composite film, a white light emitting device was fabricated by combining a single composite film with a blue light emitting diode; the device showed a high-quality white light emission, and the Commission Internationale De L'Eclairage (CIE) chromaticity coordinate of the white light emitting diode (WLED) (0.361, 0.326) was close to the optimal white color index. In this single-layer WLED, self-absorption among the luminous multilayers in traditional white light emitting diodes can be avoided. The study findings revealed that Mn-doped perovskite nanocrystalline films have many exciting properties, which bodes well for the fundamental study and design of high-performance optoelectronic devices.

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes.

The tunable dual-color emitting Mn2+ doped CsPbCl3-xBrx nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr2 treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn2+ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn2+ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn2+ doped CsPbCl1.5Br1.5 NCs are obtained. The enhancement mechanism of Mn2+ PL QY was attributed to improved energy transfer from exciton to Mn2+ d-d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn2+ doped CsPbCl3-xBrx@SiO2 and green emissive CsPbBr3@SiO2 NCs with violet GaN chips.

Advanced Supercapacitors Based on Porous Hollow Carbon Nanofiber Electrodes with High Specific Capacitance and Large Energy Density.

Hollow carbon nanofibers with hierarchical porous shells were prepared by NaOH activation of the electrospinning SiCNO fibers, followed by carbonization treatment. By adjusting the carbonization temperature, porous hollow carbon nanofibers with different Brunauer-Emmett-Teller (BET) specific surface areas and total pore volumes are obtained, both of which are explored as electrode materials for supercapacitors. It was found that the obtained products (HCF800) possess the highest BET specific surface area of 2628.10 m2/g and the largest pore volume of 2.32 cm3/g when the carbonized temperature was designed at 800 °C, thus displaying the best supercapacitor performance. The electrochemical results in a three-electrode system show that HCF800 exhibits a high specific capacitance of 330.11 F/g as the discharge current density is 1 A/g and still maintains 65.3% of its original specific capacitance when the current density reaches 20 A/g. Moreover, in a two-electrode system, HCF800 also exhibits an excellent specific capacity of 259.86 F/g at a current density of 1 A/g, marvelous cyclic stability with the specific capacitance retention of 95.3% even after 10,000 cycles, and a large energy density of 12.99 W h/kg at 1.0 A/g. Significantly, the supercapacitor performance of these porous hollow carbon nanofibers is also superior to that of many previously reported carbon materials, which proved them to be worthy candidates for high-performance electrode materials.

Stable Bandgap-Tunable Hybrid Perovskites with Alloyed Pb-Ba Cations for High-Performance Photovoltaic Applications.

The intrinsic poor stability of MAPbI3 hybrid perovskites in the ambient environment remains as the major challenge for photovoltaic applications. In this work, complementary first-principles calculations and experimental characterizations reveal that metal cation alloyed perovskite (MABa xPb1- xI3) can be synthesized and exhibit substantially enhanced stability via forming stronger Ba-I bonds. The Ba-Pb alloyed perovskites remain phase-pure in ambient air for more than 15 days. Furthermore, the bandgap of MABa xPb1- xI3 is tailored in a wide window of 1.56-4.08 eV. Finally, MABa xPb1- xI3 is used as a capping layer on MAPbI3 in solar cells, resulting in significantly improved power conversion efficiency (18.9%) and long-term stability (>30 days). Overall, our results provide a simple but reliable strategy toward stable less-Pb perovskites with tailored physical properties.

Elimination of S Vacancy as the Cause for the n-Type Behavior of MoS2 from the First-Principles Perspective.

Molybdenum disulfide (2H-MoS2) based low-dimensional nanostructure materials have great potential for applications in electronic and optoelectronic devices. However, some of the properties such as the origin of the native n-type electrical conductivity (EC) observed in these materials still remain elusive. Here, the defect properties in the 2H-MoS2 bulk system are systematically investigated by first-principles calculation to address these issues. We find that the S vacancy VS with low formation energy cannot be the origin of n-type EC owing to its deep defect levels within the valence band region. All other donor defects such as antisite MoS or Mo interstitial MoI also have deep levels that can trap electrons leading to depressed EC. SMo and SI could be the origin of the p-type EC in 2H-MoS2, but the concentrations are expected to be rather low due to their high formation energies and can only be enhanced under S-rich/Mo-poor conditions. These results provide the underlying insights on the defect properties 2H-MoS2 and explain well the experimental observations.

General Strategy for Rapid Production of Low-Dimensional All-Inorganic CsPbBr3 Perovskite Nanocrystals with Controlled Dimensionalities and Sizes.

Currently, all-inorganic CsPbX3 (X = Br, I, Cl) perovskite nanocrystals (NCs) are shining stars with exciting potential applications in optoelectronic devices such as solar cells, light-emitting diodes, lasers, and photodetectors, due to their superior performance in comparison to their organic-inorganic hybrid counterparts. In the present work, we report a general strategy based on a microwave technique for the rapid production of low-dimensional all-inorganic CsPbBr3 perovskite NCs with tunable morphologies within minutes. The effect of the key parameters such as the introduced ligands, solvents, and PbBr2 precursors and microwave powers as well as the irradiation times on the production of perovskite NCs was systematically investigated, which allowed their growth with tunable dimensionalities and sizes. As a proof of concept, the ratio of OA to OAm as well as the concentration of PbBr2 precursor played important roles in triggering the anisotropic growth of the perovskite NCs, favoring their growth into 1D/2D single-crystalline nanostructures. Meanwhile, their sizes could be tailored by controlling the microwave powers and irradiation times. The mechanism for the tunable growth of perovskite NCs is discussed.

Superior B-Doped SiC Nanowire Flexible Field Emitters: Ultra-Low Turn-On Fields and Robust Stabilities against Harsh Environments.

Low turn-on fields together with boosted stabilities are recognized as two key factors for pushing forward the implementations of the field emitters in electronic units. In current work, we explored superior flexible field emitters based on single-crystalline 3C-SiC nanowires, which had numbers of sharp edges, as well as corners surrounding the wire body and B dopants. The as-constructed field emitters behaved exceptional field emission (FE) behaviors with ultralow turn-on fields (Eto) of 0.94-0.68 V/µm and current emission fluctuations of ±1.0-3.4%, when subjected to harsh working conditions under different bending cycles, various bending configurations, as well as elevated temperature environments. The sharp edges together with the edges were able to significantly increase the electron emission sites, and the incorporated B dopants could bring a more localized state close to the Fermi level, which rendered the SiC nanowire emitters with low Eto, large field enhancement factor as well as robust current emission stabilities. Current B-doped SiC nanowires could meet all essential requirements for an ideal flexible emitters, which exhibit their promising prospect to be applied in flexible electronic units.

Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Room-Temperature-Processed Ga-Doped ZnO Nanoparticles as the Electron Transport Layer.

Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m2 and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.

SiC Nanowire Film Photodetectors: A Promising Candidate Toward High Temperature Photodetectors.

In this study, UV photodetectors (PDs) based on SiC nanowire films have been successfully prepared by a simple and low-cost drip-coating method followed by sintering at 500 °C. The corresponding electrical characterizations clearly demonstrate that the SiC nanowire based PD devices can be regarded as a promising candidate for UV PDs. The PDs can exhibit the excellent performances of fast, high sensitivity, linearity, and stable response, which can thus achieve on-line monitoring of weak UV light. Furthermore, the SiC nanowire-based PDs enable us to fabricate detectors working under high temperature as high as 150 °C. The high photosensitivity and rapid photoresponse for the PDs can be attributed to the superior single crystalline quality of SiC nanowires and the ohmic contact between the electrodes and nanowires.

Study of Ac Dielectrophoretic Process of SiC Nanowires: A Universal Method for Alignment of Semiconductor Nanowires.

In this study, the dielectrophoretic processes of SiC nanowires suspended in three typical solvents, (highly purified water, ethanol and isopropanol) were systematically investigated. Optical microscope and SEM characterizations were used to observe the order of SiC nanowires on the surface of gold microchannels. The gold microchannels were induced by Ac dielectrophoresis of the corresponding dispersion solutions of SiC nanowires, with a concentration of 0.1 mg/mL. The study shows that the dielectrophoresis process is an effective way of synthesizing highly oriented SiC nanoarrays using isopropanol solution. The results also show that the arrangement of SiC nanowires on the interdigital electrode configuration not only depend on the kind of solvent used, but also on the applied frequency (1000 Hz~1 MHz) and voltage (1 V~20 V).

Highly Efficient Photocatalytic Hydrogen Evolution in Ternary Hybrid TiO2/CuO/Cu Thoroughly Mesoporous Nanofibers.

Development of novel hybrid photocatalysts with high efficiency and durability for photocatalytic hydrogen generation is highly desired but still remains a grand challenge currently. In the present work, we reported the exploration of ternary hybrid TiO2/CuO/Cu thoroughly mesoporous nanofibers via a foaming-assisted electrospinning technique. It is found that by adjusting the Cu contents in the solutions, the unitary (TiO2), binary (TiO2/CuO, TiO2/Cu), and ternary (TiO2/CuO/Cu) mesoporous products can be obtained, enabling the growth of TiO2/CuO/Cu ternary hybrids in a tailored manner. The photocatalytic behavior of the as-synthesized products as well as P25 was evaluated in terms of their hydrogen evolution efficiency for the photodecomposition water under Xe lamp irradiation. The results showed that the ternary TiO2/CuO/Cu thoroughly mesoporous nanofibers exhibit a robust stability and the most efficient photocatalytic H2 evolution with the highest release rate of ∼851.3 µmol g(-1) h(-1), which was profoundly enhanced for more than 3.5 times with respect to those of the pristine TiO2 counterparts and commercial P25, suggesting their promising applications in clean energy production.

Shape-Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers.

1D mesoporous materials have attracted extensive interest recently, owning to their fascinating properties and versatile applications. However, it remains as a grand challenge to develop a simple and efficient technique to produce oxide nanofibers with mesoporous architectures, controlled morphologies, large surface areas, and optimal performances. In this work, a facile foaming-assisted electrospinning strategy with foaming agent of tea saponin is used to produce thoroughly mesoporous ZnO nanofibers with high purity and controlled morphology. Interestingly, mesoporous fibers with elliptical cross-section exhibit the significantly enhanced photocatalytic activity for hydrogen production, as compared to the counterparts with circular and rectangular cross-sections, and they also perform better than the commercial ZnO nanopowders. The unexpected shape dependence of photocatalytic activities is attributed to the different stacking modes of the mesoporous fibers, and a geometrical model is developed to account for the shape dependence. This work represents an important step toward producing thoroughly mesoporous ZnO nanofibers with tailored morphologies, and the discovery that fibers with elliptical cross-section render the best performance provides a valuable guideline for improving the photocatalytic performance of such mesoporous nanomaterials.

Long-lived and well-resolved Mn²âº ion emissions in CuInS-ZnS quantum dots.

CuInS2 (CIS) quantum dots (QDs) have tunable photoluminescence (PL) behaviors in the visible and near infrared spectral range with markedly lower toxicity than the cadmium-based counterparts, making them very promising applications in light emitting and solar harvesting. However, there still remain material- and fabrication- related obstacles in realizing the high-performance CIS-based QDs with well-resolved Mn(2+) d-d emission, long emission lifetimes as well as high efficiencies. Here, we demonstrate the growth of high-quality Mn(2+)-doped CuInS-ZnS (CIS-ZnS) QDs based on a multi-step hot-injection strategy. The resultant QDs exhibit a well-resolved Mn(2+) d-d emission with a high PL quantum yield (QY) up to 66% and an extremely long excited state lifetime up to ~3.78 ms, which is nearly two times longer than the longest one of "green" QDs ever reported. It is promising that the synthesized Mn(2+)-doped CIS-ZnS QDs might open new doors for their practical applications in bioimaging and opto/electronic devices.