Actively Tunable "Single Peak/Broadband" Absorbent, Highly Sensitive Terahertz Smart Device Based on VO2.

In recent years, the development of terahertz (THz) technology has attracted significant attention. Various tunable devices for THz waves (0.1 THz-10 THz) have been proposed, including devices that modulate the amplitude, polarization, phase, and absorption. Traditional metal materials are often faced with the problem of non-adjustment, so the designed terahertz devices play a single role and do not have multiple uses, which greatly limits their development. As an excellent phase change material, VO2's properties can be transformed by external temperature stimulation, which provides new inspiration for the development of terahertz devices. To address these issues, this study innovatively combines metamaterials with phase change materials, leveraging their design flexibility and temperature-induced phase transition characteristics. We have designed a THz intelligent absorber that not only enables flexible switching between multiple functionalities but also achieves precise performance tuning through temperature stimulation. Furthermore, we have taken into consideration factors such as the polarization mode, environmental temperature, structural parameters, and incident angle, ensuring the device's process tolerance and environmental adaptability. Additionally, by exploiting the principle of localized surface plasmon resonance (LSPR) accompanied by local field enhancement, we have monitored and analyzed the resonant process through electric field characterization. In summary, the innovative approach and superior performance of this structure provide broader insights and methods for THz device design, contributing to its theoretical research value. Moreover, the proposed absorber holds potential for practical applications in electromagnetic invisibility, shielding, modulation, and detection scenarios.

Out-of-plane polarization modulated band alignments inß-In2X3/α-In2X3(X = S and Se) vdW heterostructures.

The construction of two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy to overcome the intrinsic disadvantages of individual 2D materials. Herein, by employing first-principles calculations, the electronic structures and potential applications in the photovoltaic field of theß-In2X3/α-In2X3(X = S and Se) vdW heterostructures have been systematically unraveled. Interestingly, the band alignments ofß-In2S3/α-In2S3,ß-In2Se3/α-In2Se3, andß-In2Se3/α-In2S3heterostructures can be transformed from type-I to type-II by switching the polarization direction ofα-In2X3layers. It is highlighted that the light-harvesting ability of theß-In2X3/α-In2X3vdW heterostructures is significantly higher than the corresponding monolayers in nearly the entire visible light region. Interestingly, type-IIß-In2S3/α-In2Se3↓ heterostructure can achieve the power conversion efficiency of 17.9%, where theα-In2Se3layer acts as a donor and theß-In2S3layer displays as the acceptor. The present research not only provides an in-depth understanding that the out-of-plane polarization ofα-In2X3monolayers can efficiently modulate the band edge alignment of theß-In2X3/α-In2X3vdW heterostructures, but also paves the way for the application of these heterostructures in the field of photovoltaics and optoelectronics.

Deciphering the roles of ammonium doping for lead-free (NH4)xCs3-xCu2I5 perovskites to regulate the photoelectronic properties.

Inorganic ammonium (NH4+) is the simplest amine cation with perfect symmetry, the smallest radius and many H atoms, allowing itself to be used as a potential dopant in achieving high-quality perovskite materials. As a composition-modulation strategy, NH4+-doped (NH4)xCs3-xCu2I5 (0 < x < 1.5) lead-free perovskites were successfully synthesized via the eco-friendly ball milling method in this work. As the ammonium content increases, the lattice constants of (NH4)xCs3-xCu2I5 shrink and the grain sizes increase. The doping of NH4+ effectively passivates the lattice defects, suppresses the non-radiative recombination and tunes the energy band structure, resulting in better fluorescence properties. UV-pumped deep-blue LEDs based on (NH4)xCs3-xCu2I5 phosphors were fabricated, which showed improved performance and tunable emission. These results demonstrate the potential of the NH4+-doping strategy for improving the performance of lead-free perovskite optoelectronics.

Correction: Tunable deep-blue luminescence from ball-milled chlorine-rich Csx(NH4)1-xPbCl2Br nanocrystals by ammonium modulation.

Correction for 'Tunable deep-blue luminescence from ball-milled chlorine-rich Csx(NH4)1-xPbCl2Br nanocrystals by ammonium modulation' by Hongfei Xiao et al., Chem. Commun., 2022, 58, 3827-3830, DOI: 10.1039/D1CC07125D.

Tunable deep-blue luminescence from ball-milled chlorine-rich Csx(NH4)1-xPbCl2Br nanocrystals by ammonium modulation.

For the first time, a novel class of deep-blue (DB)-emitting Csx(NH4)1-xPbCl2Br (0.3 ≤ x ≤ 1) perovskite nanocrystals (PNCs) were prepared by a facile ligand-assisted one-step ball milling method. The resulted PNCs are characterized by high chlorine content (66.7%) and excellent color purity. Their photoluminescence position can be finely modulated from 434 nm to 447 nm, which extends notably beyond the current Rec. 2020 color standard, by the NH4+ content. Among them, Cs0.3(NH4)0.7PbCl2Br shows the highest quantum yield close to 40%. The PNCs exhibit high phase and optical stability under ambient conditions and UV light according to the NH4+ content. This work offers a new avenue to produce DB perovskites for future full-color displays and optoelectronics.

Synergistic Effect of N,N-Dimethylformamide and Hydrochloric Acid on the Growth of MAPbI3 Perovskite Films for Solar Cells.

Perovskite solar cells have emerged as a promising next-generation electrical power generating tool. However, imperfections in perovskite films are one of the crucial factors preventing the commercialization of perovskite solar cells. Passivation has proven to be an effective strategy to reduce the density of defect states in perovskite crystals and inhibit ion migration. Although significant work on chloride ion and N,N-dimethylformamide (DMF) has shown that the additives are able to passivate different types of trap defects, systematic studies on the effects of DMF and HCl on perovskite crystallization when used in conjunction with each other are elusive. Here, we systematically investigated the synergistic effect of DMF and hydrochloric acid (HCl) on methylammonium (MA+)-based perovskite films with the two-step spin-coating method. As a Lewis base, DMF coordinates well with Pb2+ to facilitate a decrease in the number of defects, thereby improving the carrier separation and transport, while HCl improves the overall perovskite film morphology. Addition of 20 µL HCl/20 µL DMF to 10 mL of methylammonium iodide/isopropyl alcohol solution afforded ca. 500 nm thick perovskite films with no observable defects within the grains. The process allowed fabrication of devices with an active area of 0.16 cm2, which produced power conversion efficiencies up to 18.37% with minimal hysteresis.

Design of C3 N4 -Based Hybrid Heterojunctions for Enhanced Photocatalytic Hydrogen Production Activity.

Semiconductors and metals can form an Ohmic contact with an electric field pointing to the metal, or a Schottky contact with an electric field pointing to the semiconductor. If these two types of heterojunctions are constructed on a single nanoparticle, the two electric fields may cause a synergistic effect and increase the separation rate of the photogenerated electrons and holes. Metal Ni and Ag nanoparticles were successively loaded on the graphitic carbon nitride (g-C3 N4 ) surface by precipitation and photoreduction in the hope of forming hybrid heterojunctions on single nanoparticles. TEM/high-resolution TEM images showed that Ag and Ni were loaded on different locations on C3 N4 , which indicated that during the photoreduction reaction Ag+ obtained electrons from C3 N4 in the reduction reaction, whereas oxidation reactions proceeded on Ni nanoparticles. Photocatalytic hydrogen production experiments showed that C3 N4 -based hybrid heterojunctions can greatly improve the photocatalytic activity of materials. The possible reason is that two heterojunctions could form a long-range electric field similar to the p-i-n structure in semiconductors. Most of the photogenerated carriers were generated and then separated in this electric field, thereby increasing the separation rate of electrons and holes. This further improved the photocatalytic activity of C3 N4 .

Regulation of photoluminescence properties of graphene quantum dots via hydrothermal treatment.

Graphene quantum dots (GQDs) have fascinating photoluminescence (PL) properties with promising applications in bioimaging, fluorescent sensing and the photoelectrics field. In this work, PL properties of GQDs obtained from different carbonaceous precursors including carbon fibers, graphite powder, graphene oxide (GO) and reduced graphene oxide (RGO) were regulated via a simple hydrothermal reduction. Upon hydrothermal treatment, the fluorescent peaks of the original GQDs were blue-shifted to 440 nm and their PL intensities were enhanced by about 2 times. Furthermore, the full widths at half maxima (FWHM) of the fluorescent peaks were narrowed. The improved PL properties of the GQDs were mainly attributed to the change of oxygenated groups on the GQDs surface, with most hydroxyl and epoxy groups of the GQDs removed, while carboxyl groups were largely intact. Different from chemical modification methods, the improvement of PL properties of GQDs by a hydrothermal method revealed the effect of different oxygenated groups on the GQDs surface on their PL properties, helping to clarify the PL mechanism of GQDs.

Production of aqueous colloidal dispersions of carbon nanotubes.

Stable homogeneous dispersions of carbon nanotubes (CNTs) have been prepared by using sodium dodecyl sulfate (SDS) as dispersing agent. To our knowledge, it is the first report to quantitatively characterize colloidal stability of the dispersions by UV-vis spectrophometric measurements. When the sediment time reaches 500 h, the supernatant CNT concentration drops as much as 50% for the bare CNT suspension, compared to 15% with the addition of SDS. Furthermore, after 150 h, no precipitation is found for CNT/SDS dispersions, exhibiting an extreme stability. Zeta potential, auger electron microscopy, and FTIR analysis are employed to investigate the adsorption mechanism in detail. It has been concluded that the surfactant containing a single straight-chain hydrophobic segment and a terminal hydrophilic segment can modify the CNTs-suspending medium interface and prevent aggregation over long periods. The morphology of the CNT dispersions is observed with optical microscopy. An intermediate domain of homogeneously dispersed nanotubes exhibits an optimum at 0.5 wt% CNTs and 2.0 wt% SDS.