Morphology control represents an important strategy for the development of functional nanomaterials and has yet to be achieved in the case of promising lead-free double perovskite materials so far. In this work, high-quality Cs2AgBiX6 (X = Cl, Br, I) two-dimensional nanoplatelets were synthesized through a newly developed synthetic procedure. By analyzing the optical, morphological, and structural evolutions of the samples during synthesis, we elucidated that the growth mechanism of lead-free double perovskite nanoplatelets followed a lateral growth process from mono-octahedral-layer (half-unit-cell in thickness) cluster-based nanosheets to multilayer (three to four unit cells in thickness) nanoplatelets. Furthermore, we demonstrated that Cs2AgBiBr6 nanoplatelets possess a better performance in photocatalytic CO2 reduction compared with their nanocube counterpart. Our work demonstrates the first example with two-dimensional morphology of this important class of lead-free perovskite materials, shedding light on the synthetic manipulation and the application integration of such promising materials.
Distinguishing and understanding the nonradiative recombination of charges are crucial for optimizing quantum-dot light-emitting diodes (QLEDs). Auger recombination (AR), a well-known nonradiative process, is widely recognized to occur in QLEDs. However, it has not yet been directly observed in a real working QLED. Here, the AR effect is verified in the QLED at temperatures of <150 K. At low temperatures, the QLED exhibits a unique S-shaped external quantum efficiency (EQE) evolution as the driving current density increases. Experimental and modeling results indicate that this S-shaped EQE results from the asynchronous changes in the behavior of injection of electrons and holes into the quantum-dot emission layer. At low driving voltages, both electron and hole currents are limited by the Fowler-Nordheim (F-N) tunneling behavior. The relatively low barrier for electrons leads to overwhelming electron injection and seriously imbalanced charges in the quantum dots, triggering the AR process. As the voltage increases, the electron current within the emission layer is no longer governed by F-N tunneling but limited by space charges. Then, charge injection becomes balanced, and the EQE increases. These results offer valuable insights into the charge injection and recombination processes within QLEDs, as well as implications for device design.
Abstract Although cadmium (Cd)‐based nanocrystals have enabled high‐performance quantum‐dot light‐emitting diodes (QLEDs), their mass production is likely to be affected by environmental protection policies. Among all the potential Cd‐free candidates, Cu‐In‐Zn‐S (CIZS) nanocrystals (NCs) have attracted particular interests. Still, the performance of the corresponding LED is currently limited by imbalanced charge injection and luminescence quenching, which are both related to the ZnO‐based electron transporting layer (ETL). This work demonstrates that ZnO nanoparticles (NPs) doped with Sn, Mg (Zn 1− x − y Sn x Mg y O), and passivated with Cl are promising to resolve the above issues. All‐solution‐processed QLEDs based on Cd‐free CIZS NCs are fabricated by using Zn 0.9 Sn 0.1 O NPs as the ETL, and the peak external quantum efficiency (EQE max ) was nearly twice that of ZnO (EQE max = 1.74%). The main reason is that the incorporation of Sn can reduce the conductivity of ZnO by an order of magnitude. Combining the advantages of Zn 0.9 Sn 0.1 O, Zn 0.8 Sn 0.1 Mg 0.1 O@Cl NPs are designed by the co‐doping of Mg and Cl passivation. The EQE max and current efficiency based on Zn 0.8 Sn 0.1 Mg 0.1 O and Zn 0.8 Sn 0.1 Mg 0.1 O@Cl as ETLs are further increased to 4.84%, 14.00 cd A −1 and 5.53%, 15.99 cd A −1 , respectively. The positive effects of Mg ions can remarkably optimize energy level structure to balance charge injection, while Cl can further passivate defects. The findings offer a new guideline for developing Cd‐free light‐emitting diodes.
Inorganic/organic hybrid light-emitting diodes were easily fabricated with a thin film containing water-soluble cadmium selenide nanocrystals and poly(N-vinylcarbazole) as an emitting layer by a spin-coating method. The cadmium selenide nanocrystals were synthesized in aqueous solution with L-cysteine hydrochloride as the stabilizer and were transferred from the aqueous solution into chloroform by a cationic surfactant cetyltrimethyl ammonium bromide. A broad emission spanning the whole visible wavelength range was obtained from the inorganic/organic hybrid devices whether poly(N-vinylcarbazole) was present in the devices or not, and the electroluminescence intensity of the devices increased as the applied voltages increased. However, an obvious blue-shift of the wavelength was observed with the increasing applied voltages in the device with poly(N-vinylcarbazole). Accordingly, the emission color of the device made with poly(N-vinylcarbazole) could be tuned from white to blue by varying the applied voltages, but the emission color of the device made without poly(N-vinylcarbazole) was almost constrained in the white region. This can be attributed to a limited contribution of poly(N-vinylcarbazole) emission to the electroluminescence spectra under the higher applied voltage. By comparing the electroluminescence intensity and the current-voltage characteristics of the devices made with and without poly(N-vinylcarbazole), the performance of the device with poly(N-vinylcarbazole) was improved greatly, which indicated that poly(N-vinylcarbazole) played an important role in the carrier injection and transportation in the device with poly(N-vinylcarbazole).
Mesostructured metallic substrates composed of square pyramidal pits are shown to confine localized plasmons. Plasmon frequency tuning is demonstrated using white light reflection spectroscopy with a wide range of structure dimensions from $400\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3000\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Using a simple plasmon cavity model, we demonstrate how the individual pit morphology and not their periodicity controls the resonance frequencies. By measuring the surface-enhanced Raman scattering (SERS) signals from monolayers of benzenethiol on the same range of mesostructures, we extract a quantitative connection between absorption, field enhancement, and SERS signals. The match between theory and experiment enables effective design of plasmon devices tailored for particular applications, such as optimizing SERS substrates.
A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag₂S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S-C bonds or Ag-S bonds. Pure Ag₂S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200 ° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190 ° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag₂S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200 ° C. The formation mechanism has been discussed in detail in terms of selective S-C and Ag-S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag-S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals.
Cu(i) ions were incorporated into CdS/ZnS core/shell nanocrystals through a cation exchange strategy, and the photoluminescence could be effectively tuned by varying the dopant position from the outside ZnS shell to the inside CdS core.
Ternary alloyed Cu2–xSySe1–y nanocrystals (NCs) were synthesized by using a simple and phosphine-free colloidal approach, in which sulfur powder and 1-dodecanethiol (DDT) were used as sulfur sources. In both cases, the crystal phase transformed from cubic berzelianite to monoclinic djurleite structure together with the morphology evolution from quasi-triangular to spherical or discal with an increase of sulfur content. Accordingly, the near-infrared (NIR) localized surface plasmon resonance (LSPR) absorption of the as-obtained sulfur-rich NCs exhibited obvious red-shift of wavelength and widening of absorption width. When the sulfur powder was chosen as sulfur sources, the LSPR wavelength of the as-obtained alloyed Cu2–xSySe1–y NCs could be tuned from 975 to 1230 nm with a decrease of selenium content in the NCs. In contrast, the region of the red-shift could be up to 1250 nm for the alloyed NCs synthesized by incorporation of different DDT dosage into the reaction system. The different sulfur sources and the electron donating effects of the DDT as a ligand played an important role in the LSPR absorption tuning. This deduction could be testified by the post-treating the quasi-triangular Cu2–xSe NCs with DDT under different temperatures and over different reaction time, which exhibited a red-shift of LSPR wavelength up to 450 nm due to coordination of DDT to Cu atoms on the NC surface while incorporating some sulfur anions into the lattice. This study offers a convenient tool for tuning the LSPR absorption of copper chalcogenide NCs and makes them for application in biological and optoelectronic fields.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)