Enhanced Stability and Highly Bright Electroluminescence of AgInZnS/CdS/ZnS Quantum Dots through Complete Isolation of Core and Shell via a CdS Interlayer.

An approach for synthesizing AgInZnS/CdS/ZnS core-shell-shell quantum dots (QDs) that demonstrate exceptional stability and electroluminescence (EL) performance is introduced. This approach involves incorporating a cadmium sulfide (CdS) interlayer between an AgInZnS (AIZS) core and a zinc sulfide (ZnS) shell to prevent the diffusion of Zn ions into the AIZS core and the cation exchange at the core-shell interface. Consequently, a uniform and thick ZnS shell, with a thickness of 2.9 nm, is formed, which significantly enhances the stability and increases the photoluminescence quantum yield (87.5%) of the QDs. The potential for AIZS/CdS/ZnS QDs in electroluminescent devices is evaluated, and an external quantum efficiency of 9.6% in the 645 nm is achieved. These findings highlight the importance of uniform and thick ZnS shells in improving the stability and EL performance of QDs.

Remarkable Electrical Conductivity Increase and Pure Metallic Properties from Semiconducting Colloidal Nanocrystals by Cation Exchange for Solution-Processable Optoelectronic Applications.

The authors report a strategic approach to achieve metallic properties from semiconducting CuFeS colloidal nanocrystal (NC) solids through cation exchange method. An unprecedentedly high electrical conductivity is realized by the efficient generation of charge carriers onto a semiconducting CuS NC template via minimal Fe exchange. An electrical conductivity exceeding 10 500 S cm-1 (13 400 S cm-1 at 2 K) and a sheet resistance of 17 Ω/sq at room temperature, which are among the highest values for solution-processable semiconducting NCs, are achieved successfully from bornite-phase CuFeS NC films possessing 10% Fe atom. The temperature dependence of the corresponding films exhibits pure metallic characteristics. Highly conducting NCs are demonstrated for a thermoelectric layer exhibiting a high power factor over 1.2 mW m-1 K-2 at room temperature, electrical wires for switching on light emitting diods (LEDs), and source-drain electrodes for p- and n-type organic field-effect transistors. Ambient stability, eco-friendly composition, and solution-processability further validate their sustainable and practical applicability. The present study provides a simple but very effective method for significantly increasing charge carrier concentrations in semiconducting colloidal NCs to achieve metallic properties, which is applicable to various optoelectronic devices.

Fabrication of Colloidal Cesium Metal Halide (CsMX: M = Fe, Co, and Ni) Nanoparticles and Assessment of Their Thermodynamic Stability by DFT Calculations.

We synthesized colloidal cesium metal halide CsMX (M = Fe, Co, Ni; X = Cl, Br) nanoparticles (NPs) and assessed their crystal stability by density functional theory (DFT) calculations. We successfully synthesized Cs3FeCl5, Cs3FeBr5, Cs3CoCl5, Cs3CoBr5, CsNiCl3, and CsNiBr3 NPs. CsMX NPs with Fe and Co exhibited Cs3M1X5 and Cs2M1X4 structures depending on the reaction conditions; however, CsNiX NPs exhibited only the CsNiX3 structure. The differences in structural stability by central metal ions were explained using spin-polarized DFT calculations. The analysis revealed tetragonal Cs3M1X5 and orthorhombic Cs2M1X4 structures to have similar thermodynamic stabilities in the case of Fe and Co, whereas the hexagonal CsMX3 structure in the case of Ni was the most stable. Moreover, the calculation results were the same as the experimental results. In particular, cobalt-related Cs3CoBr5 NPs easily developed into Cs2CoCl4 nanorods with an increase in temperature.