Insights into the formation mechanism of two-dimensional lead halide nanostructures

Short-Chain Acid Additives to Control PbI2 Crystallization in Hybrid Perovskite Films

The quality and the performance of hybrid perovskite (HP)’s films strongly depend on the complete conversion into MAPbI3 of a spin-coated solution of methylammonium iodide (MAI) and PbI2. Highly crystalline PbI2 on a substrate limits such a conversion and, consequently, the HP’s solar cell performances. We investigate for the first time the use of short-chain organic acids as additives in a non-complexing solvent like γ-butyrolactone (GBL), that can retard retard the crystallization of PbI2. Based on XRD analyses of the spin coated films, the acetic acid is the most effective additive in retarding the PbI2 crystallization, making Pb2+ available for a subsequent reaction with MAI. These results open a new experimental path for fabricating perovskite films by single or sequential step methods involving acid additives.

Halide perovskites as disposable epitaxial templates for the phase-selective synthesis of lead sulfochloride nanocrystals

Colloidal chemistry grants access to a wealth of materials through simple and mild reactions. However, even few elements can combine in a variety of stoichiometries and structures, potentially resulting in impurities or even wrong products. Similar issues have been long addressed in organic chemistry by using reaction-directing groups, that are added to a substrate to promote a specific product and are later removed. Inspired by such approach, we demonstrate the use of CsPbCl₃ perovskite nanocrystals to drive the phase-selective synthesis of two yet unexplored lead sulfochlorides: Pb₃S₂Cl₂ and Pb₄S₃Cl₂. When homogeneously nucleated in solution, lead sulfochlorides form Pb₃S₂Cl₂ nanocrystals. Conversely, the presence of CsPbCl₃ triggers the formation of Pb₄S₃Cl₂/CsPbCl₃ epitaxial heterostructures. The phase selectivity is guaranteed by the continuity of the cationic subnetwork across the interface, a condition not met in a hypothetical Pb₃S₂Cl₂/CsPbCl₃ heterostructure. The perovskite domain is then etched, delivering phase-pure Pb₄S₃Cl₂ nanocrystals that could not be synthesized directly.

Phase-selective approaches, such using reaction-directing groups, are often seen in traditional organic chemistry and catalysis. Here authors use perovskite nanocrystals as disposable templates to drive the phase-selective synthesis of two colloidal nanomaterials, the lead sulfohalides Pb₃S₂Cl₂ and Pb₄S₃Cl₂.

Nonlinear microscopy of lead iodide nanosheets

Lead iodide (PbI₂) is a van der Waals layered semiconductor with a direct bandgap in its bulk form and a hexagonal layered crystalline structure. The recently developed PbI₂ nanosheets have shown great promise for high-performance optoelectronic devices, including nanolasers and photodetectors. However, despite being widely used as a precursor for perovskite materials, the optical properties of PbI₂ nanomaterials remain largely unexplored. Here, we determine the nonlinear optical properties of PbI₂ nanosheets by utilising nonlinear microscopy as a non-invasive optical technique. We demonstrate the nonlinearity enhancement dependent on excitonic resonances, crystalline orientation, thickness, and influence of the substrate. Our results allow for estimating the second- and third-order nonlinear susceptibilities of the nanosheets, opening new opportunities for the use of PbI₂ nanosheets as nonlinear and quantum light sources.

Recent Advances on Properties and Utility of Nanomaterials Generated from Industrial and Biological Activities

Today is the era of nanoscience and nanotechnology, which find applications in the field of medicine, electronics, and environmental remediation. Even though nanotechnology is in its emerging phase, it continues to provide solutions to numerous challenges. Nanotechnology and nanoparticles are found to be very effective because of their unique chemical and physical properties and high surface area, but their high cost is one of the major hurdles to its wider application. So, the synthesis of nanomaterials, especially 2D nanomaterials from industrial, agricultural, and other biological activities, could provide a cost-effective technique. The nanomaterials synthesized from such waste not only minimize pollution, but also provide an eco-friendly approach towards the utilization of the waste. In the present review work, emphasis has been given to the types of nanomaterials, different methods for the synthesis of 2D nanomaterials from the waste generated from industries, agriculture, and their application in electronics, medicine, and catalysis.

Micron-Size Two-Dimensional Methylammonium Lead Halide Perovskites

Hybrid lead halide perovskites with 2D stacking structures have recently emerged as promising materials for optoelectronic applications. We report a method for growing 2D nanosheets of hybrid lead halide perovskites (I, Br and Cl), with tunable lateral sizes ranging from 0.05 to 8 μm and a structure consisting of n stacked monolayers separated by long alkylamines, tunable from bulk down to n = 1. The key to obtaining such a wide range of perovskite properties hinged on utilizing the respective lead halide nanosheets as precursors in a hot-injection synthesis that afforded careful control over all process parameters. The layered, quantum-confined ( n ≤ 4) nanosheets were comprised of major and minor fractions with differing n. Energy funneling from low to high n (high to low energy) regions within a single sheet, mediated by the length of the ligands between stacks, produced photoluminescent quantum yields as high as 49%. These large, tunable 2D nanosheets could serve as convenient platforms for future high-efficiency optoelectronic devices.

Colloidal lead iodide nanorings

Colloidal chemistry of nanomaterials experienced a tremendous development in the last decades. In the course of the journey 0D nanoparticles, 1D nanowires, and 2D nanosheets have been synthesized. They have in common to possess a simple topology. We present a colloidal synthesis strategy for lead iodide nanorings, with a non-trivial topology. First, two-dimensional structures were synthesized in nonanoic acid as the sole solvent. Subsequently, they underwent an etching process in the presence of trioctylphosphine, which determines the size of the hole in the ring structure. We propose a mechanism for the formation of lead iodide nanosheets which also explains the etching of the two-dimensional structures starting from the inside, leading to nanorings. In addition, we demonstrate a possible application of the as-prepared nanorings in photodetectors. These devices are characterized by a fast response, high gain values, and a linear relation between photocurrent and incident light power intensity over a large range. The synthesis approach allows for inexpensive large-scale production of nanorings with tunable properties.