Precursor-Mediated Synthesis of Shape-Controlled Colloidal CsPbBr₃ Perovskite Nanocrystals and Their Nanofiber-Directed Self-Assembly

Abstract

Shape control is often necessary to tune the optical and electronic properties of nanocrystals (NCs) and is mostly achieved through manipulation of surface ligands and processing conditions. Here we present a versatile synthesis of colloidal CsPbBr 3 perovskite NCs of various shapes (nanorods, nanocubes, and nanoplatelets) from an inexpensive steroidal Cs precursor: cesium cholate (CsCh). Cesium cholate has several advantages over the most commonly used Cs precursor (cesium oleate or Cs 2 CO 3 or CsOAc) such as low cost, nonhygroscopicity, and better reproducibility in the perovskite synthesis. Due to the solubility of this Cs precursor in polar solvents such as methanol, a miniscule polar environment is created during the nucleation and growth of the nanocrystals leading to the serendipitous formation of nanorods at 180 °C, whereas using a biphasic mixture of 1octadecene and methanol, the morphology changes to nanocubes. By lowering the reaction temperature (90 °C), nanoplatelets with 8−9 monolayers thicknesses are formed. These colloidal NCs of a variety of shapes are strongly luminescent with a green emission having narrow emission line widths (16−17 nm) and high quantum yields (96% for nanocubes, 94% for nanoplatelets). Furthermore, hybrid materials of nanocubes and organogel of a dimeric bile acid-derived ester gelator are obtained through coassembly in which nanocubes arrange along nanofibers with stable, sharp, and bright green emission. This enables spatial ordering of nanocubes ranging from micrometer to centimeter scale in thin films, which is crucial for advanced optoelectronic applications. To date, there is no report in the literature on the anisotropic organization of perovskite CsPbBr 3 nanocubes triggered by supramolecular coassembly involving organogel nanofibers.

Amplifying Surface Energy Difference toward Anisotropic Growth of All‐Inorganic Perovskite Single‐Crystal Wires for Highly Sensitive Photodetector

“…[ 11 ] Among them, the solution growth process has paid much attention due to the advantage of high yield, controllable, as well as low cost. For solution growth PWs, the widely reported growth mechanism is an oriented attachment by utilizing the dipole moment feature of quantum dots, at the same time, kinds of factors include thermal, [ 6a ] ultrasonic, [ 6b ] light, [ 12 ] high pressure, [ 11a ] polar solvent, [ 13 ] halogen vacancies, [ 14 ] and supramolecular [ 15 ] have been demonstrated could trigger the quantum dots oriented attachment.…”

Methanol-induced fast CsBr release results in phase-pure CsPbBr3 perovskite nanoplatelets

“…38,39 By controlling the surface ligands, reaction temperature and additives, several shape variations of perovskite nanomaterials have been achieved, including NCs, nanorods, nanowires, and nanoplatelets (NPLs). [40][41][42][43][44][45][46][47][48] However, taking CsPbBr 3 as an example, even though the Cs : Pb : Br ratio is set precisely to 1 : 1 : 3 in the precursor, the nal products are always accompanied by CsPb 2 Br 5 impurities, which are known as nonemissive wide bandgap components. [49][50][51][52] These impurities introduce undesired energy states and act as charge blockers, decreasing the charge mobility.…”

Introducing B-Site Cations by Ion Exchange and Shape Anisotropy in CsPbBr3 Perovskite Nanostructures

“…This limits the design of anisotropy in these nanomaterials, as this requires control of facet-directed growth. Considering the case of the most widely studied and the most stable CsPbBr 3 perovskite nanocrystals, different anisotropic nanostructures such as rods, disks, and wires have been synthesized, facets have been tuned, and ion exchange has been carried out, − but there is not yet an established report on their time-dependent successive growth with transformation from one dimension to another. The absence of a clear mechanism of directional growth suggests that either these lead halide perovskites do not follow any facet-directive growth or their true mechanism is still hidden.…”