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

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 CsPbBr3 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 Cs2CO3 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 1-octadecene 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 CsPbBr3 nanocubes triggered by supramolecular coassembly involving organogel nanofibers.