Flexible Polymer-Assisted Mesoscale Self-Assembly of Colloidal CsPbBr₃ Perovskite Nanocrystals into Higher Order Superstructures with Strong Inter-Nanocrystal Electronic Coupling

Abstract

Surface passivating ligands, although ubiquitous to colloidal nanocrystal (NCs) synthesis, play a role in assembling NCs into higher-order structures and hierarchical superstructures, which has not been demonstrated yet for colloidal CsPbX3, (X= Cl, Br, and I) NCs. In this work, we report that functional polyethylene glycols (PEG6-Y, Y =-COOH and-NH2) represent unique surface passivating ligands enabling the synthesis of near uniform CsPbBr3 NCs with diameters of 3.0 nm. The synthesized NCs are assembled into individual pearl necklaces, bundled pearl necklaces, lamellar, and nanorice superstructures, in-situ. It is believed a variety of forces, including van der Waals attractions between hydrophilic PEG tails in a nonpolar solvent and dipole-dipole attraction between NCs, drive mesoscale assembly to form superstructures. Furthermore, post-synthetic ligand treatment strengthens the argument for polymer-assisted mesoscale assembly as pearl necklace assemblies can be successfully converted into either lamellar or nanorice structures. We observe an ~240 meV bathochromic shift in the lowest energy absorption peak of CsPbBr3 NCs when they are present in the lamellar and nanorice assemblies, representing strong inter-NC electronic coupling. Moreover, pearl necklace structures are spontaneously assembled into micrometer length scale twisted ribbon hierarchical superstructures during storage of colloidal CsPbBr3 NCs. The results show that the self-assembled superstructures of CsPbBr3 NCs are now feasible to prepare via template free synthesis, as self-assembled structures emerge in the bulk solvent, a process that mimics biological systems except for the use of non-biological surface ligands (PEG6-Y). Taken together, emergent optoelectonic properties and higher-order superstructures of CsPbBr3 NCs should aid their potential use in solid-state devices and simplify scalable manufacturing.

A hybrid blue perovskite@metal–organic gel (MOG) nanocomposite: simultaneous improvement of luminescence and stability

“…28 Plenty of effort has been devoted towards integration of perovskite NCs into numerous polymers, silica and other crystalline materials, but, so far, the porous MOG matrix has never been used to host perovskite NCs. [29][30][31][32] Therefore, porous MOG would be a new addition as a host matrix for encapsulating perovskite NCs.…”

Self‐Assembly of Perovskite CsPbBr3 Quantum Dots Driven by a Photo‐Induced Alkynyl Homocoupling Reaction

“…Among them, synthesis of large‐sized perovskite nanocrystals has been proved to be a straightforward and empirically reliable strategy . For instance, Sardar obtained ordered perovskite superstructures with strong inter‐crystal electronic coupling using flexible polymer‐assisted self‐assembly of CsPbBr 3 nanocrystals; Tian and Rogach realized spontaneous assembly of CsPbBr 3 into cuboid crystals with high intensity blue emission; Sargent and Bakr reported halogen vacancies‐enabled ligand‐assisted self‐assembly of PQDs into nanowires, as well as CsPbBr 3 nanowires with sharp photoluminescence; Moreover, 1‐dimensional CsPbBr 3 superlattice chains were synthesized by hot‐injection method, and the stability of nanocrystals was improved due to collective properties from the nanosheet unit . The above studies have indicated that surface chemistry of PQDs, or more specifically the use or not and the type of capping ligands selected, have played a very critical role in obtaining large‐sized perovskites.…”

Close-Packed Ultrasmooth Self-assembled Monolayer of CsPbBr3 Perovskite Nanocubes

“…Nanocubes of CsPbBr 3 have a tendency to fuse into single crystals, 33 − 36 making them ideally suited for a self-assembled thin film and luminescent nanopatterned devices. However, the major problem behind their self-assembly is that due to their ionic nature they readily dissolve in a polar environment, while in a nonpolar solvent, they have a tendency to cluster 37 due to strong vdW attractions between the long capping ligands. Therefore, preventing colloidal aggregation to enable close-packed monolayer thin films remains an open challenge.…”