Solvent-Assisted Self-Assembly of CsPbBr₃ Perovskite Nanocrystals into One-Dimensional Superlattice

Abstract

The self-assembly of colloidal nanocrystals into ordered architectures has attracted significant interest enabling innovative methods of manipulating physicochemical properties for targeted applications. This study reports the self-assembly of CsPbBr3 perovskite nanocrystals (NCs) in one-dimensional (1D) superlattice chains mediated by ligand–solvent interactions. CsPbBr3 NCs synthesized at ≥170 °C and purified in a nonpolar solvent, hexane, self-assembled into 1D chains, whereas those purified in polar solvents, including toluene and ethyl acetate, were disordered or formed short-range two-dimensional (2D) assemblies. The NCs assembled into 1D chains showed red shifts in both the absorbance and photoluminescence spectra relative to those of disordered NCs purified in a 50/50 hexane/ethyl acetate mixture. Microscopy and X-ray diffraction results confirmed the formation of polymeric nanostrands in hexane followed by organization of the NCs into 1D chains along the nanostrands. Our results suggest that excess aliphatic ligands remaining after purification of the NCs complex with ionic Cs+ and Br– species through a hydrophobic effect; further, the alkyl chains of these ligands interlace with each other through van der Waals forces. Collectively, these interactions give rise to the nanostrands and subsequent self-assembly of CsPbBr3 into 1D chains. In polar solvents, the minimization of repulsive forces between the solvent and the ligands drives proximal CsPbBr3 NCs together into short-range 2D assemblies or disordered clusters. Our solvent-assisted self-assembly approach provides a general strategy for designing 1D superlattice chains of nanocrystals of any geometry, dimension, and composition by simply tuning the ligand–solvent interactions.