Template-Assisted Assemblies of Perovskite Nanocrystals

Abstract

Highly ordered nanocrystal (NC) assemblies, namely superlattices, have been investigated as a building block of novel bright (quantum) light sources because of their unique collective superfluorescent emission based on enhanced inter-NC interactions[1,2]. Thus far, the primary preparation method for perovskite NC superlattices has been drying-mediated self-assembly, in which the NCs spontaneously assemble into superlattices while the solvent evaporates. However, a drawback of this method is the lack of controllability on the position and size of assemblies, making it difficult to place NC assemblies in photonic structures like microcavities and realize NC assembly-based devices. Here, we demonstrate template-assisted self-assembly of CsPbBr3 NCs to achieve precise control of the geometrical features of NC assemblies. NC assemblies are formed using drying-mediated assembly on a substrate with hollow, lithographically-defined template structures made from SiO2. The templates have lateral sizes of a few micrometers and 220 nm height and are fabricated with a similar method as developed for templates in inorganic-semiconductor growth [3]. After drop-casting a solution of NCs, we allow slow evaporation of the solvent and remove excess NCs from the substrate surface afterwards. Thus, NCs only remain in the templates, and position and size of these NC assemblies can be controlled by changing the design of the hollow structures. Furthermore, we find that the yield of successful assemblies depends on the ligands and solvents used, as well as on the geometry and number of openings of the hollow templates. We investigate the photoluminescence (PL) properties of these template-assisted NC assemblies. Micro-PL studies at cryogenic temperature allow to evaluate the homogeneity and quality of the assemblies. Moreover, we perform time-resolved PL measurements where we observe signatures of cooperative photon emission. Lastly, we assess the stability and robustness of the assemblies. Our results provide an important step forward for the development of optical devices that harness embedded perovskite NC assemblies. Reference [1] G. Rainò et al., Nature 563, 671-675 (2018) [2] I. Cherniukh et al., Nature 593, 535-542 (2021) [3] H. Schmid et al., Applied Physics Letters 106, 233101 (2015)