Highly Stable Perovskite Supercrystals via Oil-in-Oil Templating

Inorganic perovskites display an enticing foreground for their wide range of optoelectronic applications. Their beneficial optical properties, such as high photoluminescence quantum yield lend them excellent functionality and tunability, while their cubic shape makes them ideally suited for assembly of dense superstructures. Recently, highly ordered supercrystals (SCs) of inorganic perovskite nanocrystals (NCs) have been reported to possess novel collective optical properties, opening new opportunities for efficient devices. Here, we report the large-scale assembly control of spherical, cubic, and hexagonal SCs of inorganic perovskite NCs through templating by oil-in-oil emulsions. We show that an interplay between the roundness of the cubic NCs and the tension of the confining droplet surface sets the superstructure morphology, and we exploit this interplay to design dense hyperlattices of SCs. Remarkably, the SCs films show strongly enhanced stability for at least two months without obvious structural degradation and minor optical changes. Our results on the controlled large-scale assembly of perovskite NC superstructures provide new prospects for bottom-up production of optoelectronic devices based on the microfluidic production of mesoscopic building blocks.