Stacks of a Hidden Treasure: on the Self-Assemble of Perovskite Nanoplates in Organic Solvents

In recent years, perovskite nanocrystal superlattices have been reported with collective optical and electronic quantum phenomena. Regarding perovskite nanoplates, their superlattices can be easily observed on electron microscopy grids, for example, and they too present ensemble optical response. However, little is known on the self-assemble and optical properties of the perovskite nanoplates superlattices in solvents. Here, we report a simple strategy to induce the formation of these nanoplates stacks (1D superlattices) in suspension in different organic solvents. We investigate the influence of concentration and viscosity on their formation. For that purpose, we combined wide- and small-angle X-ray scattering and scanning transmission electron microscopy to evaluate CsPbBr3 and CsPbI3 perovskite nanoplates with different thickness distributions. We found that, in hexane, the concentration threshold for the formation of the aggregated stacks is rather high and approximately 80 mg/mL. In contrast, in decane, dodecane, and hexadecane, we observe a much easier formation of these stacks: the higher is the viscosity, the easier is the stacking of the nanoplates. We, then, discuss the impact of the proximity of the perovskite nanoplates in their colloidal stacks or solid superlattices in terms of Föster resonant energy transfer. We predict an efficiency higher than 50% in the energy transfer even in a low photoluminescence quantum yield scenario for both perovskite compositions.