Crown Ether-Induced Room-Temperature Formation and Phase Evolution of Copper-Based Perovskite Nanocrystals via Dissolution–Recrystallization

Lead-free Cs₃Cu₂I₅ nanocrystals have attracted significant attention as promising luminescent materials owing to their excellent optical properties. However, conventional synthesis methods, such as hot-injection and antisolvent recrystallization, typically involve multiple processing steps and require excessive amounts of ligands, making purification and process control challenging. In this study, we propose a simple one-step room-temperature synthesis route by directly mixing CsI, CuI, and crown ether in a nonpolar solvent.

Upon the introduction of crown ether, Cs₃Cu₂I₅ nanocrystals were formed under ambient conditions without the use of additional ligands or elevated temperatures. Furthermore, time-dependent phase evolution was observed after crown ether addition. Structural characterization revealed a gradual transformation from Cs₃Cu₂I₅ to CsCu₂I₃ and eventually CuI with increasing reaction time. This phase evolution is attributed to the selective complexation of Cs⁺ ions by crown ether, which promotes partial dissolution of the crystal surface followed by recrystallization.

These results suggest that the introduction of crown ether facilitates dissolution–recrystallization processes under ambient conditions, enabling the formation of perovskite nanocrystals without the need for elevated temperatures or surface ligands. This work provides a simple and scalable strategy for the synthesis and phase engineering of lead-free copper-based perovskite nanocrystals.