Directed Anion Diffusion Induces Defect Passivation in 0D/3D Perovskite Single-Crystal Heterostructures

0D/3D perovskite heterostructures have been extensively utilized in optoelectronic devices. However, synthesizing 0D/3D heterostructures with well-defined interfaces, high-exposure crystal facet orientations, and high-purity phases remains challenging due to their soft ionic nature, which complicates the understanding of ion defect passivation mechanisms in these heterostructure systems. In this study, a one-step vapor-phase epitaxial growth of pure-phase 0D/3D single-crystal heterostructures is reported with well-defined interfaces. Through a combination of various in situ measurements and theoretical calculations, it is elucidated that defect passivation in the heterostructure arises from the diffusion of bromide anions in the 0D phase across the interface, effectively compensating for vacancies in the 3D component. The 0D/3D heterostructures exhibit enhanced stability in their physical and optical properties compared to pure 3D perovskites. Furthermore, the observed decrease in bromide anion kinetic energy (from 0D to 3D heterointerface) in 0D/3D provides direct evidence of the bromide-rich form of the 3D component. As anticipated, the bulk defect density in the 0D/3D heterostructures is estimated to be an order of magnitude lower than that of pure 3D single crystals. As the first systematic study utilizing a 0D/3D heterostructure model to explore defect self-passivation mechanisms, this work offers crucial insights for designing high-performance perovskite devices.