Interfacial B-Site Ion Diffusion in All-Inorganic Core/Shell Perovskite Nanocrystals

All-inorganic metal halide perovskites (ABX₃, X = Cl, Br, or I) show great potential for the fabrication of optoelectronic devices, but the toxicity and instability of lead-based perovskites limit their applications. Shell passivation with a more stable lead-free perovskite is a promising strategy to isolate unstable components from the environment as well as a feasible way to tune the optical properties. However, it is challenging to grow core/shell perovskite nanocrystals (NCs) due to the soft ionic nature of the perovskite lattice. In this work, we developed a facile method to grow a lead-free CsMnCl₃ shell on the surface of CsPbCl₃ NCs to form CsPbCl₃/CsMnCl₃ core/shell NCs with enhanced environmental stability and improved photoluminescence (PL) quantum yields (QYs). More importantly, the resulting core/shell perovskite NCs have color-tunable PL due to B-site ion diffusion at the interface of the core/shell NCs. Specifically, B-site Mn diffusion from the CsMnCl₃ shell to the CsPbCl₃ core leads to a Mn-doped CsPbCl₃ core (i.e., Mn:CsPbCl₃), which can turn on the Mn PL at around 600 nm. The ratio of Mn PL and host CsPbCl₃ PL is highly tunable as a function of the thermal annealing time of the CsPbCl₃/CsMnCl₃ core/shell NCs. While the halide anion exchange for all-inorganic metal halide perovskites has been well-developed for band-gap-engineered materials, interfacial B-site diffusion in core/shell perovskite NCs is a promising approach for both tunable optical properties and enhanced environmental stability.