High-Efficiency Violet-Emitting All-Inorganic Perovskite Nanocrystals Enabled by Alkaline-Earth Metal Passivation

Cesium lead halide perovskite nanocrystals (NCs) have emerged as promising luminescent materials for a range of applications. However, the creation of highly luminescent violet-emitting CsPbCl₃ NCs mostly relies on doping of a limited number of small-sized metal ions or post-synthetic surface treatment of NCs. Alkaline-earth (AE) metals (e.g., Ca²⁺, Sr²⁺, and Ba²⁺) have been proposed to be able to substitute Pb²⁺ in halide perovskites, yet it remains incompletely understood whether AE metal ions can be incorporated into the perovskite lattice or can be merely situated at the surface. Here, we explore the possibility of using AE metal ions for the suppression of the formation of trap centers, which leads us to develop a one-pot synthetic passivation strategy to boost the violet-emitting efficiency of CsPbCl₃ NCs through the creation of a Ca²⁺/Sr²⁺ involved passivation layer. The photoluminescence quantum yield of violet emission reaches 77.1% by incorporating an optimal amount of Ca²⁺. A wide range of optical and structural characterizations, coupled with first-principles calculations, aid in clarifying the underlying mechanism for the AE-metal-dependent passivation of CsPbCl₃ NCs. Specifically, based on the experimental and theoretical results, a model is proposed for the observed abnormal incorporation phenomenon of AE²⁺ ions in NCs (i.e., Ba²⁺ can be incorporated into the core of NCs, Ca²⁺/Sr²⁺ can only be at/near the surface, while Mg²⁺ can neither be in the core nor at the surface). We believe that the knowledge gained here may not only offer a new perspective to obtain high-efficiency violet-emitting perovskite NCs through a one-pot synthetic passivation but can also help elucidate the functions that AE²⁺ ions play in the optimization of perovskite optoelectronic devices.